5F1 hums, quiets down when volume at maximum

[motzu]

OT primaries - have you tried reversing blue & red wires? If it's easier you can try removing the NFB loop from the speaker jack first to see if you have a OT polarity issue?

If the OT's primaries or secondaries would have been reversed, as far as I know that would have produced a piercing squeal at least as the volume pot goes up - that has never happened, and I've not had any problems with the guitar signal coming through quite gloriously either - the problem is that I have to train myself to ignore the hum. It's not "standard" 5F1 hum either, because I own another one as well (not a TAD, another prebuilt 5F1 clone) and that one definitely doesn't hum as much.

[MWJB]

"Yes, the hum dissapears when I power on without the 12AX7 preamp tube. I'm left with only the buzzing of the tubes and no change whatsoever in output level regardless of how I set the volume pot." You've lost me, with the 12AX7 pulled, you have no hum...but you still have "buzzing of the tubes"? There shouldn't be any buzzing of the tubes, either with or without the 12AX7.

[MWJB]

Good, that's one symptom eliminated.

[motzu]

You've lost me, with the 12AX7 pulled, you have no hum...but you still have "buzzing of the tubes"? There shouldn't be any buzzing of the tubes, either with or without the 12AX7.

I'm sorry, I should work on being more concise. No, there's no hum left. But all the tubes I've used so far in all of my amplifiers have a "cooking" sound, and that's what I was talking about. A normal thing.

[MWJB]

This cooking sound is present even with no 12AAX7 installed?

[motzu]

This cooking sound is present even with no 12AAX7 installed?

Well, yes, from the power and/or rectifier tube.

[MWJB]

That's not normal.

[motzu]

Pictures of the build. Can't take better ones, sorry.

[motzu]

That's not normal.

Surely, you're joking. If I only pull out the 12AX7 tube, the rectifier tube and the 6V6 remain in place and they do light up, and make a bit of a buzzing sound of their own but it doesn't come out in the speaker. I don't think I've ever owned a tube amp where the tubes were completely silent so this didn't worry me at all. Should I be concerned? Why?

[motzu]

"Finally, the third ground point is another solder lug attached to a PT screw and the chassis, and holds the AC cord ground wire and the PT ground wire." If bt PT geroun wire you mean the red/yel B+ centre tap, this should be grounded with the 16uf filter cap (& the 8uf filter cap for the screen supply @ junction of 10K & 22K power supply resistors).

Actually it looks like Victoria solders the red/yellow PT wire along with the green/yellow ground wire from the AC power cord directly to the chassis, which was the way I did it initially (save for the solder lug held in place by a PT screw). Click on the gutshot, it gets larger:

ProGuitar - Preisliste Amps

[tubeswell]

That's right - and in my layout, the red wire goes to pin 3 of the 6V6, and the blue wire is supposed to go to the cap/resistor junction. From the cap/resistor junction, there's also a wire going to pin 8 of the rectifier tube (where one of the PT's yellow wires is also connected).

Instead of wiring the blue OT wire to the cap/resistor junction, I've wired it directly to pin 8 of the rectifier tube, all the other wires connecting as specified. I don't see how this could have affected any grounding issues, but then again I might be wrong.

That is wrong - the blue OT wire is supposed to go to the 16 uF-10k resistor (B+ node) junction. Attaching it to the cathode of the 6V6 is incorrect. The OT primary needs to be connected to the B+ node

[Bruce / Mission Amps]

What's with the weird use of alligator clips? Why is floating right above a main ground point of the preamp?
Also, what is that green with black strip wire and where is it going? A left over piece that is used as a jumper?
Is that green/blk wire the primary hot wire to the fuse or ?
Is there a center tap for the 6v filament leads? A pair of 100 ohm virtual center tap leads?

[motzu]

That is wrong - the blue OT wire is supposed to go to the 16 uF-10k resistor (B+ node) junction. Attaching it to the cathode of the 6V6 is incorrect. The OT primary needs to be connected to the B+ node

Again, if you look at the Victoria 518 ( http://proguitar.de/ProGuitarPreisli.../518TInnen.jpg ) gutshot you'll notice that that's the way they do it too. Obviously you know way more about this stuff than I do, so please don't take this the wrong way because all I want to do is learn, but why is it incorrect? Because the original layout doesn't do it like that? Or is there some explainable problem with the way the wires connect? The OT primary is connected to the B+ there, just not directly - it's connected to the B+ via the wire coming from the board to the same pin on the rectifier tube that the OT primary goes to.

Again, just asking because I'd like to learn more, and I've assumed that what's good for Victoria is good enough for me (unless I got what they're doing wrong, but it does seem straightforward enough).

[motzu]

What's with the weird use of alligator clips? Why is floating right above a main ground point of the preamp?
Also, what is that green with black strip wire and where is it going? A left over piece that is used as a jumper?
Is that green/blk wire the primary hot wire to the fuse or ?
Is there a center tap for the 6v filament leads? A pair of 100 ohm virtual center tap leads?

I'm using alligator clips because I'm still debugging the build and moving some wires around, in lieu of soldering the wires. I can assure you that the clips are not causing the issue. When I first found the problem everything was properly soldered to their respective lugs.

There are no jumpers in there. The green/black wire is the 230V wire coming from the PT, and it goes to the on/off switch at the bottom of the volume pot.

Yes, I am using a pair of 100R resistors going from the heater wires (from the pilot light holder) to a solder lug held by a PT screw. You can't see that properly in the pictures, it's the top right screw and it's behind some wiring and the pilot light support.

I'm sorry, I don't understand the question about something floating above a main ground point for the preamp...

[JHow]

I think motzu is saying he put the OT onto pin 8 of the 5Y3 (as opposed to the 6V6 cathode), which should be the same thing electrically as the first filter node. I have to admit I too balked at the reference to "pin 8" initially. 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).