How to Build a Classic Valve Guitar Amp (based on the Tweed Princeton)

This video is an overview of how to build a valve (tube) guitar amp based on the guidance in Dave Hunter's book "The Guitar Amp Handbook".
It looks in depth at the history of the amp, why it is such a good project to undertake, how you can modify it, how you can build it, how to test it and finally what it sounds like.
00:00 Intro
02:33 Why Build a Valve Guitar Amp?
05:23 Overview of the Two-Stroke Amp
08:09 Evolution of the Fender Tweed Princeton to the Two-Stroke
10:32 My Modifications to the Two-Stroke
14:34 Building the Amp
16:40 Electrical Testing
20:48 How Does it Sound?
29:01 Acknowledgements and Information Sources
The Guitar Amp Handbook by Dave Hunter amzn.to/3fowwXC
Designing Tube Pre-amps for Guitar and Bass by Merlin Blencowe amzn.to/2AqCN6z
Tube Amp Talk for the Guitarist and Tech by Gerald Weber amzn.to/2ApoFKN
A Desktop Reference of Hip Vintage Guitar Amps by Gerald Weber amzn.to/3e2sBQ9
Inside Tube Amps by Dan Torres amzn.to/3cW6Hg0
Modulus Amplification - modulusamplification.com
Amp Maker - www.ampmaker.com
The Valve Wizard - www.valvewizard.co.uk
Kendrick Amps - www.kendrick-amplifiers.com
Rob Robinette - robrobinette.com/Amp_Stuff.htm
D-Labs - / @d-labelectronics
Music: www.bensound.com

[@Dude_Slick]

With the ability digitally model any amp you want, including the Princeton, Who needs to build one? The answer is that it's not about need. The real question is why the hell would I not WANT another beautiful tube head sitting atop my spare 4x12? That thing is sexy AF. Great Job.

[@Zlotyi-7]

Tubes are different.... Paul Davids made a really good video about it. Where he compares a tube amp with one of the most expensive digital modeller. Tubes sounded more live and organic, especially with half gain sounds.

[@user-1-800-spanked]

My new Mentor, Dave Hunter explains in a a way that i can understand and not get lost and say WTF, i want to learn all about tube amps, i just got a weber 5f2a for a price of 200.00 from a friend that got it for 50.00 worth of dope(crazy ) when i was younger i owned a Fender Bandmaster blackface66 i think With the fender cabinet that hat 2 Altec Lansing speakers, that i never should have gotten gotten rid of !!! another jem i had was a Blackface Fender Princeton amp with the original Jensen, in the words of Rod Stewart, i wish i knew then what i know now , when i was younger!!!!!! thank you for a very well vid, Jan

[@joecarson8281]

I've built several variations on the 2 Stroke theme and they're all the best amp I've ever heard.

[@jamesha175]

the amp used to record that first opening music tune sounds awesome now i want one of those amps

[@monto39]

Really useful info on adding a NFB loop to an amp w/a multi tap Output Transformer (connecting to the lowest impedance). I'm about at the end of building a 5E3 kit, and had recently decided to modify it to include that. Great video, very informative (+ covers something there's not much info out there on)

[@utubeaf3c0]

Just ran across this and so glad you posted another video. I love watching your two Layla videos over and over - for this novice guitarist, it's like a master class in composition and recording track analysis. Please keep them coming!

[@CrackingtheChord]

Thanks very much for the kind words. It's very much appreciated.

[@NINEWALKING]

