Tube Amp Archive

The 1.5R resistor is probably a 1R resistor with the meter leads adding 0.5R of measurement. What is the mV (DC) across this resistor? (We need to know this the calculate the tube current) That reading is zero. This reading needs to be (carefully) made with the voltmeter on the 'millivolt DC' setti...

Per the schematic on a fender deluxe reverb aa763 (most will be within that range for 6V6) it calls for -35V so your bias pot should be able to dial it more negative than that as well. Say -40 or more. Then you can adjust according to taste after you measure and get the exact plate current. -15 is ...

So I'm thinking bad reservoir cap or failing transformer. I've checked all the wiring and joints several times now. And I know it's not the tubes.

tubeswell wrote: ↑Tue May 29, 2018 7:15 pm The 1.5R resistor is probably a 1R resistor with the meter leads adding 0.5R of measurement. What is the mV (DC) across this resistor? (We need to know this the calculate the tube current)

That reading is zero.

tubeswell wrote: ↑Tue May 29, 2018 7:15 pm The 1.5R resistor is probably a 1R resistor with the meter leads adding 0.5R of measurement. What is the mV (DC) across this resistor? (We need to know this the calculate the tube current)

Ok I will check asap.

Well it isn't the tubes. Tried out another pair. Funny thing is the plate and screen measurements are good while the amp is on standby. Turn it on and they drop down low again.

What resistance do you measure from pin 8 to chassis for each 6V6? What voltage do you measure from pin 3 to chassis for each 6V6? What voltage do you measure from pin 4 to chassis for each 6V6? What voltage do you measure from pin 5 to chassis for each 6V6? Adjusted the bias pot back to halfway an...

Per the schematic on a fender deluxe reverb aa763 (most will be within that range for 6V6) it calls for -35V so your bias pot should be able to dial it more negative than that as well. Say -40 or more. Then you can adjust according to taste after you measure and get the exact plate current. -15 is ...

Voltage readings with no tubes installed are meaningless. Except for that pin 5 voltage. Better fix that before you plug in the 6V6s. Gotcha, I'll put em back in. Should the pin 5 voltage be more negative? And would involve changing the bias tail resistor or simply adjusting the pot? It was all the...

What resistance do you measure from pin 8 to chassis for each 6V6? What voltage do you measure from pin 3 to chassis for each 6V6? What voltage do you measure from pin 4 to chassis for each 6V6? What voltage do you measure from pin 5 to chassis for each 6V6? Pin 8 to chassis- 1.5 ohms With only the...

Thought I had already mentioned, but the resistance from pin 8 to ground is 1.5 ohms. They're vishay dale resistors.

Ok so I resoldered the tail resistor ground- no change. Still motorboating. Mind you, I have a 100k/.047 across the standby, so that's why it's trickling in enough to be audible. I've used that method on all my standby switches with no pops and no problems. I double checked to make sure this one is...

Ok so I resoldered the tail resistor ground- no change. Still motorboating. Mind you, I have a 100k/.047 across the standby, so that's why it's trickling in enough to be audible. I've used that method on all my standby switches with no pops and no problems. I double checked to make sure this one is ...

I actually plugged in and got barely crackling notes only at volume 10, channel 1. Vibrato channel put out no sound maxed out. It sounds like the bias voltage is too negative and it needs to be closer to zero, not further away to achieve cathode current flow. The higher preamp voltages are also a g...

Motorboating may be caused by positive gNFB, so try swapping your OT primaries (that is, the brown and blue wires connected to your power tube plates). With NO power tubes installed, please report your maximum and minimum bias voltages when turning the bias pot (like, -50 to -35). You may have to a...