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[AMPS] ZSAC for a pair of 3-500ZG's?

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Subject: [AMPS] ZSAC for a pair of 3-500ZG's?
From: (
Date: Tue, 7 Mar 2000 23:27:13 EST
Good Evening;

I just repaired a Henry 3KA for a friend. It had suffered a sorted tube, and 
blew apart the HV current-limiting resistor (25ohm/25w) and plate-current 
trip-out adj. resistor.  I replaced the bad tube and blown resistors, and the 
amp is working normally with 1500w out at 100w drive. 

I am noticing that the ZSAC current when set to the SSB position is around 
300ma Ip for 4000v Ep, and 150ma Ip for 3400v Ep when set to the CW position. 
These levels seem hi for a pair of 500Z's, and when keyed with no drive, the 
tubes get orange within 15 seconds or so. The zener diode is rated @ 10v, and 
seems to check OK. Is this a result of using Chinese tubes, or normal for a 
10v bias diode ?

I know that too low of a ZSAC results in splatter, but other than excess 
heat, what is the downside of having a higher ZSAC ?

BTW, filament voltage is around 5.2v , measured at the point the transformer 
enters the RF deck. When measured on the transformer side of the choke, how 
much higher should I be looking for to result in 5.0v at the tube ?

I appreciate the knowledge available here on the reflector. Even with the 
bickering, there is always something new to learn, being a younger generation 
ham born in the solid state era! 

73 Eric

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