Amp Wars - The Ampeg Strikes Back
ฝัง
- เผยแพร่เมื่อ 28 ส.ค. 2024
- Here's the second part of our Ampeg GU12 repair excursion.
PART 1: • What was Ampeg Thinkin...
PART 2: • Amp Wars - The Ampeg S...
PART 3: • He Heard a POP...Then ...
PART 4: • Has God Finally Forsak...
In this video we'll find out a sick 70s Ampeg can accidentally sound like a Jedi light saber. We'll also do some mods and stuff like that.
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Sounds sweet now Brad!! This video shines a light on two of the main problems today... Patience & Perseverance.
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.
Awesome repair! Loved hearing the resistor box value changes.
The only Channel I don't fast forward thought the sponsor portion of the video.
Hey, man. This was a real nice video. Working on amps is pretty insane. Some nice soulful playing, too. Music is life.
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...
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.
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
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.
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.
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.
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...
Pretty soon he'll be a pofesonal.
around 5 mins he says about using his oscilloscope
With the price of a scope being what it is now especially for audio there's no excuse for not having one.
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.
Y’all understand that he already has one, right?
This video is just what I needed, on a slow night, great tone shaping and modifications ,Brad !
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)
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.
What type of pickups are in that tele you used at the end ?
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.
It’s nice how they isolated the chassis........ proceed’s to shake the bejesus out of it.
Classic.
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.
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?
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.....
Well done Brad you saved another one.
Dangit, Brad! Every time I watch one of your vids, I see another piece of test gear I need!
Another fine fix! Great work sir.
Thank you Mr. Guitologist for another great vid. No thanks for getting your SLTS solo stuck in my head, again. Cheers!
The robot in that amp is howling "Oww Owwww Oww Oww" when you are plucking that D string
Flex!
Nice repair/mods. Sounded great!👍😎🎸🎶
That was some PERTY playin! nice to hear a different style for a change....That amp sounds amazing actually, nice, full and buttery smooth!
Another awesome video Brad, keep them coming.
sounds much better now.
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.
Could be.
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!!!!
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.
At Last !!!! Bet you'll be glad to see the back of this one (along with the Mesa).Patience is a virtue.
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.
F
32:19 I have a pair of Celestion G12s in a DIY cab, nice speakers IMO
Great repair
First thing I said when I heard that motor boating sound was "bad filter cap". You ended up replacing them at the end. ;)
Cut a notch in the sucker nozzle for the iron tip - you'll get better suction.
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..)?
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.
background music just right. thanks enjoyed.
Thanks Brad. These damned repair videos suck me in every time.
Great sound
Got that little amp crankin' and sounding good, Brad!
She sounds good. thanks for posting
The marshall lead 8412 Straight cabinet were loaded with the Celestion G12L 35w Speakers. They are not bad.
Next Ampeg you fix should be a portaFLEX!
Great Shirt :) FLEX spaghetti westerns !
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 😂
Great playing
That was a learning experience. You should specialize in those amps now you know the circuit from beginning to end. School of hard knocks learning
Hey Brad , love your Guitologist repair uniform ... Lol ... Good vid ... I shall do another shot now ...
Marshall used the G12L-35 mainly in their older Valvestate 4x12 cabinets.
Now you have a Fenpeg.
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
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. ;)
You are correct. I misspoke there.
Just another successful spankin sounding mod by the Mighty Brad😎.
I understand the comments about keeping the amp "stock", but I'd rather it Rock. As usual you have made a great performing/sounding amp. Rock on Brad!!!
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...
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)
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.
Yeah it is fine, the 3M3//51p is a part of a mixing stage.
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.
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 %)
Very nice work..!
I don't think you give your pinky enough credit when you play great job thanks
Pajamologist 🤘
Jammy work day!
The Toecutter knows you were playing guitar using your pinky Haha🤘🏼🤘🏼
Brad's a fine picker
Nice Ampeg save Brad ... with older amps you just never can tell if it's going to be a Rogue One 😆
Nailed it.. Great job Brad!
