Hi there,
Pretty simple beginner stuff here, but I don't really do much with transistor amps so I have never built a bipolar supply...
If I were to build something like this, delivering B+ and B+/2:
(...from the tubecad article here: https://www.tubecad.com/2012/05/blog0230.htm )
...in this illustration there are two resistors, I plan to use chokes but nonetheless - do the values of the chokes or resistors need to be identical?
If so, finding choke pairs is difficult. I would be motivated to build a stereo power supply if I'm going to purchase chokes. If the total demand on the power supply is about 300mA from both legs together, do both chokes need to be rated for that?
If the chokes do not need to be identical, the question of current remains. Can I have the top leg with a 200mA, as the output tubes take the larger voltage and the lion's share of the current, and a 100mA on the lower leg? The caps blocking DC make me think that this is the case... but as I looked up more examples of this kind of circuit, I kept finding that they had identical R values so... just gotta confirm...
Pretty simple beginner stuff here, but I don't really do much with transistor amps so I have never built a bipolar supply...
If I were to build something like this, delivering B+ and B+/2:
(...from the tubecad article here: https://www.tubecad.com/2012/05/blog0230.htm )
...in this illustration there are two resistors, I plan to use chokes but nonetheless - do the values of the chokes or resistors need to be identical?
If so, finding choke pairs is difficult. I would be motivated to build a stereo power supply if I'm going to purchase chokes. If the total demand on the power supply is about 300mA from both legs together, do both chokes need to be rated for that?
If the chokes do not need to be identical, the question of current remains. Can I have the top leg with a 200mA, as the output tubes take the larger voltage and the lion's share of the current, and a 100mA on the lower leg? The caps blocking DC make me think that this is the case... but as I looked up more examples of this kind of circuit, I kept finding that they had identical R values so... just gotta confirm...
I don't see any reason why both chokes would have to be identical.
I'm using this topology in a pair of 807 PP monoblocks (though with only SS rectifiers) to produce +300 and +150V from a 230VCT winding. The 300V rail is CLC filtered and the lower rail is CRC filtered, works like a charm.
I'm using this topology in a pair of 807 PP monoblocks (though with only SS rectifiers) to produce +300 and +150V from a 230VCT winding. The 300V rail is CLC filtered and the lower rail is CRC filtered, works like a charm.
Compare this with a standard bipolar power supply used in most solid state amps and you will see that it is exactly the same thing but grounded at the negative end instead of in the middle.
Ah, I figured so but had to check, cause that's where I'm at in terms of comprehension. This opens up alot of possibilities - while it's not what I'm working on now, my mind goes to... dual secondary step-up isolation transformers I.E. 0-110 : 0-220 & 0-220. There's probably a cheap 440 & 220 with massive current rating.... I wonder... OTL thoughts, those high-current regulator tubes like 6as7 or 6528. Could support a many with an isolation step up, if only they often had center-taps, so a dual secondary...
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Perhaps better to modify the schematic to show a capacitor from +600 to 0V, and another capacitor from +300V to 0V, as they are the two output voltages that have their own loading, and hence need their own output filter capacitor. The 600V and 300V loads are likely going to require significantly different current ratings, and are fed from different rectifier diode types, so won't be a 2:1 voltage ratio. That will also make it easier to choose chokes that are based on the separate current requirements of the 600V and the 300V rails.
If you place the stacked PSUs "lower" sections filter parts to the return line, the hum cancelling may occurs.
Pro the lower hum (and lower voltage capacitors needed), cons that the current of filter parts (choke, resistor) is the sum of stacked PSUs and "higher" PSU output impedance is higher.
Sample: my 801a PSE amp -one of many variations- stacked PSU.
It's the "two box" construction, the most critical "last C" is in the amplifier box.
Pro the lower hum (and lower voltage capacitors needed), cons that the current of filter parts (choke, resistor) is the sum of stacked PSUs and "higher" PSU output impedance is higher.
Sample: my 801a PSE amp -one of many variations- stacked PSU.
