How to make a Blackface Princeton Reverb sound FANTASTIC!

[@UncleDoug]

Very well done indeed......clear, instructional, and entertaining. Thanks so much for posting this video, Chris, we really enjoyed it :)

[@theguitaramptech]

There is no higher compliment, my dear mentor

[@TylrVncnt]

Wow! Legends on here

[@theguitaramptech]

@@TylrVncnt They're 2 of the best, Tylr. I believe that @Uncle Doug is THE best teacher on KZbin. I am a very proud Patreon supporter of Doug's.

[@UncleDoug]

@@theguitaramptech Thanks so much for your support and for your very kind words, GAT. We sincerely appreciate both.

[@thierrycaudron3266]

Hello from France

[@michaelgriffith6641]

I just scored a sweet 68 Princeton. It literally just arrived here in Detroit Michigan from Nashville Tennessee Thanks for sharing this video sir. I've no doubt I'll be referring back to it soon enough. Fender Amps are the best!!!

[@theguitaramptech]

Good luck Michael! I Hope my video will be of help.

[@TheGuitologist]

Nice video. Very enjoyable. Just found your channel. I might have commented on one other vid before, come to think of it. Good to have you in the amp community!

[@theguitaramptech]

Thank you Brad. I've been watching your videos for many years and have learned a lot from your honest confrontation of difficult repairs. I'm glad you enjoyed the video and am honoured.

[@TylrVncnt]

The legends sure know what’s up that’s for sure! Definitely deserve more subscribers!

[@johnpierson8398]

The design and internal construction of that amp is elegant and beautiful! Great work and troubleshooting. I learned quite a bit this time around. Especially with the bias issues this amp had. I am an electronics technician with almost 50 years experience in various industries. In my "Golden Years", I am aspiring to become an amp tech. I don't think I can reach your level, but I will try! Thanks for these videos. You are one of the best amp techs on YT!

[@theguitaramptech]

Wow! That is high praise indeed, John. Thank you John. The videos take a long time to record and edit with no reward other than self-enjoyment and comments such as yours.

[@luthiervandros]

Subscribed brother! I’ve been doing these repairs for 20 years and learn new things every day! Glad to have you here.

[@theguitaramptech]

Thank you, Luthier

[@brentduxbury5814]

Loved this video, Chris. I understood about a third of it, but got the gist on most things. After knowing you for so many years, it’s really great to see how you apply vast knowledge. Cheers 🙏

[@theguitaramptech]

Thanks, Brent!

[@henrysmith187]

The way one makes any fender blackface era amp sound great is power it on. The end. Love the vid!

[@theguitaramptech]

Hahaha! Love it Henry!

[@harrypalmer3481]

Nice 'acting' at the beginning. Not sure about "nutting [this] one out together", the phrase 'lost in translation' comes to mind! Enjoyed the video, thank you.

[@philipharrauer9103]

Great! Great! Great! I love your Videos!! More of them,please!! Chris you are awesome! Best regards from Austria!👋🏻

[@theguitaramptech]

Thank you, Phil

[@Madas905]

Always innovative, entertaining and brilliantly geeky. Well done Chris.

[@theguitaramptech]

Hahaha! You hilarious Rob. Thank you again.

[@williamkaylor1191]

Was led to your channel during a blackface binge, and here @ the top of the comments I see two of my favorite "Toob" amp instructors, Uncle Doug and the Guitologist...what nice support and validation, Chris..Subscription and thumbs up forwith!

[@theguitaramptech]

Thanks William. I admire both @uncle_doug and Brad @guitologist. Brad for being so honest and sharing his frustrations, and uncle Doug for being such a good teacher. I am a proud Patreon supporter of Doug’s channel.

[@michael_caz_nyc]

This was very informative. Enjoyed it. I am obsessed with the 65 Blackface Fender Princeton = I recently watched another fantastic video on You Tube, from Psionic Audio about Upgrading a Princeton. You may also find it interesting? I wish I know how to do upgrades, mods and tests. You guys are so knowledgable.

[@theguitaramptech]

Thank you very much Michael. Yes I watch most of Lyles videos @Psionic, but I can’t remember his Princeton one. He is excellent. Proceed with caution when you talk about upgrading and Please run quickly from any tech who says he needs to replace all of your capacitors. Lyle and I are in agreement that With that piece of history you own, it is incumbent on us to keep it as original as possible while still making it playable and reliable.

[@rightlurker4674]

Excellent video. Your explanation of ESR values was especially helpful. At about the 54:57 mark I noticed a couple of flashes of light on your window blinds. It appeared as if the flashes may have been coming from the rear of the amp, but it could have been something like car headlights coming from outside. Thanks, and please keep the videos coming!

[@theguitaramptech]

Wow ... well spotted! It was a message coming in on my iPhone, which which can see in the background above my solder sucker. 👍

[@montygore]

I enjoy your clever humor. Thanks for the great videos.

[@theguitaramptech]

Thanks Monty. After 25 years in the entertainment industry, my fellow band members or actors have called me the "King Of Corn". Its a badge I wear with pride.

[@mariannwatt2678]

Never been here before but if uncle dug and brad are here im in jerry the old marshall guy

[@theguitaramptech]

I love Uncle Doug. He is incredibly knowledgeable and a master of communication and I am a proud Patreon supporter of his. Brad, I admire for his total honesty, humility and tenacity in all things both technical and personal. I am truly humbled to be put in that company. Thank you.

