HI all, I've got an awful lot keeping me busy at the moment so not much time is available for building (especially as my 'workbench' is the dining table), but I have acquired a new piece of junk that I would like some help identifying. You guys are the people most likely to know. Apparently this was taken from an organ, but I don't know what make or model. It came with a pair of Sylvania 7591A valves which test strong on my tester , but no other valves included. it has a miniature 9 pin which appears to be the input valve with the grid on pin 7. two PTs. The OPT certainly doesn't connect to anything as straightforward as a speaker jack. there is also an Octal socket - rectifier? then there is a bank of three sockets. these are the same diameter as an octal base, but there is a 4-pin, a 7-pin and a 9-pin. Would these perhaps be connectors to external parts of the original organ? the mains lead direct connects to the 4-pin. There are also 3 'top hat' shape diodes in the circuitry if that's of any help to anyone. I've given the chassis a rub around each of the valve sockets but there are no markings. There are also components attached to the chassis that I don't recognise - can anyone tell me what they are? they look like bits of cloth clamped into a piece of aluminium with WW resistors hanging out of them.
A couple of photos attached - any clues as to what it is appreciated. many thanks.
Update: I have been trying to trace the circuit in this and have found the following:
1. the rectifier socket is wired for 6.3v and is not a heated cathode
2. mains is connected directly to pins 2 & 7 of the rectifier socket and the primary of one of the PTs. The secondary of this PT goes into the heaters and what appears to be a voltage doubler (hence the top hats). I am not sure about this, it all gets very cramped around this area with what seems to be a lot of WW resistors and electrolytics (there are 3 three-way cans)
3. pin 5 seems to be the HT off the rectifier - which then connects to the OPT and the cathode of the first gain stage (assuming the nine pin to be for a 12A*7)
4. One of the power transformers appears to be for parts of the original organ that are not in the amplifier chassis - it only appears to connect to the 'bank of sockets'.
5. The OPT appears to have the standard primary configuration, but the secondary is connected to ground and the OPT (see point 3). there are other components as well, but I don't see any connections that could be for a speaker - but it's in the cramped area.
6. I feel confident that this chassis was designed for the 7591A - the wiring for the power tubes makes sense, at least.
I am particularly concerned about Point 2 - the mains connected to the rectifier without isolation. Is this what is called a 'line power' PSU and should therefore be completely ripped out?
The OPT configuration confuses me - can anyone shed some light?
Last edited by paggerman; 09-18-2011 at 02:22 PM. Reason: More info
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