Hi Surav,
Working backwards from the filaments;
2.5V for filament +
0.25V (roughly) for common mode choke +
1.25V for current set resistor +
1.4V for current reg chip +
1.4V for voltage reg chip* +
whatever loss in R in pi filter if used.
* the voltage reg will adjust to take more voltage across itself, but with that comes heat, and I prefer to keep SS devices as cool as possible for longevity, so with a decent heatsink, it's not critical that 1.4V be across the chip, that's just the minimum. If you still have too mch voltage another CMC and small cap before the fil wouldn't hurt. they're about $2.
Get the adjustable in whatever package suits you. The TO220 should be fine, but mount each on a seperate sink, or isolate them well as the tab is also the output.
Working backwards from the filaments;
2.5V for filament +
0.25V (roughly) for common mode choke +
1.25V for current set resistor +
1.4V for current reg chip +
1.4V for voltage reg chip* +
whatever loss in R in pi filter if used.
* the voltage reg will adjust to take more voltage across itself, but with that comes heat, and I prefer to keep SS devices as cool as possible for longevity, so with a decent heatsink, it's not critical that 1.4V be across the chip, that's just the minimum. If you still have too mch voltage another CMC and small cap before the fil wouldn't hurt. they're about $2.
Get the adjustable in whatever package suits you. The TO220 should be fine, but mount each on a seperate sink, or isolate them well as the tab is also the output.
Thanks, I'll try that. My bleeder's on my first cap, which puts it before the choke. I think mine is a 5W resistor, don't remember the value any more... 25K or 220K, I think.
Why does putting a bleeder after the choke quiet it down? And I'm assuming I should be able to just move my existing resistor, I don't need multiple bleeders in there do I?
Brett, thanks a ton. I spent some time on the Digikey website last night to get an idea of what I need. I think I can get some of the stuff from a local surplus store, but I'll probably have to order some online.
Common mode chokes - what kind of specs am I looking for? And do I need 2 per 2A3, or do they come with dual windings for both legs of the filament circuit?
Hi Saurav,
Don't know really. Something about critical inductance. A 5H choke may actually have a 1H inductance at 10mA but 5H at 100mA
5W it ample for a 220K resistor..but on the small side for a 25k resistor..
Yes, that's right. Just move your existing resistor. Before soldering it in just try it with some clip leads..and experiment with the value of the resistor...to create a balance between noise and a lower b+.
Cheers,
Bas
Don't know really. Something about critical inductance. A 5H choke may actually have a 1H inductance at 10mA but 5H at 100mA
5W it ample for a 220K resistor..but on the small side for a 25k resistor..
Yes, that's right. Just move your existing resistor. Before soldering it in just try it with some clip leads..and experiment with the value of the resistor...to create a balance between noise and a lower b+.
Cheers,
Bas
I see. My choke is rated for 200mA, and I should be drawing ~120mA through it (2 2A3s, 26SL7s), so it shouldn't be that far off. Still, certainly worth a try.
True. I know the first resistor I put in there got a little hotter than I was comfortable with, so I changed it, and now I don't remember what I used.
True. I know the first resistor I put in there got a little hotter than I was comfortable with, so I changed it, and now I don't remember what I used.
Saurav said:
For Aussies, there'll only ever be one true 'little Aussie bleeder'.
An externally hosted image should be here but it was not working when we last tested it.
Most often they're a small torroid core about 25mm in diameter with two windings on them. Connect each winding in series with a filament pin with the correct polarity.
They only have two parameters, current and inductance. You'll want the highest inductance, usually 20mH or so and at least 2.5A current rating.
Saurav said:
I've never found it to. The bleeder is to ensure enough current is always drawn through the choke for a choke I/p filter to operate correctly. If you have too much current being pulled through the choke, the laminations may start to buzz in poor quality units (even if used under rating) especially if they're used in an LC and with a high voltage supply. Here a small cap (<2u) at the input can help or use chokes specified for choke input, ie Lundahls or some of the Hammond 193 series.
