Author Topic: Anybody here have any experience with fixing Ampeg tube amplifiers? (Read 5159 times)

Frankencake · « **on:** April 07, 2009, 08:37:51 AM »

This is a long shot but I am working on an Ampeg V4. It has me beat thus far and I am turning to others for support. This is no obvious problem otherwise it would have been fixed by now. I repair Fender amps in my free time but this Ampeg has me on the ropes.

azuredesign · « **Reply #1 on:** April 07, 2009, 09:11:18 AM »

Be good to have some details concerning what kind of issue you're having.
Don't know if you have a schematic for it but here's a link to one with voltages:
http://www.ampegv4.com/schematics.php

Frankencake · « **Reply #2 on:** April 07, 2009, 11:28:06 AM »

I think that I may have narrowed it down to the power transformer. I'll keep you posted.

GoatBaSS · « **Reply #3 on:** April 07, 2009, 01:25:22 PM »

Do tell.

Duke McDukiedook · « **Reply #4 on:** April 07, 2009, 01:27:45 PM »

Quote from: 78SS on April 07, 2009, 11:28:06 AM

I think that I may have narrowed it down to the power transformer. I'll keep you posted.

If your transformer is shot, that's easy- replace. I assume they have a diode bridge for the power supply with a choke coil? Diodes could be suspect.

Frankencake · « **Reply #5 on:** April 07, 2009, 05:53:41 PM »

The overall problem started when I installed a three wire cord. When I would close the standby switch, the fuse would blow. There was enough overcurrent to blow my 15 amp house breaker, after I bypassed the fuse, of course. Many diodes later, I finally gave up on myself and called an amp guy. He was nice enough to to talk me through a few things and voila! PTrans was suspect. I pulled it out and it was shorted from one of the two primary legs to secondary but still making secondary voltage. I have a bunch of reconstruction to do on it since I was taking everything apart to isolate the problem, but now I have a new doorstop. Curses! Does anyone have a power transformer for an Ampeg V4? I've heard of a Hammond trans that will work so I'm going to look in to that. Mercury Magnetics also has stuff that will work. I want cheap and reliable since I am trying to sell this amp. I just wanted to hear this thing before I sold it to really make sure that I didn't need it. Easy come easy go.-----SS

1080 · « **Reply #6 on:** April 07, 2009, 10:31:46 PM »

Which diodes blew? Please use schematic, and which secondary winding shorted with the primary?

Since the design uses 3 prong A.C. cord. I cannot see a problem installing a three wire cord. Maybe house wiring not right?

I am going by the schematic supplied by azuredesign.

Worked on lots of tube equipment. Need more info. 1080.

Frankencake · « **Reply #7 on:** April 08, 2009, 01:06:06 PM »

This is the schematic. Two of Diodes D1-D4 blew. The ones between ground and "a". When the standby switch was closed there was 125vac going through to ground. D5 also blew. The blue primaries were shorted to the red secondaries. I put the amp back together using only the black primaries and it worked. There was no continuity between the blue and black so it worked fine. I've had this amp for about four years and it was a gimme. When I got it, it had a blown half of the output transformer primary. i just bought a new one to install and then sell the amp. I can't sell it now without the correct setup on the PT but I tested it and it does work and sounds great. All I wanted was to hear the thing and then ship it. I guess I have to hang on to it for now.
FYI, the blue and black primaries were to be wired in series to accomodate 230vac. I suspect that the PT will hold up under a moderate amount of stress but it will go at some point. I couldn't get it to bow today but the GF and kid were home sick. Not enough head room, so to speak. I wish I had a dummy load for the speakers to push the thing until it might break. If I can't get it to blow then I'll sell it. Anyone know how to build a dummy load?

heffay · « **Reply #8 on:** April 08, 2009, 02:36:04 PM »

the only guy i know that fixes tube amps has glasses that i swear are made out of the same tubes!

1080 · « **Reply #9 on:** April 08, 2009, 06:10:42 PM »

Yes there is not too many people working on tube equipment.

78SS, once I got a Power transformer for a Phase Linear amp rewound by a motor rewinding place. It was expensive ,the supply voltage was a little higher that the old one ,but it worked. That was before the Internet. So do a search.

You should to able to get info on the dummy load also. All amplifier are tested with a resistive load. 8 ohm 50watt load should be good enough.

