76 ampeg V4 low output

[burymyteeth]

hey all. i have a 76 ampeg v4 that is acting super weird. basically it just has low output. it was making a sort of popping and ffffffttttting noise one night and now its not working right. however all of the tubes test good. it also seems to power test fine (signal 100 mA at 440hz at 8ohms) but i have to drive both volumes nearly all the way up to get to 100W. The bias looks just fine during power testing and idling. the output transformer has already been replaced with a mercury magnetics transformer. the plate voltage is fine. So theres no obvious problems, and I'm just throwing this out there to see if anyone has any ideas, I really appreciate your suggestions. nothing worse than your amp sounding like shit but there is no measurable change in the way its operating. oh, also i checked it with different cabinets and guitars with no effects and different channels and all the obvious stuff. thanks.

-d

[g1]

Is this the version with the distortion control?
If so, here is the schematic: http://www.ampegv4.com/images/schema...seriesDist.jpg
Try injecting your signal into the power amp in jack (or ext.amp jack) on the rear panel. See how much signal it takes to get to full power. Or run the preamp out from some other amp into the rear "in" jack and see if it is still weak.
By doing this you can figure out if the problem is in the preamp or power amp, which will make things easier.

[burymyteeth]

Is this the version with the distortion control?
If so, here is the schematic: http://www.ampegv4.com/images/schema...seriesDist.jpg
Try injecting your signal into the power amp in jack (or ext.amp jack) on the rear panel. See how much signal it takes to get to full power. Or run the preamp out from some other amp into the rear "in" jack and see if it is still weak.
By doing this you can figure out if the problem is in the preamp or power amp, which will make things easier.

thanks a lot, should have thought of this. this will definitely help me narrow it down.

[soundguruman]

"At least," it's a REAL Ampeg. That's worth quite a lot.
(NOT a Crate-Peg! Hahahqhahahahahahahahahah!)

[burymyteeth]

"At least," it's a REAL Ampeg. That's worth quite a lot.
(NOT a Crate-Peg! Hahahqhahahahahahahahahah!)

what is this "crate-peg" abomination you speak of???

[bob p]

oh please, don't feed the troll.

[soundguruman]

what is this "crate-peg" abomination you speak of???

YOU DON'T KNOW???

I will give you a short history...CRATE was the most UN-reliable guitar amp ever built ("not for continuous operation*.")

*according to their own techs, at the crate factory in Saint Louis - YES it's true, their own techs freely admitted that the amps would not operate continuously. They claimed that crate amps were built for: "temporary use only."

JUST THE OPPOSITE of a REAL Ampeg. REAL Ampegs were built to take great punishment and stress, and to continue to operate, no matter what.
EXAMPLE: A REAL Ampeg SVT can BLOW 2 output tubes, and keep right on playing. IT was MADE deliberately to do so!

TRY THAT with the Chinese SVT! (not really an SVT at all, but made to appear "as if" it were.) (Yes, it's a fake SVT)Now that you understand the difference between a real Ampeg and a fake Ampeg...you have some understanding...of what a real one is worth. The REAL V4 is similar to the SVT...

Now as I said, Crate made terrible amplifiers. Eventually, nobody wanted to buy them, music store owners stopped selling them, even techs did not want to repair them.
Crate even tried a "3 year warrantee" to entice people to buy them.
But what is a 3 year warrantee worth if the amp spends 2 out of 3 years in the repair shop??? Hahahahahahhahahahahahahahahahahahahahahahahah!!!!!!

SO, SOMEBODY HAD A GREAT IDEA: Build Crate amplifiers, and stick an "Ampeg" name plate on the outside! Make the case look "just like" an Ampeg!
NOW people will buy Crate amps again!!! Although they will "think" they are buying a real Ampeg! (how gullible you guys are...)
Of course they were not real. They were Crate amps, made to look "just like" Ampegs.
The same parts, the same circuit boards, the same terrible engineering, built by the same people who built Crate, with the same parts. ONLY it says: "Ampeg!" on the outside.
On the inside, it was NOTHING like an Ampeg. NOT even close.

BUT: tell all the sales reps to visit music stores, and explain that these are "exact reproductions" of Ampeg amplifiers! (you fell for it)
Which of course they were not. They were just made to "look like" Ampeg on the outside...

