SVT-VR Rebuild

svtman · #1 04-12-2011, 04:33 PM

Hey Guys,

New here.

I am somewhat new to online auction buying, and I happened upon a weird transaction that left me with a USA SVT-VR that looks to have sustained severe water exposure/damage. (Below is a photo of the internals for your viewing...pleasure?)

Anyway I got my money back, and I haven't been asked to send this thing back to (unresponsive) original owner.

So I'm wondering where to go from here. Amp tech says it would take $1200 dollars to fix the electronics (including replacing both boards). Seeing that you can find a used SVT-VR for near this price I'm wondering if that would be silly to drop that amount of change in this.

Also, I'm not sure if parts are sellable at this point.

What would you guys do? DIY Project? I would feel really weird taking this 85 lb beautiful (but internally compromised) amp and throwing it in my dumpster.

metron · #2 04-12-2011, 04:46 PM

Weird so you got that for free? I would part out what you can and look for another. If you look hard enough you can find a vintage one for slightly more that 1200.

JimmyM · #3 04-12-2011, 04:47 PM

geez, that's sad! i don't know what i'd do, but i'm leaning toward parting it out. the transformers, if they work, should make you a few hundy.

levis76 · #4 04-12-2011, 05:01 PM

Easy answer, get yourself a vintage VR and keep whatever looks like it might be useable as spare parts. The transformers are worth quite a bit, especially the output transformer. The tube sockets might be salvageable if they aren't corroded. Inspect the boards closely, the corrosion might only be on the surface, you may be able to clean them up.

I know the tech said it needed new boards but he was thinking in terms of $$$ vs. time (labor) and it's quicker and cheaper for him to swap boards. That and anyone who puts any kind of warranty on their work won't touch water damaged electronics. Most shops will tell you it's totalled and you need to get another one. The company I work for (a large supplier of network power products) has a strict policy on water damaged units, we don't touch them, period, for the very simple reason that we can no longer guarantee the performance of that product.

You have more time to clean it and really determine what is or isn't trashed without worrying about labor rates. Clean her up a bit and fire it up. What's the worst that can happen, it won't work or something will short and pop the breaker in your house?

svtman · #5 04-13-2011, 06:45 PM

Thanks guys.

I'm going to try and clean it up, and see what happens. There is a little microphonic noise that might be remedied by new tubes. Not going to spend a lot, but we will see what happens.

Not really sure how to go about parting it out...

Peace,

anderbass · #6 04-13-2011, 10:15 PM

There was an amp tech on here awhile back that just had a vintage SVT power amp section, he wanted to buy a preamp and head case.

Anyone remember the thread or who that guy was? That dude would probably love to buy your amp for a decent price.

svtman · #7 04-14-2011, 09:12 AM

Hey Guys,

Thanks for all the posts.

I decided to follow Levis76's advice and spend some time cleaning it up. I've had some pretty good results (after a few hours of cleaning). I may post a photo later.

I hooked her up to my 410HLF- Heritage and turned it on. There is a constant hum present in the amp. It doesn't change with increases or decreases in gain. I plugged my bass in and it plays quite nicely. Very smooth and warm, but there is that constant hum.

Could this be a tube issue? If 1 or more power tubes have gone, could it cause this? They (Sovteks) look to be several years old. Possibly original?

It's interesting that the noise doesn't get louder as I crank the amp.

If a full retube could fix this thing up, I wouldn't mind to drop the change, but I would hate to buy only to realize that there is a larger (and unrelated) problem.

Any Ideas,

levis76 · #8 04-14-2011, 10:05 PM

Constant hum sounds like noisy power supply which would not get louder with gain. If you know the input power is clean and noise free then it probably needs caps. You can check this by shutting off the rest of the house and run your amp all by itself on a dedicated circuit. A lot of devices around the home can cause noise in a tube amp. Fridge, microwave, T.V., furnace, flourescent lights, etc. If it still hums I would bet it needs caps.

If your playing sounded good and the tubes had a nice even glow they are probably fine.

Also try cleaning the tube sockets and making sure they are nice and tight. The cups in the sockets can spread a bit from taking tubes in and out and they could be corroded a bit as well. Hit them with some contact cleaner and wiggle a tube in and out a few times. To snug the pin sockets I use a jewelers flathead screwdriver and gently push them closed a bit so it will be nice and snug when I put the tubes back in.

Alex1984 · #9 04-14-2011, 10:40 PM

Also, pointing out the fact that quite a few of the early SVT-VRs suffered from a PCB problem that caused hum.

svtman · #10 04-15-2011, 05:21 PM

Hey Guys,

Yeah I think it is the caps. I've been reading about that, and the symptoms of dried out power supply caps sounds like this.

Question: I would like to try and do this as a learning experience in soldering, and electrical repair. I plan on spending time with this and being patient, so please don't lecture me, but is there a definitive and uncomplicated way to discharge the caps safely?

I have read about using a resistor, but I'm not sure what kind to get to discharge a 600volt capacitor. Also, Do you need to use any special tool to touch the resistor to the leads on the capacitor? Should I expect a pop when the leads are connected to the resistor?

Can you use a DMM to see if the caps are drained, or will this fry the meter if they aren't?

Thanks

okcrum · #11 04-15-2011, 05:27 PM

Actually you may have an iffy audio signal ground from the preamp to the power amp. Dirty connector or something like that. Check the 1/4" jacks on the amp too. Could be caps in the PS. Depending what stages they're powering, the hum might or might not go up and down with the gains.

At this point, it sounds like the amp has been saved from the dumpster. It looks like you're about 90% of the way back.

svtman · #12 04-15-2011, 05:41 PM

Quote:

Originally Posted by okcrum

Actually you may have an iffy audio signal ground from the preamp to the power amp. Dirty connector or something like that. Check the 1/4" jacks on the amp too. Could be caps in the PS. Depending what stages they're powering, the hum might or might not go up and down with the gains.

At this point, it sounds like the amp has been saved from the dumpster. It looks like you're about 90% of the way back.

Oh ok. I'll check out those connectors. Can anyone suggest a good contact cleaner that isn't overly abrasive?

Discharging caps on a SVT? Anyone? I would really appreciate it!

Thanks,

BassmanPaul · #13 04-15-2011, 06:10 PM

Get yourself a 10KΩ 10W wire wound resistor. Solder red and black leads one to each end and insulate with heat shrink tubing. Other end of the cables add insulated croc. clips of the appropriate colour. I hang mine on a hook on the wall above my bench. To drain caps connect the red to the first filter cap and the black to ground. Wait a few minutes to allow the caps to drain through the resistor. Move the clips to each filter in turn until they are all drained.

Please be very, very careful with what you are doing. The voltages in that amp ARE lethal! IMO yours is the last kind of amp that I'd recommend as a learning experience.