[ARC5] BC-221 Notes

[Richard Knoppow]

    I think I have the TM you refer to. It doesn't have the AU 
version but I have a separate sheet (actual paper) that shows it. 
The schematic is exactly what is in the calibration booklet and 
paste on schematic in the meter. Some of the values are the same, 
for instance the resistors all seem to be the same, but the paper 
caps are not. The schematic gives the value of 0.05uF while the 
actual caps are 1.8uF. I am sure there is yet another variation. 
The handbook, is it TM-11 300 (by memory) has perhaps twenty 
different variations. Mine was built by Allen D. Cardwell 
company. Cardwell sold the tuning capacitor and gear and dial 
mechanism as surplus after the war and I think Hammarlund made an 
identical or nearly identical cap.
    In a QST for about 1951, at any rate Korean war vintage, some 
outfit is advertising for the VHF version of the BC-211. No price 
is mentioned but they indicate they will pay high prices since 
they need the meters to complete some contract they had. Some 
strange stuff went on. I guess that many thought when WW-2 was 
over there would be no more war and no need for military 
equipment. Boy, were they wrong.

On 4/7/2022 6:59 PM, Brian Clarke wrote:
> 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