Rickresource Rickenbacker Forum

Says it all, do you know of any sources for this? it is a late 70's, and I have a strange story about that SVT with 6L6's in it if you'd like to hear it, no time now though.
Also any advice for recapping the same? My caps should be here soon and I've never done it before.

Bob...if you have a digital camera, take some closeups of the capacitors showing the + or - of the caps.
You should remove only 1 cap at a time and put the new one back in the same direction.
This is kinda like a battery...the + on the new battery has to be touching the same + as the old battery.
Make sure you have the amp unplugged fom the wall socket and using a long screwdriver, touch the chassis at the same time you touch each end of each capacitor.(do not come in contact with the metal part of this screwdriver)
Be careful....this amp can hurt cha'.

Best way to discharge caps is to use a wire with alligator clips on each end and one end is attached to the chassis and the other end has a 150 ohm 2 watt resistor. That way bleeds off the stored voltage over a couple seconds instead of "bang" with a screwdriver.. Switches: I'll look to see if I have any. I do have a bag of SVT lamps.

I agree with Don here. When I first started with amp mods, I didn't know any better, so I used a screwdriver to the chassis to discharge the caps. It worked with a bang, but I also blew out the metal rectifiers in the amp after a couple times of this, and I'm sure it wasn't good on the caps either to discharge so quickly. Be VERY careful in that SVT if you've never done repair like this before. SVT's have VERY high voltages in them and can kill you if you aren't careful. First rule is never have 2 hands in the chassis! Only use one hand at a time if possible, or make sure there is absolutely no voltage on the caps before you mess with them. If I'm going to be working in a chassis for awhile, I will leave my discharging clips with resistor hooked up to the main filter cap while I'm working so any residual voltage is being drained away.
Hope that helps ya Bob! I don't have any idea where to find any of the switches.
Greg

Thanks everyone, I've never done cap jobs, but I did go to school years ago for electronics and was also taught then to always keep one hand out of the chassis, I have a general idea what to do, and know enough to discharge the filter caps before, these discharge very quickly anyway, I don't know if there are bleeder resistors on them or what. I have never liked discharging electrotytics with a screw driver either, that also chews up the screw driver.
When I bought this amp (here in Lima Perú) it was the only one I had seen out here and I love these things, so I bought it and got it very cheap, three hundred bucks knowing that it needed a lot of work, how much I didn't know.
First I had to replace every single tube in it, replace a few pre amp resistors, and it still had three original Magnavox pre amp tubes, talk about microfonic! But the worst thing was that it had 6L6's instead of 6550's in it, and I couldn't find any information about conversions, one guy e-mailed me from usedampegs.com and said that guitar players used to do this in the hopes of making a big giant JCM-45 Marshall out of them, he promised to find the conversion schematic but never returned my e-mails.
Finally we moved and I got my own room to take it apart and check everything and lo and behold, the 6L6's were functioning on 6550 plate voltage and everything else for 6550's, some joker here had just plugged them in and turned it on, and for some strange reason it worked, and the tubes didn't even glow cherry red. Amazing, to say the least. I talked to a tech (I use that term loosely) and he told me, oh yeah the're interchangable! haha!
Anyway the plate voltage was 150 volts too high for 6L6's and on one side the bias was set to 0 (there are three tubes in series, one set for each side of the push pull output)and on the other side the bias was wide open as the pot was shorted, and the tubes still didn't glow! The side with the bias all the way open was running hot though but no cherry glow. These tubes were all old American tubes, some pulled from old Fender amps, as I could still see the bear trap marks on some of them. Sylvania and Phillips tubes.
the plate voltage as measured by me on a digital multimeter is 650V.
I ran it for several hours like this one night before I realized that it had not been converted for 6L6's and it actually sounded fine and sounded more like a Fender to me than an Ampeg.
I finally got some 6550's sent out to me here, put them in and what a difference, now I'm waiting for my caps and it will be done.
Anyone have any ideas what i can use for a 350 watt 4 ohm load resistor? A friend of mine used to use old toasters but wouldn't the resistance change as they heat up? And what if they pop, haha!
And I would really appreciate a switch if you have one Don, I have a hard time here in Lima finding parts and I can't find one online anywhere. If you have one, let me know how much it is. my e-mail is [email protected]

Hi Don,
Did you happen to find any of the old Ampeg white rocker switches? It's for a late 70's SVT head, I need a power switch only. the old one is a Carling, and they don't seem to have any. I haven't checked with Ampeg yet, because it is an expensive call from Lima Perú. I think it was a ten amp switch 117 V.

Hey Bob, did you recap that SVT yet? I meant to respond to your email a while ago, but I'm a lazy punk!

I did my '73 a while back (first recap *ever* for me!) and it turned out great. Kind of like learning how to drive in an AC cobra. I got some good tips from the guys on Ampage - they really know their sh*t!

I did it using two JJ 100uf/50uf 450V cans up top, and a bunch of other cans mounted inside. You won't find exact values, just make sure you are above the voltage and farad rating of the originals and you'll be ok. You will also end up with more caps than you started with, because you can't get the weird *** 70/40/40 combos - so you'll have to either make some clamps (like I did) to hold the extra ones inside, or just hotglue them to the side of the chassis. One thing that's important is if you use two cans in series for the 30uf/600V jobber - install balancing resistors in series with them - that's a *must* to prevent overvoltage in either one.

I powered mine up *slowly* with a variac and no tubes in it to make sure everything was cool. Also, measuring plate and screen voltages with an input of 12V will give you a good idea that everything is ok (voltages should be a little more than a tenth of the normal 120V operaton).

Do you have a dummy load, signal generator, and scope to bias it up?

Oh, and watch your back! Rob

Yeah, I finally did it, I got a cap kit from fliptops. It was a PIA but I'm glad I did it, now I've lost my fear of power supplies and will not hesitate to cap another amp. I took all the tubes out when I powered it up (no variac) and got out of the room! haha! I wasn't taking any chances, it is VERY hard to trace wiring in one of those, but I did the best I could to make sure I had everything correct. After about 5 minutes I checked the plate voltage which was right on so I knew it was ok. I put the tubes back in it and turned it on. this is a 220 amp by the way, I'm in Lima Perú. And no scope, signal generator or dummy load. What I plan on doing is having a keyboard player put a constant Low E in it (pure) that's the 40 hz. signal I need and hooking up a cab to it, driving it to 25 volts DC. and putting the voltmeter across K1 and K2 and balancing it that way, it should work if I can stand the low E (or actually the heighbors as I'm going to put the cab outside (it's summer here).
What's a balancing resistor? Fliptops sent me a 30 uf cap that was two caps wired in series and I also had to wire two others in series for 100 uf and 500 volts that they didn't send (they sent me a 220 uf cap instead, there is a 220K resistor in parallel with the 100 uf cap which I think they mistakenly read as the cap) So obviously I don't have them on either one. Is that an urgent thing, can I use it this way until i get some, or am I in danger of blowing up a cap? I've had it on for several hours and have had no problems, there was some hum initially but it is quieting down, especially after about ten minutes.
And I did find a source for the switches.

The head is all done and sounds great, there was a shorted grid diode that was causing the hum problem, it is now the best sounding SVT I own. I'm going to go through my other two when I get back to the States, this thing sounds like it is brand new and it was a basket case when I first got it. And I am now intimately aquainted with the SVT's schematic and wiring and also what to look for. If anyone is having any problems with an old SVT, I'd be glad to help.