Amp Wars - The Ampeg Strikes Back

[@philgallagher1]

Sounds sweet now Brad!! This video shines a light on two of the main problems today... Patience & Perseverance.

[@Treardet]

It's great to follow along with this. I have an AC-12 that I haven't used much, but now I feel like I should take it to get tuned up.

[@ColeWheeler4Lyfe]

Awesome repair! Loved hearing the resistor box value changes.

[@glenwhatley4125]

It still would have been nice to see what a clean sinewave looked like on the scope through the entire volume and tone setting range. Sometimes you can create issues that are not all that obvious with only your ears as the test. It also gives you a frame of reference when you start. Great videos. Really appreciate the passion and effort you put into these excellent as well as entertaining sessions. Keep up greasy work.

[@mikeziemba2269]

My first real amp was a Gemini II that I "borrowed" from my guitar teacher. My previous amp was a little solid state number from Monty Wards - it died unexpectedly. I was told that the Gemini did not work, so I took it apart and my father noticed a resistor that was defective. We went to the tv repair store (1971) and bought the resistor, soldered it in and it sprung to life. That amp had great tone, but was just not loud enough - people were using Marshall stacks in clubs! So, Dad and I went to Washington Music Center (aka Chuck Levin's) and settled on an Acoustic 134 which was their version of a Super Reverb, sort of. That amp had no tone, but it was brutally loud. I remember playing gigs with that amp and doing things like unclipping speakers to try to get a more reasonable volume levels. Eventually, I modded that amp by wiring the output of channel one into the input of channel two. Great care had to be exercised when setting volume levels. Around 1976 or so, I exited the music business to go to college and the amp was sold along with my treasured 1972 SG Standard. As it happens, I had a friend that had a Twin and Les Paul Custom, but he could not play. So, he "loaned" them to me until one day years later he showed up at my parents house inquiring about his gear. I wanted to buy them, but had no money since I was still in school. Reluctantly, I loaded them into his car and that was that. I could have probably bought the combo for $500 which was a good deal. Oh well...

[@VegasCyclingFreak]

32:19 I have a pair of Celestion G12s in a DIY cab, nice speakers IMO

[@jenniferwhitewolf3784]

You really do need to get a good oscilloscope. Your at the point in your technical skills where without one your going to be holding yourself back. I often use 2 or 3 at once when working on amplifiers so I can see induced ripple on power supply with signal modulation, and a current probe to monitor actual current VS voltage together at various points. A decent dual trace 100MHZ analog scope, or a 500MS DSO scope will be immensely useful. You may have seen the filter cap failure by looking at the rail before even applying signal. Your understanding of circuit function is growing...

[@TheDogPa]

Pretty soon he'll be a pofesonal.

[@ayylmao5121]

around 5 mins he says about using his oscilloscope

[@InsideOfMyOwnMind]

With the price of a scope being what it is now especially for audio there's no excuse for not having one.

[@hyperluminalreality1]

I just typed the exact same thing in another comment before seeing this one. He is ready for a scope. He is ready to step up to being an actual amp tech instead of a poker arounder. A scope is a step in the right direction. At least he is talking about one now. He could also vastly improve his knowledge by reading books like Tonnes of Tone and The Ultimate Tone series by Kevin O'connor. Dave Funk's Tube Amp Workbook. The Dan Torres book. Kendricks A Desktop Reference of Hip Vintage Guitar Amps is also good written education to apply. Those are all newer tube amp books.

[@OtherTheDave]

Y’all understand that he already has one, right?

Just found out a friend of mine is selling one of these. He junked the whole board and had a new one built re-valved it and it apparently sounds as "awesome" as yours. Sounds great.

[@Curtislow2]

The only Channel I don't fast forward thought the sponsor portion of the video.

[@GeorgeChristofi]

I would have gone for DC leaking on that cap going to the trem control. Following the path on that schematic it goes through to ground through the tone controls. I thought it might be a combo of resistance/capacitance levels that started the oscillation.

