Deluxe Reverb problem

[tyler8611]

You have to disconnect the cathode resistor if you want to measure mA current directly. Current measurement must be done with the meter in series. The point of having the 1 ohm cathode resistors is so you don't have to 'break in' to the circuit and can just measure voltage in mV across the resistor.
So your mA numbers are not valid. Your measurement of 65mV across the resistor is what you should go by. 65mV divided by 1 ohm equals 65mA idle current. At 400V plate, you are idling those tubes around 26watts. If you are lucky they may still be ok.
Somewhere around 20mA is probably more appropriate, which will measure as 20mV across the 1 ohm resistor.

Plate is 411 and 409 and power tube bias is 15.9 and 16.4. Reading for mV is 66.6 and 64.5. I put the voltage and current numbers in the weber bias calculator and got 50% dissipation.

So this way of measuring across the 1 ohm is invalid and the resistor would have to be pulled from ground?

[Leo_Gnardo]

Plate is 411 and 409 and power tube bias is 15.9 and 16.4. Reading for mV is 66.6 and 64.5. I put the voltage and current numbers in the weber bias calculator and got 50% dissipation.

So this way of measuring across the 1 ohm is invalid and the resistor would have to be pulled from ground?

About the 1 ohm resistor, it's not an invalid method, it's an either-or situation. Either you trust the resistor to be reasonably close to 1.00 ohm and then 1 mV measured across the resistor indicates 1 mA of bias current. OR break the connection from output tube's cathode and connect one lead of your milliammeter to that cathode and the other to ground, then you'll read milliamps directly thru the meter.

Something's not right about the math also, 411V x .0666A = 27.4W, way in excess of a 6V6's 12W plate dissipation rating. We might expect that if the bias voltage on the control grid is -15.9V. Quite a lot less than the -35ish volts that's expected. Similar for the other 6V6. At that rate they should be glowing orange, ow!

[tyler8611]

About the 1 ohm resistor, it's not an invalid method, it's an either-or situation. Either you trust the resistor to be reasonably close to 1.00 ohm and then 1 mV measured across the resistor indicates 1 mA of bias current. OR break the connection from output tube's cathode and connect one lead of your milliammeter to that cathode and the other to ground, then you'll read milliamps directly thru the meter.

Something's not right about the math also, 411V x .0666A = 27.4W, way in excess of a 6V6's 12W plate dissipation rating. We might expect that if the bias voltage on the control grid is -15.9V. Quite a lot less than the -35ish volts that's expected. Similar for the other 6V6. At that rate they should be glowing orange, ow!

I think that calculator subtracts the screen current from the bias number and then multiplies that by the plate volatage. That's 6W, according to them.

One of them is glowing blue, but that's it.

[g1]

So this way of measuring across the 1 ohm is invalid and the resistor would have to be pulled from ground?

Yes, if you want to use the current range of your meter (mA) you must remove the resistor or break a connection and install the meter in series. Right now, you are measuring the current in parallel with the 1 ohm resistor. Some current goes through it, and some goes through your meter. This gives you an incorrect mA reading.
If you want to leave the 1 ohm resistor in circuit, you can only do voltage (mV) measurements with your meter.
Turn down the idle current till you have 20mV across the 1 ohm resistors. What is now the grid voltage at pin5 of the power tubes? What is the plate voltage at pin3?
Is it still motorboating?

[Enzo]

I don't worry about the 1 ohm diode accuracy. I think I bought 1% ones just for the form factor. But so what if they are off 5%? If we have say 30ma current, a 5% margin is just a milliamp and a half.

[tyler8611]

Yes, if you want to use the current range of your meter (mA) you must remove the resistor or break a connection and install the meter in series. Right now, you are measuring the current in parallel with the 1 ohm resistor. Some current goes through it, and some goes through your meter. This gives you an incorrect mA reading.
If you want to leave the 1 ohm resistor in circuit, you can only do voltage (mV) measurements with your meter.
Turn down the idle current till you have 20mV across the 1 ohm resistors. What is now the grid voltage at pin5 of the power tubes? What is the plate voltage at pin3?
Is it still motorboating?

Turned it down til I had 20mV. Pin 5 - 35v. Pin 3 on both is 458. Still motorboating from having V4 in.

[g1]

That sounds much better for idle current. You are now at about 9watts or 65% dissipation. You can see how much the heavy current had been pulling down the plate voltage. And you are at -35V at the grids just like the schematic (rather than the -20V you reported earlier).

Does the normal channel function properly with V4 pulled?

[tyler8611]

That sounds much better for idle current. You are now at about 9watts or 65% dissipation. You can see how much the heavy current had been pulling down the plate voltage. And you are at -35V at the grids just like the schematic (rather than the -20V you reported earlier).

Does the normal channel function properly with V4 pulled?

Yes normal works fine with V4 pulled.

Vibrato channel- can only hear scratchy notes with volume at max. Vibrato does not kick in, even though the roach blinks, tube is good and voltages look normal.

[g1]

Ok. Motorboating and tremolo are not that far off from eachother.
Can you try disconnecting the wire that goes from the intensity pot to the .1uF/220K junction?

[tyler8611]

Ok. Motorboating and tremolo are not that far off from eachother.
Can you try disconnecting the wire that goes from the intensity pot to the .1uF/220K junction?

Yes I'll try that. The yellow wire.

[tyler8611]

Ok. Motorboating and tremolo are not that far off from eachother.
Can you try disconnecting the wire that goes from the intensity pot to the .1uF/220K junction?

Motorboating gone. Some hiss and a good amount of hum. Reverb permanently on.

[tyler8611]

Ok. Motorboating and tremolo are not that far off from eachother.
Can you try disconnecting the wire that goes from the intensity pot to the .1uF/220K junction?

It was playing at full volume, like the normal channel.

[g1]

I'm not sure if you mean the reverb and volume pots are not working? Or everything is functional except no trem? (aside from hum and hiss issues)

[tyler8611]

I'm not sure if you mean the reverb and volume pots are not working? Or everything is functional except no trem? (aside from hum and hiss issues)

Volume and tone are working. Trem isn't
Reverb is always in the signal in a very heavy amount. Neither turning rhe pot nor pushing the footswitch changes the reverb in an any way. It's always on, a lot of it.

[g1]

It would help if you could post some clear pictures of the board, pots, etc. so we can check the layout & wiring.