How does this work?

[ricach]

I rechecked voltage on pin 3 and it is as reported before -11mV. I measure R17 and it does check out around 2k7 to ground.

Voltage on C19 on VR7 side is -11mV as well (R22 still lifted). No change in voltage while sweeping the pot either.

VR7 - 250k
VR5 - 500k
VR6 - 25k
VR8 - 1M

[Joey Voltage]

Reason is, it drives it "better", specifically on very high and very low frequencies; net result is the amp sounds beefier.

That only really holds up for small signals though...... Imagine what happens in a typical high gain amplifier, when the signal is bouncing off both rails at this point.

[J M Fahey]

Hi ricach.
We have an inconsistent measurement here.
If you measure only 11 mV DC on V3, yet it has 2K7 resistance, practically *no* current is flowing through that triode.
It either is dead or unconnected.
That does not match up with what you measure on its plate, around 188V DC with a +B around 280V, which indicate 1mA is flowing through that 100K plate resistor.
Where does this current come from if it does not flow through the 2K7 resistor? (where it would make 2.7V DC appear)
We can't go on until these inconsistent pieces of data are solved.

[ricach]

Hi ricach.
We have an inconsistent measurement here.
If you measure only 11 mV DC on V3, yet it has 2K7 resistance, practically *no* current is flowing through that triode.
It either is dead or unconnected.
That does not match up with what you measure on its plate, around 188V DC with a +B around 280V, which indicate 1mA is flowing through that 100K plate resistor.
Where does this current come from if it does not flow through the 2K7 resistor? (where it would make 2.7V DC appear)
We can't go on until these inconsistent pieces of data are solved.

I agree, especially since -11mV is the reading I get from the top of the tone stack as well. I could physically ground pin 2 and see what I get on 3. Any other suggestions while I'm at it would be appreciated. I only have one shot per night to troubleshoot this.

[J M Fahey]

Don't worry, sooner or later you'll repair it for sure.
Also follow tracks, and check that ground is ground; maybe the chassis ground is not board ground, that sure makes some measurements very confusing.

[ricach]

Don't worry, sooner or later you'll repair it for sure.
Also follow tracks, and check that ground is ground; maybe the chassis ground is not board ground, that sure makes some measurements very confusing.

Grounding pin 2 and I still get -11mV at pin 3.

Grounds have been verified already. I think I'll spend an evening resoldering tube socket connections to the PCBoard. I'm also going to borrow another DVM and check against mine. I don't like how common all my readings are down at the mV level.


***UPDATE - Forgot to mention, with the tube pulled I still get same readings on 2 and 3, but pin 1 jumps to about 220V *************

[ricach]

Problem solved. Bad socket connection on pin 7 on V3. Thanks for all the help.