audio-talk

Then again, the DCR of the transformer will do just as good a job with grid current. Maybe ignore that.

I would be tempted to use a pair of resistors to ground instead of a single one, would help with any grid current that occurs.

The Sowter page specifies the frequency response with a 6k4 ohm source and 10k ohm load, but doesn't say what happens with other loads.

I would assume it to ensure the transformer secondary is loaded, may help with ringing, or may help to specify a load as reflected into the primary and seen by the source.

Square waves and a scope would be how I would experiment with this. Will vary though with the position of the volume control as ...

Don't understate just how much heat is radiated from a GM70.

I always thought the valve working away oscillating was wearing out.

You are passing a constant current through that valve at idle such that its dissipating watts of power . Why would you imagine a bit of extra RF would "wear it out". Do you think the cathode is going to run out of electrons?

Change R11 and R1 to 300k and R12 and R7 to 9k1 and adjust with the dual ganged pot.

I did of course forget to add "with suitable heatsink"

Not only have the 50k rule been neglected but perhaps many circuits are shortening the life of the valves through paracitic oscillation neglected.

I think you are tilting at windmills there. The minimum grid resistance will be in the case of fixed bias, and why would any oscillation due to Miller ...

Oh and, um, any ideas for a CCS that can pass 70mA for stage 1

70ma @ 90v is 6.3W. At 500v 200ma, a cascode of these (or one on its own, depending on how constant you want) IXTP02N50D should be fine.

https://www.mouser.co.uk/datasheet/2/24 ... 319279.pdf

Or to keep it simple IXCP10M90S

Is that someone doing a Donald Fagen impersonation?

OK, I have put the permission back, see if it makes everyone happy.

Someone asked some time ago if I could remove the option of seeing if they were online, I did that, but it only seem's to work with the updated version.

more than a few radio engineers I rubbed shoulders with reported fixed bias sounds better.

Yep, but remember one of the advantages of fixed bias is lower B+ required, so that would save the maker some pennies. Also, radio (at least WRT transmitters) was a big user of grid current, positive bias ...

That looks like it should work. Would be interesting to compare the vreg cathode with a resistor and cap.

I have to admit that the "something special" that a SET provides, is nice, and given the right speaker and more importantly music, can be magic, but the only way I could live with it (when I ...