[@michaelwhite1247]

Just awesome videos Chris. So glad you are local!!!!! and you got kudos from Uncle Doug who we all love down here in Australia!!! Thanks heaps maaaaate!!!! Love your stuff!!

[@theguitaramptech]

Thank you so much, Michael. Yes, I admire @Uncle Doug and how beautifully he explains complex topics. I believe he was a teacher...and it shows. If you're in Sydney it's be fun to say hello one day.

[@whatsstefon]

Nice work explaining ESR. Another brilliant video matey. I have an old Oahu Publishing Co. amp I did up last year. Estimate it to be around late 1940s to early 1950s. The two original can caps both have perfectly acceptable values which I measured on my old Heathkit Cap tester. Unbelievable that a cap that’s approximately 70 years old still works great. It’s the only guitar amp I kept after selling all my gear due to lack of income from COVID killing live music.

[@theguitaramptech]

Thanks Stefano. I agree. Some of those old capacitors and valves have survived way beyond their use-by date. I've never seen one of these Oahu amps. Amazing. Its an inditement of our system when many of my muso mates have had to sell their gear. The population would be up in arms if carpenters had to sell their tools, but this empathy just doesn't exist for musicians. For those reading Stefano's comment, apply power to your hibernating amps every few months to keep the capacitors "formed" (ie healthy). If they haven't been powered for a while, the amp may need to come up gently on a Variac. Stefano is a Tech and knows this.

[@whatsstefon]

@@theguitaramptech cheers matey. Here’s the Oahu vid if you’re interested. Not a very exciting fix, and apologies about my demo at the end. This bassist ain’t no guitarist. kzbin.info/www/bejne/fZvTmqGddpqJbNk Oh yeah, always bring the amp up on a variac. I’ve begun to include mine in latest videos coming out soon because some viewers asked if I do use one. Always. Keep these great vids coming matey. Great to be one of the few keeping these beauties alive.

[@andrewsutton7007]

Not a fan of Tungsol 6V6 valves (tubes) and unsurprised you lost some - they certainly aren't up to the higher plate voltages of the 65 Deluxe Reverb circa. 440 d.c. - they red-plated on me, failing mid-gig. :( Splashed on pair of NOS JAN from 1980 and hugely pleased with the outcome. Great vids and loving your stories from amp land!

[@theguitaramptech]

Mostly, I have had good luck with Tungsols, but I agree with your preference for NOS tubes. Unfortunately, the older tubes have been "cherry-picked" and we mainly get the scraps. As a repairer, I can't risk my customers' money on unknown quality. If they turn out to be crap, its me that will have to cover the cost.

[@dwightbehm2886]

RCA. does that mean radio corporation of Australia. Or radio corporation of America. Haha just a little teaser. Chris you are a meticulous repairman tech. On amps. I see you enjoy yourself very much. Between you. Uncle Doug and Terry dayton in Grand Rapids, Mi. Iv seen alot of very good information. Thank you for sharing your knowledge. If any one needs knowledge its alot of young people today. Iv looked up a few things on Utube to repair some things around the house hear. Keep up the good work. Dwight.

[@theguitaramptech]

From memory they were about $18 each. I got them from Evatco in Qld, Neville. Expensive as gold...but I wouldn't use less in an amp like this.

[@60retired]

Hey hey see you mentioned pulling those tubes when checking the grid caps for leakage👍 you know in all my years working on these tube amps I have never seen anyone else ever mention maintaining a load on the reverb driver tranny, using a dummy load on the output tranny is brought up a lot, makes sense, very good point you made. Princeton Reverb is not the only amp like that thank you for that tip. I have a reverb pan on the bench that I hook up when testing the amp with and without a guitar but it isn’t something I did consciously for the soul purpose of maintaining a load it was more for convenience but it will be now.

[@theguitaramptech]

HI 60retired! Yes, when you look at the schematic the Reverb driver is simply a small Class A circuit. I have made up a bunch of RCA dummy loads of different resistances to suit the different impedance reverb tanks.

[@waynewayne3709]

Very good clear instructions from a time served electronics tech..there's not many out there like us that will take our time to show what goes on.. Manythanks for showing those who need showing.

[@theguitaramptech]

Thank you Wayne. Much appreciated

[@montygore1200]

I have watched all of Uncle Dougs videos. I am working on watching yours and Brads videos now. I bet if you were to come and visit me we could come up with at least 50 songs we both know.

[@theguitaramptech]

I reckon we could jam for hours, Monty. My top tips for my colleagues' channels are @UncleDoug, Brad @BradsGuitarGarage and Lyle @psionicaudio. You can guess that Brad's a fellow Sydney-sider, Uncle Doug is in Texas, and Lyle is in Memphis. Thank you for including me in such illustrious company, Monty.

[@TylrVncnt]

Hey niiice playing sir! Suuuper funky, seriously very nice feel 👍

[@theguitaramptech]

That is SO nice of you, Tylr. Thank you.

[@giulioluzzardi7632]

Top job, that's a nice bouncy 1x10" fun sound, which speaker was in it?

[@dwightbehm2886]

Hey Chris. Dwight hear. You say you owned a company involved in music. Please if you don't mind. Tell me more about yourself you seem like a fine man and very well accomplished on electric guitar like you could be a sessions musician or join a professional music band. Good work on the amps. Dwight. AllenPark, michigan usa. Oh Im an old retired machanic dabbled in electronics as a hobby. Played acoustic guitar in church Chior bands I'm also a ham radio operator. Have talked radio to radio skip into Melbourne Australia. Many moons ago. You are such Fabulous people. Enjoyed the chat with someone from the down under.

