Princeton Reverb - hum but no reverb

[Bluefinger]

Hi,

I have built a BF princeton reverb clone. Apart from a couple of changed cap and resistor values in the tone stack and -fb loop and a bigger speaker and OT it is pretty much original spec.

It sounded fantastic and performed well. After a couple of hours the reverb stopped working and it started humming. if the reverb is switched off the hum goes away. with the reverb on the hum is back. the hum gets louder if the reverb pot is turned up. I don't have it here with me but it would be great to have a couple of things to check as soon as I get the amp on my bench. Any ideas? could this be a defective reverb tank (it's a tube amp doctor tank FWIW) or a leaking cap in the reverb circuit?

thanks!

[Mick Bailey]

Measure the tray's output coil resistance to see if it's open - this can cause hum and no reverb. Sometimes one of the flying leads to the tray gets disconnected, or you may have a bad or dirty phono connection.

If that's OK, unplug the return side of the reverb and with the control about half way, touch the hot connection to the lead. You should get a loud buzz through the amp to show that the recovery stage is working.

[Bluefinger]

Thanks, I'll try that as soon as I get the amp