Ampeg VT-22 noise

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joshdfrazier
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Ampeg VT-22 noise

Post by joshdfrazier »

Recently purchased one of these tagged at $600 for $230. Told the guy the OT was probably shot because only 1 of four output tubes was functioning. :D 7027 is the recommended type, but I popped in a quad of EL34's, as that is the only matched quad that I have right now.

The amp does need some work. The amp was made at a time when Magnavox was designing their amps, so the tubes are... weird. But for many, 7247 and at7's/au7's will sub fine. I do know that the 6an8 PI tube is shot, very microphonic and noisy.

Lots of pops, hiss and hum when the amp has been warmed up, and I suspect most of this comes from the aforementioned 6an8 PI. But there is this whooshing sound that occurs once you hit the amp with B+. I've attached a soundclip. I know the filter caps need to be replaced, but there are alot of them, and some of them 100uf/600v, which ain't cheap. Plus, they're all in multi cap cans that are not clearly labeled. PLUS working on this amp is a PITA bc the transformers weigh about 20lbs a piece. I'm thinking this noise is the caps, but hoping someone can confirm. :roll:
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Leo_Gnardo
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Re: Ampeg VT-22 noise

Post by Leo_Gnardo »

joshdfrazier wrote:7027 is the recommended type, but I popped in a quad of EL34's, as that is the only matched quad that I have right now.
You managed to score this dinosaur for cheap - that's good. :D

Did you make sure your output tube socket wiring is compatible for EL34? I made that mistake once - didn't make sure pin 1 (G3) is at ground - and wrecked a set of Siemens EL34 in 20 minutes. Once was enough. Some other folks have run 6L6 in these amps, and some claim 6550 or KT88 but I've found the glass on 6550 or KT88 is slam up to the transformer and would likely break if the amp was to be moved in any other way than very gently.
I do know that the 6an8 PI tube is shot, very microphonic and noisy.

Lots of pops, hiss and hum when the amp has been warmed up, and I suspect most of this comes from the aforementioned 6an8 PI. But there is this whooshing sound that occurs once you hit the amp with B+. I've attached a soundclip. I know the filter caps need to be replaced, but there are alot of them, and some of them 100uf/600v, which ain't cheap. Plus, they're all in multi cap cans that are not clearly labeled. PLUS working on this amp is a PITA bc the transformers weigh about 20lbs a piece. I'm thinking this noise is the caps, but hoping someone can confirm. :roll:
How to know what's a noisemaker until you clear a known rackety 6AN8 out of the way. Yes they're getting rarer as time goes on but until you have a good one in the socket, can't start blaming other components for making noises.

Even though the filter caps are @ 40 years old, Ampeg did select hi quality caps and I've seen most continuing to work in old VT22, VT40, V4 and V2 amps.

On occasion I've seen resistors going bad in preamp & power amp in this series of amps. Sometimes I've even had to look at the amp while on, in a dark room, and seen spooky looking sparks running along the length of dodgy resistors. Not your usual analysis method but hey, whatever works.

The caps that bring signal to output tube plates are suspicious too. Also way too big at 0.33 uF. I typically substitute new Mallory 150 0.1/630. You can pick your favorite brand. And smaller sizes to trim low end response. With 0.1, still plenty of low end and not much chance of leaky caps causing your bias to fail. Also take note that the bias supply is obtained thru a capacitor - and if that one starts going bad, output tubes will be glowing orange and melting down. Typically I put in a trim pot for the bias while tending to this end of the circuit.

Cleaning preamp tube pins and sockets can also reduce noises. Corroded connections, how well can you expect them to work?

The noises I generally associate with the VT22 are "OOF!" and the sound of my backbones crackling as I pick one up. Even a perfectly working one will do that.
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Stevem
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Re: Ampeg VT-22 noise

Post by Stevem »

6550s and 88s will work fine in the amp once the screen resistors are changed out.
The whooshing sound is likely a preamp tube.
Heavy, work on a SVT or a Fender 400PS sometime, you'LL yearn for a 60 lb amp,LOL!
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joshdfrazier
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Re: Ampeg VT-22 noise

Post by joshdfrazier »

To be honest, I sorted threw caution to the wind and popped in the el34's and hoped for the best. I know 6L6 tubes can be used in this amp, so I took a chance. So far so good. I've had it running for a few hours and the tube temp is well within reason and no signs of redplating. I really like the sound of the el84s. Thinking of keeping them in there unless someone thinks this is a bad idea.

