Hi...in need of SY's expertise here...I just implemented your screen regulation circuit in my 6V6 Magnacumfrankenvox console pull-- to go along with the RLD bias that I installed last week. It came in at ~270vdc, but the current was a measly 40mA per pair(old weak original tubes that were run hard and put up wet). So, I yanked a couple of LED's per series string to try and gain some current...and succeeded somewhat(55mA per pair)...but the screen voltage dropped to 245vdc(B+ stayed the same).
I also swapped out the 100k varistor for a 120k fixed resistor, but that gained me little in the way of current.
Silly me, I would have thought increasing idle current would have lowered B+ and not have effected screen voltage. Is this to be expected? Am I shooting at a moving target, or are the tubes just too old and grey?
thanks,
Pete
I also swapped out the 100k varistor for a 120k fixed resistor, but that gained me little in the way of current.
Silly me, I would have thought increasing idle current would have lowered B+ and not have effected screen voltage. Is this to be expected? Am I shooting at a moving target, or are the tubes just too old and grey?
thanks,
Pete
I don't see why the screen voltage should drop- unless the reg isn't working. Can you throw a couple different resistor loads across it to see if it's regulating?
SY said:
Thanks, SY. I think you're right about the reg not regulating, but what doesn't compute is the B+ remaining relatively immune. If the screen supply sags significantly, why shouldn't the B+?
I'll look at it tomorrow...it's currently past wine-thirty tonight. I would appreciate it if you gave me a range of load values. I don't have a clue about screen resistances, loads, etc... I have enough problems coming to terms with triodes, much less "beam tetrodes" and pentodes.
thanks again,
pedro
Well, let's step the current from about 10 to 20 ma. Ohm's Law: at 275V out (nominal), R = V/I = 275/.020 = 13750. At 10 ma, R = 275/.010 = 27500. These can be varied for convenience.
So since we're just approximating, let's use a 27k to start. Connect it across the output (no tubes in place). Power up, note the voltage. Power down and let the caps discharge. Now parallel another 27k with the original one, power back on and note the voltage. If it's more than a volt or so different, you've got a regulator that isn't.
Pace Fran, you might want to verify the the pass transistor and/or the 317 aren't backwards (and now smoked). That's the most common error, at least in MY lab.
So since we're just approximating, let's use a 27k to start. Connect it across the output (no tubes in place). Power up, note the voltage. Power down and let the caps discharge. Now parallel another 27k with the original one, power back on and note the voltage. If it's more than a volt or so different, you've got a regulator that isn't.
Pace Fran, you might want to verify the the pass transistor and/or the 317 aren't backwards (and now smoked). That's the most common error, at least in MY lab.
SY, boy is it now well past wine thirty here!
But, earlier today I went out, found the last tip50 I had and air-wired the circuit together as per the schematic. No joy, no smoking or heated parts, just a constant low output of voltage (245V).
I don't know if its something I've done, if its in my wiring, can't figure that out. For now I think I will just stick in a 1K resistor to each screen from the B+ just to get the thing working. After that I can refine it.
It is possible that I have the pinout on the tip 50 wrong, I had the data sheet printed out, and marked my pin numbers from that. The LM317 - I looked that up last night and got the pins there.
The tip50 is NPN - is that what the PCB layout is set for? (MJE340 is the same). I might have some MJE243 here if they would fit in.
Fran
But, earlier today I went out, found the last tip50 I had and air-wired the circuit together as per the schematic. No joy, no smoking or heated parts, just a constant low output of voltage (245V).
I don't know if its something I've done, if its in my wiring, can't figure that out. For now I think I will just stick in a 1K resistor to each screen from the B+ just to get the thing working. After that I can refine it.
It is possible that I have the pinout on the tip 50 wrong, I had the data sheet printed out, and marked my pin numbers from that. The LM317 - I looked that up last night and got the pins there.
The tip50 is NPN - is that what the PCB layout is set for? (MJE340 is the same). I might have some MJE243 here if they would fit in.
Fran
I see no regulation...~10 volts between Vin and Vout on 317, but only 0.6volts between Vout and Vadj.