Regarding NFB, there are amplifiers using low or high impedance tap. Disregarding where you plug in the speaker, there will be voltage present on all taps of the output transformer. Grids need no current. Tubes are voltage driven, so you will not take away power by taking the NFB signal from any tap. What is important is the voltage you get from the tap. Higher impedance taps have more windings and hence have higher voltage. So if your output transformer has 4 and 8 Ohm taps, voltage at 8 Ohm tap will be twice as high. Hence, if you want a certain feedback level, you will need a bigger NFB resistor value. Higher the voltage of the NFB signal and more NFB effect you get. Initially, it sounds like volume loss. But it increases headroom and lowers unwanted distortion. Guitar tube amplifiers without NFB are wilder, harmonics generate easier and distort more. Now, regarding that 3 position switch. Those label names are just that. Any connection to that type of tone is happening in the user's brain. There is nothing like that happening when you change cathode bypass. Cathode resistor does the biasing of the tube. When the tube is working, there is a Voltagd drop over the cathode resistor. That voltage drop references the ground as lower voltage than the cathode of the tube. Hence, grid leak resistor is connected to ground, and that brings the "negative" (better called lower than cathode) voltage to a grid of the output tube and that biases the tube. So, just to do a basic job, you do not even need the bypass capacitor. Why is it used then and what does the capacitance value changes? Well when people explain how the tube work they are explaing positive path. Hence only good thing happening. Though tubes are prone to their own internal NFB because of the hiw they function. I bet this is new to many people. So what bypass cap does is reducing NFB effect and making tube more efficient. That's why people will say add bypass cap and you will get more gain (talking about preamp tubes) or add more capacitance to get more power and bass in case of the cathode biased output tube/tubes. But in reality small value like 0.68 will suppres the internal NFB effect at only high frequency and will sound like a boost in the treble. Higher the capacitance more of the sonic range will be boosted. There are online bypass calculators and you can change the components and calculate the effects in gain and the frequency response. Now calling it blackface with no bypass and tweed with some and plexi with maximum is kinda silly. I might have mixed the order. What you actually get is 0.68 is top boost and 25 is full range boost. Difference in real amplifiers is way bigger. Starting from completely different tone stacks to different output tubes to different cabinets and speakers. Different bypass capacitor value can't do that. It changes the tone but not the nature of the beast. I could write a book about guitar amplifier rectification and filtering and feel under the fingers. Whole topology and execution of the schematics makes it happen. If you look at only tube or diode rectification Fender Black and Silver face amplifiers would have had no feel and would be too stiff. Same would be true for most Plexi amplifiers. But most of them feel great to play. Things are complex and one liners do not cover it. For example no NFB loop in small power amplifiers make them feel bigger. More alive to. But from like 50 Watt and more it becomes horrible and uncontrollable and to dynamic. Impossible to play.

[@jeanlawson9133]

First mention I have ever heard of a two stroke Amplifier....I mean I have heard of two stroke diesel engines,, automotive..such as SAAB ....and others two stroke motorcycles like the 750 triple Suzuki GT we dubbed water buffalo...and I have messed with amplifier off and on since I was a little Ladd....Goes to show..I am not a know it all... after listening and watching I now know why....Rock and Metal was always my interest....But this is a sound I have learned to love these days. Thanks glad I discovered this... Very interesting 🤔

[@bigbasil1908]

That's a fancy garden bench you got there, with the little table that pulls up from the seat

[@AlwaysStaringSkyward]

This is gold. Thank you!

[@miettoisdev]

amazing work

[@CrackingtheChord]

Thanks for the visit

[@wims58ej]

Wow , what an amazing video ! I had some things I didn't quite understand about the Dave Hunter instructions in the book ? You really clarified it for me . My book doesn't have the single output tube diagram either . I really wish he would have included a schematic in the instruction . It would be easier for me to understand . Thank you sir !

[@CrackingtheChord]

Glad you enjoyed it!

[@rocklamarre9717]

Good job very nice sound.

[@CrackingtheChord]

Thank you very much!

[@russellesimonetta3835]

Very nice build!! I remember the video on your princeton build!! It was a team build if i remember correctly.

[@CrackingtheChord]

Thanks Russell. Well remembered. Yes, that was building a Mojo kit under the supervision of an amp builder (Jon Dickinson) with a couple of other guys. Wouldn't have attempted a scratch build without that experience. Did everything myself on this one and there were few bumps along the way as you will have seen.

[@russellesimonetta3835]

@@CrackingtheChord yeah ,,,with amps it takes study, careful thought and problems still rear their ugly heads. When doing chassis grounds you need a heatasaurus! 100 watt iron because the chassis works as a heat sink and your solder may look good but isn't. Are you familiar with the Uncle Doug youtube channel?? He is youtubes best tube amp teacher! Explains the workings of amps from building cabs, covering them, metal working chassis, everything and then some!

[@CrackingtheChord]

@@russellesimonetta3835 Yes, I am familiar and have watched several of his videos. He's extremely knowledgeable, quirky and fun!

[@robertwhyst]

Brilliant video, and very well explained. This is a great little amp design ... just one thing about the comment that this amp wouldn't be much of use for the "louder" genre ... You can just play a nice bit of Heavy Rock or modern metal through it as well ( it doesn't harm to use pedals in combination with the amp😉), I build a very similar design not so long ago, and used it in the studio to get a certain drive tone ( normally achieved if a 4 x 12 stack is used on max volume) .... but these smaller type valve amps do the exact same trick, just at a far more "user friendly" volume. In fact these type of amps are ideal studio amps, for any style or type of music ... it really depends more on the skill and talent of a guitarist to get the best out of an amp, but this nice two stroke is a very versatile design 👍

[@CrackingtheChord]

Robert, Thanks for kind words and very interesting observations.

