[Milsurplus] ARC-5 Dynamotor

[DeWitt Clay]

Interesting. Never thought about the SCR-274N HV plate circuit being designed 
for screen modulation. How much of a difference does it make on the audio 
quality/modulation results? Changing C66, the .01 to .001 uF I mean. Might save 
the orginal .01 cap from shorting out from the higher peak voltages, hihi. 
Heathkit used .02 uF on the secondary of the modulation transformer in their 
DX-100 rigs. The original .02 cap had  already been replaced in my DX-100 with a 
.01. I have gotten reports that the signal is good and has plenty of highs. 
Somehow I didn't think .02 was neccesary so I left it at .01 uF. Lots of audio 
availible in the DX-100. How about the other caps in the SCR-274N transmitters? 
The paper caps no doubt need changing. Any recommendations there? The rigs I 
have fired up appeared to have a strong (VHF?) parasitic oscillation in the 1626 
VFO stage. 

73, DeWitt  N4QNX



----- Original Message ----
From: mac <w7qho at aol.com>
To: WA5CAB at cs.com
Cc: milsurplus at mailman.qth.net
Sent: Thu, September 9, 2010 1:23:09 PM
Subject: Re: [Milsurplus] ARC-5 Dynamotor

I've plate modulated  274N transmitters with 500 - 550 volts into the  
PAs with no C65/67 arc-over problems.  Works better, though, if one  
swaps out C66 (.01 mfd) for something around .001 or so.

Dennis D. W7QHO
Glendale, CA



On Sep 9, 2010, at 10:11 AM, WA5CAB at cs.com wrote (in part):

> If you run modulated B+ to the plates of the series fed
> units you might exceed the voltage rating of C-65 & 67. 
> None of the various
> parts lists give any electrical rating information for the capacitors.

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