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Author Topic: BC-221 restoration  (Read 1093 times)
IW5CI
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« on: December 03, 2018, 03:10:04 AM »

My winter project is the restoration of a BC-221 frequency meter.
I have finished the restoration of the chassis but now i need to build a power supply
i want to make a simple and modern power supply without spending much.
I cannot find a simple schematic can someone provide a simple scheme?

Which kind of transformer i need? secondary 6,3 V and Huh volts?
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N2EY
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« Reply #1 on: December 03, 2018, 08:32:49 AM »

http://radionerds.com/index.php/BC-221

has a treasure of information on the BC-221 and power supplies for it.

The BC-221 requires heater voltage of 6.3 volts at 0.9 amps and plate voltage of 130 volts at about 20 mA.

73 de Jim, N2EY
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W1BR
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« Reply #2 on: December 03, 2018, 11:55:07 AM »

One thing you can check is to make sure the serial number of the BC2-221 matches the serial number of the calibration book.  Quite a few were sold surplus with reprinted booklets.... each original BC-221 came with a unique calibration book.  No two were alike.
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G3RZP
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Posts: 1090




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« Reply #3 on: December 04, 2018, 08:16:58 AM »

Regulate the plate and filament supplies: use DC for the filaments. Remember that the filaments have a much lower resistance when cold, so you want the regulator to go into a current limited mode when the filaments are cold.

I have had problems with the 1 MHz crystal: I had one BC221 where the 1MHz crystal can had lost some paint and if the clamp that holds it in place was tightened, the crystal oscillator stopped working
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AC2EU
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« Reply #4 on: December 05, 2018, 08:12:57 PM »

I'm just curious as to why you are restoring this "meter".
Is it for historical purposes or to actually use for calibration?
I don't think they are that accurate. maybe +/- 100 hz?
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IW5CI
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« Reply #5 on: December 06, 2018, 07:27:11 AM »

I am planning to use it to calibrate the BC-348 receiver and art-13 trasmitter to make a vintage military station...
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SWL377
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« Reply #6 on: December 11, 2018, 11:44:44 AM »

I bought a Navy LM Freq Meter, similar to the BC 221 and with an OE ACPS. $20 at a local ham swap. Still had the original cal book and stickers from Douglas Aircraft indicating radio lab service well into the 1970s!

Amazingly it worked perfectly and was accurate to the cal book numbers.

Not as useful as a digital freq counter but really fun to use with my BC 348 and ARR 15 rcvrs. The modulated output of the LM is easier to hear than the bare carrier of the 221.

AF6IM
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N2EY
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« Reply #7 on: December 11, 2018, 01:00:51 PM »

I'm just curious as to why you are restoring this "meter".
Is it for historical purposes or to actually use for calibration?
I don't think they are that accurate. maybe +/- 100 hz?

Back in May, 1980, I used a BC-221 frequency meter and a BC-348 in the ARRL Frequency Measuring Test (FMT), just to see how close I could get with it.

The FMT required measuring W1AW's frequency as closely as possible, on 80, 40 and 20 meters. The exact "official" frequency was determined by an "umpire" using state-of-the-art calibrated gear.

The official results can be seen in QST for August, 1980, page 76.

My average error was 29 Hz. Not parts-per-million - 29 Hz. With 1940s technology.

Nowadays I use an LM-20.

----

A digital frequency counter is only as accurate as the time base. Doesn't matter how many digits it displays; if the time base is off, the measurements are all off.

A heterodyne meter such as the BC-221 can do some things a digital frequency counter cannot, such as determining the frequency of an incoming signal on a receiver that doesn't have a very accurate dial, or presetting such a receiver to a frequency.

73 de Jim, N2EY
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W5RKL
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Posts: 1104




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« Reply #8 on: December 11, 2018, 01:46:21 PM »

My winter project is the restoration of a BC-221 frequency meter.
I have finished the restoration of the chassis but now i need to build a power supply
i want to make a simple and modern power supply without spending much.
I cannot find a simple schematic can someone provide a simple scheme?

Which kind of transformer i need? secondary 6,3 V and Huh volts?