[@theguitaramptech]

You are too kind, Dwight. I also enjoy our "Chats".

[@nevillegoddard4966]

Gidday Chris! Interesting video!👍 The 'parallel' resistance of capacitors you speak of is actually the 'leakage resistance' of the cap. You didn't actually mention that. These customers that want their amp 'as original as possible' annoy the hell outta me! If you want your amp to be as original possible, take it to the bloody museum & let THEM polish your leaking or shorted resistors & capacitors ffs! If I was the repairman for this amp I would turn the job down. One o those 60 or 70 old caps could fail TOMORROW, & red plate one of the o/p tubes! And what's the first thing the customer will do if that happens? They'll throw the amp back in your face & say - "Where's my warranty? Fix this for free!". Well screw that! I'll replace all the parts I think need replacing, & just give the customer back all the dead conponents & parts in a plastic bag. MAYBE one day some anal collector or museum may want to buy it, but with all original parts. I mean, do people sell their cars with all the original spark plugs & tyres? Is the sale value of a vehicle gonna change cos it's got 'all original parts'? It's value would drop if anything. Nope. This is bs. I guess that's why I don't repair many collectors' guitar amps.

[@theguitaramptech]

Thanks for your reply, Neville. What you are saying is the opposite approach to mine. If you bought a genuine '63 Deluxe Reverb, and opened it up to find all of the blue molded caps replaced by Orange Drops would you be disappointed? I would. If I found all of the beautiful brown Mallory filter caps replaced with F&Ts would I be disappointed? Nope. I'd be thankful. My sound passes through the blue coupling caps not the filter caps. To use you car analogy, would I be upset if the tyres and plugs were replaced on my old Jaguar XJ6? Nope. I'd be thankful. Would I be upset if the twin cam 6 Jag motor was replaced with a more powerful, more reliable small block Chevy V8? I'd be furious. There's room for both approaches, Neville, so long as you are open as to what you are doing and explain the consequences.

[@theguitaramptech]

Thanks for bringing that to my attention, Neville. I did mention "leakage" at 16:10, but I could have said it again more clearly, or using different words. I’m more surprised you didn’t pick me up on calling the Bias Circuit, the Rectifier Circuit! I have to agree that I am not perfect (please don’t tell my daughter I said that). Can you please send me a link to your channel so I can see how you like to do things?

[@ofthetree]

Hi. I like your channel. Subbed. Have myself built from kit a 5f1 Champ and a 6g15 reverb. Plan a 5f2 :-) Learning some. greets from Norway.

[@theguitaramptech]

Thank you for subscribing. Good work on those builds. If I EVER get time to myself, I am going to build a 6G12, but I will go the kit route to save time on cabinet, chassis, etc. If you used a kit, which one did you choose? Were you happy with the kit and the end result? I've been to Norway a few times in my former life as a process engineer. It was in a town not too far from Lillestrom. Because it was work I never got to go to my bucket-list area of the west coast...one day!

[@ofthetree]

So you've been to Norway. Nice! I did one summer fart around by car and stayed in camping places west of the country, it was splendid. Hope you get to visit there too. The 6g15 kit i got from tubeampdoctor, kind of pricey, had to place the pt inside the chassis and it is nice and quiet. I think it interfered with the reverbpan. I also saw your video of designing your own amp. That sounded great.

[@theguitaramptech]

@@ofthetree . Thank you for your kind words. Yes, I must go to Bergen and sail the Fjords. I am sure the TAD kit would be excellent. I don't have the skills to make cabinets and chassis, so for me its a kit :)

[@ofthetree]

For sure it is lots more work making the full thing when one don't have the practrice and not to mention good tools. I made plywood cabinets for mine but not fingerjointed, turned out OK but took forever. One needs to prioritize. Yes you can take the coast boat all the way up to the north Kirkenes with stops in between. We see that boat "Hurtigruten" regularly stopping by here in the north/middle west where I am.

[@theguitaramptech]

@UCeqWByvLfRX%F0%9F%98%80z2g53GDA2IRA Yes, it would be very satisfying to build the entire project. Thank you for the tip about the Hurtigruten.

[@Stoffe958]

Really nice video. Thanks for showing this.

[@theguitaramptech]

Thank you, Chris. Glad you enjoyed it!

[@TylrVncnt]

I’m very excited to have found your channel! Not many great gtr amp youtubers, (only personally know of Uncle Doug, Guitoligist, & blueglow and they’re all great too 👍) but so awesome to find another great one!! I’m about to check out your series on amp sag! Great idea for content btw! Looking forward to more! Cheers

[@theguitaramptech]

That is excellent feedback, Tylr. Thank you. @Uncle Doug has left us with a tremendous resource of teachings that there's not much I can add to his volume of work. I am also a follower of Brad @The Guitologist, and Blueglow. Another great teacher is fellow Aussie, David Jones on @EEV Blog. Lyle @PSION Audio is prolific with uploads and there is always something to learn there. Enjoy the journey.

[@cpfs936]

You may also want to check out Colleen Fazio, D-Lab Electronics, and Lyle Caldwell at Psionic Audio.

[@vividvulpe9842]

Sounds terrific! Great instructional videos! Thanks

[@theguitaramptech]

You are very kind. It’s takes a fair bit of time to do these videos, but your comments make it worthwhile. I am so happy that you got something out of it.

