5F1 hums, quiets down when volume at maximum

[tubeswell]

Duh - pin 8 of the rectifier well that's fine.
sorry 'bout the confusion

[tubeswell]

Tubeswell wrote: "The 3 x Power Transformer secondary windings consist of a High Tension winding (the 2 x red wires with a black centre tap), a rectifier winding (the 2 x yellow wires) and a heater winding (2 x green wires with a green/yellow centre tap)." Depending on the actual PT used wire colours will vary a little, however the PT's supplied with TAD kits typically follow traditional wire colours - PT B+ centre tap is red/Yel NOT black. Champ style PT's may, or may not have a grn/yel CT depending on supplier.

I was referring to the PT wire colours in weber layout in the link

[motzu]

It's what we get for throwing around pin numbers (instead of function) and terms like "V3" (again, instead of which tube and what it does).

Point taken.

[motzu]

Duh - pin 8 of the rectifier well that's fine.
sorry 'bout the confusion

No problem, such are the perils of forum dwelling. Thank you for posting!

[jmaf]

motzu, from the pictures, here are a few tips, pardon if they're alredy there

1) I don't see a filament supply virtual ground. Either from the lamp leads or from one of the sockets, tie a 100R resistor from each end of the filament supply to ground. This will kill a lot of your hum.

2) Using this angle as reference: http://music-electronics-forum.com/a...741389-001.jpg - Try to tuck the green wires against the top of the chassis in that photo. Right there you have 2.1 Amps of noisy current right on top of unshielded grid circuits.

3) You're grounding through the chassis. Note how the Weber layout does not suggest a ground layout, it just shows arrows pointing to ground....whether you ground it right there, or to a central place, makes all the difference in the world.

4) I had a 6V6 amp here just the other day, part of the hum without the 12ax7 was unmatched output tubes. If they're not matched, it hums.

Hope this helps.

[motzu]

Problem solved, it turns out that reversing the hot and neutral wires of the AC power cord fixes the issue. Actually TAD's layout is the only one I've seen that uses that order.

Thanks to everyone for your replies!

[MWJB]

Ground preamp filter cap & carthode resistor to RH input jack ground lug. Ground Vol pot LH tab to pot body.

Remove wire from 6V6 pin 1 to main filter ground. Pin 1 needs no connection, but can be tied to pin 8.

Move plate wire from V1, pin 6 away from OT secondaries.

Try removing unused PT primaries rom rectifier socket & insulate them

[Enzo]

Isn't this a single ended amp? Only one power tube. Hard to match one.

You have determined the hum is coming into the system via the 12AX7 stages, and in fact the volume control at zero kills the hum, right? That means the input triode stage itself.

Your virtual center tap for the heaters is grounded to the chassis. Pull that solder lug out from under the bolt and let it stick into the air, now with a clip wire, connect the lug to the cathode of the 6V6, pin 8. We call that elevating the heaters. ANy help? If not, return it to the bolt, if it helps, wire it that way. We are stealing the positive voltage at the cathode to lift the heater supply away from ground.

If you plug a guitar in it plays OK, but the hum is there. If you turn the guitar volume control to zero does the hum remain or does that bring down the hum? Or electrically similar test - tack a wire from the grid of the input triode to the ground end of the input stage cathode resistor. Does grounding that grid kill the hum? Tack solder a piece of wire temporarily, don't use a clip lead for this. A clip wire can act as an antenna due to its length.

[Enzo]

Oh geez, while I was typing, you fixed it.

[motzu]

Remove wire from 6V6 pin 1 to main filter ground. Pin 1 needs no connection, but can be tied to pin 8.

Move plate wire from V1, pin 6 away from OT secondaries.

Moved the 12AX7 plate wire away from the OT secondaries, excellent suggestion, I seem to have missed that one. Indeed, the long wire from the unused pin 1 of the 6V6 to ground is at best not a very good solution. That's the next step, rewiring the power tube socket a bit.

[motzu]

Oh geez, while I was typing, you fixed it.

Thank you for taking the time to reply nonetheless, I appreciate it. Yes, it's a single-ended class A amp, putting out about 5W of raw loudness . It's great. I'm a sucker for these things and Fender Deluxes (5E3).

Answering your question about the hum, yes the hum remained even when my guitar volume was at 0 - and even with no input at all, that is with nothing plugged into the amp.

[Enzo]

Cool. The purpose of that particular question was that the guitar volume could have potentially grounded off the input when at zero. Not all guitars would work that way of course, but it was a 10 second, free check.

[motzu]

motzu, from the pictures, here are a few tips, pardon if they're alredy there

1) I don't see a filament supply virtual ground. Either from the lamp leads or from one of the sockets, tie a 100R resistor from each end of the filament supply to ground. This will kill a lot of your hum.

2) Using this angle as reference: http://music-electronics-forum.com/a...741389-001.jpg - Try to tuck the green wires against the top of the chassis in that photo. Right there you have 2.1 Amps of noisy current right on top of unshielded grid circuits.

3) You're grounding through the chassis. Note how the Weber layout does not suggest a ground layout, it just shows arrows pointing to ground....whether you ground it right there, or to a central place, makes all the difference in the world.

4) I had a 6V6 amp here just the other day, part of the hum without the 12ax7 was unmatched output tubes. If they're not matched, it hums.

Hope this helps.

I'm sorry, I've missed this post, didn't mean not answering. For completeness' sake, here are the answers:

1) Yes, I do have one, with two 100R resistors just as you described it. Unfortunately you can't see it in the pictures because the pilot light support and the fuse holder are in the way.

2) OK, will try it someday but for now it's very quiet just the way it is, after fixing the AC cord wiring. It's also pretty hard to do because those wires are thick and trying to use force to make them stay in a different position might sacrifice some tube socket pins unless I desolder them and redo the wiring.

3) You're right, of course. I was refering to the Weber layout so as not to make the TAD layout public. I don't agree with their policy at all, but I respect it. Speaking about grounding through the chassis (and with apologies for sounding like a broken record), the Victoria 518 grounds everything by soldering directly to the chassis and I haven't heard bad things about them yet. Of course, that probably goes for a small 5F1, from the 5E3 up it gets more complicated, but I guess possibly the only advantage of a very small cramped chassis is that it makes grounding through it less likely to cause big problems.

4) That's definitely not my case, as the 5F1 uses a single 6V6GT output tube, so matching tubes does not apply.

[jmaf]

Isn't this a single ended amp? Only one power tube. Hard to match one.

Duh, sorry. Tired late night reply after a couple of beers watching the world cup, my mistake.

[JHow]

Motzu: After reviewing your pictures once more, I have a question: what is the surface of your bench covered with? It looks like some kind of felt?