Egnater Rebel 20 power with no sound

[Pryde]

I got an Egnater Rebel 20 head I am trying to help fix for a friend. It is a 20w head with a set of EL84 and 6v6 tubes that can be blended

The amp powers up but absolutely no sound. Went through all the simple checks (cords, speaker, ALL NEW pre and power tubes, fuses) with no luck. All tube filaments are glowing fine.

Now I am getting 398v plate voltage and NO cathode current reading (0.0v) when using my tube bias probes on either the EL84 or 6v6 tubes?

I notice no outright visible burned caps or resistors anywhere on the board.

I can't find a schematic or voltages for this amp anywhere so hopefully someone here can lend some advice. Thank you for the help!

[The Dude]

Schematic is posted in THIS THREAD. Have you checked the cathode resistors?

[NZaudio]

You need the negative Bias voltage on all valves and check the voltages across the cathode R's, there must be a small voltage (DC). If yes, the valves should work.If you use a signal, make sure you have either a speaker or a resistor load connected to the output.(Look up datasheets for the valve bias)
But before you do anything, check the output transformer on continuity.

[tubeswell]

If you are getting high voltage on the plates but no cathode current, then most likely either your cathode is not connected to the ground return (either directly or via a cathode resistor), or your heaters aren't working. Too much bias probably wouldn't be enough to shut the tube current off completely

[Pryde]

Thanks for the schematic link.
So it looks like my cathode resistors are R201 for the EL84's and R212 for the 6V6's. just verifying.

If I am not getting any current on either power tubeset cathodes, then wouldn't the issue be further upstream (i.e. power transformer?)

Also, tell me about the continuity output transformer test?

Thanks

[Mick Bailey]

An unusual situation if the cathode resistors are OC on both sides. If you're getting plate voltage on each side then the transformer shows continuity.

I notice the screens are all connected to B+3 via QC207. My money is on there being no screen voltage - probably a bad connector. Check the screen voltages at the tube bases to make sure it's getting there.

[tubeswell]

What are the other voltages like at the B+, the other High Tension supply nodes, plates, and cathodes in the amp?

[Amp Kat]

Thanks for the schematic link.
So it looks like my cathode resistors are R201 for the EL84's and R212 for the 6V6's. just verifying.

If I am not getting any current on either power tubeset cathodes, then wouldn't the issue be further upstream (i.e. power transformer?)

Also, tell me about the continuity output transformer test?

Thanks

Measure from pin 3 to pin 3 of the 6V6's on ohms and that will be the winding resistance across the OT primaries. Find the CT of that winding and it should be very close to exactly half of that reading and do post those ohm readings if you can.

These are test of course with the amp off.

[Pryde]

OK starting with Mick Bailey's advice I took some screen voltages on all power tubes and got .-49v on all 4 pins (pin 4 6v6 and pin 9 on EL84 tubes)

so I traced back to QC207 and got the same voltage there. Next I went to R118 (B+3 on schematic) and measured -.6v on one side and +406v on the other side of the resistor.

All measurements taken with amp and standby on with 16ohm load.

Ideas?

[Pryde]

OK starting with Mick Bailey's advice I took some screen voltages on all power tubes and got .-49v on all 4 pins (pin 4 6v6 and pin 9 on EL84 tubes)

so I traced back to QC207 and got the same voltage there. Next I went to R118 (B+3 on schematic) and measured -.6v on one side and +406v on the other side of the resistor.

All measurements taken with amp and standby on with 16ohm load.

Ideas?

[The Dude]

If you got voltage on one side of R118 and not the other side, R118 is likely open. BE CAREFUL! Your are dealing with very high voltages that can kill you. Make sure all caps are discharged before you attempt any repairs.

[Pryde]

If you got voltage on one side of R118 and not the other side, R118 is likely open. BE CAREFUL! Your are dealing with very high voltages that can kill you. Make sure all caps are discharged before you attempt any repairs.

Safety Noted. I guess I will lift R118 and check its resistance unless anyone has other ideas on this. Again on one leg its measuring negative 0.6vDC and the other leg is positive 406vDC. Should this resistor have nearly the same voltage on each leg (i.e. 400v)?

[The Dude]

Safety Noted. I guess I will lift R118 and check its resistance unless anyone has other ideas on this. Again on one leg its measuring negative 0.6vDC and the other leg is positive 406vDC. Should this resistor have nearly the same voltage on each leg (i.e. 400v)?

Yes. B+3 feeds the screens of the output tubes, so it should be near plate voltage.

[g1]

R118 should have high voltage on both sides. Ballpark guess 350 to 400V on the side where you have nothing.
Also, check that C128 is not shorted.

[The Dude]

Yes, in fact before you fire it up and potentially burn up another resistor, I would measure the resistance from the dead side of the resistor to ground and make sure there are no shorts.