Wiring Questions

[bigmm79]

Working on a GSG - hope to have chassis finished soon and start wiring.
I'll probably have several wiring questions cause I'm somewhat of a newb.
Its a 300b version. I've read many posting here and had many questions answered already from the collective wisdom.

First question, if I want to put in a 6V pilot light can I just power it with one of the 6.3V heater windings? If so, how do I wire that? Take one side of winding, run to light, then from there to GSG board?

Can this siphon off enough power to negatively affect anything else?

More questions to come, I'm sure - I'll put them all in this post.

[TomMcNally]

The most common 6.3 volt lamp is a # 47 bayonet which draws
150 ma. Run a twisted pair from the lamp (insulated from ground)
to the left 6.3 vac winding right at the terminals where the
transformer connects to the board.

Gotta say, of the 70 or so amps I've built, only 2 have had
pilot lights, and the one has had the 6.3 volt lamps replaced
with 28 volt lamps to dim them down. I'd rather use the
tubes as indicators.

Good luck with the amp, yell if you need help. I've put together
a few get*set*go amps.

... tom

http://tmamps.com

[Geek]

I prefer LED's myself. Easier to mount and don't burn out if treated like an LED and not a bulb.

Cheers!

[TomMcNally]

Here's a blurry picture of how to do it, a diode
and a 1200 ohm resistor, LED goes across the
diode as shown ... it works well.

[bigmm79]

Thanks Tom. Your many posts and pictures have already answered most of my wiring questions. If my amp come out looking half as good as yours do, I'll chalk it up as a success.

[bigmm79]

Well got my amp wired up last night. Fired it up and there was some pretty serious smoking going on after 20-30 secs of warm up. Took another look
at my wiring and noticed that I had wired the left-channel tube socket incorrectly. Instead of doing it as a mirror image of the right socket, it was wired the same way. So each lead was on the wrong side of the socket.
What are the chances I did permanent damage to the tube, OPT or something else?

Nothing looks damaged or burned, including on the circuit board.
I think it was starting to melt the insulation on a wire or two, mostly, I think, the misplaced plate to OPT lead.

Fixed the wiring and it fired up with no smoking. Plays music, but the bass and upper frequencies didn't sound too hot - seemed flabby and distorted. Mid-range sounded good, a bit forward, but good.
Hopefully I didn't damage something with the incorrect wiring and
the amp will get better with some break in.

[Shannon Parks]

Well, that has happened to all of us. Can you tell us exactly how you had it wired up? Is the sound better on one channel (the channel that was always wired correctly) than the other?

Shannon

[bigmm79]

The grid lead was attached to the plate pin and the plate lead to the grid pin.
The filament leads were reversed as compared to the other tube.
Maybe had juice flowing for 45 secs tops.

Now with corrected wiring, there is audible distortion on the left channel (the one that was mis-wired).
Also the glow of the filament can easily be seen through the plate, where as on the other tube it cannot. Switched tubes and new tube on left channel, surprise, exhibits same symptoms, while tube on right channel seems fine. So maybe not tube problem but something in left channel circuit damaged or OPT damaged. Any ideas what I should look at next?

[Shannon Parks]

That's actually encouraging news - something on the board is probably fried and not a tube or transformer. Go ahead and take and post your voltages (from the voltage chart in the manual). Also see if you can test your diodes in circuit with a DMM diode checker. I bet either D2, D4, D6, or D8 is shot. But voltages will probably tell us the problem.

Shannon

[bigmm79]

D1-8 all appear to be malfunctioning according to my DM - allowing current in both directions . . . . reading 150ma anode to cathode and and 250 cathode to anode. The diodes I used in place of the rectifier tube appear to be fine - 500ma anode to cathode and nada the other way.

I guess I'll replace D1-8 before I do any more live testing.

[bigmm79]

Got is working. Couple of resistors, coupling cap and tube were done for. Re-built entirely the left-channel side of the board. Now, new tube and wired correctly and all works like a charm. What a dumb and expensive mistake. On the bright side, its a great sounding amp. Surprised at how dead quiet it is, no hum or noise at all even with my very high sensitivity speakers. Thanks for assistance.