SO NOW you know. A fake Ampeg built by Crate, is a "CRATE-PEG!"
You can thank me for coining the phrase "Crate-Peg." But what else CAN you call it???
"abomination"---that is true and correct.

[Jazz P Bass]

Mr Soapbox is at it again.
Sheesh.

[g1]

Hearsay and libel. And factually incorrect.

[Enzo]

burymyteeth, welcome to the forum.

SOundguruman is a member who loves to see his own words in print on the internet. He pops up now and then to crow about how Crate amps are defective at every level. He'll tell you that the handles will fall apart, when they are the exact same handles six other amp makers use. He'll tell you that the transistors are cheap and defective, even though they are the same Motorola and TI parts everyone else uses. He'll fill your screen with nonsense.

He cannot effectively repair the amps so be blames the factory. He spews the same nonsense at Hartke amps.

[DrGonz78]

You can thank me for coining the phrase "Crate-Peg."

Thanks!!

P.S. Don't forget that SGM likes to use Crate amps for potting flowers in the garden at his house. So on another hand he does find them useful to a certain degree still...

[bob p]

...THE OPPOSITE of a REAL Ampeg. REAL Ampegs were built to take great punishment and stress, and to continue to operate, no matter what.
EXAMPLE: A REAL Ampeg SVT can BLOW 2 output tubes, and keep right on playing. IT was MADE deliberately to do so!

TRY THAT with the Chinese SVT! (not really an SVT at all, but made to appear "as if" it were.) (Yes, it's a fake SVT)Now that you understand the difference between a real Ampeg and a fake Ampeg...

Looking at schematics, I think that the protection circuits that are present in the modern "fake SVT" make them less likely to self-destruct if something really bad were to happen. Sure, they'll still run with a blown output tube, but if a tube fails short and starts pulling huge amounts of current, the new comparator circuit in the "fake chinese amps" will cause the amp to go into protection mode while the original amps will just go up in smoke.

i actually prefer the intelligent design that uses modern technology to place limits the amount of damage that you'll suffer if something goes really wrong.

[Enzo]

The only way the old SVT could run with a blown tube was if the plate resistor opened. But if a screen shorts to a control grid, that will wipe out the bias for all three of those tubes, and the amp sure won;t play on for very long that way.

And those 10 ohm plate resistors? Well those "fake" SVTs also have a series 10 ohm resistor, it is just in the cathode lead instead of the plate.

[soundguruman]

Mr Soapbox is at it again.
Sheesh.

1. If you want me to say something good about Chinese amplifiers, then have them build better amplifiers.
2. These "Ampegs" are Crate amps. They are built exactly like Crate amps, with the same exact points of failure and engineering defects.
3. I think the same person designed both Crate and Chinese Ampeg, and I think that person is Jerry Gold.

A. This designer has no clue how to design a guitar amp.
B. This designer has no clue how a guitar amp should sound.
C. This designer has no idea about how to make a guitar amp reliable and dependable.

4. Lack of support: 2-3 years down the road, there are no critical parts available, like power transformers. Just the opposite of REAL Ampeg.
5. If you want me to shut up about it, then stop calling these amps "Ampeg," because they are obviously not Ampegs.
6. If you want me to shut up about it,Stop calling transistor amps: "SVT."

With so many great amps made in USA and UK, I am amazed that anyone would even consider buying these things. This is destroying our Manufacturing and our jobs.

[soundguruman]

The only way the old SVT could run with a blown tube was if the plate resistor opened. But if a screen shorts to a control grid, that will wipe out the bias for all three of those tubes, and the amp sure won;t play on for very long that way.

And those 10 ohm plate resistors? Well those "fake" SVTs also have a series 10 ohm resistor, it is just in the cathode lead instead of the plate.

If one tube in the Chinese SVT is even "slightly" out of match, it won't turn on or operate at all.
Just the opposite of a REAL Ampeg.
Let's not forget the 1/8 watt screen grid resistors. Pure genius.
Show me a REAL Ampeg with 1/8 watt screen grid resistors.....hahahahahahahahahahahahahhahaha!!!!!