[Hallicrafters] Re: [Boatanchors] Replacing rect tubeswithdiodesquestion

[jeremy-ca]

----- Original Message ----- 
From: "Bill Kirkland" <kirklandb at sympatico.ca>
To: <km1h at jeremy.mv.com>; <wq9e at dtnspeed.net>; <erastber at tampabay.rr.com>
Cc: <boatanchors at mailman.qth.net>; <hallicrafters at mailman.qth.net>
Sent: Wednesday, February 13, 2008 1:38 PM
Subject: Re: [Hallicrafters] Re: [Boatanchors] Replacing rect 
tubeswithdiodesquestion


>I am curious as to why you indicate that a higher B+ is ok without any 
>indication
> of how it affects the bias conditions and operating points of the tubes.
>
> Bill


You know what they say about people that make assumptions based on 
incomplete or no data.

With well over 40 years experience restoring, updating and modifying 
receivers with the benefit of a RF lab full of equipment I feel qualified to 
make that statement.

You may care to reread my prior to learn that I did specify exceptions.

At National Radio in the mid 60's the Engineering Dept authorized SS 
rectifiers in several receivers, after a full evaluation,  as a result of 
government and commercial customer requests; including those running on 50Hz 
mains. No resistors were used either.

Carl
KM1H
National Radio 1963-69



>
>>From: "jeremy-ca" <km1h at jeremy.mv.com>
>>To: "Rodger" <wq9e at dtnspeed.net>,WØQFC <erastber at tampabay.rr.com>
>>CC: boatanchors at mailman.qth.net,HALLICRAFTERS 
>><hallicrafters at mailman.qth.net>
>>Subject: Re: [Hallicrafters] Re: [Boatanchors] Replacing rect tubes 
>>withdiodesquestion
>>Date: Wed, 13 Feb 2008 11:15:42 -0500
>>
>>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
>>>>
>>>>_______________________________________________
>>>>
>>>>
>>>
>>>______________________________________________________________
>>>
>>
>>______________________________________________________________
>
>
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