...it sags a good bit when the load is halved.
...it looks to be wired correctly...have 12 volt difference between Vout and the cathode of the zener, and the TIP50 has ~ 45V across it.
...not sure what's up.
...it sags a good bit when the load is halved.
...it looks to be wired correctly...have 12 volt difference between Vout and the cathode of the zener, and the TIP50 has ~ 45V across it.
...not sure what's up.
FWIW,
this is what I'm seeing as well.
56K load
11.8V between Vin and Vout on the 317
8V between Vout and adjust
12.1V between the zener cathode and Vout
TIP50 pin 1 to pin 2 has 44V, pin 2 to pin 3 has 44V
Adjust the pot fully out, that changes to 48V each side of the TIP 50.
*******************************
SY, I've been getting a lot of help from Shoog. One of my problems at least is that I have a bad transformer - the one I was using to give me the 350V. I had music, but also a buzz (not hum). Took the Tx out, quickly rewired the B+ to the output stage B+ and all buzz was gone and the amp got a lot louder. Absolutely quiet with no hum buzz etc at all. Without his help I never would have figured that one out (something about magnetic coupling).
One of my channels now has low voltage at the driver anode (55V, splitter cathode at 58, splitter anode at 260) and also has only 45mV across the EL84 bias 1R0.
The other channel is better at 91, 94, 250V respectively and 85mV for the bias - all seems to be fairly textbook. I know the 91-94V is a bit low, but thats coming off the 320V B+ feed for now.
******************
So theres the update. I have more work to do on this, try and find out why theres lower voltage at the driver anode (Resistance to B+ same both sides across the 135K).
Any ideas greatly welcomed!
Fran
this is what I'm seeing as well.
56K load
11.8V between Vin and Vout on the 317
8V between Vout and adjust
12.1V between the zener cathode and Vout
TIP50 pin 1 to pin 2 has 44V, pin 2 to pin 3 has 44V
Adjust the pot fully out, that changes to 48V each side of the TIP 50.
*******************************
SY, I've been getting a lot of help from Shoog. One of my problems at least is that I have a bad transformer - the one I was using to give me the 350V. I had music, but also a buzz (not hum). Took the Tx out, quickly rewired the B+ to the output stage B+ and all buzz was gone and the amp got a lot louder. Absolutely quiet with no hum buzz etc at all. Without his help I never would have figured that one out (something about magnetic coupling).
One of my channels now has low voltage at the driver anode (55V, splitter cathode at 58, splitter anode at 260) and also has only 45mV across the EL84 bias 1R0.
The other channel is better at 91, 94, 250V respectively and 85mV for the bias - all seems to be fairly textbook. I know the 91-94V is a bit low, but thats coming off the 320V B+ feed for now.
******************
So theres the update. I have more work to do on this, try and find out why theres lower voltage at the driver anode (Resistance to B+ same both sides across the 135K).
Any ideas greatly welcomed!
Fran
Looks like your TIP50 is either fried or bypassed somehow. Find anything to replace it with.
Shoog
Shoog
I have one or 2 MJE243 in a TO220 package. I am completely ignorant of any of these chips. Would it be an OK substitute?
Having said that is there much point in just sticking in a new transistor. This is a completely new circuit using all new components and obvously it fired as soon as it was turned on. Something else must be wrong.
Fran
EDIT: When I get home I'll trace back here the way I have it wired what goes to what pin etc....
Fran
Having said that is there much point in just sticking in a new transistor. This is a completely new circuit using all new components and obvously it fired as soon as it was turned on. Something else must be wrong.
Fran
EDIT: When I get home I'll trace back here the way I have it wired what goes to what pin etc....
Fran
OK,
I have found a fault in my wiring of the regulator.
I have left out the link above the 56K 3W to the junction of the 200R-180K. I've checked my wiring of the TIP50 and I think thats right.
Just cause I love the humiliation of everyone knowing if I did something asssways, could someone check for me that I have the 317 wired right:
The 47R from pin 3 of the tip50 goes to pin 3, anode of zener and 200R/screen out to pin 2 and pin 1 is linked to the 56K 3W/junction of 200R/180K.