[@jamesprice6381]

G'day mate from Omegaaamps in Moravian Falls NC...i see u have much wisdom in rear view mirror! :)

[@theguitaramptech]

Thanks James…but I’m not that wise. I don’t know what you’re talking about. Please don’t make me watch my video again. By the time I finish editing I am sick of my own voice. 😂

[@darrylcarstensen5448]

I love your videos. I have watched each one more than once. I think that you have a great sense of humor. I laughed at your comment, "What's that you say, I look like a dick with my ear muffs on my head." I had to share that one with my adult son. I am looking forward to the next vid.

[@theguitaramptech]

Thank you, Darryl. I have been trying to suppress my "inner fool" but every now and again it makes an appearance.

[@dwightbehm2886]

Hello mayt. Name hear is Dwight. Nice Job there in Australia on the amp and you play guitar very well nice jazzfunk. I'm a ham operator have talked with people from your country radio direct on the 7and 14 megaherz bands. I find the austies like to talk instead of just hello goodby can i have a post card. So I find it heart warming to talk with Australians. So hello from Allenpark, Michigan USA near Detroit.

[@theguitaramptech]

AHA!Ignore my previous message Dwight where I asked about your hometown. I did a show in Chicago in 2007, but that's a close as I got to Detroit...Motown. :) I remember being very excited to be going through a town call called "La Grange"...you know what I'm talkin' about.

[@jezzbro]

Very nice video. Thank you!

[@theguitaramptech]

Thank you Jezzbro. I really appreciate comments like yours. :)

[@3MonkeysGarage]

Thanks for the video. Glad to see you have your UD certifications. I am dealing with the same voltage jump. My transformer was Originally rated at 330-0-330 but is actually pushing 380-0-380. When it gets rectified more like 469v vs the desired 410v on the plates. And that is on the lowest setting on the bias control. Plate only goes up from there. Tried some diodes on the center tap, which did give me some good results. But looked like hammered up dog s***. Swapped rectifiers, which did tame it a bit but still very on the hot side, and now throwing in the towel and ordered a cooler transformer. Getting there. After studying on it for about a good 2 weeks now, I think I could have worked it out with the old transformer. Maybe I will have a look at it again later but for now, I just want to hear some sparkles. :p

[@theguitaramptech]

Ouch! That's hot. Let me know how you get on.

[@3MonkeysGarage]

@@theguitaramptech Thanks, will do. Just sitting here rewiring heaters while I watch... and wait for parts. :p

[@3MonkeysGarage]

@@theguitaramptech Finally success. Using the 5AR4 got my voltages back in reasonable tolerance. About 446vdc with a pretty warm bias (schematic actually called for 440 there, not 410). Had some bad Hum from reverb = lack of ground to chassis on the rca jacks. note- do not use those insulators. Had a couple other hiccups but finally all is working properly now. Still may go for the 5Y3 GT and soften down the heat a bit more.

[@theguitaramptech]

@@3MonkeysGarage great work. It can be challenging to find hum sometimes 👍

[@tisnotmy-name1180]

Looking at 13:34, the simplicity, the cleanness of it, the wiring... Why and or how has it come from that to the Bassbreaker? The Bassbreaker looks like a digital solid state shemozzle with globes for glam, compared to this Princeton.

[@theguitaramptech]

You are so right, Tisnot. Sadly, I see it across the board with many once famous manufacturers that have gone from glorious to gross in a decade.

[@lestelie4410]

What a great sound!

[@theguitaramptech]

Thank you,. I'm glad you enjoyed it.

[@edwardhannigan6324]

Where ya been..? Awesome vid, great information and fix..Learning all the time...Love the demo too, you rock..Ed..U.K..😀

[@theguitaramptech]

Hi Ed. Great hearing from you again. I know, I feel bad about taking so long to upload this video. I have been so busy with repairs. I’m sure you appreciate that these take priority. I have some great videos waiting to edit and upload. I am really excited about this comparison Video I just recorded of a deluxe reverb tone master, 65 re-issue, and a gorgeous Clark hand wired. I think you’ll really appreciate this one.

[@edwardhannigan6324]

@@theguitaramptech Thanks for you reply..Love the repair stuff, look forward to anything. I wish I had your knowledge, but I'm learning..Thanks and stay safe..Ed

[@lettuceb2336]

Nice presentation, I really enjoyed watching you work through the amp. I've been throwing around the idea of converting the 65 reissue 6V6 outputs to cathode bias as I don't need the volume and wouldn't mind some earlier compression and breakup. These new amps are spec'd at 440V on the plates which seems a bit silly given the direction modern amp use is headed. Have you ever played with Push-Pull cathode-biased outputs? Any thoughts on the results? A cursory glance at the schematic looks like any imbalance in the output tubes could create some frequency mixing / interaction with the tremelo if the cathode bias lacks the necessary bulk capacitance. Cheers!

[@theguitaramptech]

Thanks Lettuce! I appreciate your comments. I agree that 440V for B+ is high, depending on the sound you’re after. Unless I’ve misunderstood your question, I’d be willing to wager that you have also played on a push-pull cathode biased amp. A vox AC10, 15 or 30. I Love that sound. The main problem with the Princeton tremolo is that the Fender Tremolo works on the bias by oscillating between normal bias (around -40v) and shutoff (more negative). With cathode bias, your grid will now be at 0v and not -40v. The negative relationship would be provided by having a positive voltage on your cathode relative to the grid. Have you thought of replacing your rectifier tube to drop your B+? The standard GZ34 (my favourite tube) is quite efficient, almost as much as a solid-state diode. Try a 5Y3. It will drop your B+ to a value that you are happier with. Maybe avoid a 5U4GB as it draws way more filament current than the other 2. Let me know how you get on.

