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 6973 VS 6CZ5 substitute

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Bob D.



Posts : 13
Join date : 2010-10-13

PostSubject: 6973 VS 6CZ5 substitute   Wed Oct 20, 2010 7:26 pm

I'm still working on my AMI jukebox amplifier. This is a stereo unit with push-pull 6973s in the outputs. Two of the old 6973s are shot, so I tried substituting 6CZ5s which seem to be the popular substitute, especially on jukeboxes. They play but the plates turn cherry red in short order, and it's obvious that they are giving off much more heat than the 6973s. BTW, they overheat in both channels. The 9673s play fine in both channels. I just wondered if anyone could spot the problem with this substitution from the schematic. (BTW, bias is fixed at -30V. The 6CZ5s are NOS that check good on my tube tester.)



Bob D.
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dberman51



Posts : 19
Join date : 2010-10-13

PostSubject: Re: 6973 VS 6CZ5 substitute   Wed Oct 20, 2010 10:42 pm

Check the wiring of pin 8, which according to the RC-27 tube manual is different between 6CZ5 and 6973.

Not sure I like that substitution. 6CZ5 is primarily a vertical deflection amplifier, while 6973 was designed specifically to be a high-fidelity push-pull audio amplifier. 6973 ratings are higher as well.



I noticed Electro-Harmonix is now making 6973s. Not inexpensive but not ridiculous either.

-David
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jukeboxman



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Join date : 2010-10-21

PostSubject: Re: 6973 VS 6CZ5 substitute   Thu Oct 21, 2010 5:02 pm

hi there , i have worked on many jukebox amps ,mostly seeburg that use 6973 -the electro harmonix remake works and sounds great.

http://www.tubedepot.com/eh-6973.html

http://www.dougstubes.com/eh.htm

i know if you use the 6CZ5 you need to tie pin 1 to pin 8 but the bias may be off.

hope this helps Gary
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Tim Tress



Posts : 12
Join date : 2010-10-17

PostSubject: Re: 6973 VS 6CZ5 substitute   Fri Oct 22, 2010 7:34 am

Check the bias, and replace the coupling capacitors to the grids, if you haven't already done so.

Tim KA3JRT
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