I will fix the link and see if the transistor is toast.
Fran
I have found a fault in my wiring of the regulator.
I have left out the link above the 56K 3W to the junction of the 200R-180K. I've checked my wiring of the TIP50 and I think thats right.
Just cause I love the humiliation of everyone knowing if I did something asssways, could someone check for me that I have the 317 wired right:
The 47R from pin 3 of the tip50 goes to pin 3, anode of zener and 200R/screen out to pin 2 and pin 1 is linked to the 56K 3W/junction of 200R/180K.
I will fix the link and see if the transistor is toast.
Fran
I'd check the transistor before powering on. When they fail, it's usually a short from collector to emitter. But they do tend to short, not open.
mm, will do. When I checked it (powered) last night I had 44V from pins 2 to 3, which should be C to E. If it was a short there I would have seen no V.
more later,
Fran
more later,
Fran
Good news - I think its working!
Well, I didn't get to try different loads (working with 56K) but the range is adjustable now over a much wider range.
Got to run out now for a little, but will try more later!
Pedroskova, not sure if you might have something similar - your readings were similar to mine.
Fran
Well, I didn't get to try different loads (working with 56K) but the range is adjustable now over a much wider range.
Got to run out now for a little, but will try more later!
Pedroskova, not sure if you might have something similar - your readings were similar to mine.
Fran
And now there are 2 working regulators!
BTW, the TIP50 and 317 were OK - I reused them and they were ok.
So I don't know what exactly I did wrong on the PCB. I have a nagging suspicion that what I made/copied was a mirror of what it should have been or something.
Anyway, one step closer now. Bias remains low and voltages on one channel aren't what they should be, but its better than its been.
Fran
BTW, the TIP50 and 317 were OK - I reused them and they were ok.
So I don't know what exactly I did wrong on the PCB. I have a nagging suspicion that what I made/copied was a mirror of what it should have been or something.
Anyway, one step closer now. Bias remains low and voltages on one channel aren't what they should be, but its better than its been.
Fran
I'm very very late to this thread - how does this amp compare to a standard Leak Stereo 20? This circuit is perfect for the chassis, and a whole lot simpler! (I have a couple, might be interesting to make this amp)
Just wanted to let you both know that I think I have this thing licked! Biases up OK now (well maybe a little low, 70mV as opposed to the 80 that SY talked about). Voltage at the driver/phase splitter is OK, again, maybe a shade low at 100-105V or so at the driver anode. It all hangs together now.
Last night though was pretty black. One of the EL84 tubes burnt out. Had turned on the amp, it was on for about 10 mins and I was the other side of the shed. I heard some crackling, looked over, saw smoke! The valve glowed almost white inside - could see this through the hole in the chassis socket. Burnt the screen resistor too.
I was sure it was something I had done, but when I got the valve inside to have a better look, I found a crack in the bottom of it. In fairness the tubes have been in and out a heap of times and those russian sockets I used were very tight to start off with. TBH I don't think they're great - I would use something else in future I think.
So I ordered some more EL84, but it will be a week or more before they get here. In the meantime I think the amp is OK but needs some tidying up on the inside.
I (and no doubt all of you who have read my various blundering!) hope that this is nearing completion now.
Fran
Last night though was pretty black. One of the EL84 tubes burnt out. Had turned on the amp, it was on for about 10 mins and I was the other side of the shed. I heard some crackling, looked over, saw smoke! The valve glowed almost white inside - could see this through the hole in the chassis socket. Burnt the screen resistor too.
I was sure it was something I had done, but when I got the valve inside to have a better look, I found a crack in the bottom of it. In fairness the tubes have been in and out a heap of times and those russian sockets I used were very tight to start off with. TBH I don't think they're great - I would use something else in future I think.
So I ordered some more EL84, but it will be a week or more before they get here. In the meantime I think the amp is OK but needs some tidying up on the inside.
I (and no doubt all of you who have read my various blundering!) hope that this is nearing completion now.
Fran