[Vintage-Audio] 7591 replacements

[Helmut Usbeck]

I'm surprised nobody offered up the 6GM5 in place of a 7591.  I've done 
several conversions in Fisher 500 receivers, plus my Pilot amp.  It's 
electronically exactly like a 7591 but uses a 9 pin "magnovar" socket.  It's 
about 2 tens of an inch taller, so what one does is drop the socket with 1/4 
inch spacers lower in the chassis.  Wire it up and away you go, along with 
fitting under the cover.
By the way using 5880's, 6L6's and other beam power pentodes is not a good 
idea because they all draw more plate and filement current than does a 7591.  
If you think 7591's are expensive try getting your hands on power and output 
transformers for these older sets.  Also if one doesn't adjust the bias for 
these other "replacement" tubes in question the fidelity can suffer also.
6GM5's go from $5.00-25.00 new.  I have no experence using the Sovtek tubes.  
The electronic specs on them indicate they are not a 7591 equivilent.  On 
paper looks like a rebased 6L6 or thereabouts.  

Regards,
Helm.  WB2ADT