Ampeg VT-22 question

[luthierwnc]

A buddy of mine is the "Keith" in a Stones tribute band. He recently got a VT-22 for the larger-gig Exile-era sound. Today he gave me a call and said the thing didn't have the headroom or volume of his VT-40. He took it to his tech who told him the amp had been well maintained and was working fine. Power tubes are fairly new NOS 7027's. I'd recommended an adjustable bias control but the guy said not to bother. The speakers were suspect but an auxillary cab sounded more-or-less the same. Both channels have the same effect so there isn't a compelling reason to suspect the preamp tubes.

Long-story short, I've had one and worked on another. They were both big and clean for days. God-awful heavy but that's another story. I told my friend to hold a decision whether to keep it or not until I had checked if other owners/techs had seen V4's that broke-up too soon and didn't have pant-leg flapping volume. Comments appreciated,

Thanks, Skip

[telemoxy]

People mod these amps to get them to break up early. You might check the component values against the original schematic. Also, sometimes the inputs are jumpered to feed the signal to both preamps at once.

You could add that variable bias pot and use a bias probe to experiment with hotter or colder biasing.

Could be preamp tubes. Check to see if a previous owner has been tweaking the preamp by experimenting with non-stock tubes in various places in the circuit. Check V4, the 12AU7 tube in the power stage. Sometimes people substitute a 12AX7 that causes distortion.

The only way to really check the power tubes is to try a set that are known to be good.

[Diablo]

Something else to consider. When I used to gig with my V4, I would always run two speaker cabinets with 4x12 in each. Band practice only required one bottom. With one 4x12 cabinet, it breaks up at lower volume. Also, if the speakers are very old, they may be breaking up early because of cone rub. My original CTS speakers in my V4 look great (perfect cones, no tears), but sound terrible now. They distorted badly any time the volume was over 1/4, but sounded fine at lower volume. Ted Weber advised that it was likely cone rub - he was correct. I replaced the speakers and the amp is perfect.

[luthierwnc]

That's the problem with not having the thing on the bench. IIRC, the reverb circuit is directly above the power tubes. The resistors in mine had sort of a brownish/tan cast to them. Young said he did try them through another 2X12 and there wasn't much difference. Also, both preamp channels had the same limitations so the components along each are either both bad or both good.

I still keep coming back to the bias. Even a few milliamps too frisky at those voltages could knock the headroom down a lot.

While we are on the subject, do you guys have a feel for how a pair of neodymium 12's would work? The weight of this thing is a factor.

Thanks, Skip

[Diablo]

I've never tried neodymium mag speakers, but my V4 was factory biased quite cold - about 50% at idle with 7027A tubes and the original and correct value of bias resistor. With the VT-22 and two twelve inch speakers, that amp should be as loud as a twin reverb.

There's an easy way to tell if the preamp is killing volume or not. Just plug another different amp's preamp output into the extension amp input on the back of the VT-22. When I plug the line output from my hot rod deluxe into the V4, it sounds like a really loud dual showman. Each channel of the VT-22 preamp only has one unique tube - a single 12AX7 for volume control and sensitivity. All the rest of the tubes are shared by both channels.

[luthierwnc]

Thanks Diablo, I'll forward that along. He's got a Blues Deville that should fill the bill nicely. sh

[Guitarist]

Great amp, I had two in stereo, I guess only the reverbs made it stereo
Keep that amp and work it out.

Once you get it sorted out, a seperate head-cab might be an option. It is easy to make an effects loop in it as you only change that Pre-OUT jack to an stereo type. It is a perfectly designed loop, but in sleeper mode. That way you can test either the pre or the power amp.

Those neo speakers would match well if they can handle the watts and/or low end. The Ampeg is picky with a perchance for top quality speakers; all else will sound like poo. I'd say go for it- the Neodyniums.

[luthierwnc]

Thanks, I'll send it along.

One thing I do remember about working on those big V's is respecting the ground wires. You can't just ground things anywhere. I recall a wire running all the way from the preamp to the main star ground. Ignore that and it hums like it doesn't know the words.

Since you can't re-cap the things with stock cannisters, you need to make little board "sleds" for the extra caps.

Skip

[telemoxy]

While we are on the subject, do you guys have a feel for how a pair of neodymium 12's would work? The weight of this thing is a factor.