It's the "two box" construction, the most critical "last C" is in the amplifier box.
Ah, that's very interesting. Thanks for sharing all this slowly-accumulated knowledge, it's very valuable. Especially the last C in the "amp" part of the amp - that's one of those "special secret sauce" kinda tid-bits... I've so far just built monoblocks, and have been kinda worried about interconnects and finegeling with a high number of contacts... I want to use just 2 XLR or 2 4-pin cables rather than some kinda 7 or 10 pin, I don't trust myself to wire all that HV DC and AC heater stuff millimeters away from each other... lots of heat-shrink I guess. But I was thinking to do AC heaters on one cable, and HV DC on another. Idk what I'm doing really, just cautious from having builds I leave on the bench 4 months trying to track down 60 cycle hum...
Random side-rail: I've been trying to remember some "secret sauce" I read somewhere about dual-chokes in power supplies, and what special trick they allow you to do, that cannot be replicated with 2 seperate coils. Alot of searching "dual choke" hasn't yielded what I'm looking for. I've just spent a year and a half too busy to pick up a soldering iron, and am getting myself back to where I was in my exploration of these topics....
So the question: what's so special about dual chokes? There's a nice deal on one rated for 630/315mA on the fleabay right now, depending on series or parallel use, but I wasn't gonna pick it up if I can't remember what it's for! I think where I saw it was in a Thomas Mayer schematic, but searching his blog doesn't bring it up... just something else I'm wondering about that I didn't think deserved it's own thread. Maybe it does, but I don't wanna start a bunch of new threads all at once....
Random side-rail: I've been trying to remember some "secret sauce" I read somewhere about dual-chokes in power supplies, and what special trick they allow you to do, that cannot be replicated with 2 seperate coils. Alot of searching "dual choke" hasn't yielded what I'm looking for. I've just spent a year and a half too busy to pick up a soldering iron, and am getting myself back to where I was in my exploration of these topics....
So the question: what's so special about dual chokes? There's a nice deal on one rated for 630/315mA on the fleabay right now, depending on series or parallel use, but I wasn't gonna pick it up if I can't remember what it's for! I think where I saw it was in a Thomas Mayer schematic, but searching his blog doesn't bring it up... just something else I'm wondering about that I didn't think deserved it's own thread. Maybe it does, but I don't wanna start a bunch of new threads all at once....
Oh, and also, back on the track of my first post, with this 2-rail supply setup, I've been reading alot of tubecad and got to this a few days ago:
https://www.tubecad.com/articles_2001/Accordion_Amplifier/Accordion_Amplifier.pdf
And I'm thinkin' about doing something like this:
Some values unlabeled, ballpark voltages, just sketching on a short amount a time before I have to clean the kitchen and get to cooking....
I don't know, the one super-tube could be enough to drive it, it could not. I don't have a mastery of spice or the time. But, if it isn't enough I'll find out. Looks like enough on the basis of my small experience, if anything I'd like to add a k-follower, and might do it with another 8608 cause I got the current for anything on the iso transformer... and cause I was reading this and am curious:
https://www.tubecad.com/2007/04/blog0104.htm
I have time to read stuff on my phone - in between work stuff. But you know, less time at a work bench...
https://www.tubecad.com/articles_2001/Accordion_Amplifier/Accordion_Amplifier.pdf
And I'm thinkin' about doing something like this:
Some values unlabeled, ballpark voltages, just sketching on a short amount a time before I have to clean the kitchen and get to cooking....
I don't know, the one super-tube could be enough to drive it, it could not. I don't have a mastery of spice or the time. But, if it isn't enough I'll find out. Looks like enough on the basis of my small experience, if anything I'd like to add a k-follower, and might do it with another 8608 cause I got the current for anything on the iso transformer... and cause I was reading this and am curious:
https://www.tubecad.com/2007/04/blog0104.htm
I have time to read stuff on my phone - in between work stuff. But you know, less time at a work bench...
