No problem, Larry. I'm talking about the output stage- that's the only place where the timing is important. The input stage can come up as lazily as it wishes.
Thanks SY. One more question. I have fairly long heater wires to the tubes. I assume I should put a 0.01 ceramic cap from tube heater pin to chassis ground?
Yes, that's always a good idea. Much of the noise in heater lines is common-mode, and that's an effective way of killing it, so use a cap from each heater pin to ground.
Belt and suspenders needed (perhaps) here -- i've found some bulging electrolytic capacitors -- what i did not appreciate is that the line voltage here in NJ, while typically low in the summer months will go over 127, and for long periods of time -- over-voltage on the filter caps causes heating.
I now use a pair of 350V in series with load balancing resistors (220k).
I became aware of the voltage problem when I used to print B&W -- the color temperature of an incandescent bulb changes with current, and as it shifted red the exposure times got longer and longer!
I'm baaaccckk:
Well, it has occurred to me that I may have done a poor job selecting the OPT. I chose the Edcor CXPP21-MS-8.6K. 21W, push-pull tube output transformer for 8.6K Ohms to 4, 8 and 16 Ohms. Freq Resp 20-20k.
My speakers are Lynn Olsen's Ariels. He advises 4 ohm taps.
Well, I have been trying to figure out the effect of different impedances, and I THINK I ghouls have chosen a lower impedance. I have been trying to find info on the effect of this for a pentode, but not having any luck, and my brain is starting to hurt.
So, gurus, before I wire up these OPTs, are they OK to use? I don't mind losing a couple of watts.
Thanks again.
Doug
Well, it has occurred to me that I may have done a poor job selecting the OPT. I chose the Edcor CXPP21-MS-8.6K. 21W, push-pull tube output transformer for 8.6K Ohms to 4, 8 and 16 Ohms. Freq Resp 20-20k.
My speakers are Lynn Olsen's Ariels. He advises 4 ohm taps.
Well, I have been trying to figure out the effect of different impedances, and I THINK I ghouls have chosen a lower impedance. I have been trying to find info on the effect of this for a pentode, but not having any luck, and my brain is starting to hurt.
So, gurus, before I wire up these OPTs, are they OK to use? I don't mind losing a couple of watts.
Thanks again.
Doug
Uhhh... autocorrect seems to have replaced "chosen" with "ghouls."
I THINK I should have chosen a lower impedance.
I THINK I should have chosen a lower impedance.
That impedance is perfectly good. Don't sweat it though, your speakers' impedance probably varies 4 or 5 : 1, and that impedance is reflected back to the primary.
Well, I seem to be unable to make a Maida reg that regs. First, I am checking it out on the breadboard. I have a 120/240 volt transformer into a bridge, then 3k3 resistor followed by CLC (100u/9H/100u). This gives about 260 volts into a 25k dummy load (about 10 mA.)
When I connect the Maida I get the same voltage whether the pot is set to 100k or 0k, about (220 volts.) The TIP50 checks ok as a diode from pin to 2 and pin 2 to 3. The zener checks Ok. I have replaced the LM317.
Also, there is something funny about the pot. I put a new one in, and it goes from 100k to 0k. Then I put it under power, recheck the pot value (without adjusting it) and it reads 24k. Then it won't go above 75k in the circuit. I checked the pot I took out (because it was doing something similar) and it now goes from 100k to 0k. So, it acts weird in the circuit.
I have re-soldered everything several times. No regulation.
Just to have another pair of eyes on this, this is what I made on perfboard:
I am stumped.
When I connect the Maida I get the same voltage whether the pot is set to 100k or 0k, about (220 volts.) The TIP50 checks ok as a diode from pin to 2 and pin 2 to 3. The zener checks Ok. I have replaced the LM317.
Also, there is something funny about the pot. I put a new one in, and it goes from 100k to 0k. Then I put it under power, recheck the pot value (without adjusting it) and it reads 24k. Then it won't go above 75k in the circuit. I checked the pot I took out (because it was doing something similar) and it now goes from 100k to 0k. So, it acts weird in the circuit.
I have re-soldered everything several times. No regulation.
Just to have another pair of eyes on this, this is what I made on perfboard:
I am stumped.
OK, you have 260V as the raw supply? If so, that's your problem right there- you want a higher voltage than that. It has to be at least the regulator voltage plus the zener voltage plus some padding. 325-350V is more appropriate.
I was just testing it with the isolation TXR because it was handy and not quite so scary to play with. I have another for the actual build. Are you saying that this reg won't work at this voltage? I know it's too low for the actual screens.
Yes, at this point, you're under the dropout voltage. You can confirm this by lowering the voltage setting resistor and seeing if the regulator functions at a lower voltage. A 25k set resistor will give you a nominal output of 150-155V or so. Does that happen?
Is that the 56K? I can just use the real TXR and see what happens. I'll report back.
Thanks again SY.
Doug
Thanks again SY.
Doug