I have a puzzling tube problem in a Hiwatt DR103 clone

[dvlp]

For the past 6 months my DR103 clone that I built has been dead quiet at idle using Gold Lion gold pin preamp tubes then suddenly I started getting a fairly loud hum at idle. After ruling out the power tubes I discovered the following:

Gold Lion tubes in v1,v2,v3 & v4 = hum
Gold Lion tubes in v1,v2 & v4 Mullard in v3 = no hum
Mullards in v1,v2,v3 & v4 = no hum
Gold Lion tube in v3 Mullards in v1,v2 & v4 = hum

I've got reissue Mullards and 161s and tried both. I also tried each of the Gold Lion tubes in v3 and they all hum.

Really weird. It would seem if all the tubes suddenly went bad that v1 would hum too but it doesn't. If there was a problem with the amp I would think it would hum regardless of what tube was in v3.

Anyone have thoughts on this mystery? I could just stick a Mullard in v3 and call it a day but it bugs me. Thanks

[ChopSauce]

Sounds puzzling for sure.

Whatever Gold Lion tube you plug in V3 it hums?

[nosaj]

Sounds puzzling for sure.

Whatever Gold Lion tube you plug in V3 it hums?

If no work has been done, start checking for a leaky capacitor. Doesn't matter if they were new 6 months ago. In Electronics new stuff can fail same day or last a long time or not.

nosaj

[dvlp]

I put a brand new, unused Gold Lion gold pin in v3 and no hum. But all if the 6 month old GL tubes still hum in v3.

[g1]

I think you need to measure your idle currents in all the tubes and see if you have a matching issue. And it may be a combination of unmatched tubes and some issue with socket #V3.

Edit: never mind, I thought we were talking about power tubes, but it's a preamp tube issue.

[Pedro Vecino]

I also tried each of the Gold Lion tubes in v3 and they all hum.

Some Russian ECC83 / 12AX7 have the bad habit of responding in that way (and worse) depending on the function they handle. I have observed it in different amplifiers. It´s not common but sometimes it happens.
Simply: do not use that tube model in that function.

[Chuck H]

What tubes are we discussing? V1, 2, 3, etc. typically refers either to the tubes as marked on the schematic OR the first preamp tube, second, third, etc. Since I don't see any "V" designations on any HiWatt schems I have to wonder. I assume we're talking about power tubes by the discussion.

[Pedro Vecino]

They should be the preamp tubes. V3 (third in line) must have a large voltage at the cathode of one of its triodes.

[Chuck H]

That's what I was thinking too. We'll see. As far as I can tell from the actual HiWatt schematic the third preamp tube has a whopping 220k ck cathode follower circuit. Though it does seem odd that where the one tube type didn't hum, now it does. And it's any of them that were in the amp.?. Not exclusive to the one used as V3.

[Pedro Vecino]

This topic is most likely associated with this problem:

http://music-electronics-forum.com/t46108/#post481622

[dvlp]

Sorry, I meant v3 as marked on the schematic. I believe v3 is the 2nd gain stage


As a side note the hum is constant regardless of the volume controls and there is no change that I can tell in the amp performance. I mean, outside of the hum the volume and tone have not changed and no irregular sounds.

[Pedro Vecino]

In the original layout, following that indication would be the socket marked with a circle. It has the 1M8 resistor and 22n capacitor next to that socket.
It would be the tube that has the cathode follower function.

[dvlp]

Thanks a lot everyone. I learned a lot researching everyone's suggestions. I'm going to try a non-Russian tube in v3 and if the problem persists I'll work thru the other suggestions.

[Chuck H]

Are the gold lion tubes Russian make?

[Justin Thomas]

Yep, those "reissues" sure are...

Justin