[ARC5] BC456 vs MD7 modulation

WA5CAB--- via ARC5 arc5 at mailman.qth.net
Tue Oct 14 13:04:45 EDT 2014


I always assumed that it was because of the VHF transmitter.  Same 
modulator had to work with it and any of the HF or MF.

In a message dated 10/14/2014 12:00:19 PM Central Daylight Time, 
duvallddennis at gmail.com writes: 
> Yes, curious indeed.  The SCR-274N xmtrs are screen modulated (by one 
> 1625 in the BC-456) while the Navy went with plate modulation (two P-P 1625s 
> in the MD-7) with their ARC-5 transmitters.  The Navy didn't get any  more 
> power out of their transmitters, though, but the (plate modulated) ARC-5s 
> are a bit easier to get tuned up right.
> 
> Dennis D.  W7QHO
> Glendale, CA
> 
> *********
> 
> On Oct 14, 2014, at 8:37 AM, J Mcvey via ARC5 <arc5 at mailman.qth.net> 
> wrote:
> 
> >I noticed that one of the differences between the two is that the BC456 
> is a single tube  class A and the MD7 is AB.
> >Is there a noticeable difference in the AM modulation?  One wonders why 
> the change was made. Was it cost, or power conservation /efficiency?  I 
> noticed that they even decrease the tube idle  bias  current when the system is 
> in CW. 
> 

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480


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