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This is my first post as a "newbie" here. I have a 1969 sunn 200S (69 code on components and printed on PT) that a musician/tech friend is working on, so Im not going to hurt myself with high voltage. Original problem was it blew fuses when switched off standby. Weve determined the PT needs replaced. I read the thread started by Rick Erickson when he replaced the PT in a 200S for a customer. I want to use the Triode PT he used, but the markings on my original PT is not marked Dynaco. On the cover it has the sunn name and logo and under that is: 3 - 6 P.T., then 28-2360, and at the bottom: USA TESTED. On the side is printed: WTC 1274 and DEC 69. My question is will the Triode P782 P.T. (the one Rick Erickson used) work in my amp too? We dont plan on modifying this amp for more output. Please advise if you know about this. Thank you much.
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Sunn used at least three different vendors for transformers. Dynaco, Schumaker (same as Fender) and Western Transformer, a local Portland outfit. 28-2360 is the Sunn part number. The Triode unit intended for the 60W Dynaco will work fine.WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
REMEMBER: Everybody knows that smokin' ain't allowed in school ! -
I'd wager the PT isn't bad if it blows the fuse when switched off of standby.
jamieComment
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Thanks for the PT info, Loudthud. Western Transformer Co. would explain the WTC printed on side. imaradiostar - Our decision on the PT was based on two tests: with PT still hooked up, at the tube rectifier one sides output was normal and the other a short. Then, with the PT all disconnected, we ran low test voltage thru power in leads and came out only one side of the outputs to rectifier. Does this make sense?Comment
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Yes, sounds like a bad PT. Does it smell funny? All the bad PT's I've seen thus far get really hot even with no load and tend make horrible electrical burning smells.Originally posted by bassicstu View Post
I've ordered stuff from Triode Electronics before- excellent quality US made transformers!
jamieComment
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hot n smelly
No smell on this one and didnt get excessively hot. I know the smell you mentioned - my Ampeg B15N smoked and smelled real bad when its trans went. could be Im wrong and the PT is ok... is there another test you know of that I could try? Thanks, StuComment
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Maybe one side of the PT is open, not shorted. That would possibly make it saturate and blow the fuse as soon as you tried to load it up.
Did you try measuring resistance from the centre tap to the two outputs?"Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"Comment
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PT Checks & Tests
Hi Steve, We did measure the resistance from main center tap to main outs and also the heater center tap and heater outs. Ohms were about the same everywhere, but the primary (power input) circuit showed 1.5 ohms though. When we sent 9volt dc battery current into this circuit, dc volts came out center taps, BUT the 9volt batt got to hot to hold and would have destructed. Is this evidence of a problem with the transformer plates or something else? This amp originally blew power fuses when switched on from standby. I pulled all the fuses and stored it for about 5 yrs. Recently I reinstalled the fuses, turned on, powered up, and played bass thru it for more than an hour! It sounded Great! Then I took it out to play, set it on standby for about half hour and the fuse went. Since then, the fuse blows when switched from standby to play. We measured 9000 ohms at one side of the B+ voltage when it was all hooked up - but this doesnt jive with the PT tests wedid above does it? - and the PT never smoked and stunk. Of course, I dont want to spend $100+ on a new PT and then find out I still have an unknown problem. Do you ( or anyone ) have any ideas or observations?Comment
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Pull all the tubes. Replace the fuse. Turn the amp on in play mode. Does it blow the fuse? If so, then the PT is likely bad, though an electrolytic capacitor could also be bad. If it does not blow the fuse, shut the amp off and put the rectifier tube in. Turn it back on again. If it blows the fuse then there is a problem with the circuitry around the rectifier tube or perhaps with the rectifier tube itself. If it does not blow the fuse, then turn it off and sub the other tubes in and try again.
GregComment
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