Amp repair where do I start

[LoveChet]

Messing with v4 solder joints. I get a reading direct short to ground on pin 459 filament. Im assuming that's not good.!

[Helmholtz]

The heater circuit is very low resistance. So with a grounded CT all heater pins will measure lower than 1 Ohm to ground.

[LoveChet]

I'm getting not a short but 50 ohms to gnd. Is that OK?

[Tom Phillips]

I'm getting not a short but 50 ohms to gnd. Is that OK?

Whenever you are measuring a low resistance, it is good practice to short your test probes together and verify the resistance reading shown on the meter. If your meter does not have a null feature to correct for the resistance of the probes, then take note of the reading when the probes are shorted and subtract it from the circuit reading you get.

50 Ohms is an unexpectedly high reading for a the heater circuit. But you are probably reading the resistance of the an artificial ground circuit which would be used of your power transformer does not have a center tapped heater winding.

[Helmholtz]

I'm getting not a short but 50 ohms to gnd. Is that OK?

50 Ohm from V4 grid pin 7 to anywhere else is not ok.

[g1]

But you are probably reading the resistance of the an artificial ground circuit which would be used of your power transformer does not have a center tapped heater winding.

That's what I thought as well, and when the two 100R resistors are used for the heater grounding, they will measure 50 ohms in circuit, so the reading makes sense.

[Helmholtz]

Sorry, bad eyes.
I read grid for gnd.

[Helmholtz]

That's what I thought as well, and when the two 100R resistors are used for the heater grounding, they will measure 50 ohms in circuit, so the reading makes sense.

If so, all tube heaters should measure roughly the same resistance to ground.

[LoveChet]

I think Im ok. I found a loose wire on socket of v4 so that's probably the issue. I just need to get everything back together and not make any shorts.

[LoveChet]

Help. How do I debug. I still get no output on pin 6 plate V4B with 75 mv signal on pin 7 grid. I soldered a loose connection on pin 5 htr and pin 6 plate. I get 200 v dc pin 6 plate, 1.5 v dc on pin 8 cathide.

[Helmholtz]

Plate and cathode voltages look ok, assuming that the B+ is around 350V.
So the tube should be working.
Are you sure you have a 75mV signal at the tube socket pin 7?
I yes, I suspect some short after your point "C" (Fx loop).

[LoveChet]

Hi Helm. Thanks for your support. I just solved it. The scope had got switched to DC so the pattern was way off screen. I hope I didn't hurt the scope!

[LoveChet]

Novice here !!!

[Tom Phillips]

Novice here !!!

This is the type of learning that creates a lasting memory.
You can read about advice in books and newsgroup discussions. However, when you actually have a personal experience like you described, there is a much better chance that you will remember it and be able to avoid similar mistakes in the future.
Hands on experience is the best!
Cheers,
Tom

[LoveChet]

When tracing the sig gen sign wave through the subsequent stages of my Fender deluxe, should I be able to get a clean looking sine wave all the way through to dummy load at around 22 watts ? I do realize that given enough signal by various controls you can get it to clip, as in sig gen amplitude, volume, mstr volume, treble etc.