[@rubenproost2552]

Yes, if you increase R12 the sound would get basier, because you change the frequency roll of of the filter it forms with c8 to a lower frequency. If r12 seems to be too low you may want to check c8 for leakage, as that would make the sound both less basy and weaker by reducing the resistance of the pair r12 and c8 (Not a guitar nut, just general electronics guy)

[@paulj0557tonehead]

The 1976 AMPEG G110 FET (FIELD EFFECT TRANSISTOR) with Tremolo/Reverb is a studio workhorse. A must have. Get one you'll see. 😊 I'm a tube head, but one day on a walk right in my path on the sidewalk , like a gift from the heavens sat a super clean Ampeg G110 TREMOLO REVERB amp 'FREE TAKE ME'. Itook it home and it worked 100%! It was like, " Hey you, tube nut. What I gotta do, track you down?" lol

[@BadToad1963]

I'm pretty sure that's the wrong style reverb tank for that mounting plane. This one is meant to be mounted horizontally, open side down.

[@TheGuitologist]

Could be.

[@telecasteroil]

This video is just what I needed, on a slow night, great tone shaping and modifications ,Brad !

[@madDadMusic]

When you get hold of schematics like that, do you copy them or record them somehow for future use? Is there somewhere you might send them for folks to use in the future?

[@ericcurtis8934]

man, i had a reverberocket r212r reissue as a teen. my favorite amp i've ever owned. too bad one of my bandmates stole it and disappeared.

[@foobar879]

F

[@TheTrashologist]

It’s nice how they isolated the chassis........ proceed’s to shake the bejesus out of it. Classic.

[@misterguitargeek]

The robot in that amp is howling "Oww Owwww Oww Oww" when you are plucking that D string

[@richardturk7162]

Well done Brad you saved another one.

[@paulcargo4233]

Us Ampeg guys are having kittens watching you mod the resistors in that GU12, it is worth a small fortune in its stock configuration. Ampeg has been using the Jensen C12-R with 7591's in push pull since the early sixties, while not the most efficient speaker they sound great and simply replacing it with something more efficient is enough to boost the 7591's volume significantly. without additional mods. You and UD have been an inspiration to me but please try to leave the vintage pieces as stock as possible. As far as chassis go I have a 64 reverberocket on my bench that is a little bigger than a carton of cigarettes and would love to have the acreage of the GU12 to work with. I have to admit your repair sounds great.

[@TheGuitologist]

I disagree. This amp isn't worth a small fortune of the current market. Ampeg GU12 is not a highly collected or regarded amp, and for good reason. There are tons of design flaws, which I pointed out in the two videos I did on it. There are better Ampegs out there. This was obviously going after the lower end of the market at the time it came out. After cramming in the reverb and trem, there is barely enough gain to move the speaker cone. I guess that's why they figured they could get away with using a vastly underrated speaker.

[@shakeyjonez]

That amp was a turd the day it was made. Someone who would pay anything significant for that hunk of crap just proves there is a sucker born every minute.

[@JSoloProjectOfficial]

The marshall lead 8412 Straight cabinet were loaded with the Celestion G12L 35w Speakers. They are not bad.

[@nokomisnichols]

sounds much better now.

[@windekind27]

Marshall used the G12L-35 mainly in their older Valvestate 4x12 cabinets.

[@SteveBlancoMusicianWarrior]

Hey, man. This was a real nice video. Working on amps is pretty insane. Some nice soulful playing, too. Music is life.

[@russellhltn1396]

10:30 Am I seeing things, or does that tone stack board have a bunch of cracked solder joints? The volume is the worst, but it looks like bass as well.

[@TimmyP1955]

Cut a notch in the sucker nozzle for the iron tip - you'll get better suction.

[@dlunsford1980]

These comments are cracking me up. You can always tell the newbies to your channel as they always bring up the exact same things. Maybe you need a disclaimer: 1. Brad has a scope but doesn't like using it as it makes for boring videos. 2. He picks with his fingers so has long nails on his right hand. 3. Yes he says Tremelo a little different than most.

[@knaggs71]

Flex!

[@philbillie]

Ampeg GU-12, That was my first amp when I was 13! My LP Black Beauty into this kicked ass. Mine was pretty bullet-proof. Love to find another one of these.

[@scottroberts3801]

Another fine fix! Great work sir.

[@deepwater2652]

Got that little amp crankin' and sounding good, Brad!

[@jman1428]

Brad were is the reverb?

