Hot Rod Deluxe Help

[photek]

I have got a friends HRDlx to have a look at and was after a bit of advice. The bias was set pretty high (90) which would explain why there was barely and clean headroom. I have adjusted it back to 71 but before I swap the valves for a set that I know are working I wondered if anyone had noticed the following or had any explanation:

When playing through it there is a sort of octave ghost note to every note played. It sounds kind of cool but obviously not right. Are valves likely to sort it out? I know how to check the caps but brick it a bit when I do!

I will swap the valves out later and bias again but the valves in there are pretty new as good quality.

Cheers.

[ICBM]

It is probably the filter caps. They seem to have used rather poor quality ones on this series and failures are quite common, probably the most common problem on the most recent version with upgraded jacks and power resistors.

But also, if it sounds oddly distorted and not very loud, it could be the other common problem of one of the PI plate resistors having failed. Remove one of the power valves and run the amp (it's safe to do this). If there's now no sound at all, the other power valve is getting no signal. (It won't be an actually dead valve if the bias was as high as 90mA.) If there's no change when you pull the first valve, put it back, pull the other one and try again. If you find one socket is dead, it's very likely to be the PI plate resistor that drives that one.

If there is a change when you pull *either* valve, both valves and both sockets are working so it isn't that... in which cases it's back to filter caps probably.

[photek]

Thanks very much for the info. Will try pulling the valves tomorrow but after that it is off to a tech I think.

[jpfamps]

I agree with ICBM, it's most likely to be the filter caps.