Crucial to match tubes when running PSE?

[G]

Hi All,

If I wanted to build a amplifier with a PSE output stage would I have to use "matched" tubes? What are the consequences if I don't? Thanks.

G

[fdegrove]

Hi,

If I wanted to build a amplifier with a PSE output stage would I have to use "matched" tubes?

What's the bias arrangement you're using?

Cheers,

[G]

Hi Frank,

I would be using one pair of tubes per side with one cathode resistor for each pair of tubes.

G

[fdegrove]

Hi Gavin,

I would be using one pair of tubes per side with one cathode resistor for each pair of tubes.

As long as the output tubes aren't grossly mismatched the common cathode bias resistor will tend to equalise the current between the pair.

If possible I'd still try not to mismatch the output tubes for some current hogging will still occur making the tubes ages unequally.

Cheers,

[dhaen]

Frank,

I've been looking at your last post for a while, wondering what's going on.

With parallelled valves, the greedier valve will starve the lesser one of current, because it sets the cathode voltage, and hence the grid bias conditions.
I think there are less problems in push-pull, but this is PSE.

Cheers,

[fdegrove]

Hi John,

With parallelled valves, the greedier valve will starve the lesser one of current, because it sets the cathode voltage, and hence the grid bias conditions.

Thing is, I DO agree with you which is why I advised against mismatched tubes.

Maybe I should have stated that more clearly...

[dhaen]

Hi,

Well Frank, what do you think of the suggestion that Gavin uses individual cathode resistors?
I believe it should be sympathetic to a greater valve mis-match than with a single resistor.

Cheers,

[fdegrove]

Hi,

I believe it should be sympathetic to a greater valve mis-match than with a single resistor

And make a part of the individual resistors adjustable?

Cheers,

[dhaen]

Originally posted by fdegrove
Hi,



And make a part of the individual resistors adjustable?

Cheers,

Now you're taking the
Still, it is the best in the world (and not probably)

Cheers,

For G:
It is possible to get a match between 2 not-too-dissimilar devices by matching their curves at 2 points. To do this, you have to tweak the bias point for one end, and the drive for the other. It's a lot of ********, and you're best to find valves that are a reasonable match.
If you have a TV with a CRT, this is how the 3 electron guns are matched.

[Colt45]

yeah, a seperate Rk for each lamp should have better current sharing. with a common Rk, the greedier tube can be greedier.