[Fwd: Re: [Johnson] Modifications]

[joel hallas]

-------- Original Message --------
Subject: Re: [Johnson] Modifications
Date: Thu, 22 Jul 2004 16:36:07 -0400
From: joel hallas <jrhallas at optonline.net>
To: "Sherrill E. Watkins" <SEWATKINS at dgs.state.va.us>
References: <A27CFBEDEA8E5C47A80B374BB0DBCEFD012D2DD0 at EX1.dgs.state.va.us>



Your points are well taken, and I agree if a 1:1 replacement were made.

On the other hand, by going to solid state rectifiers, there are at 
least two significant benefits that add to boat anchor longevity.

1. The power transformer load is reduced significantly. This is 
important if the transformers were marginal to start with, such as on my 
HRO-60.

2. The heat level is reduced significantly. The rectifier(s) often give 
off more heat than a couple of other tubes.

3. If the rectifiers are packaged in a plug-in tube base, the original 
configuration can be returned at any time, perhaps for winter operation .

As to the higher voltage, all that needs to be done is add the 
appropriate resistor in series with the common cathode connection to 
provide the required drop. This spot also makes a good point to measure 
B+ current (by measuring drop on the resistors) if you want, from the 
top of the chassis.

I see this as a "no lose" approach and have done it on a number of my 
boat anchors.

Regards, Joel Hallas, W1ZR


Sherrill E. Watkins wrote:

>While we are discussing the pro and con of modifying classic equipment, I
>would like to state that some of the worst mods to do to classic equipment is
>to "solid state" the rectifier in the power supply. Unfortunately, this is
>easy to perform and the owner thinks he has "improved" the equipment because
>he has eliminated the rectifier tube. As explained previously in articles
>both in ER Magazine and the Old Timers Bulletin, the instantaneous
>application of high voltage to the plate of a cold tube is a sure way to
>destroy the tube. Also the solid state rectifiers increase the voltage level
>over the tube rectifier thereby causing the equipment to run hotter and
>additional stress is placed on all of the components. Classic equipment will
>be damaged by the simple addition of solid state rectifiers and this must
>NEVER be performed. Also, classic equipment should be operated at a low AC
>line voltage and never at the high (120-125 levels) that is common today. My
>AC line voltage is 125 VAC and I understand this is quite common. For older
>equipment, 110 to 115 maximum would be better.-73- Sherrill W. k4own.   
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