[@goodun2974]

@@theguitaramptech , a 5V4GA tube might be a better choice than a 5Y3 as a replacement rectifier for a 5AR4/GZ34. The 5Y3 is a filament rectifier which 1) turns on faster than a 5AR4, stressing the filter caps and tubes, and 2) might be prone to arcing from the high-current draw, especially if the first filter cap is above 20 mfd. The 5V4 is an independently-heated-cathode rectifier, with characteristics similar to the 5AR4: it heats up more slowly and has greater resistance to arcing than the 5Y3, but it does have more internal voltage drop than the 5AR4 and will lower the plate voltage to the tubes a little bit.

[@theguitaramptech]

@@goodun2974 Yes, the 5V4 would be a good call for that position. Like you, I prefer the slow startup of an indirectly heated cathode and the 5V4 has the same low filament draw as the 5AR4 and the 5Y3. It would certainly have done the job. In the end, the main reason I opted for the 5Y3 is the voltage drop of 40v. The 5AR4 has a drop of 17v and the 5V4 has a 25v drop. I was after that additional 15v.But, thank you. The 5V4 is an excellent recommendation.

[@lettuceb2336]

@@theguitaramptech I didn't pick up guitar until I was in my mid 20's, and I didn't really become serious until 40 or so. Up until the last year or two I played primarily acoustics and have just recently returned to electrics. So while I'd love to claim extensive pesronal experience with various amps I cannot. What does get me into trouble is having an EE degree... but tubes are definitely not in my wheelhouse. I was reviewing schematics and took some measurements in the amp... just to make sure reality matched up. The amp is at 440V and the output tubes are biased at 21 mA. It plays well, sounds great, and for good or bad has clean headroom to at least 8 on the volume pot. Being primarily an at-home player I'd love to get a bit of breakup at lower volume, but that's not a trivial task with this design. The rectifier swap isn't a bad idea. I went forward and modded the amp. I slowed the tremelo oscillator by doubling the cap, and I swapped the negative feedback resistor for a smaller R + potentiometer to have control. Once I had these changes verified I dove in to modify the output stage to be fixed bias / cathode bias switchable. I lifted the ground legs of the 1 ohm R & diode in each leg and routed them to a 4PDT switch. One position goes to ground and the other goes to a 1500 ohm 25W rheostat in series with a 180 ohms 5W resistor (for some safety). A look at a few datasheets suggested a value in the 800 ohm range should bias the tubes near the same 21 mA... a good "safe" starting point. This gets the circuit most of the way there, but as you noted the negative bias needs to be removed. I lifted the negative supply rectifying diode cathode and connected it to one of the two remaining switch positions. In fixed mode the diode is connected per the design to the power transformer. In cathode mode I tie it off to ground (just a precaution, it's not absolutely necessary). This allows the tremelo to see a similar impedance in both bias modes... no need for a heavy-handed hard ground at the trem mix pot. The changes are in, the amp came up in both modes, bias was as expected in both, and the noise floor didn't audibly move (which was my biggest concern). I can now get power tube breakup at a lower volume and a different but nice sound. Of courese I'm not done. I need to get the function generator and oscilloscope on it to verify cross-over behavior. As it sits the trem is at roughly 50% effectiveness due to the softness of the cathode voltage. This is better than I expected given the circuit... It may have helped to disconnect the negative supply at the transformer. I'll be adding capacitance across the cathode bias resistor to create a "virtual ground". This will move behavior closer to that of a fixed bias output stage. Ideally the only difference would be a reduction of 75V (give or take) across the 6V6 pair once complete.... with no significant loss of trem or noticable "squish". I'll let you know how it goes when the caps are in. My real reason for doing this was to play with tubes and learn a bit more about their behavior. Thanks for the feedback! Cheers!

[@daliborpanjkovic9691]

Nice

[@theguitaramptech]

Thank you, Dalibor 😀

[@froggy77753]

Nice work. 👍

[@theguitaramptech]

Thank you, Jjj. I appreciate that very much.

[@johnsimons6384]

Chris, how do you safely clean the pins on the preamp tubes?

[@theguitaramptech]

An excellent question that would be the topic of another video. The quick answer is "depends". If they are old and show oxidation, I soak them in WD40 to start removing the corrosion. Then wipe off the residue, and spray with a contact cleaner. If that's not enough, I run over the pins with some 800grit wet'n'dry.

[@TheJudy79]

They already sound fantastic I don't know what your talking about

[@theguitaramptech]

HAHAHAHA! You are right of course, Shawn. I just like taking them from "fantastic" to "fantasticer".... yep. I just discovered a new word. And don't forget, unless its a collector's amp, we have to make it reliable. We tend to be critical of "collectors" vs "players". But, we need to remember that its the collectors that will keep these historically important amps intact for the next generation of players. Hopefully some of them will be collectors, too. I would hate to open a 1964 Princeton in 20 years time and see a sea of Orange Drop caps and Illinois Capacitor Filters. That's when I hang up my soldering iron.

[@mattrorke7536]

Love it! I noticed after you found the carbon resistors drifting you changed to a metal film which was on the money. Do you recommend using metal films in general?

