[Hallicrafters] Re: [Boatanchors] Replacing rect tubes with diodesquestion

[jeremy-ca]

A dropping resistor simply generates more heat and provides no useful 
function. The tubes are all rated at a higher voltage than is used, 
recapping takes care of that area and the output transformer has sufficient 
insulation. The extra B+ current drain is well under 10W.

Benefit of a resistor in a rebuilt radio =  Zero.

Benefit of a SS surge protector =  Zero also since they function at the zero 
crossing of the sine wave.

Carl
KM1H

----- Original Message ----- 
From: "Rodger" <wq9e at dtnspeed.net>
To: "WØQFC" <erastber at tampabay.rr.com>
Cc: <boatanchors at mailman.qth.net>; "HALLICRAFTERS" 
<hallicrafters at mailman.qth.net>
Sent: Wednesday, February 13, 2008 9:36 AM
Subject: [Hallicrafters] Re: [Boatanchors] Replacing rect tubes with 
diodesquestion


> Hi Gene,
>
> You also need a dropping resistor to reduce the voltage to close to what 
> would normally be supplied by the tube rectifier.  You can get a decent 
> idea of what the resistor should be by looking at what the typical tube 
> voltage drop is in normal operation, this information is available in the 
> tube data books or the NJ7P online data base is handy: 
> http://www.nj7p.org/Tube.php  I would imagine a 270 ohm 20 watt resistor 
> connected in series with the common cathode connection would get you close 
> enough.  Of course you could also use separate resistors for each 
> replacement diode, in this case the resistor value would be doubled and 
> the power rating would be halved.  I do replace a fair number of my tube 
> rectifiers with SS rectifiers and some of the Halli power transformers 
> definitely benefit from this replacement.  I always build the SS as a plug 
> in and disconnect the 5 volt heater leads from the socket to remove the B+ 
> from the 5 volt winding of the transformer since this is a fairly common 
> failure mechanism in these older transformers.
>
> A couple of other considerations:  The B+ will come up instantly and will 
> be higher than usual until the remaining tubes warm up and begin drawing 
> current so if the filter caps are marginal this extra voltage will 
> probably cause their rapid demise.  So replace any doubtful caps first. 
> By the way, even with a tube rectifier the voltage is much higher just 
> after turn on as the directly heated rectifier cathode heats up almost 
> instantly in the existing tube type rectifier.  I would also consider 
> adding an inrush current limiter to your set to further reduce the stress 
> on the transformer and tube filaments, suitable ones are available from 
> Mouser or Digikey for around a couple of bucks and they are installed 
> after the fuse and in series with the transformer primary.
>
> 73, Rodger WQ9E
>
> WØQFC wrote:
>> I want to replace the # 80 in my S-40A with diodes so I can reduce heat 
>> by less draw on the tranny.
>>
>> Can I just use two diodes that will handle the current, or is there 
>> something else I should do ~ additional parts, etc?
>>
>> Also, I would like to replace the 6H6 for the same reason, but what 
>> diodes should I use?
>>
>> I know that these items are available but in the interest of saving 
>> money, I would like to do it myself. . . .
>>
>> Comments?
>>
>> 73
>>
>> Gene, WØQFC
>>
>> www.w0qfc.com
>>
>> _______________________________________________
>>
>>
>
> ______________________________________________________________
>