[@stephenkirk1154]

Hey man, have you thought about doing a series of build videos ? So simpletons such as I, can follow along ?

[@CrackingtheChord]

Glad that you liked it enough to ask for more. Such a series is in the works.

[@airgead5391]

20:05 You are wrong about that. I always use the 16 Ohm. Remember we are talking about a transformer. To try to understand you could hook up a 8R load and measure on the 16R output tap....

[@wendyandgeoffpattison2610]

The GZ34 is a great rectifier valve, in that it has a very slow startup. Very easy on caps and resistors. Like a built-in standby switch, only better. Flows big current, and good sag.

[@joeltunnah]

"Sag" is voltage drop across the rectifier when the amp is pushed. GZ34 has very low voltage drop, so low sag. A 5Y3 has 3x as much.

[@roadglider6001]

Just found this video; and it was great. I heard about several custom built amps that allow you to use different output tubes, but never understood how it works. From my understanding of your video it happens because you use a bigger transformer. You didn't tell us how much bigger the PT needs to be? Can you share that info? And is there more to it than just the bigger PT? Is there a layout and schematic available for your two stroke amp? It sounds like this amp is what I've been looking for, for many years. Again great video and look forward to finding more of your videos.

[@CrackingtheChord]

Hi, Glad you liked it. The secret to using different output tubes is the cathode bias - essentially the tubes bias themselves. To size the PT you simply add up the current draws for each tube , ensuring that you allow for the highest current draw tube you're likely to use. You will also need a PT with a 5V tap to supply the tube rectifier heater in addition to the 6.3V taps for the other tube heaters. Luckily I found a PT that was probably a bit over-engineered for the job at a reasonable price. The layout and schematic are in Dave Hunter's book - it's a good idea to get the second edition of the book if you're contemplating a build. He updates a few things in that that are key, eg he did away with two power tubes working in parallel.

[@lanphanh]

Hi sir, I have a 2 channels acoustic guitar amp power by ac electric that I really like. I want to convert it to dc power by lithium battery, so I can carry outside. How could I find the DC output from the AC power supply, so I can feed it with DC power from the batteries? Thanks in advance!

[@michaelclark5020]

Thanks for posting this. I would be really appreciative if you could tell us or share links where to get the parts cabinets chassis components. That seems to be the hardest part is getting all the transformers and components instead of buying kits. I really need to get that pre drilled ckt board. I love the fender super reverb yes it is loud. I own a 1969. I have played smaller amps but don’t get the magic of playing like I do when I play my super. I have never played a smaller amp that can give me that feeling. That would be the ultimate a smaller amp that can make me feel as good as I do when I play my super.

[@CrackingtheChord]

Hi Michael, the links to the various suppliers are at the bottom of the description. Since I posted the video I have also discovered Tube Town in Germany :www.tube-town.net/ttstore/kits/?language=en. I actually bought the circuit board off eBay - there are various vendors. I know just what you mean about larger amps - I also have a Super Reverb - a 70s model. I particularly enjoy my Bassman 50 via a 2x12 cabinet. But it's a trade-off these days between enjoyment and hearing loss, at least for me.

[@krishalland918]

Well done sir, well done. As I am about to embark on a similar journey of my own, I have a few questions about your mods that I am considering including, if you would be so kind: 1- I can’t see the colour code on the power filter bleed resister. Maybe KZbin doesn’t show the colour well, maybe my eyes are old. Is that a 1k 2W? 2- how do you find the SS rectifier vs the Tube rectifier? Would you mind sharing the spec of the diodes and sag resister (and maybe how you switched it in)? 3- Was the NFB mod valuable? What value of pot did you use? Kind regards K

[@CrackingtheChord]

Hi Kris, glad you enjoyed it. The filter bleed resistor is 100k/2W. I got the specs for the switchable SS rectifier and tube rectifier from Rob Robinette's site. The diodes are IN4007, the sag resistor is 750Ohm/10W. The difference between the two was more subtle than expected which is the same for the NFB. Without NFB the sound is a tad 'looser' but not in a major way. Although they're not dramatic differences they're worth having for the relatively little extra work and expense. Best regards,

[@Buckers50]

Hi there, I'm currently building "my" version of the "two-Stroke and was very impressed with your video.....very clear and concise, thankyou. I was interested in how you overcame the problem of variable impedence selection sockets at the rear. The "revised" Hunter layout diagram shows the use of a switch to select between just 2 impedances, but you don't have any such switch. How did you achieve the impedance option, if at all? Phil

