Another to add to the list; Alpha never bothered to delay HV on any of their
8877 amps.
(((73)))
Phil, K5PC
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of w2cqm@juno.com
Sent: Thursday, July 28, 2005 7:15 AM
To: Amps@contesting.com
Subject: [Amps] 8877 Time Delay Query
Can anyone help with specific knowledge about the 3 minute time delay and
the application of HV on the Eimac 3CX1500A7/8877? The 8877 tube data
sheet only specifies a 3 minute filament warmup. However it does not
mention whether HV can be applied when the tube is turned on (no
excitation of course) and filament voltage applied. Ameritron (AL1500)
holds off application of HV for the full delay period. Dentron did not
in their 8877 amp with no apparent problems! I hasten to mention that I'm
not too confident about the general level of Dentron circuitry and that
testimonial. The 3CX800A7, smaller version of the 8877, date sheet
specifically admonishes the ham not to apply either RF excitation or
high voltage "...for a minimum of three minutes (of filament warmup)...to
allow for proper conditioning of the cathode surface". At this point, I'm
not certain if the 8877 is materially different from the smaller, yet
similar tube. If the application of HV makes no difference with the 8877
during the warmup period, it saves a lot of control circuitry and a
separate filament transformer; especially when both windings are from
the same xmfr. Consequently, the delay can be incorporated in the antenna
relay circuit only. In the 8877 amps I've built, I've always delayed the
application of HV just to make certain there'd be no damage. Any
comments based on first hand engineering data would be appreciated. Ron
W2CQM/3
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