Technical Meeting?

[Roscoe Primrose]

This McGown amp is using global feedback (4 ohm output tap is connected to driver). Probably not needed for UL operation but better for triode mode I guess? Can any PP guys here comment on what has sounded better in their opinion (UL with or without global feedback, triode with global feedback, triode with no global feedback etc). I'll probably play around a bit and see what I prefer but I would think that output stage output impedance would be really high with a pentode operated in triode without feedback? Too high?

Triode connected pentodes have plate resistances comparable to "true" triodes, for example, the 6L6GC has a triode connected plate resistance of 1700ohms, which is about the same as a 45...

We've probably hijacked this thread enough at this point, if you want to continue this discussion, it probably ought to have it's own thread...

Roscoe

[FerdinandII]

Roscoe figured it out, per usual.
The toggle switch is a lever, with a pivot somewhere in the middle.
Visualize what the bottom half of the lever is doing......

Unless I am completely misreading the wiring on the switch?

It is a 3 pin, 2 position switch. Pin 1 has a UL tap going to it. Middle pin goes to Grid 2 (resistor in series). Pin 3 leads to the primary. Switch towards Pin 1 is UL and switch toward Pin 3 is triode mode?

[TubeDriver]

Roscoe figured it out, per usual.
The toggle switch is a lever, with a pivot somewhere in the middle.
Visualize what the bottom half of the lever is doing......

Unless I am completely misreading the wiring on the switch?

It is a 3 pin, 2 position switch. Pin 1 has a UL tap going to it. Middle pin goes to Grid 2 (resistor in series). Pin 3 leads to the primary. Switch towards Pin 1 is UL and switch toward Pin 3 is triode mode?

Makes perfect sense!

[TubeDriver]

This McGown amp is using global feedback (4 ohm output tap is connected to driver). Probably not needed for UL operation but better for triode mode I guess? Can any PP guys here comment on what has sounded better in their opinion (UL with or without global feedback, triode with global feedback, triode with no global feedback etc). I'll probably play around a bit and see what I prefer but I would think that output stage output impedance would be really high with a pentode operated in triode without feedback? Too high?

Triode connected pentodes have plate resistances comparable to "true" triodes, for example, the 6L6GC has a triode connected plate resistance of 1700ohms, which is about the same as a 45...

We've probably hijacked this thread enough at this point, if you want to continue this discussion, it probably ought to have it's own thread...

Roscoe

That makes sense and probably accounts for much of the gain loss (transformer primary is now too high)?


Will start new thread if I have any more questions.

[dberning]

See new topic thread.

David

[craigh]

Are we still planning a meeting for next week?

Craig

[dberning]

I have not heard of a lot of interest here. What happened to Mr. Antique Sound Labs? Is anybody else interested in such a meeting as an observer, or just to listen to some tunes and drink beer? One issue is that I don't have central air conditioning, so if it is supposed to be a hot weekend we should postpone.

David

[craigh]

I have my dead Dynaco ST-70.
Craig

[dberning]

Looks like Roscoe has got the Antique Sound Labs worked out, so perhaps I could simply take a look at your ST 70 without the group get together if you like, Craig.

David

[craigh]

I'd appreciate that. I have no clue where to begin. It hasn't been plugged in & hooked up in about 6 years.
Craig