[rperry]

   
Hello All,
Ive been working on a GE-g97, it's been close to a total rewire due to a Lot of rubber wire. I have it recapped and wired. After initial power up just a slight speaker hum. No reception at all. I have a weak 42 tube im waiting to arrive. But this one wire has me scratching my head on the field coil. I don't see anywhere it would go and seems strange to leave the factory like that. hmm?

[mark123]

Hello GE -

Tough to tell from your photo, but could that wire be an unused center tap on the secondary? What does the schematic indicate?

[rperry]

    I think your right, i haven't seen where they just leave it hanging loose before.

[jcassity]

seems to me a wire hanging out like that would act like an antenna ,, helping more noise and local distortion to get in...

[35Z5]

Assuming a F96 & F97 are at least similar, field coil is in the power supply filtering ripple.

   

What's shown on schematic of 42 output is output transformer, humbuck winding & voice coil. You should measure resistances to determine just what purpose the loose wires serve, I'd suspect are to humbuck winding. It's resistance is listed as .2 ohm, while field coil is 880 ohms. Output transformer primary is 500 ohm and secondary .8 ohm.

Note the hum buck winding isn't absolutely required, will operate bypassed though probably with increased hum level. Polarity of that winding determines if hum is reduced or actually increased.

[rperry]

The f-96 and G-97 are very similar, ive been working off both schematics. The humbuck winding is a separate set of winding's ( thanks! Ive been wondering what those leads were doing). All of my resistances are within spec. The loose wire is .8 ohms which is in line with the center tap on the drawing. So I guess its possible it was built that way. I have a faulty candohm and Im waiting for my power resistors to come in to rebuild that part of the circuit, it should come to life after that, hopefully..

[rperry]

I got the candohm problem sorted out, Speaker has a hum, But no response to dial or anything, I injected a signal on the blue wire (see diagram above) going to output transformer, and I can just make out the tone if I stick my ear into the speaker cone. If Im correct that is pointing towards a problem in my output transformer. which is strange since the resistance measurements where correct. Am I on the right track here?

[35Z5]

You'd need a very large signal to push any real amount of volume through the plate(blue) lead.

Can you get anything from the control grid(pin 4)?

http://www.nj7p.org/Tubes/SQL/Tube_query.php?Type=42

[rperry]

No sound on pin 4 either, I can hear it picking up broadcast but it's VERY faint.

[35Z5]

What are 42 voltages on pins 2, 3 & 5?

[rperry]

275, 255, 15 respectively

[35Z5]

Can you inj signal from center tap of volume control? Volume approx half advanced.

[rperry]

negative, no signal

[35Z5]

Ummm, how about injecting signal into pin 4 of 42? If that isn't passing signal problem definitely in output section.

Are you sure the output transformer primary(blue, 500 ohm) is connected to plate and not one of other windings?

[rperry]

    I started investigating the speaker and output transformer again and I made a few discoveries. On the connector where the "green" wire attaches the solder and wire are missing from the pin. (see Picture) also when I took my initial resistance readings I made an error. Where the schematic is showing 5 ohms across the speaker leads I have .9.. So it looks like I'm on the hunt for a new output transformer.