Currently bidding on a 6an8, and it's at 2 cents right now. Fingers crossed.
Tube socket cleaning is definitely in order, and I will definitely check the caps and resistors your mentioned. This amp seems to have been someone's touring rig, as it looks pretty rough. Probably has a lot of play time on it.

And yes, it is heavy, obviously. My old bandmate used to have one of these. She was kind of small so I always ended up carrying it.. Ugh. Mine weighs in at 96lbs. No wheels either!
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Leo_Gnardo
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Re: Ampeg VT-22 noise

Post by Leo_Gnardo »

joshdfrazier wrote:
Currently bidding on a 6an8, and it's at 2 cents right now.
I was lucky/smart to do some ebay shopping in the early 2000's before things went loony. Still have half a dozen 6AN8 & should'a got more. Good luck on your ebay bid & if not, keep lookin'.
Tube socket cleaning is definitely in order,
Tube pins too, might pay to do those first. I use strips of 600 grit wet/dry paper, dry, and do the shoe shine boy routine. Once that's done you've turned each pin into a miniature file and on reinsertion that will often scrape away corrosion where it counts in the sockets.
This amp seems to have been someone's touring rig, as it looks pretty rough. Probably has a lot of play time on it.
New York Dolls / David Johansen Band had a backline of Ampegs like this and blew the lid off the sound meter back in the day.
My old bandmate used to have one of these. She was kind of small so I always ended up carrying it.. Ugh. Mine weighs in at 96lbs. No wheels either!
Reminds me of my first "roadie" job. Around Jr Hi School age there was a beautiful girl in my church who played accordion :shock: through a brand new silver face Twin Reverb. The accordion was enough of a burden to lug in so I always wound up hauling in the Twin. Hm.. I wonder whatever happened to . . . the Twin Reverb. :roll:
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gui_tarzan
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Re: Ampeg VT-22 noise

Post by gui_tarzan »

joshdfrazier wrote:Recently purchased one of these tagged at $600 for $230. Told the guy the OT was probably shot because only 1 of four output tubes was functioning. :D
Did you really think it was bad or did you tell the guy that just to get the price down?
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Diablo1
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Re: Ampeg VT-22 noise

Post by Diablo1 »

You better bump up the size of the screen resistors to run EL34s. Most V4s have 470-ohm, 2-watt screen resistors. I'd suggest using 1K/3 watt.
joshdfrazier
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Re: Ampeg VT-22 noise

Post by joshdfrazier »

I never really suspected the OT to be bad. These have a reputation for having pretty rugged iron, so yea. Just haggling. Something weird though, 3 of the 7027 tubes were in fact toast. I've never actually seen a tube burn up, so that was kind of alarming to see 3 dead ones. I have two matched 6L6gc pairs that I put in the "just to see" and the amp made a loud hum and some of the tubes began redplating like I've never seen. That freaked me out a bit. But all is well with el34
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Leo_Gnardo
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Re: Ampeg VT-22 noise

Post by Leo_Gnardo »

joshdfrazier wrote:I never really suspected the OT to be bad. These have a reputation for having pretty rugged iron, so yea. Just haggling.
You get the daily haggler prize then. But there will be enough in there for you to spend your time & money on. FWIW I did get a VT-22 chassis in for repair @ 20 years back and both transformers were toast. What a shame. I pulled out what parts I could & off it went ta da dumpity-dump.

