What tube should go here? 1935 Oahu restoration

jthomas666

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922
I don't follow. Are you saying there should be one?

I'm close to the edge of my knowledge, but I believe that these old speakers have an electromagnet to actuate the voice which would require dc current. That part of your schemo seems to go through the rectifier.
 
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I think what has been suggested is that the socket was never meant for a tube. It's likely that there was a mating connector - something that looked like the base of an octal tube - that plugged in to that socket.

It was common to use an octal socket for an umbilical of some sort. Sometimes they would connect to peripheral circuits to provide power and possibly accept a signal. Think phono or radio receiver, or maybe a control panel with volume and tone controls. I don't think the octal socket here served any of those purposes, but as was stated by @zenitB in post #5 it was not uncommon to connect the field coil this way when it served the double duty of a power supply filter choke.

Try constructing a schematic with that in mind. It might end up making sense.
It appears that it may be for a plug in cap can. This is totally outside of my expertise. Hence the reason I presented this here. I have no engineering back ground. My hope was that someone could look at my description or my schematic and point me in the right direction. This was probably too much to expect. Thanks for looking.
 
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The schematic shows shows what goes on there. The power tube cathode goes t9 ground through one pin. The field coil voltage and the B+ to the OT are connected through this socket. You can see the connections for the plate and screen voltage as well.
 
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305
The schematic shows shows what goes on there. The power tube cathode goes t9 ground through one pin. The field coil voltage and the B+ to the OT are connected through this socket. You can see the connections for the plate and screen voltage as well.
I'm not sure I follow. Are you saying this is intended as an empty socket?
my only question then would concern pin 3. It has only one lead. If it wasn't connected to something in the socket why is it there? Any ideas?
 
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6,478
They may have used a connector that looked very much like a tube socket...as found in many organs. In fact, it is hanging there in your picture in post #15....at least that is what I would expect since that plug feeds the field coil. That connection at pin 3 is shown in the schematic.....it feeds one end of the field coil. This is also the lead that feeds through that .005 cap the B+ to the OT as well as the plate voltage. The screen grid voltage and preamp voltage comes off of the other end of the OT primary.
 
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They may have used a connector that looked very much like a tube socket...as found in many organs. In fact, it is hanging there in your picture in post #15....at least that is what I would expect since that plug feeds the field coil. That connection at pin 3 is shown in the schematic.....it feeds one end of the field coil. This is also the lead that feeds through that .005 cap the B+ to the OT as well as the plate voltage. The screen grid voltage and preamp voltage comes off of the other end of the OT primary.

the connector has a different plug in location, below the 6V6.

jthomas666 found this on Reverb:
How about this:

https://reverb.com/item/1652770-valco-made-oahu-1x8-tube-combo-amp?device=ios-app

Cap Can.

Sorry about my earlier answer. I see that you figured out the field coil connector.

and these photos show a plug in cap can in the vacant spot.
 
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6,478
the connector has a different plug in location, below the 6V6.

jthomas666 found this on Reverb:


and these photos show a plug in cap can in the vacant spot.

my bad......I failed to notice that third socket....the one near the 4-pin socket. Jtomas found the answer. If one were wanting to do the work, tracing the circuit would have found the amp lacking in capacitors....unless the caps in the can had been replaced with singles. And...tracing the circuit would have answered all questions.....but one would need to be there with the amp to do that.
 
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my bad......I failed to notice that third socket....the one near the 4-pin socket. Jtomas found the answer. If one were wanting to do the work, tracing the circuit would have found the amp lacking in capacitors....unless the caps in the can had been replaced with singles. And...tracing the circuit would have answered all questions.....but one would need to be there with the amp to do that.
well, thanks for following up. this is another can of worms, though. maybe a new thread idea, "what caps should go here?" thanks again to everyone that helped to investigate this thing.
 

jthomas666

Member
Messages
922
The plug-in cap can may be a single value cap. If you trace the circuit comparing the schematic to the wiring in the amp (like Steppin' Wolf mentioned), you'll figure it out. Caps are much smaller now and you may be able to replace it in the circuit OR it may have already been replaced.

I guess (because I am not an engineer) I would start by making a photocopy of the schematic and crossing off each cap you find in the amp, systematically. Whatever cap you haven't crossed off the schematic when you are done is the missing one.
 
Messages
305
The plug-in cap can may be a single value cap. If you trace the circuit comparing the schematic to the wiring in the amp (like Steppin' Wolf mentioned), you'll figure it out. Caps are much smaller now and you may be able to replace it in the circuit OR it may have already been replaced.
That would work if I had a schematic other than the one that I made from the circuit, including the omissions. As it is the schematic I drew up is the only one that I have.
 
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