BF Bandmaster rebuild troubleshooting

[MWJB]

If you are dropping a volt accross the 470ohm resistor, then the tube is drawing 2mA...it should be drawing twice that - 4-5mA. Triode A (pins 1, 2, 3) are turned off. Either pin 1 is not connected to the plate resistor, or pin 3 is not connected to the cathode resistor.

Carefully check the socket (if you have a spare socket, don't bother with the checking, just put it in).

[rocky101]

If you are dropping a volt accross the 470ohm resistor, then the tube is drawing 2mA...it should be drawing twice that - 4-5mA. Triode A (pins 1, 2, 3) are turned off. Either pin 1 is not connected to the plate resistor, or pin 3 is not connected to the cathode resistor.

Carefully check the socket (if you have a spare socket, don't bother with the checking, just put it in).

I already swapped sockets since that was my initial thought also. I am curious though why when I get a ground reference through the DMM at pin 7 the amp has sound? I am just wondering if I am looking at the wrong part of the circuit cause Pin 1 & 3 are definitely connected

[MWJB]

I'd be more curious as to why triode A isn't working...whether it is the whole problem, or not, it needs sorting.

Check integrity of wire at PI pin 7, check heater connections/voltages at PI.

Your DMM impedance should be higher than the pin 7 path to ground anyway? Shouldn't be showing pin 7 a path as it's already got one (pull tube & check resistance from pins 2 & 7 to ground, check idle voltages at pins 2 & 7).

[Bruce / Mission Amps]

If we are talking about the phase inverter tube;
With respect to ground, measure the B+ voltage delivered to the junction of the 82K and 100K plate load resistors. Note that.
Now move your your DVMM ground connection to that junction and with the red lead, measure the DCV at the other ends of the two resistors one at a time.
If there is none on one side then no matter what you think that resistor is open or not soldered somewhere.
They should be similar voltages, but not exact... if one is really high, closer the supplied voltage, then that triode is not turned on.
So, if it's not on, then there are very very few things that can cause that and it will be easy to figure out why... and usually it has to do with the cathode not being connected.
If one side of the triode's plate resistor has very low voltage then it could be a bad resistor or totally the wrong value or, the triode is drawing high current and the voltage will be way lower too.
Besides a bad tube, there are very few things that can cause that.... typically an ungrounded grid resistor, etc.

And are sure that tube socket is wired right? Following the wires back to the eyelet board have me messed up.. like the socket is wired wrong.
I can't quite tell from the picture what the lugs look like but see my attachment
*************************

Never mind I got it figured out from my picture and it looks right... my eyes are just not what they used to be with dark images.
Sorry...

[JHow]

Is there any DC on that grid pin 7?

[rocky101]

I'd be more curious as to why triode A isn't working...whether it is the whole problem, or not, it needs sorting.

Check integrity of wire at PI pin 7, check heater connections/voltages at PI.

Your DMM impedance should be higher than the pin 7 path to ground anyway? Shouldn't be showing pin 7 a path as it's already got one (pull tube & check resistance from pins 2 & 7 to ground, check idle voltages at pins 2 & 7).

The heaters are 3.2v at pins 4&5 and 2.6v at pin 9 on all preamp tubes. I am getting around 1M ohms at 2 & 7 with the tube pulled and 15v at 2 and 8v at pin 7.

[rocky101]

If we are talking about the phase inverter tube;
With respect to ground, measure the B+ voltage delivered to the junction of the 82K and 100K plate load resistors. Note that.
Now move your your DVMM ground connection to that junction and with the red lead, measure the DCV at the other ends of the two resistors one at a time.
If there is none on one side then no matter what you think that resistor is open or not soldered somewhere.
They should be similar voltages, but not exact... if one is really high, closer the supplied voltage, then that triode is not turned on.
So, if it's not on, then there are very very few things that can cause that and it will be easy to figure out why... and usually it has to do with the cathode not being connected.
If one side of the triode's plate resistor has very low voltage then it could be a bad resistor or totally the wrong value or, the triode is drawing high current and the voltage will be way lower too.
Besides a bad tube, there are very few things that can cause that.... typically an ungrounded grid resistor, etc.

And are sure that tube socket is wired right? Following the wires back to the eyelet board have me messed up.. like the socket is wired wrong.
I can't quite tell from the picture what the lugs look like but see my attachment
*************************

Never mind I got it figured out from my picture and it looks right... my eyes are just not what they used to be with dark images.
Sorry...

The wire you pointed out is just a long wire folded over. Anyway I did what you said, with respect to ground the B+ at the junction of the plate load resistors is 455v, with the ground connector at the junction I am getting 214v at the end of the 100k and 0v at the the end of the 820k. It took out the 820 and replaced it with a new one(measured with DMM). Still I am getting 0v, I am also replaced the wire going into pin 1 just in case and still 0v.

[Bruce / Mission Amps]

The wire you pointed out is just a long wire folded over. Anyway I did what you said, with respect to ground the B+ at the junction of the plate load resistors is 455v, with the ground connector at the junction I am getting 214v at the end of the 100k and 0v at the the end of the 820k. It took out the 820 and replaced it with a new one(measured with DMM). Still I am getting 0v, I am also replaced the wire going into pin 1 just in case and still 0v.

OK.. something is still open there or the eyelet or 82K resistor is somehow grounded on the tube side ... oh, and it is an 82K resistor not 820K.

[rocky101]

OK.. something is still open there or the eyelet or 82K resistor is somehow grounded on the tube side ... oh, and it is an 82K resistor not 820K.

Yeah 82k is what I meant Anyway. I separated pin 3 and 8 and only hooked up one side of the tube at a time and took measurements. With pin 8 disconnected I can get voltage across the 82k (Pin 1) with both 3&8 hooked up I get no voltage across the 82k(with reference to gnd at the junction of 82k and 100k). Conversely with pin 3 disconnected I am getting the other side of the tube to work also, but they don't work together. what I am finding is that no matter what, I am getting only 60 volts at the junction of the 1M resistors, 470 and the 22k resistor.

[MWJB]

I still suspect the socket, replace it, don't bend the tube socket pins 3 & 8 over each other & solder, use an old resistor leg or similar to bridge pins 3 & 8 whilst keeping them vertical.

[rocky101]

I still suspect the socket, replace it, don't bend the tube socket pins 3 & 8 over each other & solder, use an old resistor leg or similar to bridge pins 3 & 8 whilst keeping them vertical.

I have a few new sockets on order so we will see. Hopefully that will solve it, if not then I'll be back at square one.