The following link is Surplus Conversion Manual Vol 1 which covers the BC-221 on page
5. There's a power supply schematic and discussions of the 221.

http://w5rkl.com/wp-content/uploads/2015/02/Surplus_radio_conversion_manual_vol1.pdf

Although the power supply schematic shows 6.3VAC, I highly recommend you rectify the
the filament voltage into 6VDC. I have found powering the filament using 6.3VAC results in
hum on the 221's output signal. A simple half wave rectifier and capacitor filter will do the trick.

I also have Surplus Conversion Manuals Vol 2 and 3 along with

"The Command Set Round Up"

and

"Guide to ARC"

on my website. Click the following link then scroll down to the
Surplus Conversion listings.

http://w5rkl.com/manuals/

73
Mike W5RKL
www.w5rkl.com
RMC(SW) USN RET

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SWL377
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« Reply #9 on: December 11, 2018, 05:06:23 PM »

N2EY wrote: "The official results can be seen in QST for August, 1980, page 76. My average error was 29 Hz. Not parts-per-million - 29 Hz. With 1940s technology."

Outstanding job OM upholding the BC 221's accuracy reputation many decades after it was superseded by digital electronics. 29 Hz is impressive.

How in the world did the mfrs prepare and print thousands of UNIQUE BC 221 and LM calibration books before the days of digital measurement automation?

I have heard there is an IRE journal article about how it was done. Had to be labor intensive.

AF6IM




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G3RZP
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Posts: 1090




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« Reply #10 on: December 12, 2018, 01:23:17 AM »

Apparently they built a test machine at, I believe, Philco, which did it automatically.
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G3RZP
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Posts: 1090




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« Reply #11 on: December 12, 2018, 01:27:14 AM »

Another very good use for the BC221 is checking the transmission for gross distortion, chirp, key clicks etc. The AF output is tailored to increase as the audio frequency goes down, so care is needed on telephony if trying to figure if the signal is too bassy....

Although one can use another receiver, there is the problem of overload, which the BC221 pretty well avoids.
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N2EY
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Posts: 5042




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« Reply #12 on: December 12, 2018, 05:36:16 AM »

N2EY wrote: "The official results can be seen in QST for August, 1980, page 76. My average error was 29 Hz. Not parts-per-million - 29 Hz. With 1940s technology."

Outstanding job OM upholding the BC 221's accuracy reputation many decades after it was superseded by digital electronics. 29 Hz is impressive.

Thanks but it really wasn't that hard once the technique was understood.

How in the world did the mfrs prepare and print thousands of UNIQUE BC 221 and LM calibration books before the days of digital measurement automation?

They made a semi-automated system to do the job.

The calibration books were made up using a specialized system using 127 tubes:

http://www.jproc.ca/ve3fab/bc221.html

 More detail: (scroll down to page 98):

http://americanradiohistory.com/Archive-Electronics/40s/Electronics-1944-05.pdf

I have heard there is an IRE journal article about how it was done. Had to be labor intensive.

See above - it wasn't labor intensive at all.

There are ways to generate a new calibration book if one doesn't have the original, too.

73 de Jim, N2EY
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SWL377
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« Reply #13 on: December 12, 2018, 11:17:28 AM »

That automated calibration book system is amazing for the era. What ingenuity. Thanks.

In 1972 I saw a HUGE ENORMOUS stack of overhauled (as described in the bid catalog) like new LM freq meters at a govt surplus auction at Alameda NAS in CA. They were all boxed and foil-cloth encapsulated. Several were opened to show a examples. Couldn't tell them from new and I looked very closely. They had brand new cal books. There were hundreds. They sold as a lot for a price that worked out to about $6 each. Probably all were scrapped. Never saw any on the retail surplus mkt. 

The same auction had a huge pile of OHd ART 13s. They had a few of these opened and unlike the pristine LMs, the ART 13s looked just awful. Dented, scratched and gouged, crude repaints that looked like the sets weren't even cleaned before respraying. Saw grime painted over on one. Allegedly OHd internally but I wonder to what extent. The went as a lot for about $16 each as I recall.

AF6IM
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