Interstage - is it pointless?

[dhaen]

Yep,the more current these need to swing the worse distorsion levels get.

It's my "golden watt" that I'm most concerned about.
After all many designs only quote distortion at that power.

Cheers,

[fdegrove]

Hi,

That's one reason you often only find IS Xformers in low wattage designs.

Other than that I think Joels' got a valid point even though biasing tubes in the very negative voltage range has nothing frightening to me.
Just pick the tube for the job and you're done.

Ciao,

P.S.Corbieres tonight.

[dhaen]

Frank,

As you might have noticed from my IP, I was at work. So I think the earlier Corbieres taunt was below the belt!

I'm home now, but dry tonight.

Of course IS transformers or CR are "horses for courses".
It would be counter-productive using an IS in the EL34 amps now under disussion in the other thread.

Good-night,

[fdegrove]

Hi John,

I know,I know I'm such a b*****d.

It would be counter-productive using an IS in the EL34 amps now under disussion in the other thread.

Agreed,so at least you sleep well tonight,ful moon and all that...

[Joel]

Originally posted by tubesguy
In addition, the secondary of the interstage can be a fine place to inject the voltage required for fixed bias of the output tube, if your tastes run to that method.

Yeah, I thought that would be nice. I want to use fixed bias on the UX-201A's.
Anyway, if I just RC couple two of them, with 22k plate resistors, I can get a gain of 36, which is getting near a reasonable input sensitivity for the amp.

Or, maybe I should just give up on the antiques.

[fdegrove]

Hi Joel,

Or, maybe I should just give up on the antiques.

Hey,as long as you can dig'em up?

You seem to have good sources on old tubes,I'd sell those to the Japs and make a killing.

Kidding,

[dhaen]

Joel,

Or, maybe I should just give up on the antiques.

Ok, I'll take them off your hands

What stages are you thinking of using them for?
How will you power the filaments?

Cheers,

[Joel]

I don't have any one source Frank, but since I'm often willing to risk it and buy "untested" tubes, I rarely pay more than $5 US for anything. So, now I have a shoebox full of globe 01-A's sitting next to the one full of 6SN7's... God, I love eBay.

Originally posted by dhaen
What stages are you thinking of using them for?
How will you power the filaments?

John - they will be the two gain stages in a PSE 71-a monoblock (maybe). Volume control after the first 01A. Filaments will be DC, using the rectifier circuit from my 6F5/71A circuit I posted before. It works really well. I also like not having to mess with balance pots and all that. Makes for a clean schematic.

I breadboarded a single stage last year, and was happy with the performance - even if the volume was too low. I think cascaded stages will solve that issue.

Joel

[dhaen]

Joel,

A transformer is on the bench in front of me now.
I've got nearly 15V RMS on it's input. That is just below the IS voltage required in my amp to get 1 watt output, but the most I can get without having to introduce "unknowns".

The THD measures 0.02%. That's just above the lowest I can read (0.015); due to equipment limitations.

Since the transformer is "gapped" for 40mA, for use in SE, I'd better introduce some DC:

With 15mA DC, which is the most I can easilly get from a 9v battery without oscillator loading:
The THD measures 0.025%. There are extra lengths of wire, and a DVM in circuit now, so I would give there figures some tollerance.

Result:
At the power I'm most interested, there is no significant measurable distortion introduced by my IS transformer.

My ears had told me this already, but it is satisfying when the 2 test methods agree.

No doubt the large signal figures will be considerably "worse".
Until I finish my chassis, I can't properly measure the overall low power distortion.

Now can I get back to my chassis metalwork PLEASE

Cheers,

[dhaen]

Qualifyer:

The test was done at 1KHz. This is the only frequency at which I can measure distortion.
At lower frequencies it will definately be worse!

Cheers,