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

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Subject: [Amps] Do 8875's die fast after weakening?
From: "Jim Thomson" <>
Date: Thu, 19 Mar 2015 18:53:48 -0700
List-post: <">>
Date: Tue, 17 Mar 2015 21:56:45 -0400
From: "Carl" <>
To: "Kim Elmore" <>, <>
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.


##  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

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