Yes, i guess it's working at half power?
Check around for the rewinding of the transformer or parts on the Internet. Good Luck.

Frankencake · « **Reply #10 on:** April 09, 2009, 10:37:41 AM »

Fliptops.com has a direct replacement for me for the meager sum of $189.50. It isn't working at half power but since it is not using the second set of primary windings is has about half of the reserve of power. I imagine if I set it up outside with a 2 ohm load and fired mortars over to the next hillside with my guitar, there would be a bit of "sag". The power transformers are overbuilt in order for them to double as a 230vac trans. I played it this morning. It sounds great and doesn't feel too squirrely. I have to find a cabinet that is rated for over 40 watts since I am using my Super Reverb as the test speaker. Those speakers tend to break up a bit soon since they are not rated for that kind of power. MO' money, MO' money. MO' money!

1080 · « **Reply #11 on:** April 09, 2009, 05:49:55 PM »

Good to hear.
If the supply voltage is still 545volts dc, I just wonder if the supply current would be the same? May be it does not matter in this case & your very lucky.

The price of the rewind transformer was around that price 15 years ago.

The customer loved that amp.

Tape off those unused primaries.

I bet lots of today's electronics will not be around and still be working that long.

fuzzybutt · « **Reply #12 on:** April 09, 2009, 06:04:46 PM »

i had this picture in my mind of the 8x10 cabinet i had on my ampeg rig when i played bass. damn that thing rocked

Frankencake · « **Reply #13 on:** April 09, 2009, 06:26:09 PM »

Quote from: fuzzybutt on April 09, 2009, 06:04:46 PM

i had this picture in my mind of the 8x10 cabinet i had on my ampeg rig when i played bass. damn that thing rocked

Quote from: 1080 on April 09, 2009, 05:49:55 PM

Good to hear.
If the supply voltage is still 545volts dc, I just wonder if the supply current would be the same? May be it does not matter in this case & your very lucky.

Tape off those unused primaries.

I bet lots of today's electronics will not be around and still be working that long.

The supply current will be half of what is was but voltage is the same. That's not to say that it will not be enough but it will be half of what it used to be. I trust it so far. I can't or won't sell it like this but I'll use for my own pleasure. I think that these transformers were overbuilt since that seems to be what Ampeg did with all of their stuff. Why have two primary windings supplying the same voltage to the same place? The answer is so they could use them in parallel for a 230vac application and still supply the 545 B+.
This amp will still be here when I'm gone. The digital crap that they make is already gone, as far as I'm concerned.

I just left the unused primaries with the insulation stripped off as much as I could floating around the inside of the chassis. I tied one to a pack of firecrackers. That'll make some ones night.
You know, I never thought of doing that before. That would be a great practical joke to play on a band mate. The old "pack-of-firecrackers-that-get-set-off-when-the-power-switch-is-flipped-on" trick. Hmmm. Who's gonna be the first victim?

Fuzzybutt, I'll pay for the shipping if you are giving it away.

The partner to the V4 is Ampegs 4x12 V4 cabinet. I am playing it through a 4x10 low wattage cab for testing and I can't imagine if I had a quad of 12's rated for higher wattage. I might be able to start a rust, paint and skirt removal business.

fuzzybutt · « **Reply #14 on:** April 09, 2009, 06:29:58 PM »

i havent owned that rig for 20 years lol.

Jonesy · « **Reply #15 on:** April 10, 2009, 12:05:42 PM »

That schematic reminds me of my Magnavox stereo, with the 12AX7's, hum balance and the like.. similar architecture.

Kinda surprised they didn't use a 5U4G recifier tube, rather than the silicon bridge rectifier...

Duke McDukiedook · « **Reply #16 on:** April 10, 2009, 12:18:41 PM »

Newer design, solid state recifiers are cheaper and more stable than tube rectifiers.

Frankencake · « **Reply #17 on:** April 10, 2009, 02:14:18 PM »

Quote from: Dukiedook on April 10, 2009, 12:18:41 PM

Newer design, solid state recifiers are cheaper and more stable than tube rectifiers.

Quote from: Jonesy on April 10, 2009, 12:05:42 PM

That schematic reminds me of my Magnavox stereo, with the 12AX7's, hum balance and the like.. similar architecture.

Kinda surprised they didn't use a 5U4G recifier tube, rather than the silicon bridge rectifier...