[@CrackingtheChord]

Hi Phil, Good question. I bought a suitable transformer from Modulus Amplification that has three taps - 4, 8 and 16 Ohms - and wired up three output sockets. There were two reasons for this. Firstly 16 Ohms gives, I believe, the most efficient transfer of power - Dave Hunter's design has only 4 and 8 Ohm outputs - and secondly I didn't trust myself with a switch. I know that putting a 8 Ohm speaker into a 4 Ohm socket isn't the end of the world but putting a 4 Ohm speaker into a 16 Ohm socket might be. For safety's sake therefore I went with the separate output sockets. Cheers. David

[@Buckers50]

@@CrackingtheChord Thanks for the reply David. My solution is to use (hopefully) switched (DPDT) sockets, so when the speaker jack goes into whichever socket is relevant, it automatically connects the NFB resistor to the relevant secondary winding on the OT (Hammond 125ESE in my case). Watch this space!! Best Regards Phil

[@CrackingtheChord]

@@Buckers50 Great stuff Phil. Let me know how you get on. Cheers. David

[@Buckers50]

@@CrackingtheChord Hi David, I can confirm that the DPDT (although SPDT will suffice) sockets were perfect for the job of allowing multiple options at the rear of the amp, ie 4, 8, or 16 ohms. In essence you need a normally broken contact, which only "makes" when the jack is inserted. This allows the OT output to get mixed with the NFB on only the relevant tap on the OT, and get directed towards the speaker, leaving the other terminals simply floating (open ended). HTH Regards. Phil

[@CrackingtheChord]

@@Buckers50 Hi Phil. Very interesting! Thanks for letting me know. I'll look at that for the next build. Cheers. David

[@yernickle]

What did you think of the tone voices tweed,blackface and plexi?

[@CrackingtheChord]

Depends on the valve used and the volume setting. Generally speaking, would say that the tone voices are 'in the ballpark' rather than completely authentic.

[@justovision]

I wonder what the issue with your princeton build was? I built mojotone's champ kit a year or two before this video came out and it's a great amp. That said my main practice amp now is a Monoprice princeton clone I got for $99 with the output switched to a 6k6. The plate current is different but I've had no issues I wanted more breakup at lower volumes.

[@justovision]

I did also add a pot for variable negative feedback to the champ build. Not a huge difference in my experience.

[@CrackingtheChord]

As I said in the video I was delighted with the results so there was no particular issue. It worked fine when first switched on - much to my surprise - and there was no motor boating or excessive noise. It gives what I consider great tone at low volumes.

[@peterroyle7082]

Hi , Cannot thank you enough for this video !!!! I am a retired Cabinet Maker , Guitar player , and have been inspired by you video to attempt to build a Two -Stroke amp , I have the Dave Hunter book and am in the process of purchasing all the components needed . Today I studied the layout plan of the amp and found what I think is a mistake !!! I'm a novice electronics person so can only express it thus . At the centre of the board there are 2 capacitors that are .220 uf which are in place , but to the left of those there is a figure .25uf/50v , but there is no symbol showing this component in place . Please could you say if this is a printing error . Thank you again . Peter , Herne Bay UK .

[@CrackingtheChord]

Hi Peter, glad you liked the video. The .25uf/50v is a misprint. If you look at the parts list there are only two of these caps listed. One is in the power supply and one is in the V1 boost section. Hope this helps. Best wishes for a successful build, David.

[@peterroyle7082]

@@CrackingtheChord David. I thought that may be the case , but had to be sure . Being a beginner I had to clear my mind before going ahead with it . Thank you again . Peter .

[@jurrione]

That amp would be great with a master volume and effectsloop. I am looking for a plan for a 3 to 5 watt amp with reverb or effectsloop to make a small top. Ideas anyone? Also a maser volume is a must. A cranked Champ sounds great, but it is too loud for my house and effects have to go in the front. This amp with volume, tone, master volume and reverb/effectloop.

[@CrackingtheChord]

Hi, for an effects loop check out Tube Town's kit (LND 150) and for a Master Volume check out the VCB/VVR kit for single ended amps from Amp Maker. Funnily enough I was intending to do these myself.

[@jurrione]

I will have a look. Thanks.@@CrackingtheChord

[@turtle7633]

lol the knobs really do go to 11 that's great

[@mycomment474]

Marshall made a head that goes to 11. It was just a typical head, with different markings, as you can probably guess. And another that went from 11 to 20.

