Seeking Valves

[Nowhere-Man]

Here they're called Ground Fault Circuit Interrupters (GFCI or just GFI) and I thought they tripped at 6mA though mains voltage here is of course only 120V.

A fair percentage of heat in a resistor exits through the leads.

Due to the fact there was some concern about my enveloping the series resistor in heat shrink, I changed this yesterday. I didn't want to come across as overly stubborn or dismissive of safety concerns. So, the body of the resistor is now exposed to air. I was playing it last night and some time after I switched off and carefully felt the body of the resistor. It wasn't really all that hot. The GEC is a very well designed, spacious radio and doesn't get hot like my Ultra does as there is more space. Anyway, that job is now taken care of.

I was a bit concerned about the HT feed to the smoothing can. I'd hate for that to ever come off. I wouldn't fancy as 270 volt wire recklessly swinging around at any time. I'll have to tie and anchor it.

Here is a good question you can all have a good think about:

In Chas Miller's Radio And Audio handbook, he devotes a few paragraphs to Silicon rectifiers. He basically recommends starting with a 1 K series resistor or even up to 2 K. The major point he makes is that the DC Ripple voltage that emerges at the silicon diode cathodes will be 1.414 the A.C. 260 volts. That would be 360 D.C. roughly.

Yesterday, after doing that little job, I decided to retest the voltage at the cathodes of the silicon diodes. I got 290 volts. The other side of my 220 Ohm smoothing resistor I got 280 odd volts. The output tube anode voltage ought to be about 280 so I was happy with the tests.

So, I can only assume the 2 caps I shunted across my diodes explain the fact I wasn't getting 360 volts at the cathode. It must be Chas was talking about a rectified ripple just using silicon diodes. For sure, I saw no signs of any high voltage D.C. so I was finally content to just smooth the current out a bit with a 220 Ohm series stopper.

According to theory the supply voltage of 260 A.C. ought to be out of phase with the voltages across the capacitors so that must account for the drop? I guess it would be interesting to do a test using just the diodes (but not on the radio).