[Amps] Do 8875's die fast after weakening?

[Carl]

----- Original Message ----- 
From: "Jim Thomson" <jim.thom at telus.net>
To: <amps at contesting.com>
Sent: Thursday, March 19, 2015 9:53 PM
Subject: [Amps] Do 8875's die fast after weakening?


> Date: Tue, 17 Mar 2015 21:56:45 -0400
> From: "Carl" <km1h at jeremy.qozzy.com>
> To: "Kim Elmore" <cw_de_n5op at sbcglobal.net>, <qrv at kd4e.com>
> Cc: amps at contesting.com
> Subject: Re: [Amps] Do 8875's die fast after weakening?
>
> The 8873, 8874, and 8875 are all identical internally and just the 
> external
> anode determines the plate dissipation.
>
> The MLA-2500 cooling is adequate for the 1000W CW INPUT the amp was 
> designed
> for since that was the FCC rule at the time. Tune up for 700-800W key down
> output and the tubes last forever; PEP SSB will be around 1000W.
>
> There are 3 flavors of the 2500, the original has a single HV and the
> Continuous Duty switch changes the fan speed.
>
> The 2500A (not marketed as an A) has a dual voltage HV and the B version 
> is
> the same minus 10M/12M.
> As with most Dentrons there are often minor differences even during a
> production run.
>
> The 100 Ohm 25W input swamping resistor must be in place for 70-100W
> exciters, many took them out when tubes were cheap so they could get over
> 1500W out......real stupid IMO.
>
> Carl
> KM1H
>
> ##  I thought the B version...or some later version had a band switched or 
> relay switched  tuned
> input, with the usual  pi nets for each band ???
>
> Jim  VE7RF



A few real late ones did and so did the Clipperton L but models didnt change 
that Im aware of.

Carl
KM1H