Sounds great man! Great job!
Great video Brother! You made something cool out of that tired old thing.
Love the new vibes, too!
excellent job u did on this one brad sounds amazing,love this amp.lotsa mojo
12:22 Damn, I wish you could get those speakers for 8-9 bucks these days. LOL
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.
I know, that is pretty much a joke.
I can only imagine what the repair cost!
That oscillation makes it sound like Doc Brown's amp from BTTF.
Great repair video!
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
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.
Awesome job on that amp man
Ok. Impressed. Subbed. Lol. Nothing like meeting critical thinkers of logic that also share love and passion for music arts and it's gear. Though I quit tearing shit apart years ago , it will be my pleasure learning these diode and chips with glorious soldering iron goodness. All with great adult criteria.. Much unlike the ones trying to pass off opinions and grammar school level music theory like Mr. return it. Lmao
Yeah, but take a look at the regulars here who are adamantly repeating that he needs an oscilloscope to service any electronics properly. Without a scope, you have no idea what is exactly happening. You cannot look at the actual signals or how a component is treating the signal. Of course with a scope his vids would be 10 minutes, because that is how long it would take to pinpoint the problem with proper test equipment. He recently tried to find the problem in a Mesa combo. He ended up taking apart the whole Mesa Boogie amp to parts bin pieces because he could not fix it after several attempts without a scope. Massive failure there. The amp went from playing on stage to being parts bin fodder because of power tube bias runaway that Bradley could never fix. I guarantee that he would have fixed it if he would have used an oscilloscope and 3 multimeters monitoring different voltages in the circuit. He would have been able to pinpoint the problem and correct it instead of gutting the amp he could not repair. Not impressive.
He has one Hugo.
HUGO FUGUSEV I'll admit that that video was painful for even me to watch. Maybe the moral of the story is not to even waste our time on those amps.
You're so wrong and you don't even know what you're talking about dude. That amp had a conductive board or some other issue that a scope would not have helped in anyway to isolate. If you think that, then please, by all means, give me detailed analysis of what I should have done to determine the problem given what I showed in the Mesa video. Maybe your very first TH-cam video could be about that.
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!
One hell of a VCO!
Got it sounding great in the end bro. ATB
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.
That’s sounds cool like Lou reeds metal machine album. Lol
Surprises me still that in 72' they were using those circuit boards in there. Would have pegged that one for a class A only.
Fine video, Brad. You done good, kid.
Nice one Brad, Cheers.
The end result sounds good, but I am confused as to why you modified the circuit in an attempt to get rid of the noise? I am fairly certain that Ampeg wouldn't have released an amp that had that noise so to draw a conclusion that their circuit design caused the noise and that modifying it was necessary doesn't make sense to me. I am not busting your balls, just trying to learn. Thanks Brad for your videos. I am learning a lot.
This is Part 2 of this repair. One of the main complaints is the amp is very quiet.
My bad. Didn't realize that was the same amp. Good work though. Sounds great
sounds great love Celestion very nice
I would think that it is for what you would call bed room musicians.
That amp has gone all EDM/Electro New Wave...
Sounds like the nuke amp on back to the future.
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.
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.
There is a Part 1 to this video linked in the description. I go into that in that video.
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.
is it possible they neutered the first stage to avoid blowing the lower wattage speaker
Great video, Brad! The amp sounds great, though the better part of it is your vituosity. Keep triggering us ol' timers by making repairs sans o'scope...
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.
do input jacks all have resistors on them? also woul a jack to speaker have some sort of resistor on the speaker input?
First thought, ground loop, or maybe needs aluminum shielding
Thanks Brad. Nice work. After you got through playing then, could you fry bacon on it?
Keep Rocking in it, not of it !
is that oscilation or modulation between hum and mororboating (oscilation)?
Ampegs new ring modulator fx.
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?