[@pympin87]

is it possible they neutered the first stage to avoid blowing the lower wattage speaker

[@ghramsey1681]

First thing I said when I heard that motor boating sound was "bad filter cap". You ended up replacing them at the end. ;)

[@Mikeywil0003]

12:22 Damn, I wish you could get those speakers for 8-9 bucks these days. LOL

[@powerdog242]

Mikey You sure can, as long as you’re satisfied with also getting a wage of 70 cents per hour, like they did at the time. But seriously, $9 in 1957 is equivalent to $81 today. Which is pretty comparable to the modern cost of name brand speakers in. A new Eminence Cannabis Rex, for example, has an MSRP OF $89.99.

[@Mikeywil0003]

I know, that is pretty much a joke.

[@fireantsarestrange]

Surprises me still that in 72' they were using those circuit boards in there. Would have pegged that one for a class A only.

[@DavidBrown-it9ig]

I can only imagine what the repair cost!

[@greenhornfarmer3598]

That was some PERTY playin! nice to hear a different style for a change....That amp sounds amazing actually, nice, full and buttery smooth!

[@UrryKurtz]

Dunno. There is nothing wrong with 2M2 + 51pF. SLO100 and your favorite Mesa have 2M2 with some 80-470pF tone shaping part. Marshalls and Laney have 470k + 270-470pF etc...

[@brainndamage]

As do Fenders (where the reverb amd dry signals are mixed) in fact it seems like they're doing exactly the same thing here. Attenuating the signal between stages is good for distorted tone (gain staging)

[@hyperluminalreality1]

Fender Twin Reverb amps use a 3.3M or 4.7M resistor with a 10pf cap across it for tone shaping. A resistor with a small cap bypass is the STANDARD tone shaping used between stages in most high gain amps. Even Trainwreck amps used them. Still no scope to really look at what is happening and immediately pinpoint the problem in the circuit either. This is kid stuff, really. I like Bradley, but I think it is time he moves up to being a real amp tech instead of a poker arounder. Read more books, like the Torres book, The Dave Funk workshop book. London Power books like Tonnes of Tone and The Ultimate Tone 1 and 2 etc.

[@drmaawenz]

Yeah it is fine, the 3M3//51p is a part of a mixing stage.

[@TheGuitologist]

You guys are missing the forest for the trees here. This amp is QUIET in stock form. Sure that grid stopper and cap network aren't unusual in a lot of amps, but this isn't those amps. There is just NO VOLUME in this amp design! It has exactly two gain stages in the preamp with a James style tone stack shoved in between them. Not exactly a Fender Twin, is it? I have literally played 5W Fender Champs that were louder than this thing. They have to use .1 coupling caps just to eek out as much low end gain as they can through the amp and they still tried to keep it clean. The couple mods I did are easily reversible if some other tech thinks he's smarter than me and wants to put it back to stock. He'll very quickly find out I was right though. The changes I made made the amp louder. I appreciate the critical eye. But if you venture into dick measuring, I'm going to have to insist you get off your asses and post your own videos detailing the brilliant work you're doing with amplifiers, preferably the model in question.

[@UrryKurtz]

Don't be so grumpy comrade. :) Treble bleeding cap adds some crispiness and responsive-ness/active-ness. Dunno how to describe in English. :) And there are lot of popular mods - to add a small cap to gain pot in amps & to guitar volume pots etc. It adds more gain and prevents farts from bass strings. You tried different resistors without cap. So my point was - you play well on any type of old crap but owner might dislike tone change. %) We already seen this amp. Who wants this Jedi to return in the next episode? %) Regarding my brilliant work with amps I have to admit I'm lucky I build amps for pleasure as a hobby. Besides lot of pedals for last decade I built 3 SLOClones, couple of SE amps and number of tube preamps. So from my limited experience I can tell this thing has not many gain stages and cathodyne phase inverter (with 1/2 of 12DW7 ). No wonder it's quiet and speaker is rated low. You could try to replace 12DW7 with 12AX7. You are welcome %)

[@Howlinblind]

Great repair

[@rockabillycat1954]

That oscillation makes it sound like Doc Brown's amp from BTTF.

[@ovation99]

At Last !!!! Bet you'll be glad to see the back of this one (along with the Mesa).Patience is a virtue.