[@theguitaramptech]

Thank you for your insightful question, Matt. In general, I mostly use metal films in my repairs. They are quieter, and more stable, and smaller for their wattage capability. My main objection is that horrible blue color. Wherever possible I will pay a premium to get brown metal film resistors. Vishay is one such supplier. Of course there is the legend of the mystic sound of carbon composition resistors. I am a skeptic, but have an open mind just in case I hear the difference one day. Note: I will never replace an old resistor or component in a vintage amp unless it has failed, or drifted too far away from spec. We are custodians of the past, and have no right to the wholesale exchange upgrade of vintage components.

[@mattrorke7536]

@@theguitaramptech excellent! Thanks for the reply. Love the videos.

[@joepipino]

Great video!! I've got one without the Fender name on the grill cloth. What year would that have been made and is it worth more? Thanks

[@theguitaramptech]

What a beauty! I'd be thinking it may be a nearly 1964. The badge was attached later in 64. Have a look at the transformer date code. I only repair the amps, not sell them. A vintage equipment store in your area would be the better judge of value.

[@joepipino]

@@theguitaramptech Many thanks! Much appreciated!! What numbers should be on the transformer code and the tube diagram that point in that direction?

[@theguitaramptech]

Hey Joe, I explain about Tube Charts in my video "Fender Blackface ProReverb.". Look up EIA transformer date codes. EG If it is 606-4***, it will be Schumacker (606) made in 1964 (4).Have fun

[@joepipino]

@@theguitaramptech Thanks again! Cheers!

[@tombryan1]

I disagree to a point. Plug in a set of 1950's NOS Hytron Smoke glass brown base 6V6's and hear the difference, plus they handle high current if they are true NOS, it's no contest. The single orange blob cap sticks out like a sore thumb, there are better choices if the owner wants originality, or the look of it anyway. Power diode drop the B+ with a heat sink to get the the voltage down to 410 or so.

[@theguitaramptech]

Sorry Tom, I'm not sure what part you disagree with. Good suggestion, but my customer would not have approved installing multiple power diodes on a heatsink. Certainly, I agree with you about a NOS set of 50's 6V6s. I have been stung so many times in buying NOS and second-hand valves. I can't pass them on to my customers, so I just wear the loss. I am sure there are reputable dealers in the US or maybe UK, but by the time they get to Australia my customer is either pissed off with the wait time, or the cost.

[@uptownphotography]

Excellent video. I watched part of it as (getting late here in the NYC Area (1AM) so I'll watch the rest tomorrow). Question: I have been considering the reissue Princeton Reverb. Are the reissue Fender Amps worth upgrading components? Or even going a step further and rewiring with a turret style board rather then the PCB board that they are made with today? Also, by any chance do have have a video where you upgrade components in the newer PCB models? I can across your channel by accident (Happy Accident)...Excellently done and a ton of great information that you explain very well. All the best from the U.S....Gave you a Sub too. Phil NYC Area

[@theguitaramptech]

Hi Phil! Thanks for your question. Are the Princeton Reverb Reissues any good? YES! Sure, Fender cheaped out on some parts, but I wouldn’t suggest pulling out new parts that won’t last for 10 years to replace them with parts that will last for 20 years. May as well get use out of what you paid for. Two easy ways to vastly improve the tone out of these reissues is (1) The setup. I can almost guarantee that the bias will be set way too hot. Also, you can tailor your sound by trying different V1 tubes. I like a 12AY7, but also give a 5751 a try. (2) The speaker. I have a (real) 1968 Princeton, and the biggest improvement was in upgrading the speaker. I have a 12” Weber in mine. It’s a Deluxe-killer! My mate has a 10” JBL in his ’64. Awesome sound. Doing a turret board will probably open a can of worms. I have a Super Reverb in my workshop where someone had tried the PCB to Turret conversion and I have to sort it out. What a mess! Where is the noise coming from? Bad earthing? Poor layout of the filament supply? Poor soldering? All of the above? I know that turret board amps can sound better than a PCB, but a turret board has SO MANY opportunities for screw-ups. Let me know which path you take on your Princeton.

[@uptownphotography]

@@theguitaramptech Thanks Chris for your detailed information. I appreciate it. Question: Generally speaking...How would a 12AY7 affect the sound in V1? Same question if I were to use 5751 in V1. Thanks....Time for bed. 1AM again... Phil NYC Area

[@theguitaramptech]

@@uptownphotography Excellent question, Phil. I do the 12AY7 mod in all my Fender amps. With a gain of 45, a 12AY7 is not going to push the next stage, tone stack recovery (also one of V1’s two triodes), into non-linear operation. I prefer to leave that to later stages, ideally the power tubes. More importantly, and to my taste, a modern 12AY7 sounds better than a modern 12AX7 (gain of 100). Even though it's in the same family as a 12AX7, the 5751 (gain factor of 70) is definitely worth trying for even the most doubting of all Thomases.

[@uptownphotography]

@@theguitaramptech Hi Chris. Thanks for that information. It might be worth a try at that. I like what you're saying and i am a believer in pushing the power tubes myself rather then all on the pre amp tubes. The one sound that has been alluding me, with dual channel amps, is the gain channel is mostly good for heavier distortion, but not really that great for a warmer (and cleaner) over driven sounds. I only have owned one amp personally that had a clean channel that you could push into over drive and also had a lot of note bloom (into the harmonics). It was first generation Mesa Boogie Mark IIA model I bought new in 1979. But then something happened to it and the clean would only do clean. This is a mystery to me to this day why the amp stopped doing overdrive and the note bloom in the clean channel. I'd love to share the chronology with you (if you're interested ) as to what happened and maybe you would have insight as to what might have happened because of your expertise and background...All the best... Phil NYC Area

[@theguitaramptech]

@@uptownphotography sure Phil. You can email me at [e-mail] but it’s questionable as to how effective I could be 10,000 miles from you. 🤷🏻‍♂️

[@rossvanuatu2666]

Loved the video Chris! What's your opinion on swapping the Princeton's output transformer for something like the TO20 to achieve additional headroom?

