[Amps] Replacing 3-500Z tubes with 4-400A tubes

[Carl]

The SB-220 cools the filament pins.

Carl
KM1H


----- Original Message ----- 
From: "Bill Fuqua" <wlfuqu00 at uky.edu>
To: "John King" <k5pgw at yahoo.com>; <amps at contesting.com>
Sent: Tuesday, December 06, 2011 9:15 AM
Subject: Re: [Amps] Replacing 3-500Z tubes with 4-400A tubes


>  One possible issue with the 4-400A is that it has a metal shield around
> the glass seals on the base.
> The cross flow cooling used in some amplifiers does not work well and an
> additional fan
> may be need to cool the seals.
>   Maybe someone can comment on this that have had personal experience
> making the conversion.
> 73
> Bill wa4lav
>
>
>
> At 04:20 PM 12/4/2011 -0500, John King wrote:
>>I have several very good 4-400 A tubes and have replaced a pair of bad
>>3-500Z tubes with a pair of 4-400A tubes in a Heath SB 220 amp.
>>
>>I have noticed much lower resting current being drawn when keyed up. I
>>have noticed about 200 watts less power output with 100 watts drive. The
>>4-400A tubes are as new.
>>
>>I made no changes to bias or other parameter adjustment. I would
>>appreciate the benefit of your knowledge and experience regarding the tube
>>substitution. Thanks and 73, John, K5PGW
>>_______________________________________________
>>Amps mailing list
>>Amps at contesting.com
>>http://lists.contesting.com/mailman/listinfo/amps
>
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