[ARC5] [Milsurplus] BC-221AK Question

[howard holden]

I have both the LM-18, which I just use with a makeshift supply, and a BC-221 (not sure which series, but it has 110V supply in it). Don't know which I prefer, perhaps the LM, they're both running fine. I use it with my GO-9 occasionally if I want to set it to an exact freq. Nice meters. Just remember they were built in WW2 (80+ years old) so they're not going to be as stable as when they were new.

73, Howie WB2AWQ
________________________________
From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> on behalf of Mark K3MSB <mark.k3msb at gmail.com>
Sent: Tuesday, September 2, 2025 8:47 AM
To: Ken Gordon <kgordon2006 at frontier.com>
Cc: ARC5 <arc5 at mailman.qth.net>; List Milsurplus <milsurplus at mailman.qth.net>
Subject: Re: [ARC5] [Milsurplus] BC-221AK Question

Over the weekend I rebuilt the power supply.   It's using the original chassis and it's not going to win any prizes,  but it's providing 150V regulated voltage and 6.3 VAC now.

Added a new cord and fuse etc.   The internal wiring was horrid;  I'm surprised it didn't short the B+ at some point....    fixed that stuff.

A winter project is going to be doing a complete rebuild of the PS on a new chassis.

The audio choke in the picture I posted is obviously not 150H..... in fact at 1 Kc it measures 1H.

I have a hanger queen BC-221M and I extracted the choke from it.    Its 250 H at 1 Kc and it will have to do,

Of course, the form factor is different so I'm going to have to bolt it on.

[image.png]

73 Mark K3MSB







On Wed, Aug 27, 2025 at 8:34 PM Mark K3MSB <mark.k3msb at gmail.com<mailto:mark.k3msb at gmail.com>> wrote:
Hi Ken

>> The cap is part 9-2, not 0-2 and it is supposed to be 0.001 uF.

Yes, my typos.   Too lazy to roll over to the bench and get my glasses........     :-)

[image.png]

.... and thus the motivation for my question....

[image.png]

[image.png]

The internal HB Power Supply was a "Widow-Maker" Special......with leaky caps!!!

I will rebuild the PS tomorrow and power it up (after dressing the connections associated with the replacement components.....and using the correct parallel capacitor.

73 Mark K3MSB




On Wed, Aug 27, 2025 at 7:46 PM Kenneth G. Gordon <kgordon2006 at frontier.com<mailto:kgordon2006 at frontier.com>> wrote:
On 27 Aug 2025 at 18:56, Mark K3MSB wrote:

> I have a BC-221 whose ID plate says  BC-221E.   It is not an E
> variant.
> From the tubes, front panel controls, and TM11-300,  I think it's the
> AK variant.

I have two -AKs here: unfortunately. in storage, not in the shack. :-(

> Looking at the front panel,  what is supposed to be behind the two
> antenna connectors?

Well, only ONE is an antenna connector: the "other" one is a ground connector...or should be.

> I tried discerning it from TM11-300.   I think it's supposed to be a
> 150 H Choke (Part 24) in parallel
> with a 0.01 uF cap (Part 0-2).

The cap is part 9-2, not 0-2 and it is supposed to be 0.001 uF.

>    Can anyone confirm?

Well, a 150 H choke would be physically fairly large for a "small" choke. I would have to go to my storage building and open one of my -AKs up to check, and cannot do that just now.

I hope Wayne can help. If all else fails, I'll make a run to my storage and take look as soon as I can.

BTW, the -AK version is one of only two other versons which include AF modulation capability. None of the others have that. This makes the -AK a fully functioning signal generstor.

Ken W7EKB
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