Randall pro-tube 2000 no sound. HELP!

[Jerm]

Plate voltage= 472
Bias= a. 23.5
** * * * B. 29.8
** * * * C. 23.8
** * * * D. 36*

Can hear white noise but cannot get the amp to recognize the instrument. You can hear the tone change (in the white noise) when messing with the pots. It's amplifying a signal just no the instrument. *What could this be??? * *

[Jazz P Bass]

Randall 2000

The problem may be in the tubes before the tone control.
From there back to the guitar the signal is being lost.
So...
Does the guitar & cord work in another amp?
Yes?
Try changing the first input tube.

[Jerm]

Yes, I have tried playin guitar with the same cable through another amp and no problem found. I forgot to mention that I had tested all the tubes and they are all in good shape. For the heck of it I tried replacing the first input tube and still nothing. I don't know if this will matter but I do not have the reverb box hooked up.

[Jerm]

Bump

[52 Bill]

Bad input jack or input wiring?

[Jerm]

Checked and the Jack and wires are good. Any other ideas? Thanks by the way.

[Jazz P Bass]

Randall 2000

So you have pretty much eliminated external things that you can do.
Time to open her up.
With your meter on Vac check the heater voltage. Preamp tube Pin#4 & 9.
Pin #3 of the output tubes will give you a B+Vdc reading.
Check Pin#5 of the output tubes. That is your C- (bias Vdc)
Go across all of the tubes & notate the Vdc readings on pin 1& 6 Vdc, Pin 2 & 7, & Pin 3 & 8 of the preamp tubes.

[Jerm]

Preamp tubes pin# 4 and 9 are reading 6.7 vac. B+ is reading 465vdc. C- readings are (-47, -47 and -49,-49). The preamp tubes where all over the place. they are...... With the ground lead on pin #1. Pin #1 and 6 (12ax7's... -5.71, 136, 116, 4.65 and 12at7 reading 4.3). with ground lead on pin #2. Pin # 2 and 7 ( 12ax7's... 0, 194, 10.5, -0.11, and 12at7 reading 0). With ground lead on pin #3. Pin # 3 and 8 ( 12ax7's... 0, 190, 16.57, -.14 and 12at7 reading 0)

**note** on testing across preamp tube pins # 2 and 7. The tube reading 10.5 I got alot of loud popping and static. and the tube reading -.11 got radio interference. Thank you in advance!

[Jazz P Bass]

Amp Testing

Just wondered why you are moving your ground lead.
Leave it at ground.
Do the peamps again.
Pin ! & 6 are plate Vdc.
Pin 2 & 7 are grid Vdc.
Pin 3 & 8 are cathode Vdc.
Measured in respect to ground.

[Jerm]

My bad. A misunderstanding. Ok.... The new measurements are... Pins 4 and 9 both read 3.3 vac. Pins 1 and 6 on the 12at7 read (232 and 226). On the 12ax7's they read (213 and 0) (212 and 329) (194 and 328) (233 and 226). Pins 2 and 7 on the 12ax7 read (44 and 42) 12ax7's read (0 and -.11) (0 and 10.5) (0 and 194) (0 and 0). Pins 3 and 8 on the 12at7 read (63 and 63). On the 12ax7's read (1.61 and -0.028) (1.77 and 18) (1.37 and 195) (2 and 2)

[Jazz P Bass]

Randall 2000

The 12ax7 that has "0" volts on pin 6.
That may be a problem.
It sounds like the resistor attached to the pin is open or not connected.

I do not have a schematic, so you are our eyes & ears.

[Jerm]

There is one resistor ( brn, blk, ylw, gld ) across pin 1 and 6 of only one of the preamp tubes. Nothing is connected to pin 6 on two of the preamp tubes. With my meter set to ohms the resister was reading 102. Does that help any?

[Jerm]

Bump.

[Jerm]

Will a picture help out?