Ephphone EA-12RVT tremolo doesn't work

[Tech. Tom]

The tremolo doesn't work on this amp. This amp has an OA2 tube in it . None
of the schematics I have found for this amp show an OA2 tube, they all show a GZ-34
and I don't think they cross to each other.

Someone has written the tube number on the chassis next to each tube and
OA2 is written on it. There has been some previous work done on this
and I am wondering if anyone know if it uses an OA2 or GZ-34.

I will attach pictures of this amp. Any help is appreciated.
Thank you.
Tom

[g1]

The OA2 is used in the trem circuit.
Does yours have 6L6 or 7591's ?

[Tech. Tom]

This amp has 7591 output tubes.

[g1]

Depending on the actual tube complement, have a look at Gibson GA-35RVT, or 45 or 55.

[Tech. Tom]

Thanks, the GA-35RVT looks closest to what I have.

[oc disorder]

The Gibson site seems to have a few more vintage schematics since I last visited.
Down the bottom there are some Epiphone Schematics , the EA-16RVT has 7591 output tubes, solid state rectifier and a OA2 !





http://www.gibson.com/Files/schematics/EA-16RVT.jpg

[Jazz P Bass]

The tremolo doesn't work on this amp. This amp has an OA2 tube in it . None
of the schematics I have found for this amp show an OA2 tube, they all show a GZ-34
and I don't think they cross to each other.

Someone has written the tube number on the chassis next to each tube and
OA2 is written on it. There has been some previous work done on this
and I am wondering if anyone know if it uses an OA2 or GZ-34.

I will attach pictures of this amp. Any help is appreciated.
Thank you.
Tom

The OA2 is indeed used in the Tremelo circuit.
It is a voltage regulator tube, not a rectifier tube.(GZ-34).

The closest in that respect would be the 16RVT.
But that uses a transformer for the Phase Inverter.

[Tech. Tom]

Thanks for all the help. It seems I have a defective optic coupler identified as Z1 on the schematic.
I have about 220V on one side of it but no B+ on the plate of the 12AU7. It reads open.

Does anyone know where I can get one of these?

[Jazz P Bass]

I believe that it is an incandescent lamp in that roach.

The Weber OPT-5 may work if you get the 12 volt version.
https://taweber.powweb.com/store/chansword.htm

[oc disorder]

some more food for thought and experimenting !

I presume JPB subtracted the anode voltage from the supply voltage which gives a 12 volt drop.

The guys in this forum seem to have luck with a 6838

Vintage Amps Bulletin Board ? View topic - Gibson Minuteman GA-20RVT Tremolo problem
and
Vintage Amps Bulletin Board ? View topic - Epiphone Electra EA-26 RVT tremolo roach broken

"by PeterS on Fri Sep 16, 2005 4:09 pm
I had exactly this problem with my Gibson Hawk, and here's the solution: take apart the unit by carefully carving all the rubbery stuff out of the end that has the light bulb, being careful not to damage the end with the photoresistor. Pull out the bulb. You need a replacement bulb with the right electrical characteristics. I never found one that had that AND was the same size, but I made it work with a bulb number 6838 which is fairly common and is 28 volts 24 mA. It is small, so I put a few layers of heat shrink on it until it was a snug fit in the metal tube."



12V Microlamps (2-Pack) : Microlamps | RadioShack.com

12V Microlamps (2-Pack) Catalog #: 272-1092
Rated 12V with a current of 60mA.

6838 bulb 28 volts 24 mA

(Australian URL have to check with USA one)
http://au.mouser.com/ProductDetail/C...UIZaTPeBGAA%3d

EDIT :Looks like the 6838 is the one !

http://music-electronics-forum.com/t20583/

http://www.digikey.com/product-searc...8-ND&x=15&y=22

[Tech. Tom]

Thanks for the info. I will try it.

[Tech. Tom]

I want to thank you Jazz P Bass. The OPT-5 worked fine in this amp. The original optocoupler was beyond repair...someone got to it before I did.
Tom