[@theguitaramptech]

Thanks Timothy. Yes, the TO20 is an excellent transformer, but, I would definitely not change the OT on your blackface, or even on my drip edge Princeton. The OT is a critical component to the sound that you love. Don't even talk about the drop in resale value. If you want more clean headroom, first ensure that it is biased correctly (60% for headroom) and put a 5751 or (my preferred) 12AY7 in V1. If that's still not enough, sell it to fund a Deluxe Reverb. Let me know how you get on.

[@luthiervandros]

@@theguitaramptech if you don’t mind removing one wire to add in a resistor, then a 470k or 1m resistor to the pi input wi help control the flatulence in a big way. But there so much so much you can do with 12w and a 10”.

[@Matan2222222]

Thanks You for the detailed video! Where can I find the 3 prong cable conversion. I saw your way of installing it but it seems like everyone do it differently.. Thanks!

[@theguitaramptech]

You are correct, Matan. Everyone does it differently. Here are a few things to remember: FIRST. Turn off Mains power and remove the power cord from the wall. SECOND. Check that first step AGAIN. Then, 1. Clip the Death Cap. I usually leave it in place but disconnected. 2. The Neutral goes straight from the power lead to the PT (power transformer). If you have convenient place to connect it (eg the disconnected Ground Switch) then use that. Otherwise, I connect the 2 wires with good mechanical join and shrink wrap them securely. 3. The Active goes to the INSIDE connector of the fuse FIRST (furthest from chassis) 4. The other end of the fuse goes to the Power On switch. 5. The other side of the power switch connects to the Line of the PT. Many people like to wire the switch before the fuse, even Uncle Doug, who I admire greatly, but that is NOT correct in many countries for safety reasons. I understand Doug's reasoning, but please don't. A flick of the switch will make for a very bad day. If you have any doubts, please DO NOT follow the above instructions and take it to someone who is more comfortable with death...like your typical Amp Tech.

[@Matan2222222]

@@theguitaramptech Thank You for the great explanation! In your video you go from the ACTIVE to the power switch and from the power switch to the outside connection of the fuse and the inside connection is connected to the power transformer. The description you wrote to me is exactly what you do in this video?

[@rossvanuatu2666]

@@Matan2222222 I noticed this too Matan. Active is shown connected straight to switch and from there to the fuse.

[@dwightbehm2886]

If I'm going to be watching your vids . hear on utube ay Chris I hope you dont mind if I put a spot of Brandy in my cup of coffee.

[@TylrVncnt]

Wow, I can’t believe the NOS supplier claimed they were “matched”... do you mind sharing which supplier that was? It could’ve been a rare mistake (maybe..) but not a good look at all 😬

[@theguitaramptech]

You're right, Tylr. It's not a good look for the supplier. I had bought quite a few tubes off him and they were all good, but not this time. He lost a good customer. It may have been a tube-tester issue. It may have had a bump in shipping. It's getting harder and harder to find good NOS tubes which may test as OK but are microphonic. The good ones were cherry-picked by the amp community 10 or 20 years ago. The seller is in Australia, and I will give him the benefit of the doubt by not naming and shaming.

[@shckltnebay]

Just got a 68 all original except for Power transformer, I guess I better change the bias cap? I've got 410v on the plates and 22 ma on the grids

[@theguitaramptech]

Wow! That's fantastic, Eric. I also own an original drip edge Princeton. Yes, I would definitely check the ESR on your capacitors, especially if you're going to gig it. Your bias is a little hot at 75% dissipation. I would increase the 27K bias resistor until you can tone that bias down to about 65%. Start with a 33K. If you have an oscilloscope, check you don't reduce the bias to the point of crossover distortion. While you're there, can you please increase the bias cap voltage rating from 25uF/50v to 25/100 or even 47/100?

[@shckltnebay]

@@theguitaramptech Great advice, ill be replacing the can cap with individual 20/500 caps and the bias with a 100/100 sprague

[@theguitaramptech]

@@shckltnebay sounds great Eric. I’d watch going too big on your first bias cap. You don’t want the tubes to start conducting before your bias voltage gets negative enough. 100uf should be ok, but I’d go with 47 in my amp. If you have an indirect heated filament like GZ34 you should be ok.

[@moodyga40]

ESR and LSR in caps

[@theguitaramptech]

Hi Ian. I am sorry for not understanding what your comment means. I'm not sure if you mean LSR as in Low Series Resistance (a good thing) or ESL as in Equivalent Series Inductance, (which is not relevant at audio frequencies).

[@shckltnebay]

Is there any reason to go to 100uf for a bias cap when you have a choice of 33uf and 50uf?

[@theguitaramptech]

Hi Eric. I like to increase the bias cap for a couple of reasons: Better filtering and a more stable voltage. This goes with a word of caution. You don't want the cap so large that it will not charge up in time to provide a sufficient negative voltage to the control grid before the plate voltage. With a tube rectifier, we have a bit of time while it comes on line and ramps up its B+. That was a good question. Thank you.

[@TeleCaster66]

Man, the low strings sound like crap! Is the speaker bad or what?

