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

[martin manning]

Yes.

[Raoul Duke]

Been poking and prodding all day and I feel like I’m narrowing it down, but needed to stop on a positive note - so I ran through the PI set-up process again and the setting had changed slightly. I imagine it’s because everything is drawing voltage now; but she’s zero’d out again. It’ll be nice when I can hear it, lol.

I’ll poke more tomorrow I guess…

Martin - meant to ask: if I can keep working my way through the schematic/voltages you posted - should the problem become clear? My impatience is nagging me to look under the board - but I’m game to continue deciphering the electro-hieroglyphics if it’s likely I’ll get there.

Follow-up question: when I installed the PA in and modified the 2nd gen layout from the new files you posted in the eyelet board plans - were there any jumpers I should have eliminated? Based on my last F-up, thought I’d ask, lol.

Thanks!

[martin manning]

if I can keep working my way through the schematic/voltages you posted - should the problem become clear?

Signal voltage measurements will help isolate the problem, i.e., if the voltage looks reasonable a one test point, and then unreasonable at the next, the problem is either between those two points, or possibly at or after the second point if there is something loading the circuit, like a short to ground. Then it might help to break the signal path at that point to see if the reading becomes reasonable. Signal tracing can be faster than checking the wiring piece by piece against the schematic by narrowing the place to look. It seems like you have some issue early in the preamp, so you might just want to recheck the wiring starting from the input.

My impatience is nagging me to look under the board - but I’m game to continue deciphering the electro-hieroglyphics if it’s likely I’ll get there.

There isn't much under it. I would try to verify the jumper connections with a DMM before lifting the board.

when I installed the PA in and modified the 2nd gen layout from the new files you posted in the eyelet board plans - were there any jumpers I should have eliminated?

AFAIK the DIY eyelet board diagram for the 2nd Gen shows the jumpers and flying lead connections correctly.

PS I replaced the schematic with voltages I posted earlier. I updated some pot values and resulting voltages for "noon" settings. The new schematic may be a bit easier to read, too.

[Raoul Duke]

Thanks, I’ve got that revised chart up now.

Been reviewing everything from the jacks forward.
Question: on the layout - should the 270k resistor tying Bright and Deep be tied into the 10k running to ground? The leads seem to touch as drawn, but I didn’t wire it that way. All that stuff hung on that deep switch was a challenge to sort out. Actually, that whole area was like building a watch.

IMG_0360.jpeg

Verified all the jumpers under the board, so I’m not as eager to lift it now, lol.
I’ll start checking voltages.

[martin manning]

Question: on the layout - should the 270k resistor tying Bright and Deep be tied into the 10k running to ground?

No, it connects from Volume wiper to Deep switch.

[Raoul Duke]

Ok, that’s how I did it.
I should be getting 1.8vac at that connection or lug 3 of the volume, correct?

At the treble pot I get 3.1, 2.2, 2.0 vac (lugs 1-3 respectively).

At the 10nf where it goes to NC1/NO2 I get .45vac (should that be 12.2?).

[martin manning]

OK, new schematic posted. I realized that while electrically the same, my scheme was not like the layout. I'm now showing DPDT switches for Bright and Deep with the components connected exactly as in the layout. Take a look at that.

I should be getting 1.8vac at that connection or lug 3 of the volume, correct?
At the treble pot I get 3.1, 2.2, 2.0 vac (lugs 1-3 respectively).
At the 10nf where it goes to NC1/NO2 I get .45vac (should that be 12.2?).

Yes, and yes. The 450 mV at NC1/NO2 is way too low. I think you've found where the signal is lost. 3.1 at the top of the trebel pot vs. my 3.7 is ok.

[Raoul Duke]

Got the new chart here. I was making my way through the other one with the help of the larger schematic and the layout, but I was a little tentative about it, lol.

So is this a “reflow” the eyelets in that chain or is the cap bad or? What would be the next logical step? I measured the cap in circuit with my cheap Amazon capacitor DMM and it’s still reading the right value. This is new territory for me.

[martin manning]

If you have something like 1.8V at the top of the volume pot, what about the wiper (lug 2)? That should be ~200 mV at noon, and you should be able to control it with the knob from zero up to what you measured at the input (lug 3). If that checks out, and after the next stage the output (at the plate) is very low, half a volt instead of 12V, something is wrong with that stage. Could be a bad solder joint, but there are other possibilities. Do you still have good DC voltages, ~190 on the plates and 1-1.5V on the cathodes?

[Raoul Duke]

The volume sweeps from 0 to 2.2v on wiper (lug 3 reading) with 310mv at noon.

V1 Plates- A - 183, B - 196
Cathodes- A - 1.6, B - 1.4

V2 plates: A - 220, B - 211
Cathodes A - 117, B - 131

[martin manning]

Ok good. Spoke to soon above, the reason for the low voltage at the output of the next stage could be caused by inadvertent grounding in the OD relay area. You could disconnect the lead coming off he coupling camp and see if the voltage comes up.

[Raoul Duke]

So disconnect the 10n and measure at NO2?

[martin manning]

No measure at the open end of the 10n.

[Raoul Duke]

Got it, give me a minute and I’ll let you know

[Raoul Duke]

462 mV on the lifted lead.

Relay then?

Wait, no. That’s what we already have. So the other direction then? But the plate voltage and the B+5 are good - so it’s got to be the cap, right?