New build troubleshooting (schem updated)

[3choplex]

(Cross Post)
Finished building my first design the other night, thanks for the help on the schematic. It has two-phase, full-wave SS rectification (1N4007s), 2 gain stages, a DC coupled cathode follower, FMV tone stack into a 5e3 power section, with octal tubes in the preamp. I'm using a mag components tweed deluxe power transformer (355v per side).

Firing it up using a light bulb limiter and no tubes resulted in voltages about 200vdc higher than I expected. Is that normal for no load? I don't get what could make the voltages that high.

V1 plate 426
V2 (DC coupled Cathode Follower) plate 515, grid 220
V3 plate 473
PI (cathodyne) plate 496, grid 46
Both 6V6s screens 537, plates 542
OT B+ 542

Power supply nodes:
post rectifier, pre sag resistor 544
node 1 534 (expected 360)
node 2 533 (expected 320)
node 3 512 (expected 200)
node 4 510 (expected just under 200)

On the OT, I measured between the primaries, and they measured 120 ohms and 142 ohms, respectively from the B+ to the 6V6 plates. I tried measuring from the B+ and 6V6 plates to the speaker outs and got infinite ohms. Is it bad that I can’t get a resistance reading between primary and secondary?

The heaters measure 3.2vac.

Any idea why the DC voltages are so high? Am I ok?

[Geezer]

Is that normal for no load?

Yes.....if the lamp limiter shows no high current conditions, then put the tubes in & repeat the procedure. If the limiter again goes dim, then remove it, plug directly in (no limiter) & fire it up. If no smoke, then check the voltages. I suspect they will be more "in-line" with expectations.

With no tubes in the sockets, there's no current flowing, nothing to draw the voltage down.

G

[3choplex]

With tubes installed, the light bulb limiter dims for maybe 3-4 seconds, then glows brightly. Would a bad OT cause the light bulb limiter to light up brightly? (With no tubes, it stays dim.) I am getting no sound whatsoever. Using the "tap test" from the Jack Darr book, I get no sound at all, including when I tap directly on the OT primaries. (I tapped lightly on all the plates and the 6V6 screens with a long screwdriver.)

I've checked my wiring and it matches my schem, grounds have continuity, etc. I can see the heaters going in the 6V6s, although none of the tubes get too warm (I'm assuming because of the limiter). I have voltages where I should without tubes, and none where I shouldn't. (I haven't tested voltages with the tubes in and limiter plugged in.)

[3choplex]

Thanks, Geezer. I went for broke and took some measurements with tubes installed and no limiter last night. The voltages were close to what I expected, and none were causes for serious concern.

Still doesn't work, though. I need to dig out a spare OT I have lying around.

[Danskman]

I would check the speaker connection; did you use a two-jacks configuration ("main" and "ext" speaker?)? If you did, be sure to connect the speaker to the 1st jack (main), as it's often a switched jack and it's a short to ground when not used.
Without a schemo or some pics, it's hard for me to help you further...
HTH,
Danskman

[3choplex]

Just one speaker jack, connected directly to the 8 ohm lug of the OT. I should probably mention that I'm using a chassis and OT from a 1940s PA. When I desoldered the OT connections, the 4 ohm and 16 ohm lugs basically disintegrated--I am confident it was not my soldering skills. That's a big part of the reason I am suspicious of the OT.

Here is the accurate schem:

[sluckey]

If you turn that volume control down, then the cathode follower will likely melt. You can cap couple to the volume pot or better yet, move the volume pot to the wiper of the treble control.

[3choplex]

A buddy just pointed out that my heaters are way over the current my PT can supply--2.1 amps, and its rated for 1.65. Next step, deal with that.

[3choplex]

If you turn that volume control down, then the cathode follower will likely melt. You can cap couple to the volume pot or better yet, move the volume pot to the wiper of the treble control.

(Sluckey's comment is on an earlier version of the schem where the vol was before the tone stack.)