[ARC5] BC-221 Notes

[Brian Clarke]

Thank you Richard,

Somewhere I have a TM that covers very many of the BC-221 letter variants. I
was surprised at the range of values of components in the circuits and could
find no Theory of Operation section that explained the variations.

I have just become the new owner of a VHF variant - a TS-323 / UR, whose
hard-copy circuit looks familiar. It has a commercially-built mains power
supply that works well. Unfortunately, the 323 doesn't work. So, I need to
put on my Sherlock Holmes persona. It's built like a brick out-house -
dozens of 6/32 screws to remove to get at the circuitry. 

Then back to fixing the modulator in my URM-25D. Oh what tangled webs we
oldies weave!

73 de Brian, VK2GCE

-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of Richard Knoppow
Sent: Friday, 8 April 2022 10:45 AM
To: arc5 at mailman.qth.net
Subject: [ARC5] BC-221 Notes

     I have a BC-221 AU. The modulator did not work on the VFO 
although it did on the crystal oscillator. I decided to fix it 
and replaced a couple of bypass caps. The reason for this post is 
to warn others that the schematics may be quite innacurate. Both 
those included in the meter (pasted in the cover) and its 
handbook. The circuit is OK but some of the values are way off. 
In this case I decided to replace a couple of Micamold flat paper 
caps. The schematic shows them as 0.05uF, in fact they are about 
2.0uF and the smaller ones don't work. I will have to get some 
modern caps of the right value. I am not sure the old ones are 
bad but my experience with Micamold is not encouraging. The 
warning is to look carefully at what is in the rig and don't 
trust the handbooks. BTW, I am aware that there were many 
versions of the BC-221. This schematic is in both the printed 
handbook and in the calibration handbook in the meter as well as 
a pasted in schematic. Anyway, I can fix my mistake but its 
frustrating.
-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL
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