[AMRadio] Type 83 in TV7 replacement

[Donald Chester]

On 6/2/2020 6:18 PM, CL in NC via AMRadio wrote:
> Does anybody have info on replacing the 83 in a TV7 with diodes?  What size dropping resistor is needed to maintain calibration?  Is there another tube rectifier that will do the job?

Why replace the 83 instead of just getting another tube?  Last time I checked they were still widely available (although I haven't had to buy a replacement tube for anything in several years, so if the supply has dried up I wouldn't know).  I  recall seeing plenty of them in the flea market last time I was at Dayton a couple of years ago.

The 83 is a MV tube, so the voltage drop across each diode section is constant, about 15 volts, regardless of current.  A silicon power supply diode usually runs about .75 volts constant forward drop as I recall.  Double-check the RCA tube manual to see what the exact voltage drop is, then for each half of the 83, wire enough 600 or 1000v PIV 1 amp diodes in series to bring the total forward voltage drop up to be approximately the same as the 83.  Last time I checked, 600v 1A diodes were cheap - about 20¢ each, so even 20 of them in series, or 40 in all would still run only about 8 bucks, probably about the same as a new 83 from one of the on-line tube vendors.

Don k4kyv