[@theguitaramptech]

Hahaha! We’ll spotted, but thankfully not the speakers. I made this video before one of my mates told me that I shouldn’t be recording at 0dB…more like -12dB. I confess. I’m old school and worrying about a non-existent S/N ratio. I was clipping the preamp stage my mixer. Hopefully my audio will be improving in future videos. It’s a work in progress. Thank you for listening closely enough to hear it.

[@JOAQUINARMIJO]

I own a 1966 Champ Amp, how far is it from the Princeton circuit?

[@theguitaramptech]

The champ is quite similar to a tweed Princeton. From brown face onwards, the Princeton dual 6V6. Check out the schematics.

[@JOAQUINARMIJO]

@@theguitaramptech Tweed Princeton, interesting. The original 6.5 speaker sounds bigger than it is. Have you herd of “The White” amp High Fidelity. The side line Leo made and name after Forest white.

[@theguitaramptech]

@@JOAQUINARMIJO yes I’ve heard of The white Amp, But I’ve never seen one. I’d be surprised if there was one in Australia.

[@russellesimonetta3835]

That amp isn't the usual princeton!! It's a AA764!!! Not the usual AA1164!! Leo Fender didnlt like that amp!! He wanted it dialed back because it was Fenders high end STUDENT amp!! Cheaper pots a lower output rectifier. That amp had gain and great tone!! The Fender engineers brought that circuit back after Leo sold tge company. Also many rockers loved the sound of that amp but too low wattage for the times. The Mesa Boogie amp guy got his start by taking those amps a turning them into 40 watt, then 50 watt then 70 watt amps !!!! Carlos Santana walked into Mr. SMITHS shop and they asked him to try one of those hot rodded princetons and loved it. He said boy this amp boogies!! And a brand was born!!!

[@theguitaramptech]

Excellent knowledge, Russell. I really appreciate your input and knowledge. I also love the early Mesa amps, but I think Randall got sucked into the black vortex of "I will make it more complex...because I can" which often comes at the cost of tone. Thank you

[@russellesimonetta3835]

@@theguitaramptech I'm more of a loreologist! I dive deep into speculative knowledge. For example what amps did Clapton and Allman use on layla, Claptons beano jtm 45. What's useful fact vrs speculation. Capacitor and resister controversy's . It floats my boat. I'm an old drummer who played alongside all of these classic amps. But the tube amps always fascinated me! I have enough knowledge to build amps but the wife won't let me!!!! Yeah the mesa's ,,,they tried to cater to the heavy rockers. Never met a Mese I liked. Mesa also hides critical schematic info so people find it difficult to repair or clone them.

[@theguitaramptech]

@@russellesimonetta3835 Cool perspective. loreologist! That's a first for me. I have heard many wonderful Mesa amps (mainly the early ones). I have been well supported by the Australian Distributor for Mesa, but the fact remains that his amps are unnecessarily complex, often at the expense of tone. Time to build that amp Russell!

[@MuscleDad420]

Ripper!

[@theguitaramptech]

👍

[@jothanankrogh]

The big multicans seem to last forever

[@theguitaramptech]

They defy common sense with all the heat bottled inside a tin can, but you speak the truth, Jonathan. I have left in the cans from Blackface Princetons when they checkout as good.

[@moodyga40]

Restuff the caps

[@theguitaramptech]

Yeah, that would look very nice, Ian, but who's got time to do it, and it would be unlikely a customer would want to pay for it. I've seen Uncle Doug do it, but I would worry that the next Tech (or me) would see it and replace it thinking it was 60 years old!! LOL!

[@nevillegoddard4966]

@@theguitaramptech Yeah, Uncle Doug usually puts a little note in the doghouse letting the next tech know the old caps have new caps in em!

[@fivepiece]

The real question is "how can we make a Princeton REISSUE sound fantastic?"

[@theguitaramptech]

That’s an excellent question fivepiece. If it were my amp, I would put a 12AY7 in V1, change the phase inverter to a 12AT7, and get that damn biased set up properly. I reckon that would sound pretty sweet. 🥰

[@GertjanRoossien]

I hear you say "law and common sense" , what is that in these days?

[@theguitaramptech]

HAHA! Yes, I hear you, Gert-Jan.

[@sheaiek]

Step 1: do nothing Step 2: play

[@moorec1053]

It is weird how stupid some guys are about the parts in their amp. The caps are 50 YEARS Old...... if bot now, when..??? And..... if he replaces ONE, your amp is no longer "Original"..... so why not replace the rest of them. There is NO Magic in parts. They are there to perform a certain job at a certain voltage. It does not matter if they are Blue or Yellow, Carbon or Metal, Oil or Plastic. This amp does NOT sound "original" with 50 year old Elytics. But it WILL sound original with new filter caps

[@theguitaramptech]

Yes, many people share your point of view. I just happen to not be one of them. Briefly: Your sound does not pass through electrolytic filter caps, so change away. Your sound DOES pass through coupling caps and Blue, Yellow, Red or Green don't sound the same. If you're not sure about it, try replacing all of the coupling caps from YOUR old Fender with the cheap green poly caps from a hobby store. You may not hear the effect of one capacitor being changed but you will hear the combined effect. That's why shot gunning an amp will ruin it.

[@dwightbehm2886]

Why not use a 5Y3 rectifier? It can supply enough plate volts and current for 2 6v6s with tremolo and reverb especially a Russian 5y3. It will lower the plate supply volts alittle more.