You must have a look at the bias voltage. If it's so low it runs EL34's satisfactorily, then it's too low for 6L6 or 7027 for that matter. No wonder 6L6's go red-plate. And possibly that's what wrecked the old 7027's besides lots of wear and tear. I t'ink something's amiss with that bias circuit.
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Stevem
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Re: Ampeg VT-22 noise

Post by Stevem »

A lot of play time can be a good thing in regards to the filters anyway!
Over the passed winter I went thru a guys V4 and all the filters but for the one in the bracket ring still checked out good on my ESR meter!

You might want to check into the adapter that Tubes and more has to put a 7199 that can still be had in new manufacture to replace the 6AN8.
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JazzGuitarGimp
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Re: Ampeg VT-22 noise

Post by JazzGuitarGimp »

gui_tarzan wrote:
joshdfrazier wrote:Recently purchased one of these tagged at $600 for $230. Told the guy the OT was probably shot because only 1 of four output tubes was functioning. :D
Did you really think it was bad or did you tell the guy that just to get the price down?
My thoughts exactly... It's one thing to haggle, but quite another to be deceitful just to get a better deal.
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Leo_Gnardo
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Re: Ampeg VT-22 noise

Post by Leo_Gnardo »

JazzGuitarGimp wrote:
gui_tarzan wrote:
joshdfrazier wrote:Recently purchased one of these tagged at $600 for $230. Told the guy the OT was probably shot because only 1 of four output tubes was functioning. :D
Did you really think it was bad or did you tell the guy that just to get the price down?
My thoughts exactly... It's one thing to haggle, but quite another to be deceitful just to get a better deal.
At the time of the transaction who knew? and the seller could have said no.

Heck one of my crustomers has a VT22, works perfectly (I fixed it) and he's been trying to sell for the last 10 years, can't even get $200 for it because everybody knows what a pig it is to move. So he continues to play it at home, dialed way way down.
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joshdfrazier
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Re: Ampeg VT-22 noise

Post by joshdfrazier »

Purchased this amp from a local retailer that moves alot of gear. This had been sitting for a few months and I think he just wanted it gone. Even if this was a private sale, like Leo said, he could have said no.

Also, a large 30uf, 600v cap had a big hole in it, as if it exploded. Turns out it was two 80uf 300v caps in series. Also, this cap doesn't seem to see voltages over 430, so I don't get the 600v rating. I replaced some preamp resistors, some were beginning to crumble due to heat/age. The whooshing startup sound is definitely in the preamp somewhere. The tone controls affect the sound when it's happening. I'm thinking bad caps or resistors maybe?

Anyway, plate voltage is 560, screens are at 357 and bias is at -32. Also, pin1 (g3) is not grounded. I should do this, yes?
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Leo_Gnardo
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Re: Ampeg VT-22 noise

Post by Leo_Gnardo »

joshdfrazier wrote:Purchased this amp from a local retailer that moves alot of gear. This had been sitting for a few months and I think he just wanted it gone. Even if this was a private sale, like Leo said, he could have said no.
He likely paid some poor schmo $50 or 100 for it or allowed that much on a trade-in. Doubt he lost $ on the deal. Probably happy to get rid of a "stone."
Also, a large 30uf, 600v cap had a big hole in it, as if it exploded. Turns out it was two 80uf 300v caps in series. Also, this cap doesn't seem to see voltages over 430, so I don't get the 600v rating.
Those "dynamite sticks" are now a problem in lots of old amps. I replace 'em with Solen film caps rated 630V. Good caps, nothing funny going on in there.
Anyway, plate voltage is 560, screens are at 357 and bias is at -32. Also, pin1 (g3) is not grounded. I should do this, yes?
I don't see how your EL34 have survived this far without G3 grounded. That whoosh you hear could be your money disappearing into a fresh set of EL34's.
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joshdfrazier
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Re: Ampeg VT-22 noise

Post by joshdfrazier »

After I grounded g3, the whooshing noise is gone. But I don't know if its because I replaced the 600v cap, cleaned all pins and sockets or what. Also, the hum is greatly reduced.

I think I'm going to tackle the bias circuit next. Something seems to be amiss, in order for it to burn out tubes like it did. I will also install a bias pot, probably 50k, once I figure out what's going on.
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