Looking for Ampeg Schematics. (Original SVT, SVT Blue Line, SVT-II, etc)

Luis Fabara · #1 02-27-2011, 03:00 PM

I recently started a music store where I live , and as a side service we get to hold some tube amps in the shop for repairs such as Mesa's Marshall's, etc.

Im in the process of aquiring a SVT-II amp for myself as a reference amp to be used in the store, but have also several SVT's in various conditions coming into the shop for repairs in the next following weeks.

An original Black SVT, a Blue Line SVT , a Black Line SVT and 2 more I don't have enough info yet. Also a new Korean
SVT-CL

I have 6550 tubes, 12DW7, 12BH7 , 12AU7 and 12AX7 in stock.

What would be the right procedures to start testing/diagnosing this amps and what other tubes could be required in the process or what mods can be performed to work with my stock tubes.

Any help on restoring this beautiful amps to full working /low noise condition would be helpful.

Schematics, procedures , links, etc will be greatly appreciated.

BassmanPaul · #2 02-27-2011, 04:06 PM

With respect Luis, this is not something that you can learn across the internet. Working on high, read lethal, voltage equipment is not something to be undertaken lightly. Folk go to school for several years to gain the knowledge needed. Add to that the experience of actually doing the work - often gained by being mentored by an existing tech.

Luis Fabara · #3 02-27-2011, 04:12 PM

We have Electronic Engineers/Technicians in house, and I think I have a little knowledge of how tube amps work not to blow myself in the process.

What Im requesting is schematics, experiences, to have before-hand knowledge on how to treat this specific amps.

Thanks for your comment though.

Jerrold Tiers · #4 02-27-2011, 04:50 PM

The best overall reference for older stuff may be the Groove Tubes "Tube Amp Book"

I'm no big fan of theirs, but there's a lot of information in there as far as schematics. Volume 4 is the latest I have, I don't know if they even still publish it.

Got mine from Aspen Pittman at Namm, but it may be available from used sources.

if you have specific unit wants, I have Ampeg info, mostly for newer units.

JimmyM · #5 02-27-2011, 05:21 PM

Quote:

Originally Posted by Luis Fabara

We have Electronic Engineers/Technicians in house, and I think I have a little knowledge of how tube amps work not to blow myself in the process.

if i could blow myself i'd never leave the house!

BANG! ZOOM!

Luis Fabara · #6 02-27-2011, 08:50 PM

Quote:

Originally Posted by JimmyM

if i could blow myself i'd never leave the house!

BANG! ZOOM!

Hahahahah.

English English.

"BLOW-UP" blow myself up.

Jeff Scott · #7 02-27-2011, 09:32 PM

Quote:

Originally Posted by Jerrold Tiers

The best overall reference for older stuff may be the Groove Tubes "Tube Amp Book"

I'm no big fan of theirs.....

+1, on both counts.

Luis Fabara · #8 03-03-2011, 04:50 PM

This seems to be an 80's SVT, Im not sure as there is no serial number in the back. The standby is behind.

It is working ok, but seems to distort too early (at 3 of volume)
and has a hum with all controls at zero.

We require to fix the hum and restore full power.

Any help dating this amp and the proper schematics?

Thanks in advance.

Luis Fabara · #9 03-03-2011, 05:19 PM

Quote:

Originally Posted by Jeff Scott

+1, on both counts.

Will be getting one soon. I think the latest version is on Amazon.

Luis Fabara · #10 03-03-2011, 05:58 PM

These are some pics from behind without the grille.

Any ideas on wich version is this one?

It has 5 12AX7's ,2 12BH7's, 1 6C4 and 6 6550's. Inside it only says SVT.

MTI perhaps?

JimmyM · #11 03-03-2011, 06:39 PM

ya, i'd say mti, too, since they changed the pre tubes but not the driver and phase inverter tubes. not an original box or grill, though, but i think you knew that

i totally dig that look, though.

as for distortion, svt's usually start to distort around 11:00, which would probably translate to 3 or 4 on the dial.

Luis Fabara · #12 03-03-2011, 07:04 PM

Quote:

Originally Posted by JimmyM

ya, i'd say mti, too, since they changed the pre tubes but not the driver and phase inverter tubes. not an original box or grill, though, but i think you knew that

i totally dig that look, though.

as for distortion, svt's usually start to distort around 11:00, which would probably translate to 3 or 4 on the dial.

Thanks for that info man.

I just tried again with my ATK. it seems to be clean only on 1 of volume. At 2, you can hear the bass distorting already (9 :00)
At 5, (noon) it sounds like a high gain guitar head!

Yeah the box/grill were made here, and the logo is from another amp... this was totally restored a while ago, but it still has that hum, and I feel its lacking bass. I have tested the newer SVT-CL and it seemed cleaner and meatier, so this one must have some component failing or is probably badly biased, I will check that tomorrow when I disassemble it.

deaf pea · #13 03-03-2011, 07:51 PM

Luis . . . there used to be a schematics website that you could reach from ampeg.com . . . I checked and it wasn't there . . . OK, found it . . . www.unofficialampeg.com . . . go there . . . that page has what you're looking for (without having to buy Aspen Pittman's tube amp book) . . .

. . .

Suerte . . .

Luis Fabara · #14 03-03-2011, 07:56 PM

Quote:

Originally Posted by deaf pea

Luis . . . there used to be a schematics website that you could reach from ampeg.com . . . I checked and it wasn't there . . . OK, found it . . . www.unofficialampeg.com . . . go there . . . that page has what you're looking for (without having to buy Aspen Pittman's tube amp book) . . .

. . .

Suerte . . .

Gracias amigo!

Luis Fabara · #15 03-03-2011, 08:05 PM

It seems that the SVT Schematics on the website are for the original 12WD7 design. There is no MTI specific schematic for the 12AX7-only preamp.

Does anyone know the differences in preamp design from the original? What components are different in this version?

My guess is that I could mod the MTI to be just like the original SVT with the 12DW7. Has anyone performed this mod?

Jeff Scott · #16 03-03-2011, 09:19 PM

Given that the hum is constant regardless of volume control setting it most likely needs new power supply filter caps and pretty much a good overhaul by someone who is truly certified to do tube amp repair as its can be quite dangerous in there.

Jeff Scott · #17 03-03-2011, 09:21 PM

BTW, the book is worth getting.

This book is also a great one to have:

http://www.kendrick-amplifiers.com/m...tegory_Code=05

Luis Fabara · #18 03-03-2011, 09:55 PM

Quote:

Originally Posted by Jeff Scott

Given that the hum is constant regardless of volume control setting it most likely needs new power supply filter caps and pretty much a good overhaul by someone who is truly certified to do tube amp repair as its can be quite dangerous in there.

Allright, so the rectification stage caps first thing to check tomorrow, good advice, thanks.

Luis Fabara · #19 04-20-2011, 11:36 PM

I got a Cap Kit from Fliptops.net and a new Hum Balance Control. Replaced all the caps. New Tung Sol 6550. Biased at 25ma per tube, and it is running VERY WELL NOW!

I found the previous tech had used very cheap chinese caps that were about 1/3rd or 1/4th the Size of the german caps I got from fliptops.

The hum was drastically reduced, there is just a slight hint of hum in the background. I also replaced the microphonic 6C4WA with a NOS GE JAN 6C4WA.