Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Grantorino on December 03, 2025, 09:11:19 am
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Hello again EL34 world.
No reverb sound. Tried swapping tubes. The tank and RCA cables were replaced. Original tank is retained. Both tanks pass signal using the 'tap test' (the new tank is much stronger), but neither tank produces guitar reverb. Suspected reverb send circuit issue.
I am looking to source an appropriate Reverb Transformer for a 90's hand-wired Vox AC-15. I believe the original is dead, owing to the resistance readings:
- Primary 37ohms out of circuit (I believe should be 200-300ohms)
- Secondary 920 ohms out of circuit (I believe should be 4-12 ohms)
The original transformer is marked 'Drake Transformers TRX 00001 and is a pin-mounted unit. Small, no wires.
Next to the transformer, resistor R7 was visually burned out. Originally 10k 1W, I replaced it with a 2W and on testing the reverb, the new resistor started to discolour so I powered down.
V3 pins 1 & 6 measure only 57V with tube in or tube removed.
Read about the amplifier here - https://www.voxshowroom.com/uk/amp/15tbx_hood.html
The tank and RCA cables were replaced. Original tank is retained. Both tanks pass signal using the 'tap test' (the new tank is much stronger), but neither tank produces guitar reverb. Suspected reverb send circuit issue.
I've attached a few pictures of the suspect transformer and the original burned-out resistor. There is also a screenshot of 'Parts is Parts' website, which used to stock the drake unit.
I have also attached a schematic which I have been referencing, though I think the amp I have is slightly different - the board is stamped AC15-62-00, NOT AC15-62-02.
Thank you.
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The common Fender Reverb Transformer will work in that circuit. Mounting it would require a little bit of creativity.