Before I Drive Myself Nuts!!

[Yorkie]

Hi All,
Back on the VHF90 (yawn!!).

All wired up, valves in, connected to variac. Start with 25v across the Variac terminals to the switch (off) 25v measured across the mains leads from the switch to the variac. I've turned the radio switch on and then measures 6v at variac terminals and 6v across the switch. Have I got a problem (short) if so, have I wired the switch correctly??

What next?

Regards

Rob

Don't need a variac Rob - I know they have their advocates but I'm not sure when or why this variac malarkey took a hold. About the only reason I can think of for which I'd consider using a variac would be to reform smoothing caps by bringing the voltage up slowly over time, but I've got a cap reformer anyway, and personally, I'd only do that with the valves removed and with the variac connected across the caps - not via the mains lead (which would be useless in a set with valves removed as there'd be no power from the rectifier to the smoothing caps).

I'm not even sure that valves take kindly to being run at below their correct voltage via a variac.

Better I think to run the radio through a lamp limiter - if there are any problems, the bulb lights up - not the set. If the bulb doesn't light or glows only dimly, and the set seems to work OK, switch the mains directly to the set, by-passing the lamp limiter, at which point the volume might increase slightly.

If the set works OK, and you want some reassurance that all is as it should be, you can put a meter on the DC voltage range across the resistor between the smoothing/reservoir caps to see what voltage is being dropped, then if you divide the resistance of that resistor into that voltage, you'll reveal what HT current is being drawn by the set, (Ohm's Law: I = V/R), and whether it is what you'd expect it to be. Then you can carry out voltage checks compared to the circuit to see if they look about right.

Good luck with it.