Randall RD-5 not happy..

[Jon Snell]

Your output stage is working. Did you check the speaker and connection?

[Helmholtz]

Some cheap meters don't block DC in ACV setting and interpret DCV as ACV. I also have one of those but never use it for ACV.
When set to ACV and measuring a 9V battery I get a false reading of 18VAC. About same factor of 2 as with your values.

[Sea Chief]

Your output stage is working. Did you check the speaker and connection?

Hi Jon,

great that the output stage & PT seem ok.

1st thing I did was test continuity across speaker: 6ohms or so, with usual tiny crackle audible.

Connection.. I've pushed amp's crimp on- wires firmly onto speaker lugs, feel them going on fine. They exit from the OT, so can't check them that end I don't think.

Thanks. SC

[Jon Snell]

Have you an oscilloscope as you now need to trace the signal to get to where it ends and there will be the problem.
It is more than unusual for a single ended amplifier to be completely silent. They all hum slightly.

[Sea Chief]

Have you an oscilloscope as you now need to trace the signal to get to where it ends and there will be the problem.
It is more than unusual for a single ended amplifier to be completely silent. They all hum slightly.

Hi Jon. Ok get the gist of what you're post implies- alas no, I don't have an oscilloscope.

I'll put my ear right next to the spkr though/ try again.. it was pointing away up til now.

If I still get nothing, my 'logic' might ask wouldn't the symptoms now suggest the OT has failed. Has this Q have any validity-?

Cheers. SC

[Jon Snell]

Unusual to have the transformer fail without signs of heat damage but I am open to learning.
Disconnect the speaker and measure the resistance of the output speaker winding. It should be a very low value >1 Ohm. The primary side slightly higher at between 22 Ohms and less than 5k Ohms, (on a dc meter).
If they comply, the transformer is OK.
Did you check the speaker without the transformer connected? Use a PP3 battery.

[Sea Chief]

Total silence from the speaker, ear right next to/ not even the tiniest hiss. Hmm..

[Jon Snell]

PP3 test? The speech coil should at least click.

[Sea Chief]

PP3 test? The speech coil should at least click.

Yup.. done this/ heard the expected prominent click, definite signs of life.

forgive me.. measure reistance across output speaker wires with amp on, or off?

thanks SC

[Jon Snell]

Amp off because there will be no loudspeaker load. Same for the primary.

[Sea Chief]

Amp off because there will be no loudspeaker load. Same for the primary.

Yup understood Jon. Ok across the two output speaker wires: I'm geting infinity symbol / zilch ohms, nothing at all.

thanks SC

[Sea Chief]

Jon Snell I do find a possibility. My detective work (probably accounts for little!).. bear with me:

There's a 'MUTE' switch on the back (tiny push in-out placcy thing) which is missing.. the button's awol/ seems snapped off, leaving a 5x5mm hole in the chassis on the back, & only the base of the switch left, with its 4 tiny legs in the pcb.

I've just 1/2 removed the small pcb its on to get a view (as I spotted a disconnected secondary OT wire, which as there seems no vacant terminal for it to go onto, seems likely correct as is: possibly a 16ohm tap-?). Also on this pcb, are junction posts from the OT to the spkr wires (all seem ok), 3x placcy pcb mounted jack RTN/ SEND etc etc.

So to me the awol switch, is "in the vicinity of things that can possibly interrupt the flow > out > to the spkr" (that's my logic!)

IE I wonder in its sheered off state, if it's now simply stuck in the MUTE position-?

[Jon Snell]

If it is muted, that would explain it.
Tapped secondary at either 4 or 16 Ohms I expect.

[Sea Chief]

If it is muted, that would explain it.
Tapped secondary at either 4 or 16 Ohms I expect.

Awol switch left arrow, identical present switch right arrow..

[Sea Chief]

Upside down pic sorry, this might be better..