[@maynardjohnson3313]

is that oscilation or modulation between hum and mororboating (oscilation)?

[@rdpurdom]

Why does everything sound distorted, like there’s a fuzz tone on it?

[@Teleman73]

Next Ampeg you fix should be a portaFLEX!

[@johntaylor7496]

Thanks Brad. These damned repair videos suck me in every time.

[@michaelkassner5082]

Ya, I knew what you meant, not sure about anyone else. All said, I enjoy your videos. You get results and that's what matters.

[@bengalvin9932]

1:40 wasn't that a radiohead song?

[@kenjimac2211]

Funny, when you are soldering a component in place a puff of solder smoke comes at the direction of my face. Out of habit, I hold my breath 😂

[@demantoid418]

She sounds good. thanks for posting

[@BOZZONECOMICS]

Great sound

[@testbeeld2877]

How does everyone get the ddario NYXL stickers? I buy the strings but never find the sticker?

[@rileypaterson7117]

Great playing

[@christieslote5953]

Hey Brad ... Don't know if you upgraded your Variac ... but there's a mod that can do to get the Variac to display right info, right at the time you turn it on......

[@TheGuitologist]

I did mod it to zero later on.

[@JJ-JOHNSON]

Another awesome video Brad, keep them coming.

[@killercurl1]

i wish i could understand what you do.... i love this kinda stuff. i can mechanic my way around most things... but electronics seem like engineering and a lot of "thinking" thank you for sharing your gifts.....

[@Eddy63]

Hey Brad , love your Guitologist repair uniform ... Lol ... Good vid ... I shall do another shot now ...

[@ctcards2636]

Wow what a difference in volume with the 3.3k on R4. A few different parts in that design were bogus. But you got it sounding so much better and solved that. Nice Job :-) This is the 3rd Ampeg video ive watched in the last 24 hours on your channel. :-) I have very little experience with Ampeg tube amps.

[@ctcards2636]

What type of pickups are in that tele you used at the end ?

[@chrisf6216]

Thank you Mr. Guitologist for another great vid. No thanks for getting your SLTS solo stuck in my head, again. Cheers!

[@malungtvnews]

do input jacks all have resistors on them? also woul a jack to speaker have some sort of resistor on the speaker input?

[@Blaydrnnnr]

Speaking of speakers....I salvaged an old Kalamazoo "Bass" amp from a friend, the cab was destroyed, I pulled the chassis and controls in hopes of re-installing them into a custom head cab.. ( hasnt happened yet, since I need to find help figuring a few things out..) but since the speakers were sealed in a closed cabinet, before throwing the destroyed cabinet out, I cracked the sucker open, and found a pristine pair of Jensen C10P speakers. They are now installed in a custom wood cab I made myself, but strangely enough, I contacted Jensen to find out for sure the power rating of these speakers, and Jensen told me, they dont have specs on those speakers, dating 1966. I was flabbergasted, that a company as old as Jensen, wouldnt be able to trace these back. The woman on the phone told me that back in the sixty's, they sold speakers to third party vendors for their applications, so they may not have a record of the versions sold to Kalamazoo ( Gibson). I've found a few things on the internet about these speakers, but nothing concrete. I figured, since Kalamazoo made three versions of the "Bass" amp, ( one labeled "Bass 50", another labeled "Bass 30", and one labeled just "Bass"....mine is a "Bass" ) that from the power tube configuration, it was probably a 30W'r. So the speakers may be 15-20w ceramic speakers? Maybe...I have them in a stained dove tail pine cab, and use them with a few low wattage amps I have...kinda weird huh? If you ever get time, That old Kalamazoo could really use a pro's help.....( hint, hint)

[@TheRockGuitarChannelShow]

Brad's a fine picker

[@InTheSh8]

3:24 It is the early version of Alexa, whoi, whoi, whoi! Want's to tell you, she's hurt when you pick the strings too hard, LOL!

[@208414]

Is there a reason that you use a signal generator rather than something like a looper pedal playing a loop of actual guitar signal? I would think having a genuine guitar signal would make it easier to know how the modifications are affecting the tone of the amp.

