[luvdunhill]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif it is worth note that a well designed PSU for a tube amp dosnt need anywhere near the capacitance of a SS amp. experience says that the QUALITY of the capacitors is almost more important than the capacitance.

it's not quite that simple, as the PSU for tube amps (usually) involve chokes

 

[spritzer]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif it's not quite that simple, as the PSU for tube amps (usually) involve chokes

Very true and tube amps often have tube rectifiers and they can't handle large capacitors.

 

[nikongod]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif it's not quite that simple, as the PSU for tube amps (usually) involve chokes

but this thread isnt about inductors, its about caps and which ones sound good.

perhaps i got ahead of myself, and assumed that the design would have at least one choke in it.

even using a resistor to smooth ripple in the PSU (yuck), I would still not go overboard with capacitance.

something nice with using less capacatance (minimum sufficient amount) is that the amp is more likely to dump ALL of the HV before the tubes cool.

 

[Budgie]

A tube power supply may or may not have an inductor. It is a design choice not a must.
With a tube circuit's high voltage it doesn't take a large cap to provide filtering and supply duty.
The film in oil caps are much faster at current delivery then a "lytic" type.
They are well worth trying, and can be purchased relatively cheaply.

 

[luvdunhill]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif perhaps i got ahead of myself, and assumed that the design would have at least one choke in it

Just trying to keep you honest

Budgie:

true, but capacitance needs to be proportional to the current demands of the circuit. For example, if you have 10A current draw, you best be thinking high capacity, not quality.

 

[Budgie]

I agree, and thats were the good news is.

A tube circuit is a high voltage / low current device. To make them drive current hungry devices, like speakers, a transformer is used to convert high voltage/ low current AC to low voltage/ high current AC that speakers work with. Ohms law will give us a quick dirty example- 300 volts at 10 amps is 3 kilowatts. 300 volts at one tenth of an amp is 30 watts.

We are kinda hi-jacking this thread, so back to the subject at hand-

The question was regarding electrostatic phones and they work at very low currents but high DC voltages for the polarizing supplies.

 

[Budgie]

duplicate - my bad

 

[Pars]

Hope this doesn't further derail this thread (fat chance

), but I figured when all you toobies was gathered around, I'd toss this out for your input.

This is the schematic for the PSU of my Counterpoint SA5.1 preamp. THis schematic is actually for the SA5... differences in the heater supply (mine uses 6V heaters, LM350K regulator, etc.). Note that this PSU uses an EZ81 rectifier, but only has a CRC filter (it feeds a HV regulator section comprising a couple of tubes and additional caps, etc. in the main pre chassis). Space in the PSU is very limited. Also note that for the CRC filter, the first cap is 100uf, which is above the max. datasheet value of 50uf.

I've tried modeling this in Duncan's PSUDII to see what improvements I could make (maybe do an RCRC?). I've dropped the first cap to 47uf/500V (Cerafine), and the 2nd in mine is a 100uf/500V Cerafine.

Any suggestions for how I could improve this with the space constraints? Or just live with it as it is?

 

[spritzer]

Quote:

Originally Posted by Budgie /img/forum/go_quote.gif The question was regarding electrostatic phones and they work at very low currents but high DC voltages for the polarizing supplies.

They do need quite a bit of current in the LF and HF for some of the models but as a general rule the ESP amps are mostly about voltage swing.

 

[Budgie]

Pars, No easy upgrade that I can think of that does not take up some space.

(edit)- Weird to find a 100mfd cap on the rectifier. I would think that stressed the tube, but maybe the recommended range has a wide safety margin. Can you sneak in another cap in parallel with the second cap to get the total up? The resistor should soften the inrush enough to keep the rectifier happy.

(edit#2) I guess the rule should for power supply filtering should be "Give it a try (within limits) and see what you like".

 

[Pars]

Quote:

Originally Posted by Budgie /img/forum/go_quote.gif Pars, No easy upgrade that I can think of that does not take up some space. (edit)- Weird to find a 100mfd cap on the rectifier. I would think that stressed the tube, but maybe the recommended range has a wide safety margin. Can you sneak in another cap in parallel with the second cap to get the total up? The resistor should soften the inrush enough to keep the rectifier happy. (edit#2) I guess the rule should for power supply filtering should be "Give it a try (within limits) and see what you like".

Yeah, the 100uf cap (1st one) would seem to be stressful, but when modeling this in PSUDII, it doesn't go overcurrent by much (I haven't run it for quite awhile now), and it is only right at startup. The ripple looks much lower with the stock configuration that anything I have been able to do with a 47uf first cap and CRC, RCRC, etc.

When you guys talk about chokes in tube PSUs, you are talking henries (not uH), right? And I presume these things are about the size of transformers? Or can you get some that are physically small(er)?

I went into it a bit here, where you can see what the space issue looks like if you care to.
diyAudio Forums - counterpoint Sa 5.1

Thanks,

Chris

 

[Budgie]

Yes, you need fairly large inductors to get much advantage. Size of a power transformer.

Looks like the original design was a well thought out compromise. Have you had any problems with the rect. tubes failing?

I guess the next option would be an outboard power supply. More stuff to squeeze into the stereo rack, though. And another cable to add to the mix.

 

[luvdunhill]

Quote:

Originally Posted by Budgie /img/forum/go_quote.gif The question was regarding electrostatic phones and they work at very low currents but high DC voltages for the polarizing supplies.

Okay, sure the headphones might work at low-ish currents, however the currents in the amp itself are another story! This depends how far into class A you wanna go

 

[Pars]

Quote:

Originally Posted by Budgie /img/forum/go_quote.gif Yes, you need fairly large inductors to get much advantage. Size of a power transformer. Looks like the original design was a well thought out compromise. Have you had any problems with the rect. tubes failing? I guess the next option would be an outboard power supply. More stuff to squeeze into the stereo rack, though. And another cable to add to the mix.

Nope, no problems with rect. tubes that I'm aware of. This is an outboard supply. I suppose I could build something in a bigger chassis if I wanted to.

My main impetus was in removing the original 100uf caps which were bad, I burned the PCB up a bit (well quite a bit) and had layed a new one out. I figured if I wanted to change anything, now would be the time...

 

[spritzer]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif Okay, sure the headphones might work at low-ish currents, however the currents in the amp itself are another story! This depends how far into class A you wanna go