[NJARC] Radio Repair Questions

Tue, 16 Mar 2004 20:46:50 -0500

Thanks for the replies.  I remember the old Harmon Kardon Citation II 
stereo amplifier had a built-in meter for adjustment of grid bias on 
each of the output tubes and for adjustment of  a.c. input-signal 
balance.  This level of attention to detail is not really necessary on a 
radio, is it?  I suppose checking the grid bias wouldn't be to 
difficult.  Grant

[email protected] wrote:

>On Mon, 15 Mar 2004 22:24:15 EST [email protected] writes:
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>>"matched" tubes are usually not truly matched, but  approximately equal
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>in 
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>>transconductance as measured on a tube tester. They probably never stay
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>>"matched" very long. For the purpose of  getting the GE to play It is
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>not at all 
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>>neccesary to match tubes. Depending on the heater voltage your "?" 
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>reading on the 
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>>one tube may be meaningless.  If your radio sounds garbled or 
>>distorted you  will want to check that the tubes are ok  by
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>substituting them with 
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>>known good ones before tearing into the circiutry. 
>>Marty 
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>Grant and Marty
>All of the "tube matching" (or any other device matching come to think
>about it) I am aware of has to do with plate current at a specified grid
>voltage.  This is done to prevent output transformer core saturation when
>unequal currents are present in Class AB amplifiers.  It is near
>impossible to match more then a few basic tube parameters as Marty
>indicates.  Just a complicated machine, those vacuum tubes!
>Regards,
>Jim
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