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Fixed my fried Ampeg V-4 today and it was quite simple

Natron

Member
Messages
59
Backstory: A few days ago, I saw an ad for a local guy selling an early-version Ampeg V-4 for $200. I emailed him right away asking for details. Turns out there were two catches. 1. It didn't come with power tubes. 2. He was fairly certain the output transformer was blown. I told him I'd take it anyway. I figured it'd be a fun project.

What it did was, 1/2 second after you flipped the power switch on, the 6A power fuse would blow. I tore it down the day after he dropped it off and couldn't find any signs of arcing, shorts, blown components, overheating, etc. The filter caps had been replaced recently so I was doubting those went bad. There were no power tubes in it and I took the preamp tubes out as well so a shorted tube wasn't causing the issue. There were no other defects I could find, visually. I told a friend of mine about it and he agreed to come over today with all of his testing equipment since he builds musical equipment for a living.

He came over and poked around for about a half hour, testing the transformers (which, thank goodness came up with no shorts he could find) and tracing the flow of power through the amp. He decided it could only really be bad filter caps, bad rectifier diodes, or some freakish unknown problem with the output transformer. We started simple and desoldered all the rectifier diodes to check them out.. Guess what. TWO of them were shorted. Walked down the road, picked up a $2.50 worth of replacements, walked back, soldered them in, replaced the fuse, flipped on the power, and it powers up juuuust fine now. So $202.50 total + buying dinner and a beer for my friend for helping + $76 matched quad of replacement 7027A tubes = great deal on a V-4, if you ask me. I'm excited! Can't wait to try this out on the 4x12 I have coming this week!

 

BluesForDan

Silver Supporting Member
Messages
8,727
I had a v-4, back when I was wet behind the ears and didn't know **** all about stuff. I'd love to give one another a go, with what I know now.

what are you using for speakers?
 

Natron

Member
Messages
59
I had a v-4, back when I was wet behind the ears and didn't know **** all about stuff. I'd love to give one another a go, with what I know now.

what are you using for speakers?
Currently just have that Genz Benz 2x12 and later this week, I'm getting a Marshall 1960BV (Celestion Vintage 30s) from a fellow local forum member (hey Todd!).
 

dewman

Member
Messages
5,750
thats a killer story...keep an eye on her for future problems, although its likely that when the power tubes blew they may have taken out the diodes - so maybe the future will be just great. Get higher rated voltage diodes. If I remember right about my VT-40, I replaced them with higher voltage ones after a tube blow out...wow- those amps have enormous volume and low end...very cool sounds!
 

Natron

Member
Messages
59
thats a killer story...keep an eye on her for future problems, although its likely that when the power tubes blew they may have taken out the diodes - so maybe the future will be just great. Get higher rated voltage diodes. If I remember right about my VT-40, I replaced them with higher voltage ones after a tube blow out...wow- those amps have enormous volume and low end...very cool sounds!
I couldn't find higher voltage diodes than the ones that were in there.... 1000V ones were already there. But yeah I seriously have NO clue how I'm supposed to use this non-master-volume amp in my apartment with paper thin walls.
 

soulohio

Senior Member
Messages
10,999
I use an airbrake on 'the VT40'...also, a bad monkey will not only give you a nice wee push but you can also dial down the volume...gawd, i jammed with the amp two days ago and my left ear feels like there is a sponge in there...watch out...them ampegs are dangerous....but i am getting the nicest wah-like QOTSA tones outta that thing...thanks again Dewey!
 

JLee

Gold Supporting Member
Messages
2,829
I couldn't find higher voltage diodes than the ones that were in there.... 1000V ones were already there. But yeah I seriously have NO clue how I'm supposed to use this non-master-volume amp in my apartment with paper thin walls.
Good luck with that! I run mine at a mismatch to reduce the headroom. Still loud as f**k! But it gets the most awesome grind imaginable!
 

Natron

Member
Messages
59
Good luck with that! I run mine at a mismatch to reduce the headroom. Still loud as f**k! But it gets the most awesome grind imaginable!
Hmm... and I just checked the THD Hotplate manual online that states it's safe to mismatch the impedance of the Hotplate and amp as long as the Hotplate is equal to or greater than the set impedance of the amp... V-4 on 8ohm, Hotplate is 16ohm. According to them, I CAN use it...

Makes me nervous though. I don't want to end up with that OT blown afterall..
 

soulohio

Senior Member
Messages
10,999
Good luck with that! I run mine at a mismatch to reduce the headroom. Still loud as f**k! But it gets the most awesome grind imaginable!
could you elaborate on what you are doing? what is mismatched? why does this reduce the headroom? does this technique work on other amps?

i need more grind out of an OR120 and I have yet another VT40 that needs a good going over. If I could get them to grind at a lower volume i would be a happy camper.
 

Unabender

Member
Messages
684
So you actually did not fix it yourself like the title suggested :) Nothing wrong with that, congrats on the amp.
 
Messages
1,009
very good score there. You saved enough on that amp that maybe you could afford to power-scale it...make it perfect for any setting.
 

Scott Auld

Administrator
Staff member
Messages
12,315
Hmm... and I just checked the THD Hotplate manual online that states it's safe to mismatch the impedance of the Hotplate and amp as long as the Hotplate is equal to or greater than the set impedance of the amp... V-4 on 8ohm, Hotplate is 16ohm. According to them, I CAN use it...
I believe you are correct, you can use a 16ohm Hotplate with an 8ohm amp. Make sure the speakers are 16ohm. :)
 




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