18-12-2017, 12:03 PM
Had a bit of a snafu with the tfmr I wound. After wiring up the LH CH PSU I found the heater DC supply doing odd things. The OP would drop to 1.1v. I found the cause, the crowbar protection circuit that should fire an SCR at 13v was on. It's exactly the same as it's twin apart from the source of C106D SCR's. Farnell didn't have any so I got 5 off ebay. Needs more investigation.
As mentioned I screwed up when I wound the tfmr, I wound the winding for 11v, that should have given me 15.4v DC prior to the LM317 minus a volt for diode drop. I'm actually getting 13.7v DC. This isn't enough headroom; with a load, IE valves, this drops to 10v ish. Bummer.
After some head scratching I found a little tfmr with secs of 16.3V (19v measured) which I just might be able to squeeze in. However I am going to see if I can pinch a bit of current off the 18.9v AC EL34 heater windings. This should be ok, though not ideal, as they are massively over wound.
To add to the fun and games the phase splitter isn't working. Still it's nice to be doing some electronics after fettling the case and metal bashing for a few weeks.
Lastly, as I have no OPT, could I use two big arse resistors as loads for the EL34 OP stage? The OPT pri Z should be 1900 ohms, could I use to girt big 1k resistors as temporary loads?
Andy.
As mentioned I screwed up when I wound the tfmr, I wound the winding for 11v, that should have given me 15.4v DC prior to the LM317 minus a volt for diode drop. I'm actually getting 13.7v DC. This isn't enough headroom; with a load, IE valves, this drops to 10v ish. Bummer.
After some head scratching I found a little tfmr with secs of 16.3V (19v measured) which I just might be able to squeeze in. However I am going to see if I can pinch a bit of current off the 18.9v AC EL34 heater windings. This should be ok, though not ideal, as they are massively over wound.
To add to the fun and games the phase splitter isn't working. Still it's nice to be doing some electronics after fettling the case and metal bashing for a few weeks.
Lastly, as I have no OPT, could I use two big arse resistors as loads for the EL34 OP stage? The OPT pri Z should be 1900 ohms, could I use to girt big 1k resistors as temporary loads?
Andy.
