Wurlitzer Sideman Transformer ID help!

Jim Lahey

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I acquired a power amp from a Wurlitzer Sideman with the intent of scavenging the parts to build a guitar amp. The amp itself has one 12ax7 preamp tube and a pair of EL84s in push-pull (I'm assuming). I didn't find any diodes and there was an empty octal tube socket that I'm guessing was for the rectifier. From what I've found on the web, the Sideman was manufactured from 1959-1965. My intent for scavenging these parts was to build an AC-15 type amp.

After pulling the transformers, sorting out the continuity of the windings, and passing voltage through them to identify the ratios, I have come up with the following diagrams and measurements for the PT and OT (see attached). Note the voltages I've measured represent an unloaded circuit.

The numeric codes stamped into both transformers are indicated on the diagrams. I wasn't able to find any information on these using the code numbers. I also wasn't able to find any equivalent modern construction transformers to compare to (at least for the PT).

My questions to the forum are the following:
For the PT:
1) What's the deal with a 136V B+ secondary and how is it possible to power two EL84s and a 12ax7? I measured that multiple times and got the same result. That voltage doesn't seem to be particularly useful in a tube amp.
2) What purpose does a 34V secondary serve? Would this be used for a rectifier filament?

For the OT:
1) For two EL84's in push-pull, the secondary output represents 12 ohms. 12 ohms? From what I could find, the Sideman had a 4ohm speaker. Something doesn't add up. I ran 10 v ac into the secondary an measured 260 v in the primary (130 CT). I calculated a winding ratio of 26.

If you have any insight into these transformers and their specs as measured, your input would be greatly appreciated. I'm hoping I didn't acquire some old doorstops.
Thanks in advance.
 

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sds1

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Do you have a schematic for this unit?

Regarding the PT, the schematic will show application of those windings. The 136VAC winding could be connected to a voltage doubler type rectifier. The 34VAC winding might be for fixed bias reference.

Just speculation.
 

Jim Lahey

TDPRI Member
Joined
Dec 6, 2020
Posts
22
Age
42
Location
Great White North
Do you have a schematic for this unit?

Regarding the PT, the schematic will show application of those windings. The 136VAC winding could be connected to a voltage doubler type rectifier. The 34VAC winding might be for fixed bias reference.

Just speculation.
Thanks so much for your reply.
I've spent much time searching for anything related to this unit (including a schematic) and have come up empty handed. I found this (see attached pics) inserted into one of the octal sockets. Maybe it has something to do with the voltage doubler rectifier you mentioned?
 

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