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Hmm. I'm no expert on the Accordion Amp but I think you need to pay attention to what each tube's input signal is referenced to, ie the cathodes rather than to ground. The schematic on page 7 in your link shows ecatly what I mean, note how the upper secondary winding of the interstage transformer is referenced to the upper tubes cathode.
BTW, I just got this big mains transformer with a 180-0-180V 0,5A secondary that I'm planning to use in a small transmitter tube SET that will require a bit over 400V for the input and output stages and around half of that for the cathode/source follower driver stage. I'm planning to use solid state diodes as rectifiers, possibly with a damper diode in series with the low voltage rail to provide a delayed startup for the driver stage in case I'll be using Mosfet drivers.
And yes, I bought two different chokes for the rails, one 130mA for the high voltage and a 100mA for the low voltage.
BTW, I just got this big mains transformer with a 180-0-180V 0,5A secondary that I'm planning to use in a small transmitter tube SET that will require a bit over 400V for the input and output stages and around half of that for the cathode/source follower driver stage. I'm planning to use solid state diodes as rectifiers, possibly with a damper diode in series with the low voltage rail to provide a delayed startup for the driver stage in case I'll be using Mosfet drivers.
And yes, I bought two different chokes for the rails, one 130mA for the high voltage and a 100mA for the low voltage.
It might be hard to see, but I did draw in a lead to the top grid marked "B sub g" to indicate a grid bias voltage, would be about 210v, exactly what I'm going for on the 8608/e55l (B sub 2) so I figured I'd just use another RC off the B+. I coulda wrote "B sub 3" or "grid bias" but, anyways...
I had originally drawn in a self-bias resistor but switched for grid bias when I realized the voltage was exactly what I want on the B+. On the lower tube, or half tube, lower valve, it is just cathode bias.
I really don't understand everything that is going on with the interstage transformer scheme you are talking about though. That's actually going over my head (surprising I know). This:
But he does eventually present an AC-coupled version that seems to be pretty similar to what I'm thinking, on a certain level:
He uses grid bias both top & bottom, but on top it is just right off the B+ rail as I was thinking to do. I don't know if it's important if the bottom is cathode and the top grid bias - I figured as long as the bias point was the same, we were in business. But! If I needed to grid bias the bottom, it would be easy to do -21v with batteries, rechargable lithium cells come in 7v. I'd need to look closely at some battery bias examples as I haven't done it before, but I grasp the concept at least....
And to your new transformer - that's awesome, big current low voltage is hard to find, which is why I'm thinking about isolation transformers. It's more confirmation that I'm at least roughly on the right track, too, with this kinda supply scheme.
I've used damper diodes on one amp, 6by5g dual diodes. But I recently got a box of mixed TV tubes on Craigslist that had 13 6au4 tubes so I think I'll be using those soon. I may just not use rectifier tubes anymore - they're expensive and probably lower lifespan.
I had originally drawn in a self-bias resistor but switched for grid bias when I realized the voltage was exactly what I want on the B+. On the lower tube, or half tube, lower valve, it is just cathode bias.
I really don't understand everything that is going on with the interstage transformer scheme you are talking about though. That's actually going over my head (surprising I know). This:
But he does eventually present an AC-coupled version that seems to be pretty similar to what I'm thinking, on a certain level:
He uses grid bias both top & bottom, but on top it is just right off the B+ rail as I was thinking to do. I don't know if it's important if the bottom is cathode and the top grid bias - I figured as long as the bias point was the same, we were in business. But! If I needed to grid bias the bottom, it would be easy to do -21v with batteries, rechargable lithium cells come in 7v. I'd need to look closely at some battery bias examples as I haven't done it before, but I grasp the concept at least....
And to your new transformer - that's awesome, big current low voltage is hard to find, which is why I'm thinking about isolation transformers. It's more confirmation that I'm at least roughly on the right track, too, with this kinda supply scheme.
I've used damper diodes on one amp, 6by5g dual diodes. But I recently got a box of mixed TV tubes on Craigslist that had 13 6au4 tubes so I think I'll be using those soon. I may just not use rectifier tubes anymore - they're expensive and probably lower lifespan.