Hello Saurav,
I do have the same kind of problem with a choke-input for a monkey power-amp. I wanted to have achoke-input but the transformer didn't give enough tension. Adding 1 microfahrad directly after the 5r4gyb did give the right tension with a test with the total current that will be drawn ( load by 10000 Ohm ) But when you double the resistance to the value that will be the actual bleeder in the future the tension will go up about 70 volts. Of corese it will go down when it will also be charged by the amplifier itself. But i think by changing the power transformer to one that will give a higher tension, you can reduce the 1 microfahrad and i think the differences in tension with several loads will be minimalisized. First i will see how it sounds and then i will try to get some new transformers. Ed
I do have the same kind of problem with a choke-input for a monkey power-amp. I wanted to have achoke-input but the transformer didn't give enough tension. Adding 1 microfahrad directly after the 5r4gyb did give the right tension with a test with the total current that will be drawn ( load by 10000 Ohm ) But when you double the resistance to the value that will be the actual bleeder in the future the tension will go up about 70 volts. Of corese it will go down when it will also be charged by the amplifier itself. But i think by changing the power transformer to one that will give a higher tension, you can reduce the 1 microfahrad and i think the differences in tension with several loads will be minimalisized. First i will see how it sounds and then i will try to get some new transformers. Ed
Hi Brett,
Here's my PSU, posted earlier in this thread: http://www.diyaudio.com/forums/showthread.php?postid=209793#post209793. I have a 3uF cap after the rectifier, and the choke is a Hammond 193J, rated for 200mA.
I'm not 100% sure it's the choke that's buzzing. I tried putting my ear close to the amp last night (without burning myself), and I cannot figure out which piece of iron is buzzing. I touched all of the transformers (power, choke, 2 filaments), and none of them seems to be vibrating more than the others.
Here's my PSU, posted earlier in this thread: http://www.diyaudio.com/forums/showthread.php?postid=209793#post209793. I have a 3uF cap after the rectifier, and the choke is a Hammond 193J, rated for 200mA.
I'm not 100% sure it's the choke that's buzzing. I tried putting my ear close to the amp last night (without burning myself), and I cannot figure out which piece of iron is buzzing. I touched all of the transformers (power, choke, 2 filaments), and none of them seems to be vibrating more than the others.
Saurav said:
Hold a screwdriver on the P/T and the choke, with the other end resting on your ear. The loudest on is the problem child.
If that's inconclusive, unmount the choke from your chassis, and solder some extension leads in if neccessary, and move it so it's sitting on something else, and try again.
I'm assuming here that you'll take all safety precautions and use an insulated screwdriver to avoid any home ECT.
More tomorrow.
I'll be sure to leave my wife written instructions to send you my remains 
Thanks, that's a good idea. I considered buying a stethoscope, but I think my wife still holds on to the hope that I have a few shreds of sanity still remaining somewhere inside me. If she saw me listening to my amp with a stethoscope, that would probably be the last straw.
Thanks, that's a good idea. I considered buying a stethoscope, but I think my wife still holds on to the hope that I have a few shreds of sanity still remaining somewhere inside me. If she saw me listening to my amp with a stethoscope, that would probably be the last straw.
OK, I tried the screwdriver thing, and I'm still alive to report on it. I think the power transformer is buzzing more than the choke, but the choke seems to be buzzing a bit too. My filament transformers are under the hood, and I didn't try the screwdriver thing on those. Maybe this weekend.
Should I just raise the iron on rubber grommets and use metal washers/rings for the grounding? I'm assuming that the chassis is contributing to the audibility of the buzz.
Should I just raise the iron on rubber grommets and use metal washers/rings for the grounding? I'm assuming that the chassis is contributing to the audibility of the buzz.
OK, I made some changes last night. Loosening up some mounting screws definitely identified the PS transformer as the buzzer, and not the choke. The choke is vibrating slightly because I can just about feel it, but I can't hear it without the screwdriver. I tried moving the bleeder, and it didn't make any noticable difference, probably because my amp is drawing enough current through the choke as is. Anyway, I mounted the PS transformer on grommets, making sure that I still had continuity between the frame and the chassis (scraped off paint, used metal washers). Things seem a lot quieter now.
I also took the advice someone had given me earlier and added a pot to the voltage divider for the 6SL7 heater. Now the heater voltage is nicely centered between the two cathodes, instead of being at the limit for one of the cathodes. I also added the caps from B+ to the 2A3 cathodes, and changed the output transformer to 5K (again based on someone's advice here). And after all that, I listened for a couple of songs and then went off to play video games. So it sounds better, but I'll have to listen some more
Thanks for all the help and advice. The regulated DC 2A3 filaments are next up on my lest.
I also took the advice someone had given me earlier and added a pot to the voltage divider for the 6SL7 heater. Now the heater voltage is nicely centered between the two cathodes, instead of being at the limit for one of the cathodes. I also added the caps from B+ to the 2A3 cathodes, and changed the output transformer to 5K (again based on someone's advice here). And after all that, I listened for a couple of songs and then went off to play video games. So it sounds better, but I'll have to listen some more
Thanks for all the help and advice. The regulated DC 2A3 filaments are next up on my lest.
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