[Hallicrafters] Solid Stating an HT-37

[Paul Kraemer]

David
I agree, especially with the low voltage type substitutuions. The natural 
characteristics of the rectifier warm up gives an excellent soft start to 
the supply and the tubes aren't difficult to find---yet. Until they are no 
longer available I will continue to use them for such applications. If it 
ain't broke---don't fix it.
Linear amps and transmitters, different story as the high voltage is usually 
controlled seperate of the filaments anyway. Solid state rectifiers with the 
reduced voltage drop and obvious benefits from no broken glass and spilled 
mercury are a definate plus there.
My 2ct's worth.
Paul K0UYA
----- Original Message ----- 
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "David Thompson" <thompson at mindspring.com>; 
<Hallicrafters at mailman.qth.net>
Sent: Friday, June 20, 2008 11:38 AM
Subject: RE: [Hallicrafters] Solid Stating an HT-37


> Replacing gaseous rectifiers such as 866/3B28 with solid state does not
> cause any problems because unlike vacuum tube rectifiers these rectifiers
> have very little internal voltage drop so the high voltage will change 
> only
> a few volts.
>
> Usually replacing a 5R4 with a solid state rectifier causes no problems
> because tubes such as the 6146's can handle the increased voltage with no
> problems.  Actually this replacement is an excellent idea in the HT-32/37
> transmitters with the insulation problems of the power transformer.  If 
> you
> make you own replacement SS rectifier, watch when you disconnect the 5V
> filament leads to the 5R4.  The schematic shows the DC connection to pin 8
> on the rectifier socket. I have found some connected to pin 2.  With the 
> 5R4
> it didn't matter which pin was used.  With the filament winding removed 
> from
> the socket, it does.
>
> Replacing low voltage rectifiers such as a 5V4 or 5U4 is another matter.
> Here you want to add series resistance to keep the LV at the same level as
> before as increased voltage can affect the performance of some circuits.
> The heat dissipated by the resistor sort of defeats the whole purpose of
> converting to solid state.
>
> David
> KC2JD/4
>
>> -----Original Message-----
>> From: hallicrafters-bounces at mailman.qth.net
>> [mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of David
>> Thompson
>> Sent: Friday, June 20, 2008 11:46 AM
>> To: Hallicrafters at mailman.qth.net
>> Subject: Re: [Hallicrafters] Solid Stating an HT-37
>>
>>
>>
>> It is true that the solid state replacements usually have slightly higher
>> voltage.  I use solid state 866/3B28 replacements in my old Henry
>> 2K and the
>> high voltage increased just over 100 volts which is not a problem in the
>> amp.  Increasing the voltage can be a problem in older receivers as often
>> the components were maxed out or marginal at best.
>> The Globe Chief is a good example of the transformer being
>> marginal and even
>> a slight increase can blow it!
>>
>> Some of the solid state replacements so propular in the Drake and Collins
>> equipment did cause problems so that they came with a notice
>> regarding using
>> them
>> in certain models.
>>
>> Dave K4JRB
>>
>>
>> ______________________________________________________________
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