[@Wh1ddee]

Aloha Brad - Not certain of this is accurate, but audio dudes if yore advised me that speakers are more prone to be damaged by under power. Speaker rating exceeds the power an amp can provide. The way it was explained to me is that speakers blow when insufficient power causes the magnetic field to collapse, causing the speaker to snap back with sufficient force to cause damage. The logic is that an amplifier with greater headroom will allow the speaker to travel the full range smoothly and will never snap violently due to amp derating, over heat, basically driving an amp to death. That may be why the original speaker has a lower power rating than the amplifier. If the original speaker is 15W and the amp is rated at 19W, there is 26% headroom to allow for amp derating at high temperature, or general degradation. Love your vids, and shit posts!!!!

[@toddjones5382]

Nailed it.. Great job Brad!

[@jscan]

And for years I've thought I'm doing something wrong with a solder-sucker because I have to pump it so often - glad to see that a pro has to work the same way.. Nice work Brad. Could it be this video is stuffed with ads (which I'm not used to on your vids..)?

[@fireantsarestrange]

Im gonna try building a Princton or a Twin kit.. May stick with something really simple first.

[@TheGuitologist]

Princeton would be a good start.

[@MrBrymstond]

First thought, ground loop, or maybe needs aluminum shielding

[@williamsquires3070]

(@21:15) - I noticed that VR3 (the volume control) is labeled as a 1 Megohm linear pot; shouldn’t it be a log-taper pot, since this is an audio application?

[@TheGuitologist]

The volume control has pretty good sweep as it is. It doesn't jump in volume going from 0 to 2. It does reach max volume around 7 on the dial.

[@srtamplification]

Now you have a Fenpeg.

[@jimbeaux4988]

I want a pedal that sounds like 3:32. It should be called FlexFuzz.

[@bradleycoffin1767]

Pajamologist 🤘

[@BIZARBIES]

Jammy work day!

[@AEFXGTS]

You know, you can take those 6 nuts off on the under side of the chassis and that aluminum plate comes off to give you access to all the components on the board. That's why that plate is there, to give you easy access to the components.

[@TheGuitologist]

There is a Part 1 to this video linked in the description. I go into that in that video.

[@SeanKerns]

Dangit, Brad! Every time I watch one of your vids, I see another piece of test gear I need!

[@danashcroft961]

That amp has gone all EDM/Electro New Wave...

[@waltersmetak]

One hell of a VCO!

[@dhix2388]

background music just right. thanks enjoyed.

[@tommyconancoates7097]

That Ampeg has onboard effects!!! It's an oscillating 1/2 a pitch shifter with mild overdrive, too bad it's probably too late to return for a full refund.

[@rickkillian2378]

Awesome job on that amp man

[@jonnybeck6723]

Another great vid... thanx Brad. Better than movies fer me anyway. Did you have any more thoughts as to the lack of cooling in this oh so strange design? Cheers

[@TheGuitologist]

7591 run hot. The direct mounted 7591 are a bad design, clearly. No breathing holes is a bad design too. The chassis is made in sections though and there are some small gaps that help dissipate some heat, but it could have been better. Some louvered breathing holes in the top and bottom would have been nice.

[@michaelkassner5082]

In troubleshooting that ampeg you said r4 might be shorted. Resistors never ever short as they dissapate heat the resistance (from handlng to much current)as goes toward infinity (open). Love watching your videos. Not trying to judge, just paying attention. You rock

[@TheGuitologist]

Yeah, watching back, I misspoke there. Probably I meant to say "open". Or I thought I was talking about the cap. You knew what I meant. ;)

[@TheGuitologist]

You are correct. I misspoke there.

[@theshowersherpa70]

What song are you playing at 21:45 while replacing R14?

[@TheGuitologist]

Not sure offhand. It was from the KZbin royalty free library.

[@bberker3418]

Im at 20: 19 into this Im guessing that c17 isnt about bright it is to stop oscillation and its the problem. lets see what happens.

[@bberker3418]

as I suspected. when the resistor R23 starts to wane ,.oscillation will return. Especially since you took the resistor value even closer down to Oscillation. But what do i know.

[@Nomad_za]

I have an Ampeg BA-115, it too is terribly soft and a Marshall MG100DFX plays much louder than it can. I need help with is because it overheated. I have the schematics of it but I can not read schematics. I want to replace the Caps which are 4700 UF 50v 85 Degrees celcuis and MOSFET IRPF9140 and IRPF140, but I cant find these parts at all. I am from South Africa, so I cant even send the AMP in to you.