[@alexcooper2956]

You have 2 stroke engines. Guitar amps are either single ended or push-pull

[@CrackingtheChord]

Alex, you are indeed correct but 'Two Stroke' is what the designer of the amp (Dave Hunter) decided to call it so who am I to argue?

[@peterperson1]

6:20 You might need to get your sharp eyes checked. V4 is the rectifier tube, V2 is the single remaining output/power tube.

[@CrackingtheChord]

Thanks for pointing that out Chris. It's nice to know that someone's paying close attention!

[@IndianaDoug]

Clever. But why 2 stroke? Only 4 Strokes have valves.

[@CrackingtheChord]

We like engineering jokes here! For the uninitiated the original concept was based on two valves (tubes) operating in tandem rather than push/pull - hence Two Stroke. The revised and simplified design did away with one of the output valves, leaving the standard single ended layout.

[@IndianaDoug]

@@CrackingtheChord well I’m in luck, I’m both a engineer and a jokester. Thanks for not getting bent out of shape, many do unfortunately.

[@joeltunnah]

The "current limiting" safety device is called your FUSE! 🤦🏻

[@CrackingtheChord]

Actually it isn't. A fuse doesn't limit current, it simply breaks the circuit at a pre-determined level which, depending on the size of the fuse selected, could have irreparably damaged expensive components. There is plenty of guidance on the 'net. To anyone reading this never rely on a fuse when powering up your amp for the first time.

[@joeltunnah]

@CrackingtheChord to anyone reading this, if your fuse isn't protecting your amp, you've chosen the wrong fuse. And if you can't even wire the fuse correctly to protect the rest of the project you're already in over your head. "Dim bulb" indeed!

[@CrackingtheChord]

We like a bit of controversy here at Cracking the Chord - it makes life interesting. We always abide by KZbin's conduct rules and never insult anyone no matter how tempting. The fact is that using a dim bulb tester is standard practice in the valve amp and vintage TV/radio communities. Just Google it!@@joeltunnah

[@joeltunnah]

@CrackingtheChord in all seriousness, I've been involved in radio and amp building/repair for 25 years, and I've only heard about this "dim bulb" thing in the last 3 months, on KZbin. Not a single person on any of the forums I read and participated in 15 years ago ever mentioned needing or using such a device. Did you learn about it from KZbin?

[@CrackingtheChord]

If you search online for "dim bulb tester" you will find countless references. A particularly good source is Rob Robinette's webpage - robrobinette.com/Tube_Amp_Startup.htm So, in answer to your question - not from KZbin @@joeltunnah

[@fostexfan160]

It was getting interesting until I googled the rip off price!! How much?? For that?? And you have to build it yourself?? Lots of gullible folk in the snake oil amp business

[@CrackingtheChord]

Mate, I built mine from scratch. That's the point of the video and I had a lot of fun doing it. I can also tweak the tone to my taste. But if you want to waste your money on kits........

[@fostexfan160]

@@CrackingtheChord Daddy chill !!.....It's still a kit that you built....whether you source the components yourself or buy a kit.......not much difference in price?

[@CrackingtheChord]

Not so. The Victoria Amps Two Stroke kit is $1900 - mine cost me $500!

[@mycomment474]

Dave Hunters amp build doesn't work. Plus, good luck trying to source the power transformer he recommends.

[@buzzedalldrink9131]

maybe you don’t know what you are doing there are many people who have build them and use them and if you cannot figure out a compatible transformer that will work maybe you should not be messing with guitar amps

[@mycomment474]

@@buzzedalldrink9131 Maybe you shouldn't be messing around making outrageous posts on YT comment sections Mr Smarty pants. If you're so competent you would have left the make/brand, etc transformer along with the specs that match Hunter's obsolete transformer that would be compatible with Hunter's DIY amp. But, you didn't, which leads me to believe you shouldn't be messing around with electronics or guitar amplifiers. Stop drinking so much, that way you won't be so buzzed when you write comments on social network(s) trying to belittle others. FYI, many built them BEFORE that particular transformer was obsolete. And/or found a used Fender transformer.

[@gilldanier4129]

@@mycomment474 Your comment was useful twofold, one that it instructs people to drink less alchahol when making comments and two it may stop people messing around with electronics and or guitar amplfiers when they don't know what they're doing. This was a precise and clear warning to any would be incompetent youtube commenter thinking of commenting under the influence of alchahol. Further more, the clever irony of your youtube name (mycomment474) has been noted.

[@jargero8203]

This is a video showing off a build, not an actual instructional build...