Ultralinear pse

mark_titano · 5th November 2007, 07:22 PM

Hi all

Surfing on the web I’ve found a schematic of an interesting pse amplifier. In the output stage there are three 6550 in UL. I’ve never seen before such a solution, so I’d like to know what you think about the connection of more than one screen grid to the same UL tap (43%).
Do you think it could produce any problem to the local feedback mechanism?

Thanks

Mark

Eli Duttman · 5th November 2007, 10:54 PM

Mark,

I don't see why it can't be made to work well. The 3 paralleled O/P tubes need to be very closely matched for gm and reasonably well matched for plate current. "Fixed" bias, with an individual adjustment for each tube, allows the idle current for each tube to be set, "perfectly". "Fixed" bias implies modestly sized grid leak resistors. So, low impedance driver circuitry is in order.

5th November 2007, 07:22 PM	#1
mark_titano diyAudio Member Join Date: Oct 2004	Ultralinear pse Hi all Surfing on the web I’ve found a schematic of an interesting pse amplifier. In the output stage there are three 6550 in UL. I’ve never seen before such a solution, so I’d like to know what you think about the connection of more than one screen grid to the same UL tap (43%). Do you think it could produce any problem to the local feedback mechanism? Thanks Mark

5th November 2007, 10:54 PM	#2
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Mark, I don't see why it can't be made to work well. The 3 paralleled O/P tubes need to be very closely matched for gm and reasonably well matched for plate current. "Fixed" bias, with an individual adjustment for each tube, allows the idle current for each tube to be set, "perfectly". "Fixed" bias implies modestly sized grid leak resistors. So, low impedance driver circuitry is in order. __________________ Eli D.

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