• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Theta Amp problem

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I have 2 Theta tube amps, monoblocks, (on the covers) "Theta Power Amplifier, SCN OPT, made in usa", both very modified, uses a 6AN8 and 2- 6550's. One amp works & the other blows fuses. The schematic I was given is roughly similar to the configuration. Am getting close, to finding the short but does anyone have a schematic for these? or experience with them?

In a past posting on rebuilding a Theta w/KT88's someone wrote that they had schematics on some Theta components but since I'm new here I am not allowed to email members yet. Could someone help?
 
Theta Amp - Update

Thanks to Craig, but I was getting close, it turned out to be a shorted rectifier diode. The rectifier was designed to have 2- 1N4006 diodes in series on each half of the transformer output and one 1N4006 on the bias output (reversed). I had one diode replacing two marked with an M (circle around it), RQ 170, 8336. Looks the same as a TO-41(?) basic diode.

Now, the "modifier" added photo-flash capacitors for the filter capacitors and with some basic testing they seem to be OK but 2 of them have slightly swollen ends & that always worries me. I'm of the opinion that it is best to put the P/S section back together as designed on the schematic, then I should have the correct voltages to work with. Does anyone care to offer any helpful comments, advice, jokes?
 
Theta Amp

I've been looking for caps. in the online distributors I normally use but so far nothing close enough has been found. I even tried looking in Radial, Axial, and Screw mount styles!

I guess it's "back to the books" to remember what I've forgotten about Power Supply design. As far as I can remember it's the resistance of the filter, including ESR of components, that determines the voltages after the filters. Whatever it is, I'll figure it out & might even have a P-supply design program hidden in a folder on the PC somewhere!

Re: Rectifier diodes, the NTE catalog lists all the 1N4xxx diodes and recommends using the 1N4007 in most cases because it has a higher voltage capability so that was easy.

Thanks, Dave
 
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