2nd Gen Build Started (that didn’t take long…)

[martin manning]

18.4 in, 11.8 to the relay and the DIN. Drops to 5.7 when the switch is in Manual.

Not sure I'm understanding this... The regulator output voltage drops to 5.7? The relay coil should get 12V in, and 0V out (it's grounded) with the switch in manual. 11.8 is pretty far from 12, too.

[Raoul Duke]

That’s what I thought too, but it seems to just cut it in half.

I have continuity from the dedicated ground lug under the pilot light to the PS board ground, top two rows of the Manual switch, DC- input on the relay board, and the DIN ground when in Manual; and when I put it in Pedal - I have continuity only with the top row of the switch to ground.

Just checked the wiring and everything matches the drawing dated 2/19.

[Raoul Duke]

I think I was measuring wrong. I was only measuring DC+.

When measuring across - and + when switched to Pedal it goes from 11.8 to 0 and the blue wire at the DIN goes from 0 to 11.8. The brown wire always has 11.8 in either switch position.

Apologies for the confusion, as I work through the flow, the answers start to materialize. I just start in the wrong place sometimes.

[GAStan]

I was just looking at the layout for the 50w Gen 2 and the black goes from the pedal jack to the switch with no connection to reference it to the +12v. Maybe I'm missing something.

[martin manning]

Glen, I noticed that earlier and it was corrected. I also added a post to the 2nd Gen File thread with that update.

Raoul, ok cool all good then. 11.8 is a bit lower than expected, but if it holds that then it will work fine.

[GAStan]

Martin, I see your post now, thank you for pointing it out. Great catch! I also see Mr. Duke's photo removing all doubt as to whether that very wire is tied to ground.

[Raoul Duke]

Thanks guys!

I notice that when measuring other voltages there’s always a little up and down variation - even though small. That 11.8 stays rock solid no matter where I measure it from. I imagine that’s the regulator doing its thing?

[martin manning]

Yes, your line voltage is probably floating around a bit, but the regulator levels all that out as long as it has enough headroom.

[Raoul Duke]

Got the board in and I think all the PI stuff wired up as well:
- B+3 on the PS filter board
- V4&5 bias to pins 6
- Bias pot W
- Power amp in jack

IMG_0201.jpeg

Questions:
1. Does the PI tube socket lead dress look ok?
2. Any reason not to zip tie the power amp in jack wiring to the power amp out coax to try and get more space?
3. I flew the NFB wire up and over to the OPT secondaries - is that the best route?
4. Does anything look suspect and did I forget anything?

Thanks!

[ijedouglas]

Got the board in and I think all the PI stuff wired up as well:
- B+3 on the PS filter board
- V4&5 bias to pins 6
- Bias pot W
- Power amp in jack
IMG_0201.jpeg

Questions:
1. Does the PI tube socket lead dress look ok?
2. Any reason not to zip tie the power amp in jack wiring to the power amp out coax to try and get more space?
3. I flew the NFB wire up and over to the OPT secondaries - is that the best route?
4. Does anything look suspect and did I forget anything?

Thanks!

1. Does the PI tube socket lead dress look ok? Yes, I run the cathode from the other side so it doesn't cross anything
2. Any reason not to zip tie the power amp in jack wiring to the power amp out coax to try and get more space? no
3. I flew the NFB wire up and over to the OPT secondaries - is that the best route? I've seen HAD run them together. Try it both ways and see if it makes a difference
4. Does anything look suspect and did I forget anything? Didn't see anything

[Raoul Duke]

Thanks Ian!
Now that I look at it - the cathode makes total sense - but never occurred to me. I think I’m taking the layout diagram too literally (again, lol).

I appreciate the feedback

[ijedouglas]

Thanks Ian!
Now that I look at it - the cathode makes total sense - but never occurred to me. I think I’m taking the layout diagram too literally (again, lol).

I appreciate the feedback

Take a look at some of the 2nd/3rd Gen gutshots

[Raoul Duke]

Power amp test completed. Good news/bad news:

Good news is everything responded as it should. No smells, flashes, strange noises. Loaded voltages posted below.
Bad news is my power tubes are pretty unbalanced - like 10 mV apart when trying to bias. It’s an old set of fat bottle Ei that I’ve had hanging around. Would’ve been nice if they worked out but I knew I was taking a gamble.

Also found another set of Apex matched JJs that had the keys busted off. Look like they still have vacuum and I know they have less than an hour on them. Might try those next.

Voltages:
B+1 - 465 (little high?)
PI plates - 172, 184
PI cathode - 56.9
Heaters - 6.8

Opinions welcome as I consider my next move with tubes…

[martin manning]

I'd say that's mostly good news; everything is working as intended. B+1 will come down a little with the rest of the tubes and FET, so it's fine.

Not much you can do about the output tubes except get some that are better matched. Definitely give those JJ's a try. A separate bias pot for each tube is a logical improvement for dealing with mismatched tubes, but it only goes so far. I believe Fuchs has that feature.

[Raoul Duke]

Thanks for the feedback Martin!

Just tried the JJs and they bias within 2 mV of each other - so I’ll use them.

My PI tube plates are about 10v apart; does this indicate a grossly mismatched tube?

EDIT: just did a quick google search and found that this isn’t extreme. I’m going to try another tube just for giggles.