[Amps] 8877 Plate Voltage

[Carl]

All it takes is a single parasitic to toast things. I believe in minimizing 
that possibility no matter how small.

Carl
KM1H


----- Original Message ----- 
From: "Jim W7RY" <jimw7ry at gmail.com>
To: "Jim Thomson" <jim.thom at telus.net>; <amps at contesting.com>
Sent: Sunday, July 01, 2012 10:16 AM
Subject: Re: [Amps] 8877 Plate Voltage


>I don’t use a suppressor. But I do use the Eimac socket and good shielding.
> My 8877 is perfectly stable at 4100V.
>
>
> See:    http://s900.photobucket.com/albums/ac206/w7ry/8877%20Amplifier/
>
> 73
> Jim W7RY
>
>
> -----Original Message----- 
> From: Jim Thomson
> Sent: Sunday, July 01, 2012 6:01 AM
> To: amps at contesting.com
> Subject: [Amps] 8877 Plate Voltage
>
> Date: Sat, 30 Jun 2012 16:33:23 -0500
> From: Charles Bibb <zedkay at 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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