Ive heard that the Harbach fan provides less actual cooling.
A cleaned and lubed original fan, correct placement of the blade and the
little top plate in place should be all that is required.
Replacing the contacts is a good step as well as using real solder with the
right temperature rating. Ive also found many 220's with poor original
soldering that contribute to the initial overheating.
Carl
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <amps@contesting.com>
Sent: Wednesday, December 07, 2011 6:48 AM
Subject: [Amps] SB-220 filament pin cooling was: Re: Replacing 3-500Z tubes
with 4-400A tubes
>I have had recurrent trouble with filament pins coming unsoldered in my
> SB-220 during heavy contest operation, even though I have the
> replacement Harbach fan that is supposed to move something like 30% more
> air. I recall, years ago, reading that a lot of the heating might be
> due to relatively high resistance between the pins and their socket
> clips. The same author, if I remember right, also opined that the
> heating would, over time, cause the clips to lose their temper,
> aggravating the problem.
>
> I went in and swapped two of the grid clips for the filament clips on
> each socket, polished the pins and the inside of the clips, and put a
> small fan on top of the tube compartment to help move air through.
> Haven't melted a filament pin since. Fingers crossed.
>
> 73, Pete N4ZR
>
> The World Contest Station Database, updated daily at
> www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com,
> spots at telnet.reversebeacon.net, port 7000 AND now
> at arcluster.reversebeacon.net port 7000
>
>
>
> On 12/6/2011 4:32 PM, Carl wrote:
>> The SB-220 cools the filament pins.
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message -----
>> From: "Bill Fuqua"<wlfuqu00@uky.edu>
>> To: "John King"<k5pgw@yahoo.com>;<amps@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@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>> _______________________________________________
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>>>
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