Between my Fender Twin Reverb and now the V4, neither of them have a tube rectifier. I believe that the 100+ watt design requires a faster power response than a 5U4 can supply. Sag is what they call it. The Silicon diodes are definitely more responsive. The age has nothing to do with it though as this is a late 60's early 70's amp. Solid state amps didn't come to the mainstream until the eighties; much that same with bike electronics. Tubes sound better and points run with more assuredness that that early solid state crap. The 70's were an end of an era. I guess that my stable of 70's amps and bikes pays homage to the bell bottoms and casual sex. I'll give up my bellbottoms but I won't give up my __________ (fill in the blank).

Jonesy · « **Reply #18 on:** April 11, 2009, 05:18:03 AM »

Good point about the wattage. You're running a 100+ watt amp, whereas my "Maggot-Box" is only running around 35 watts or so per channel. It may be primitive by today's standards, but the tone quality and depth us like nothing else I've ever heard.

I have seen plug-in replacements for the 5U4, etc rectifier tubes that can convert them to solid state. Only thing is you have to go back and re-bias the driver tubes as you don't have the voltage drop across the 5U4 plates anymore.

Frankencake · « **Reply #19 on:** April 11, 2009, 07:10:57 AM »

Quote from: Jonesy on April 10, 2009, 12:05:42 PM

That schematic reminds me of my Magnavox stereo, with the 12AX7's, hum balance and the like.. similar architecture.

Kinda surprised they didn't use a 5U4G recifier tube, rather than the silicon bridge rectifier...

Ampeg was bought and run by Magnavox. I think that the schematic says the name.

Frankencake · « **Reply #20 on:** April 11, 2009, 07:26:45 AM »

Quote from: Jonesy on April 11, 2009, 05:18:03 AM

Good point about the wattage. You're running a 100+ watt amp, whereas my "Maggot-Box" is only running around 35 watts or so per channel. It may be primitive by today's standards, but the tone quality and depth us like nothing else I've ever heard.

I have seen plug-in replacements for the 5U4, etc rectifier tubes that can convert them to solid state. Only thing is you have to go back and re-bias the driver tubes as you don't have the voltage drop across the 5U4 plates anymore.

This "Maggot-box" you are talking about is a stereo amp? I've often tried to find a junk one of those as they are out there just like old Hondas. I'd like to see the look on my girls face when I come upstairs with that. "Move over Sony, Here comes old tech!" And I have the power to rebuild them!!! Boowhoohaha!
One of the downfall of the solid state rectifiers is that they tend to bang the downstream components if you don't have a standby switch. The lack of the tube rect. makes for a sharp spike. It can play havoc with your electrolytic capacitors. I have an old Vibrolux on my bench that had a SSR. The caps are relatively new but two of the have slowly shorted and then finally blew. It shorted the power trans primary because of such an overload. My theory is that since there is no standby switch on this amp, that and the combination of the SSR made it meltdown----ss

GoatBaSS · « **Reply #21 on:** April 11, 2009, 07:31:46 AM »

Hey Hey HEY!!!
Solid state has its place! I have had fenders and ampegs, but my Acoustic, Kustom, Laney and Peavey have pushed some very long term good sound.
That being said I miss my Mesa D 180 and my Music Man RP100.
Good thread

Frankencake · « **Reply #22 on:** April 11, 2009, 08:42:22 AM »

I'll take a solid state amplifier if I am using it for bass. I'm not much of a fan if it's used for guitar. I see a lot of requests for JC-120's as backline. Usually, they are for keys but some of them are used for guitar. I don't like them as amps personally, but someone who uses them regularly can really make them sing. I am thinking of some African guitarists and some Jazz guys that I have seen.
But if you really want to peel some panties, use a tube amp.

754 · « **Reply #23 on:** April 11, 2009, 09:16:40 AM »

It aint tube, but my Sansui BA/Ca 3000 still sounds great..
but I think you guys are talking guitar amps?

fuzzybutt · « **Reply #24 on:** April 11, 2009, 09:44:56 AM »

i would almost give up my suzuki titan for a set of machintosh tube amps. i have a pair of 30 year old bose 601's that would work REAL nice with em.

News:

Author Topic: Anybody here have any experience with fixing Ampeg tube amplifiers? (Read 5159 times)

fuzzybutt

fuzzybutt

fuzzybutt