Thanks, Skip

I have had a couple of occasions to experiment with a 90 watt Traynor Custom 90 combo that comes stock with a pair of Celestion New Century neos and they sounded great every bit a Celestion speaker.

More important I was able to compare the Custom 90's weight with a Traynor Custom 50 beside it packing a single Celestion Vintage 30. Both amps weighed the same even though the Custom 90 has twice the output, twice the number of speakers plus a larger cabinet. The New Centuries sound at least as good as the Vintage 30 as an added bonus.

I have a 12" Celestion in my VT40 combo which is the two power tube, single 12" speaker version of your VT22 and it sounds great. The New Centuries are on my list of things to change on the VT40 to reduce its weight without sacrificing tone.

[Dave Curtis, dB AudioTech]

Thanks, I'll send it along.

Since you can't re-cap the things with stock cannisters,

Skip

Why not? I've done 4 or 5 of them. If you're lucky, the cardboard covers will come off the old ones, and you can glue them onto the new ones. If not, C20 has to be insulated (over 600VDC to ground in standby; Ouch!). You can restuff a 47uF into the cardboard tube for C18 (2X20uF in parallel). Even though www.tubesandmore.com is having a 20% off sale, it's probably still more expensive than discreet caps...

[luthierwnc]

That's nice work. Modern electronics just isn't a 600 volt world.

I sold my friend a Gemini I a couple years ago that he really likes for that particular era in their set. I've encouraged him to consider a pre/power amp and a 2X12 to amp the Gemini. He said he would sell the VT so that chapter may be over.

Thanks again and I hope you can find a place to play those beasts! sh

[Dave Curtis, dB AudioTech]

That's nice work. Modern electronics just isn't a 600 volt world.

Thanks, I've attached a few more pics. Actually, it wasn't back then either. Ampeg used a voltage doubler with some caps in series to obtain a high voltage rating; hence the hot cap can. The white wire in the pic below connects a section of one cap to the case of the other.

I sold my friend a Gemini I a couple years ago that he really likes for that particular era in their set. I've encouraged him to consider a pre/power amp and a 2X12 to amp the Gemini. He said he would sell the VT so that chapter may be over.

I haven't tried a Gemini. I've heard they're good.
These pix are from a customer amp, although I own a VT22. That one is still going strong on the original caps & OP tubes... (cobbler's children syndrome) used it with the bass the other night. I changed all the 12**7s with t'funkens, and that sounds pretty nice.

Thanks again and I hope you can find a place to play those beasts! sh

One thing about the VT22: that lonesome handle is some engineer's version of a sick joke. I only use it to get it up to my chest to do the "bear hug" carry. And yes, I use it whenever I can... sometimes atop a V4 cab; plenty clean headroom with guitar (it really doesn't have to be loud) It's nice & growly with bass. I have a roadcase that the chassis fits into for those small-room bass gigs. Oh, and you're welcome!

[Dave Curtis, dB AudioTech]

Grrr. Pix:

[luthierwnc]

Hi Dave;

Looks like he'll be sending it out here for the full Monty. Depending on the state of the caps I might be trying some of your tips.

Yesterday I got to air out a couple of my Dumble clones with my guitar teacher. One in particular had some exceptional cleans. We got to talking and he used to have a VT-22. When I told him about this one he sort of looked at me for a second as if I had gotten tongue-tied and botched my explanation. Not clean and loud?

My experience suggests either the bias is just way out (this one hasn't been modded with a pot) or a resistor has drifted/baked way out of spec. Could be a coupler. On mine, which was probably from the middle of the lifecycle, all of the reverb components had broiled from sitting over the power tubes. When I started to unsolder one of the resistors, the lead pulled out before I even got the iron on the joint. I'll give them all a small yank when it arrives.

If you ever get the chance, give the Gemini I (G-12) a listen. It is sweet, fairly clean and about 20 watts. Perfect for the little shotgun clubs around here. I think it has the best reverb (same as the Reverbrocket) in the Ampeg line -- which makes it the best anywhere. Still kinda big and heavy for the output but that's not a bad price to pay.

Cheers, Skip

[jaysg]

Can you measure the output power of both the owner's VT-40 and subject VT-22?