What's a planet?
I just got my hands on an old Silvertone Twin Twelve, Model 1474 Tube Amp. I am not an amp repair expert, by far. It is missing one speaker. Powers up, all tubes were lit. No sound, just some popping noise. I found a leaky cap. ( 16v 100uf)So I took the chassis in to my local electronic parts store. The salesman looked at the amp and sold me a new cap that he reccomended, not exact matching values cap. Also, noticed a bad resistor (was graying and looked burnt) so he sold me one (1 watt, schematic says all resistors .5 watt unless noted) OK, I replaced the parts, plugged it up and the biggest "PLANET" started smoking. I quickly turned it off and unplugged it. Can someone please tell me if I did something wrong or if the guy sold me the wrong parts, or both. Any help in the right direction will be greatly appreciated. I want to get this great amp back to life. I want to hear what it will really do. Oh, I have the schematic if that will help. Thanks, Mike
What's a planet?
Can you take pictures or be more specific compared to the schematic what was changed?
I worked on one just last month. Initially the owner just wanted a grounded 3 wire power cord and a checkup. I gave him the usual options about replacing the power supply filter caps but money was an issue for him. He picked it up and I had it turned on (about 1 hr) and demonstrated that both channels were working OK and the tremolo was fine. He went away happy but I found out the next day that the amp blew its fuse when he went to a Friday night jam session. It blew immediately.
He got the amp back to me after a week's time. One of the power supply caps was a dead short and a 2nd one was also bad. There's just no predicting when old caps will go bad.
Like the fellow on the oil filter commercial says "you can pay me now or pay me later".
What I refer to as a PLANET, is indeed the big red cap with the word PLANET on it. In fact there are 3-4 of them. The one that blew is the biggest one. I'll take some pics later and post them. And also, this Silvertone is model 1474, made around 1961. Thanks, Mike
Uh, thanks, but I don't really need to look at pictures of blown caps.
My WAG is that the components you replaced allowed the amp to function well enough to send smoke out of what was already a bad cap.
It is perfectly reasonable at this point to start a component by component inventory of what you do and don't have to work with. Power tranny. Pull the rectifier tube or disconnect the bridge and check it. At least ohm out the output tranny. Inspect for burned / arced tube sockets are the plate resistors anywhere close to original value. A variac would be handy, a light bulb limiter essential. Once you know you've got enough parts that work to be worth proceeding, replace every single electrolytic and we'll go from there with the light bulb and variac thing.
Thanks for everyones advise. The blown/smoking cap was some other idiots previous work. Took it to a local tube repair guru named T. Guy. Found the smoking cap wasn't supposed to be in there in the 1st place....... Both output tranny's were bad, replaced with two 30 watt. Found and replaced, many bad caps and resistor's. Last night, I went ahead and replaced all other caps and most resistors. Now this amp sounds like it should. The reverb dont work, I think the crappy tank supposed to have magnets? idk. I'll search this form for the reverb issue. I've heard the reverb sucks, bad ??? I like the tremelo, though. This project has helped inspire and educate me. I have learned so much from this forum and Mr. T. Guy. from Gray, TN. I am grateful and always open, for any advise. Thanks, Mike.
Also, My Silvertone 1474 Twin Twelve - The last digit of the chassis is 1. not 0, as in other 1474, Could not find the exact schematic, anywhere. Mine has a different tube layout in the peramp section. And is labeled as so on the chassis. . I've looked at every Silvertone schematic, I could find, but never the exact match. Worked off the 1474 schematic. Anyone know the deal?
one thing about those silvertones to watch out for -- lots of people obtain them as cheap hotrodding platforms, but they aren't really durable enough to stand up to hotrodding. if you're thinking about modding the amp, proceed with caution.
example: the cheesy little OT is way underspec for the power of the amp. it saturates quickly and rolls off a lot of HF response, giving the amp its characteristic voice. people always try to up the amp's power and the OT always blows. many people try to replace the little OT with a bigger OT, and start a vicious cycle of making other parts of the amp blow up. the PSU is a pretty lame compoent. its voltage doubler circuit isn't the most robust design. if you push it, it will fail too. in many respects, hotrodding a silvertone is like playing whack-a-mole, where new problems keep popping up every time that you make an "upgrade".
my personal opinion about silvertones is that they're nice little amps for what they are, and that too many of them have become lost as a result of ill-conceived hotrodding efforts. their PTP wiring and their low power design and low end components makes them a less than suitable platform for modding. my personal preference is to use an old fender as a modding platform, and restore the silvertones to their original design, crappy reverb and all.
JMO, of course.
I agree with BobP. The one I was working on recently used a lot of solid conductor wire with thin insulation - exactly the stuff the telephone company used to use in our houses and offices for land lines. Not a lot of insulation value for medium to high voltages. I also noticed they didn't spend money on grommets for insulating where wires pass through metal openings.
Some of the old Silvertones have a cheezy disfunctional reverb piezo instead of the traditional spring/tank. Another reason to avoid using these amps as a modding platform.
Last edited by Gunny; 04-21-2010 at 01:17 AM.
I also have a 1474 Twin Twelve from 1961. I'd like to find a reverb unit for it or ,since I have a space accutronics tank, a way to mod it to drive this tank. I know I need a reverb transformer. Mine had all kinds of issues with bad tube sockets, caps and open resistors but still has the 2 tiny output transformers which are hanging tough.
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