[@SIXSTRING63]

Sounds like a cap issue causing motor-boating/ oscillating . I've had filter caps induce this kind of tones with weird harmonics like that. Still watching so we'll wait and see. Update : Yeah, I’ve heard that before in my times under an amp hood. Filter caps will induce those weird oscillating tones and strange harmonic overtones. I always put the amp on the scope as soon as it hits the bench if it powers up. It will tell you a lot in a hurry. You need a good tone generator, load resistor and use the scope. Will save you a lot of time and aggravation and you won’t have listen to the tone ring your brain for an hour 🤪 I have and old analog 25mhz scope for general probing and the 4 channel Rigol 1054Z digital scope for checking a lot of things on the output, RMS, frequency at the output to see if its matching what’s going in and most importantly the waveform. I like to see the clip point, crossover distortion points ,and ripple and oscillating . Things that aren’t always audible.

[@scotthewitt6047]

I don't think you give your pinky enough credit when you play great job thanks

[@74dartman13]

Nice repair/mods. Sounded great!👍😎🎸🎶

[@Aceroxx02]

Hey Brad, question: You're an amp guy so who better to ask? A while back I had bought a Marshall MG250DFX (the older model with an actual power switch, not the new one with the big round button). Anyway, the chassis stopped working one day and I'm not versed enough in amps to repair them. So I took the chassis out, converted the rest of the combo as a 212 cab and use a Marshall head with it now. my question is, I'm selling the old chassis for parts or repair. What price would you put on something like that?

[@Dadas0560]

Love the new vibes, too!

[@Chris66JTM45]

Nice Ampeg save Brad ... with older amps you just never can tell if it's going to be a Rogue One 😆

[@harrybullari2896]

Sounds great man! Great job!

[@robertcalkjr.8325]

Thanks Brad. Nice work. After you got through playing then, could you fry bacon on it?

[@VacuumTubes]

You didn’t lose gain. When you put the sig gen on pin 7 (the grid), it was being amplified a ton. When you probed into the plate (pin 6) you injected the sig gen after an entire gain stage. You will naturally have less output then from the speaker as the first preamp stage was just bypassed. Also, probing the plate before the cap is allowing high voltage DC going back to the sig gen. Generally it should probed after that coupling cap, or probe at the next gain stage grid.

[@TheGuitologist]

You're mistaken. The signal gen was injected via the gator clip to the V1 grid, not through the probe.

[@VacuumTubes]

The Guitologist ok. That wasn’t very clear. At 5:45-6:00ish it sure appeared like the sig gen was being fed in at pins 6 and 7.

[@brivington2011]

Great repair video!

[@brich2929]

Fine video, Brad. You done good, kid.

[@TheMeatman73]

hey brad been watching your channel for a while mostly from my phone think I messaged you once about building an amp for me from a amp I was going to buy on ebay but my phone went down and now I have a pos phone that never notifies me for emails anyway I have this old school pioneer sx 1080 that Ive had for a really long time well anyway bout 7 yrs ago my son plugged a aux cord into the phono jacks in the back to listen to music from his phone well it overloaded the left side circuit and now the left side is super low volume was wondering if you ever work on those kind of things at all the stereo is worth 1000 or more when in perfect working condition I have been into vintage electronics for most my life and have a collection of old gear like that and this was my favorite silver faced amp from the era just a question I thought I would pop your way I know you mostly work on guitar amps and tube stuff so just a question

[@Jennifer_Prentice]

Ill bet you get the whole "Cut your Coke Nails" all the time. lol

[@Ro-Bucks]

Sounds like the nuke amp on back to the future.

[@arnyarny77]

dear mr guitarologist my amp i bought just over a year ago, my problem is i hate noisy amps. i understand about the 60 cycle hum, bad cables, dirty power sources, etc etc, but i have a gut feeling it may be something else, oh and the tubes i had replaced and biased, i believe it may be a bad ground or something simple, that's just an uneducated guess on my part, what can you suggest? taking to local tech? i don't think there are too many where i live thx

[@TheGuitologist]

Bad grounding schemes are the #1 cause of hum outside bad preamp tubes.