Randall RD-5 not happy..

[Sea Chief]

Hi chaps,

I have a little Randall RD-5, with no sound. I notice the red led power light on ok.. but no glow/ no life it seems in the tubes.

Schematic is here, from another MEF thread in fact.. RD5 {Schematic}.pdf

Could you help? Thanks if so, SC

[Jon Snell]

Check F1

[Sea Chief]

Check F1

Hi Jon. F1.. yes 1st thing I did: I put DMM across & get continuity. Oddly it looks a bit singed, fuse glass a little cloudy, so I thought 'EASY!'.. but wasn't expecting to get continuity.

Sorry my schematic link seems not to work.

(here's link to another RD5-C thread, schematic a few posts down. https://music-electronics-forum.com/...equests/47288- thx)

[Jon Snell]

You will always get continuity as you have valve heaters and the transformer winding completing the circuit.

[Sea Chief]

You will always get continuity as you have valve heaters and the transformer winding completing the circuit.

Aha.. so with a similar fuse in an amp, you must remove it to test?

thanks SC

[Sea Chief]

Ok tested the fuse removed.. & it seems fine/ continuity. Hmm..

[Jon Snell]

Re fit the fuse and test for 6.3volts AC between pins 2 & 7 of V3 (6V6). If you have, the heaters will be lit, if not check the transformer output.

[Sea Chief]

Re fit the fuse and test for 6.3volts AC between pins 2 & 7 of V3 (6V6). If you have, the heaters will be lit, if not check the transformer output.

Can I do with the tubes all removed Jon-? makes things alot easier.

thanks SC

[Sea Chief]

Re fit the fuse and test for 6.3volts AC between pins 2 & 7 of V3 (6V6). If you have, the heaters will be lit, if not check the transformer output.

Hi Jon, shoved tubes in. Ok I am not getting any voltage (vac) across pins 2 & 7 of the 6v6. I did notice the valves were not lit from the off.

[Pixel]

Do the leds inside the amp light up?

[Jon Snell]

Check for 6.3volts or so on the transformer.

[Jon Snell]

If you have heater AC voltage coming onto the board (the LED you say lights up) then there is a bad connection between the 6V6 pins 2 or 7 and the AC supply. The 12AX7 heaters will be lit if the LED is lit, if not there is two bad connection issues.

[Sea Chief]

If you have heater AC voltage coming onto the board (the LED you say lights up) then there is a bad connection between the 6V6 pins 2 or 7 and the AC supply. The 12AX7 heaters will be lit if the LED is lit, if not there is two bad connection issues.

Does the led lit signify that I have 6.3v coming in then-? that would be a big positive if so. I thought it must be a 240v led power light.

Maybe I should just resolder the 6v6 pins 2 & 7 points where the xfmr wires connect to them.

great help- thank you Jon.

[Jon Snell]

Yes, LED1 connects through R61 from pin7 of the 6V6 to ground. Just before the voltage trippler. If it is lit, pin7 has AC on it. The other leg pin2 comes from the AC winding.
So, if there is 6.3 ish volts AC across pins 2 & 7 then the valve is faulty or at least I would suspect that or the spigot has broken off and it is incorrectly inserted.

[Sea Chief]

Yes, LED1 connects through R61 from pin7 of the 6V6 to ground. Just before the voltage trippler. If it is lit, pin7 has AC on it. The other leg pin2 comes from the AC winding.
So, if there is 6.3 ish volts AC across pins 2 & 7 then the valve is faulty or at least I would suspect that or the spigot has broken off and it is incorrectly inserted.

But I don't get 6.3v across pins 2 & 7 tho.

Its a good start I get 6.3v @ pin 7 though as you say I must have. Surely if I pull the 6v6 I can still read across pins 2 & 7.. I seem to recall this is doable. Would that rule out the 6v6 if I still don't read 6.3v across-?