Date: Sat, 30 Jun 2012 16:33:23 -0500
From: Charles Bibb <zedkay@telepak.net>
Subject: [Amps] 8877 Plate Voltage
Starting a new project.
I'm collecting parts for a new HB 8877 amp. One really nice part
that I've recently acquired is a massive transformer for the HV
supply. This transformer came out of a commercial FM transmitter
that ran an 8877 at 1 kw continuous duty.
While that power supply used a choke-input filter in the HV supply, I
want to run the higher voltage obtained by a cap.-input filter. With
a cap.-input filter, however, the HV supply will be a tad over
4150VDC, using the "best" primary taps available. Can wire for
higher, but not any lower.
My question(s) is/are: How critical is Eimac's "absolute maximum
ratings" as far as plate voltage is concerned. I know that under
load, with acceptably regulation, the plate voltage will be about
where I want it at 3800V. Is the slightly-too-high potential on the
anode under no-load a problem? Or, should I just not worry about it
and "let 'er rip, tator chip".
Anyone have experience here?
73,
Charles – K5ZK
## The B+ can be sky high on RX. On TX... sucking normal idle current.. it
will drop a bit.
The actual voltage on the tube..when driven, will be almost double the the key
down B+ voltage.
The AC RF voltage on the pi net will back feed..via the plate block caps..back
onto the anode. ( when driven)
That’s why the 8877 will hi pot test to well over 8 kv....it has to.
## Expect 2.5 kw pep out with your loaded B+. And use a suppressor...and
a glitch R in the B+ lead.
Jim VE7RF
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