12-07-2013, 07:28 AM
Thanks for reading my post and for responding so quickly Gary - it's so long since I used to buy carbon rod resistors back in the 50s that I've lost touch with their wattage ratings and I was just guessing at the likely wattage. You're right of course about working out the requirements from the circuit. I'll fit a couple of parallel resistors temporarily to bring the set onto spec, check the voltage drop and hence the current being drawn, then calculate the wattage from that. The 2K7 one is for HT smoothing and carries the full DC HT. The smaller of the two is R5 on the Trader Sheet 1133 and is in the screen grid potential divider to V1 & V2. I might find when I power the set up, that the screen voltage at that point isn't far off the required 80V - 15
% high isn't too far off.
The set did work before doing anything at it, though volume was low. I haven't yet tested the valves so I won't know what state they're in. The resistor in anode feed to V3 (R11 on the Trader Sheet) should be 680K and has drifted up to 1M1 (62% high), so that, coupled with the high HT smoothing resistor won't have helped matters. (I've replace R11). As might be expected, the cathode by-pass cap (25uF 25V has gone to heaven, but the smoother/reservoir caps are fine. I don't normally stuff caps, but modern 15uF 25V caps are so tiny that they look a bit silly and it's only a few minutes job to stuff the can of the original cap so I often do that.
As I'll be passing this set on, I don't want to do so unless it's safe and working to spec. (I'm passing it on - not palming it off!).
% high isn't too far off.
The set did work before doing anything at it, though volume was low. I haven't yet tested the valves so I won't know what state they're in. The resistor in anode feed to V3 (R11 on the Trader Sheet) should be 680K and has drifted up to 1M1 (62% high), so that, coupled with the high HT smoothing resistor won't have helped matters. (I've replace R11). As might be expected, the cathode by-pass cap (25uF 25V has gone to heaven, but the smoother/reservoir caps are fine. I don't normally stuff caps, but modern 15uF 25V caps are so tiny that they look a bit silly and it's only a few minutes job to stuff the can of the original cap so I often do that.
As I'll be passing this set on, I don't want to do so unless it's safe and working to spec. (I'm passing it on - not palming it off!).
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'







