Blues Jr has a neg voltage turning off V1A.

[vintagekiki]

Nothing personal.
On a lot of topics, except where it is needed (Theory & Design), there is persistent proof, about who knows or thinks to knows.
Empty expert discussions develop, where after tenth replay, forgets what thread is about.
I personally trust every individual if he thinks for himself that knows, so there is no need to prove knowledge (or ignorance) through futile replay.

Luthin You has a problem with Blues Jr.
Did he ask define “xxxxxx”. It's not.
Is our replays helpful to him. They are not.
Luthin You expect help. Let's go with a concrete solution.

What Next.
If on both sides R10 (100K) voltage is Uz=265V, and on R11 (1.5k) voltage is 0V, it means that defective tube V1, cold solder on tube socket V1 or defective tube socket V1

[Enzo]

The tube not conducting doesn't mean the same thing as being in cutoff. I could be wrong, but as I read some posts here, I think some think they are the same thing.

What could be more basic than an open resistor? Nothing. But why has it not been checked already? Instead of trying to decide if the negative on the grid is this or that, just check the part. I fear one of these threads that goes for 100 posts and nothing accomplished. We should not think up reasons not to check something.

I believe in Occam's Razor. Tube is not conducting. Far more likely to me that the heater is unlit on that side, rather than somehow an odd grid voltage is responsible.

[Luthin You]

Thanks everyone , I want to make clear I have measured 100K plate resistor and 1500 Cathode resistor with no short to ground , also grid to ground and grid to vol pot all ok and measured from tube socket through flat cable . It has me foxed but I think I will replace Ck , one component must be faulty . I have tried multiple tubes. There is also a strange signal developing in the P.I. at exactly 200hz ( 4 X mains here) and with reverb and master off. Although it is not a sine wave .V1A has heaters both bright . Thanks again

[Luthin You]

See output originating in P.I. with no input and everything turned off.

[vintagekiki]

V1A has heaters both bright

Upload measured DC¹⁾ voltage values from tube V1 at both anodes (pin 1 and pin 6) and both cathodes (pin 3 and pin8)

[Helmholtz]

See output originating in P.I. with no input and everything turned off.

Looks like 100Hz to me.

[vintagekiki]

See output originating in P.I. with no input and everything turned off.

Does "everything turned off" mean that On-Off main switch in Off position, or just that pots is on min.
Reverb does not have its foot switch, so there is possibility that something from it leaking though it at min. post #34
It would be help upload scope 1 kHz from both anode V1 tube (pin 1 and pin6)
Attention. Both anodes V1 are under +HV DC voltage

[g1]

Don't worry about odd noises until you fix the no signal issue and have all shielding (back cover) in place.
This series of amps is very susceptible to hum and noise when doing work on the unit. Dress of the ribbon cables is also critical.

[Helmholtz]

Just curious, do you get a (negative) voltage reading in a low DCV range with open meter leads?

[Helmholtz]

.... forgets what thread is about.

Sorry, thread is about the reason for the negative V1A grid voltage.

[vintagekiki]

...thread is about the reason for the negative V1A grid voltage.