Ampeg SVT (old school) amp help - 60s/70s

[sleepy_monkey]

These are the values of the resistors that were paralleled in place of the 4.7k 15w resistor.

 

[agedhorse]

If you want a vintage SVT, I think there is a good chance you will come out ahead buying an amp that is already sorted.

This sort of project makes sense for someone who can do the work the themself, as the parts alone could cost more than the amp is worth in working condition.

Agreed, and in this case (like many on the internet), we have no idea what the rest of the story might be with the amp. It's also difficult to determine which specific amp is being discussed as it's jumped around a bit.

 

[beans-on-toast]

These are the values of the resistors that were paralleled in place of the 4.7k 15w resistor.

The parallel resistance yields 4.1K so more current would pass than designed. A 4.7K 15W wire wound cement resistor should be used. The 15W is important as the cement resistor will blow if this is exceeded for too long a time. Best to stick to the design spec for this reason.

 

[sleepy_monkey]

The parallel resistance yields 4.1K so more current would pass than designed. A 4.7K 15W wire wound cement resistor should be used. The 15W is important as the cement resistor will blow if this is exceeded for too long a time. Best to stick to the design spec for this reason.

Thanks. Fliptops has those and the electrolytic caps. I’m going to order the resistor and the caps to replace the paper caps and take it to a tech and see what they can do.

 

[Wasnex]

Thanks. Fliptops has those and the electrolytic caps. I’m going to order the resistor and the caps to replace the paper caps and take it to a tech and see what they can do.

If you are going to get a tech to fix the amp, I suggest NOT poking around and replacing components. The failed components often help the technician understand how and why the amp failed in the first place. By replacing components you are possibly concealing important facts that the tech will need to do the job.

Also if you are not an experienced technician, it's very possible that you will cause unnecessary damage in the process of replacing components.

 

[sleepy_monkey]

If you are going to get a tech to fix the amp, I suggest NOT poking around and replacing components. The failed components often help the technician understand how and why the amp failed in the first place. By replacing components you are possibly concealing important facts that the tech will need to do the job.

Also if you are not an experienced technician, it's very possible that you will cause unnecessary damage in the process of replacing components.

Good point. I’ve got a few options for techs….now just trying to decide who to take it to. Only one offered to do a bench test to then let me know how much it would be. They have tester tubes, but admittedly wouldn’t be replacing the resistor before checking it out. They did say they would test the transformers and that they would have a good idea of an exact cost. We’ll see.

 

[JimmyM]

sleepy shared more photos with me and this amp looks like it has not been touched accept those blown resistors. All the other tubes are there and are original GE/USA made ones so most likely are still OK.
No other components show visual damage.

While resistors are fairly easy and cheap (for a tech), disassembling a vintage SVT is not the most pleasant job ever. So it will likely cost more than you expect just to do that. I paid a lot to restore my 69 SVT and don’t regret it, but it can be rather costly no matter the repair, so it’s a bit of a gamble.

 

[bobyoung53]

I have two heads like that, with the white rocker switches I believe that's the last iteration made from about 1976-79. The date should be on the electrolytics if they're original. Mine had a '76 and a '77, they couldn't be any older but could be newer. The dust covers are off two of your speakers, I would try to get some before you use it, without them dust and dirt could get in the voice coil. It also has one replacement speaker, as long as it's a 32 ohm speaker it should be ok. I would at least bring it to a good tech who knows them and get an estimate. I would spend some dough on it, for my money they're the biggest sounding heads going and once you get one straightened it will usually last forever with periodic tube replacements. I would get a matched sextet of JJ's, going to run you about 400 bucks but I would get the estimate first. 12DW7's are still available too although they are also higher than they used to be, 25-30 bucks.

 

[sleepy_monkey]

Took it to a tech for a bench test. He’s old school and worked on a bunch of SVTs. Thoughts on this??

 

[beans-on-toast]

Took it to a tech for a bench test. He’s old school and worked on a bunch of SVTs. Thoughts on this??

Diagnostics not unusual from many techs. Tubes are expensive..

 

[Wasnex]

Took it to a tech for a bench test. He’s old school and worked on a bunch of SVTs. Thoughts on this??

I read the estimate as parts plus about 3 hrs of work. It's a lot of money, but I don't think it's out of line for a stuffed SVT.

If the tech has a good reputation, decide how much you want to spend. If it's too much, sell the amp cheap.

Keep in mind this is an estimate. There may be additional problems.

 

[jmpiwonka]

It’s seems reasonable to me, if you really want an SVT and the tech has a good reputation.

 

[agedhorse]

If the quality of the work is proportional to the cost, it may not be so bad...

 

[JimmyM]

Took it to a tech for a bench test. He’s old school and worked on a bunch of SVTs. Thoughts on this??

It ain’t doing you any good broke! I don’t know that you need TADs, but there’s not going to be a significant savings if you go to a cheaper brand. I think it’s quite reasonable (I paid about that much for a similar makeover in 2008), and he can bias it up all nice and tidy.