Looking for service bulletins for Ampeg VT-60/120

[jamesmafyew]

I just finished fully rehabbing a run-down VT-120 1x12 combo. I have heard that there are service bulletins out for these amps that recommend installation of jumper wires because certain PCB traces are prone to overheating or causing fires (!). I emailed LOUD to see if they'd send them to me, but they won't because I'm not an authorized warranty service center. I've figured out a lot about the amp and how to make the grounding better, improve reliability where there are marginal components, etc. But if there are known safety issues with the PCB traces, I would like to know what they are before I put this thing into regular use.

If anyone has the service bulletins and would be willing to send them to me, it would be much appreciated. My email is atomiumamps@gmail.com.

I put up a post on my blog about the changes I made to the VT-120 -- maybe it could be helpful to others:
Ampeg VT-120 epic overhaul | Electronic States

[Enzo]

I'm not aware of such bulletins. They may exist, but I've never seen them. I'd be surprised of Loud had much, since the amps are over 20 years old, LONG before Loud bought the SLM amp lines. If you call them and ask for a service bulletin, unless you are a service center, they won;t even bother to look up whether there is such a bulletin, because they won;t be sending one out to you even if there is, so why use up the time?

The only wiring that overheats in tube amps is generally the heater wiring. Those are the only wires that have to carry any current. And it is usually a connection that fails, not the wiring itself.

Look in your unit, is ther any wiring or conections that look like they overheated? If not, chances are it will continue that way. It has lasted 20 years without failing in that way.

[jamesmafyew]

Well the amp supposedly can handle either 6L6s or EL34s, according to the manual. The bias voltage has a very large range, -30 to about -60. It's never had anything but 6L6s in it... so that makes me wonder if the heater traces are sufficient for 6L6 heater draw, but cook when using EL34s.

I've successfully used it with 2x6550s in the power section, but now I'm thinking twice about trying it with 4xEL34s or 4x6550s.

Here's a picture of the backside of the PCB, the heaters are the wide traces running left to right across the board, just above the power tube sockets:
http://local.anchorstates.net/images...20-gutshot.jpg

[Enzo]

I have a layout drawing that shows traces.

[jamesmafyew]

If you have that layout in an easily-accessible electronic version, and wouldn't mind sending it to me, I'd appreciate it. If it's a paper copy, then don't worry about it.

Thanks for the help!

[Enzo]

Actually it is an 11x17 paper copy. It would have to be scanned in two pieces and gray-scaled.

[oc disorder]

Ampeg VT 120 Pictorial (layout)

Here you go.. dunno where I got it...bit big but all the better to etc etc.....
drawn 1989..

[jamesmafyew]

Wow, thanks a lot.

[Enzo]

Wow indeed. That's great, and see the handwritten VT120 bottom center? That is my handwriting. My 11x17s are folded in half with three-holes on either end so it fits in a binder. At the edge of the fold I write the model like an index tab. Your scan is of my page. God knows from when.

I did eventually find an 8x11 reduction of that scan.

I no longer have that original, I still have the VT60 which is the same board. Seems to me many years ago I sent a bunch of my duplicate files to KB, he may have wound up with that one, so perhaps he provided the scan of it.

ANyway, glad you found that.

[kc2eeb]

Hi!
Would it be possible to re-post the pictures from this? Each picture comes up as an ad to buy lottery tickets. I'm refurbishing A VT-60 and it would be most helpful.
Best regards.

[oc disorder]

Hi Kc2eeB and welcome to the forum
I will repost the layout .. can't help with the photos from jamesmafyew

Sometimes you can get lucky using the wayback machine .. I had a look it's only been saved once and unfortunately
there are only 2 exterior photos.
see here :-
Ampeg VT-120 epic overhaul | Electronic States
The text is still there.. perhaps if you contact him he may be able to help...

I zipped it up as the forum had a server crash and thinks the file is still there and wont allow a double post or some such..

[kc2eeb]

Thank you so much! It's most appreciated. Sorry for the delay in responding.
So far, I have the chassis out of the cabinet and marking the leads so it all goes back together correctly. It seems Ampeg did not mark the component locations, so this will be most helpful. Thanks again!

[oc disorder]

Here it is again.. Thanks Enzo...

(Had a request although the repost was in an offshoot thread)

[jamesmafyew]

I may as well chime in for posterity as well. The hosting for those pics on the original blog post is long expired -- and it'll be a while before I get around to fixing all my old posts there. But I'll upload the pictures here in case it helps someone.

This particular amp had an interesting story, by the way. It came to me as scrap because the original owner didn't think it was worthwhile to fix. After I overhauled it, I sold it to a guy in Louisiana. Didn't have an issue during the several years he had it, until he took it to a local tech for routine maintenance. The tech was confused by what I had done to the amp, and mangled a few things trying to 'return to stock'. The weird thing was that the original owner who had first dumped it with me bought it back on ebay (yes, the same exact amp) and brought it back to me again to check over. Still working just fine, after I repaired some of the ill-advised 'repairs' from the LA job. The original owner is very happy with it and he spent less on it than he would have to just pay me to do all that work in the first place.

[kc2eeb]

Wow, "a blast from the past!" Thanks so much, again! I did repair the amp, did not do the star ground (maybe eventually) and it sounds great!