Decoupling...

[Mike H]

Oh, Mike - I thought you were going to solve the puzzle for us ?

He's probably giving it some deep thought first.

First, during and after, still have no answer to the orginal question.

[RhythMick]

Foot in mouth time. I think I see what is being said. Say using my amp as an example, at idle the HT is 1000V @ 180mA = 180W. At say a power out of 30W the HT delivers the 180W plus 30W so the HT bounces around to the dynamics of the music not so much to the frequency changes but a little as the load is non-linear as are the valves and all other things coz nothing is perfect. Class A amps do increase the HT current draw depending on power out. Prolly explains why low Z rectifiers have an effect esp on dynamics and bass, IME anyways.

As the HT bounces around to the dynamics not so much frequency variation, then maybe caps in the HT are not so "critical" as say a SE amp where usually the AC signal is coupled to the OPT via the HT cap.

And so the idea is a seperate front end power supply is still advantagous coz HT still bouncy.

I'll be interested to try this but I just stuck my 10H chokes in the bias supply ... hmmm ...

Cheers,
Stephen

I have a box full of chokes I'm not using. Literally. Your welcome to borrow them.

[IslandPink]

Foot in mouth time. I think I see what is being said. Say using my amp as an example, at idle the HT is 1000V @ 180mA = 180W. At say a power out of 30W the HT delivers the 180W plus 30W so the HT bounces around to the dynamics of the music not so much to the frequency changes but a little as the load is non-linear as are the valves and all other things coz nothing is perfect.

I'm relieved this does actual happen - but disappointed we haven't found a source of CO2-free energy .

[izzy wizzy]

I have a box full of chokes I'm not using. Literally. Your welcome to borrow them.

Thanks. Just had a rummage in the shed and have a tx, choke for choke input and mercury to give it a go in one channel to see if there's something to go forward with. This has the advantage of getting rid of some heat; the decoupling resistors disappate about 50W.

Cheers,
Stephen

[RhythMick]

Ok but if you decide you'd like the chokes let me know. I have audio note probably around 20 or so sat doing nothing.

[Enzoastro]

Hi I'm new on here, and far from an expert but I was under the impression that the energy going into the speakers (the 30w above) in a classA stage comes from a reduction in dissipated heat in the anode rather than more current drawn from the ht?

Enzo

[Nick]

Hi I'm new on here, and far from an expert but I was under the impression that the energy going into the speakers (the 30w above) in a classA stage comes from a reduction in dissipated heat in the anode rather than more current drawn from the ht?

Enzo

Yes, agreed, but then something needs to heat the anode up again.

[Enzoastro]

I'm afraid I'm outside my knowledge here!
A stab in the dark,
In a class A SET stage.
If you used a regulated for V and I power supply I'd suspect you'd if anything get an increase in power out due to its stiffness. So no extra power going in, to power the load or recoup lost heat into the anode. I'd suspect over a cycle the power drawn from the power supply would be ~equal at idle and up to the point where it started producing non trivial levels of H2.
That's my gut feeling, based on nothing at all!
Clearly during that cycle there are big fluctuations in the current draw though. Not arguing that the decoupling methods discussed wouldn't produce benefits, they obviously do.
I could probably test it by adding an R to an ht supply and looking for sag between idle and full output. Suspect this wouldn't be cutting edge research!
Enzo

[Nick]

I have tried simulating this, the interesting point is the transition between no and full output (ie a transient), what you see is a change in current, with a time constant related to the primary inductance of the transformer. Its not a huge change in current, but it is there, so would be altered by supply impedance.

Interesting thought is that it would not be seen by constant sine wave tests.