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

[Jim Thomson]

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