Ampeg SVT 7 PRO U2 (ICE2A165) repair

[Khefer Kaos]

Hi all!
I have a SVT-7 PRO over my workbench who simply don't work if I connect the Preamp Board (or another 12v charge).
First to all, the amp came from another tech with a really bad mess with the U2 & asociated components of this PSU (practically all the PCB behind U2 was carbonized). I repair the mess with the carbonized section, replace the ICE for the big one (ICE2A265) and replace too all the PSU components next to U2; then I plug the AC cord (with a protection light bulb to prevent shorts) and the amp simply don't work at first.
I disconect the Preamp section and again plug and switch to On and the Main Board works fine, with all the voltajes perfectly regulated, so I connect just the filaments of the 12AX7 to 15v and ground and again the PSU don't work, simply can't handle any other charge connected to +15v -15V. I probe the preamp & output boards on a working SVT7 PRO from a friend an the boards are all fine (and put the preamp and output SVT7 boards of my friends amp and don't work) so I know that they're working properly.
Any suggestions to check the PSU section?
Thanks in advanced...

[nosaj]

Hi all!
I have a SVT-7 PRO over my workbench who simply don't work if I connect the Preamp Board (or another 12v charge).
First to all, the amp came from another tech with a really bad mess with the U2 & asociated components of this PSU (practically all the PCB behind U2 was carbonized). I repair the mess with the carbonized section, replace the ICE for the big one (ICE2A265) and replace too all the PSU components next to U2; then I plug the AC cord (with a protection light bulb to prevent shorts) and the amp simply don't work at first.
I disconect the Preamp section and again plug and switch to On and the Main Board works fine, with all the voltajes perfectly regulated, so I connect just the filaments of the 12AX7 to 15v and ground and again the PSU don't work, simply can't handle any other charge connected to +15v -15V. I probe the preamp & output boards on a working SVT7 PRO from a friend an the boards are all fine (and put the preamp and output SVT7 boards of my friends amp and don't work) so I know that they're working properly.
Any suggestions to check the PSU section?
Thanks in advanced...

Do you have a spare 12ax7? So what happens if the 12ax7 is removed? Will it still power up? What are your voltages on the tube socket?
nosaj

[Khefer Kaos]

Do you have a spare 12ax7? So what happens if the 12ax7 is removed? Will it still power up? What are your voltages on the tube socket?
nosaj

Yeah, I probe anoher one, nothing changes. The amp came with a JJ 12ax7 who works fine too. The Main Supply doesnt work with or without 12ax7, just works if I disconect completely the preamp Board. Without preamp, all the Main voltajes go perfectly fine (+ -15 V, +300v, + -55v and -43v measures perfec). I conect the 12ax7 filaments directly to +15 and GND without conect the preamp board and the power supply doesnt start running.
It's something weird haha...

[nosaj]

Yeah, I probe anoher one, nothing changes. The amp came with a JJ 12ax7 who works fine too. The Main Supply doesnt work with or without 12ax7, just works if I disconect completely the preamp Board. Without preamp, all the Main voltajes go perfectly fine (+ -15 V, +300v, + -55v and -43v measures perfec). I conect the 12ax7 filaments directly to +15 and GND without conect the preamp board and the power supply doesnt start running.
It's something weird haha...

If I' understanding you correctly and I'm not sure I am.
Your preamp board possibly still has a short on it.

Also from what I understand SMPS power supplies do not generally like a dim bulb tester. You also need to be very careful with the smps supplies.

Can you post any pics of the repair section?

Thanks,
Jason

nosaj

[Khefer Kaos]

If I' understanding you correctly and I'm not sure I am.
Your preamp board possibly still has a short on it.

Also from what I understand SMPS power supplies do not generally like a dim bulb tester. You also need to be very careful with the smps supplies.

Can you post any pics of the repair section?

Thanks,
Jason

nosaj

Ok, tomorrow I post some pics. The preamp is working right, I put it on another SVT7 and all are perfect, not shorts or malfunctions, just works like a new one...

[Khefer Kaos]

Sorry, I can't post photos, i don't know why. Whatever I follow doing some tests:
I work the PSU without bulb dim, but with no differences, so again, disconection of +-15V (and even 300v to 12ax7) was the only way to work with.
Putting an external power supply to the preamp was one solution (300v, +-15v), so whit this, the amp works great (ICE chip runs normaly and cold). So I'm thinking in let the PSU +-15 only supplying the power amp section and do another supply for the preamp.
Any suggestions???

[glebert]

My 7 Pro has had problems with U2, and I switched from a real tube to a Retrovalve FET replacement to get rid of the tube heater load. I actually like the sound better.

[Khefer Kaos]

Retrovalve FET its a "Solid State Valve"? One of the options on my mind, was to rid off the Valve and doing this stage with two fets and a bias of 4.5v like a valve emulator...

[glebert]

Retrovalve FET its a "Solid State Valve"?

Yes. http://www.robertsaudiotech.com/designs/retrovalve.php

I find them really useful debug tools as well, rather than having some "golden 12AX7" or something. I have to say the LED bulb inside is a little bright if they were trying to emulate the soft glow of a tube heater.

[clintronics]

Revision H01 SVT7

H01
New Power Management IC (U2)
Current IC overheats. New IC ICE2A265 runs cooler.
Replace U2 0026347 with 2046141.

[mikeskory]

I'm in Michigan looking at the exact same issue. Ampeg SVT7 with blown U2, open R46 and bad D9. Can I chime in with questions along this line or would you rather I start anew? Thanks, Mike

[Chuck H]

To all that have been reporting this members posts... I believe there is a lack of adware blocking on their media and I don't perceive this as intentional spamming. Member checks out otherwise as far as I can tell.

[nevetslab]

If this is in regards to the Retrovalve link, I found that an interesting device, never having seen them before. It does figure someone would have built such devices for commercial sale by now....I've just never come upon them before.

[Jazz P Bass]

This patent is from 1973.

US3742261 SS Device _Vacuum Tube Replacement.pdf

[lowell]

Hey guys… it seems as the U2 IC upgrade chip ICE2A265

is now obsolete.

any suggestions on a replacement?