[Hammarlund] Hammarlund Digest, Vol 125, Issue 6

[radiomanL]

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)
>
>
> ----------------------------------------------------------------------
>
> 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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> End of Hammarlund Digest, Vol 125, Issue 6
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