[Hammarlund] more questions HX-50

Mon Jun 9 14:48:45 EDT 2014

I have some Radio Shack rectifier silicon diodes rated 1.5 A  at 1000V. 
GP15M is the model number. Dont know if this is a Radio Shack model 
number or not. Will these work? Otherwise I will have to order them if I 
need to use the 1N4007's. If I am safer to use the 1N4007 diodes I would 
rather.

Thanks-Bob-W0YBS

On 6/9/2014 10:23 AM, radiomanL wrote:
> use 1N4007 1 amp 1KV or if you can find them the PTC205 2.5 amp 1KV .
>
> andrew
> kd5pnt
>
> ----- Original Message ----- From: <hammarlund-request at mailman.qth.net>
> To: <hammarlund at mailman.qth.net>
> Sent: Monday, June 09, 2014 11:00 AM
> Subject: Hammarlund Digest, Vol 125, Issue 6
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>> Today's Topics:
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>>   1. More questions HX-50 (Robert Sauvan)
>>   2. Re: More questions HX-50 (Kenneth G. Gordon)
>>
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>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Sun, 08 Jun 2014 19:44:32 -0600
>> From: Robert Sauvan <rsauvan at beyondbb.com>
>> To: hammarlund at mailman.qth.net
>> Subject: [Hammarlund] More questions HX-50
>> Message-ID: <53951180.8090806 at beyondbb.com>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>>
>> Hi all,
>>
>> I have been digging into the cluster of weird wiring in my HX-50 that I
>> have been inquiring about. What I have found is the original owner has
>> added 470K 1/2 watt resistors in parallel with the diodes at the power
>> supply. C104, C105, C109, and C110. What would be the purpose of adding
>> those? Also, during his rewiring, I noticed 2 types of diodes. 1 type
>> looks like a little torpedo, the other type looks like a very very small
>> resistor but is all black and no markings. Im guessing 2 of them are the
>> original diodes and 2 are replacements. Anyone possibly thinking the
>> same? Also, the schematic lists these diodes as "Diode, Silicon". If I
>> were to replace all 4 of the diodes, what would I use? There does not
>> seem to be any type of rating or spec of any kind labeled in the
>> schematic. Let me say, the radio is working fine, this modification just
>> bugs the heck out of me cuz it is a butcher job. Do I dare take these
>> resistors out of circuit. I need to look a bit closer to make sure this
>> isnt tied to any other mod which might be affected. Any ideas and help
>> would be greatly appreciated.
>>
>> Thanks-Bob-W0YBS
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>> ------------------------------
>>
>> Message: 2
>> Date: Sun, 08 Jun 2014 20:13:28 -0700
>> From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
>> To: hammarlund at mailman.qth.net
>> Subject: Re: [Hammarlund] More questions HX-50
>> Message-ID: <53952658.16882.23AA880 at kgordon2006.frontier.com>
>> Content-Type: text/plain; charset=US-ASCII
>>
>> On 8 Jun 2014 at 19:44, Robert Sauvan wrote:
>>
>>>
>>> Hi all,
>>>
>>> I have been digging into the cluster of weird wiring in my HX-50 that I
>>> have been inquiring about. What I have found is the original owner has
>>> added 470K 1/2 watt resistors in parallel with the diodes at the power
>>> supply. C104, C105, C109, and C110. What would be the purpose of adding
>>> those? Also, during his rewiring, I noticed 2 types of diodes. 1 type
>>> looks like a little torpedo, the other type looks like a very very 
>>> small
>>> resistor but is all black and no markings. Im guessing 2 of them are 
>>> the
>>> original diodes and 2 are replacements. Anyone possibly thinking the
>>> same? Also, the schematic lists these diodes as "Diode, Silicon". If I
>>> were to replace all 4 of the diodes, what would I use? There does not
>>> seem to be any type of rating or spec of any kind labeled in the
>>> schematic. Let me say, the radio is working fine, this modification 
>>> just
>>> bugs the heck out of me cuz it is a butcher job. Do I dare take these
>>> resistors out of circuit.
>>
>> OK. Here's the story: at the time that HX-50 was made, silicon diodes 
>> were
>> not being able to be manufactured to very close specs, as they are now.
>>
>> It was very common practice, and actually necessary, to parallel each 
>> diode
>> in a string of them with at least 470K ohm resistors in order to 
>> equalize the
>> voltages across them. If you DIDN'T do this, you would find some diodes
>> would have voltage across them that was in excess of the voltage they 
>> were
>> capable of withstanding.
>>
>> This was due to the VERY variable internal resistances of those diodes.
>>
>> However, at least within the last 20 years, diodes are made to such 
>> close
>> specifications that those equalizing resistors are no longer needed.
>>
>> If that HX-50 (drifty fifty) was mine, I would simply replace those 
>> diodes with
>> modern 1KV or 2KV at 1 amp diodes and completely dispense with the
>> resistors.
>>
>> They would no longer be needed.
>>
>> Ken W7EKB
>>
>>
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