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RE: Scott 233 tube recomendations

Posted by Eli Duttman (A) on June 26, 2008 at 21:23:49

In Reply to: Scott 233 tube recomendations posted by Mark W. on June 26, 2008 at 14:36:32:

Talk to AA sponsor Jim McShane about your tube needs.

It is not possible to do better than a Mullard made GZ34/5AR4. You are set there for many years.

ElectroHarmonix (EH) 7591As are your best bet in O/P tubes. Yes, JJ is also producing 7591As, but JJ's Octal based stuff has been plagued by QC problems.

The Sovtek 12AX7LPS gets (IMO) the nod for those "holes". The Russian tube is clean and quiet. Of particular interest to you is the fact that tube shields fit over the 'LPS well. The other good current production 'X7s could give you trouble with the shields.

RCA made GOOD tubes. More of the same, if you can get 'em, for the 6U8 spots. Siemens made 6BL8s would be fine too.

Look at the schematic for the Scott 233. Notice the 470 KOhm grid leak resistors on the 7591A O/P tubes. That must change. Scott and Fisher "cheated". 300 KOhms is limit for "fixed" bias 7591A grid leak resistors. Tubes from circa 1960 tolerated the liberty taken. Current production will not. Drop the grid leak resistor value to 270 KOhms or less.

BTW, in a unit of that age, replacement of all OEM electrolytic capacitors is absolutely routine.

Eli D.

• Scott 233 Schematic   (Open in New Window)

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