Strange noise in H.R. Deluxe

[Pedro Vecino]

I found an H.R. Deluxe with a strange problem: 15 or 20 seconds after switching on through the standby, very slight noises are heard (tick-tick-tick...) and after that the problem is generated: lowering the volume control (clean channel) to zero appears a hum (discrete) that decreases as the volume goes up.

In the second channel the same thing happens with the drive (gain) control but in a more relevant way.

Itīs similar to a typical grounding problem in poorly constructed amps (with a bad ground distribution) but it can not be that because those amps does not have problems in that aspect and this appears after the tick-tick noises.

Removing the first 12AX7 the noise stops. The amp has a new filtering and supervised welds. Itīs mechanically stable and the tick-tick noise is only heard when the amplifier is turned on when it is cold previously. Once hot turning it on again the hum appears instantly.

Can anyone offer any clue about the possible origin?

Schematic here: https://www.thetubestore.com/lib/the...atic-Rev-B.pdf

Thanks to all.

[drewl]

Is there a cell phone nearby?

[Chuck H]

Maybe not a grounding issue, but a decoupling issue. Similar in effect. The HR series amps share a HV node for like phase preamp stages. When the filter for that node begins to fall below optimal performance the amps get hinky. Strange then that Fender chose to use crappy Illinois capacitors in those amps. Replacing them ALL (with a better quality part) would be the first thing I would do as a matter of course since it usually becomes an issue eventually anyway. If the problem persists you could troubleshoot it after.

[Pedro Vecino]

Thanks. I saw the problem both on the floor below (quick tests) and on the top floor (where I work). I usually have the phone in the one below.

It has new F&T filter capacitors installed but the problem was with both. I ended up so tired that I pushed it aside to continue with other amplifiers. I did not expect surprises with H.R. Deluxe amps

This afternoon I connected it and it works perfect. No noise of any kind. Itīs very strange because the voltage is always perfect and I've never seen any signs of contamination.

This issue intrigues me about what could have happened. I do not know where to start although the question about the phone certainly got my attention. I will have it under observation.

Thanks again!

[Pedro Vecino]

Finally the noise returned. It appeared and disappeared randomly although it needed time for it.

When removing one of the power tubes the noise suddenly ceased. I measured it on the tester (Hickok 800) and indicated leakage in position 1. It took the needle to the end. I do not remember exactly what electrodes correspond to it.

I would never have suspected of it.

On these occasions one feels silly, although I must say that the tubes looked very good