Using a silicon diode rectifier instead of an AZ31 valve

[AlanBeckett]

I'd be inclined to put a Resistor across it to avoid it floating, say 1k.

Alan

[Old Sparky]

I'd be inclined to put a Resistor across it to avoid it floating, say 1k.

Alan

I fitted an 820 ohm 0.5w resistor across the 4v winding tags on the mains Tx, which, according to my calculations, means ca 5mA is drawn by this resistor. 3.5vAC is measured across the resistor with my DMM. Is it likely that any (long term) problem will be caused by leaving the AZ31 plugged in (it's heater is o/c), with the rectifier diode & series resistor wired to the valve base so that the valve's anodes & cathode are, in effect, common with those of the 1N4007?

[AlanBeckett]

Sounds good.

Alan

[Old Sparky]

I've now completed the repair, and reinstalled the chassis into it's cabinet. The radio is working very well on all 3 wavebands , although the frame aerial is prone to picking up the digital 'hash' so prevalent these days, which wipes out all but the strongest signals. AFAIK, there's no real cure for that!
Here are a few pictures taken after my repairs!

[Nick]

I've now completed the repair, and reinstalled the chassis into it's cabinet. The radio is working very well on all 3 wavebands , although the frame aerial is prone to picking up the digital 'hash' so prevalent these days, which wipes out all but the strongest signals. AFAIK, there's no real cure for that!

Put the equipment in a Faraday Cage

[AlanBeckett]

That's a very neat layout under the Chassis.
I wish they were all like that.
Well done.

Alan

[Old Sparky]

That's a very neat layout under the Chassis.
I wish they were all like that.
Well done.

Alan

Most of it is as Roberts made it, Alan. As you see, I've just replaced all the waxies on those tagboards, plus a couple of resistors & electrolytics, then fitted new Volume & Tone Controls, Reservoir & Smoothing Caps, a replacement o/p transformer & LF smoothing choke. The 1N4007, surge limiting resistor, and shunt capacitor are wired on the rectifier v/holder pins. Altogether, despite one wax cap. tucked into a hard to get at place behind the w/c switch bracket, the P5A has been quite an easy radio on which to work

[Nick]

Very neat job - nice to have an "open" chassis with access. Great result.

[Alan Douglas]

I'm sure I remember reading a history of Roberts but I don't think I bought the book in the 1980s; does anyone know of a Bulletin article or something?

[Old Sparky]

Very neat job - nice to have an "open" chassis with access. Great result.

Maybe this thread should be in the 'Restoration Stories' section, given that, over time, I've described what I've done to get the P5A working again!