Fender Hotrod Deluxe noice

[nito]

my HRDL have got some strange humm, there is no noticable ground issue, all the tubes have been changed and i cant get bias voltage above about 45mv. and it got this constant noice:

any ideas?

[Jazz P Bass]

Hot Rod Deluxe bias

You might want to try lowering the bias to 25-30 mv.
45mv per tube is cooking.
Remember, idle bias is just that.
Idle.
You only need "enough" to get rid of crossover distortion.

[nito]

You might want to try lowering the bias to 25-30 mv.
45mv per tube is cooking.
Remember, idle bias is just that.
Idle.
You only need "enough" to get rid of crossover distortion.

for what i have read the factorysetting is about 65-70?
also i talked to a shop and their guess was a capasitor that is defect and i also got a scheme for the amp, but now i need to know if it is correct to locate the specs of each capasitor and then do a meassuring?
im totally novise here and want to learn.

[Jazz P Bass]

FFRD bias

Factory spec for bias is 60mv.
That is for both tubes.
30 mv per tube.
Personally, I feel this is not an amp to "learn" on.
There are some pretty hefty voltages in there.
The main board has to come out if you want to replace any components.
A real PITA.

[nito]

yes, i know, and ofcourse you have to drain the amp before putting your fingers in there

[Enzo]

Are you telling us the test point that should have 60mv only has 45mv and no higher? or did you mean for each tube?

My guess is that if you are trying to get the test point up to 60mv and can't, that one of your power tubes is not conducting. If only one side conducts, not only will your bias reading be low, but that also would cause excess hum due to the imbalance. You would be turning the bias up so the remaining tube is up from 30 to 45. I bet it runs hot that way.

Hold the back of your finger close to each power tube, and see if one seems warmer than the other.

This all has nothing to do with the little orange glowing heater in each tube.

Power off and unplug from the wall. Look CLOSELY at the solder on the power tube socket pins. Are there any small cracks in the solder around any pins? I usually just resolder all the power tube socket pins when I open one of these amps anyway.

With power on but the power tubes removed, check voltages on the power tube socket pins. This you can do from the outside. Ground your meter and probe pins 3 and 4 of each power tube socket. There should be B+ there. I forget what, 450-500v or thereabouts. Looking to see if it is missing anywhere. Also, is bias on pin 5 of each socket? -50v or so.

[nito]

Enzo, yes i meant at Testpoint when i said 45 mv.
thanks for all the input i will check your points.