BC-221 power supply.

[QQVO6/40]

Y1 circuit diagram.docx

Greetings all.

I have an Australian designed and built Y-1 external power supply for the very capable BC-221 wartime frequency meter.
Circuit of the Y-1 power supply below.As part of the HT voltage regulator there is 2 x 1.5 Volt in series and they are in series with the cathode of the 6J7G shown as V3 on the circuit.
The 6J7G is the regulator valve that drives G1 of the pass valve the 6V6G shown as V2 on the circuit diagram.

The setup, as is, with the batteries in place works quite well to power my BC-221 meters.

What I was wondering is if it is possible to replace the 2 x !.5V torch batteries with a string of diodes or a zener diode.

The batteries are only used as a reference voltage and I believe do not supply any current to the circuit.

I have another Y-1 power supply that many years ago somebody neglected to remove the batteries. Oh what a mess. Recoverable with quite a bit of work.

With my advancing years I would hate to forget to change the batteries in my pristine Y-1.
And so to my query about a simple mod.

Thank you in anticipation.
Cheers.
Robert.

[QQVO6/40]

Try again!
I'm getting older.

Cheers Robert.

[Jez1234]

I can't see any reason why it wouldn't work.

[QQVO6/40]

Greetings all.

Thanks Jez for your reply.

On further thinking I might use a 5 Watt 3V zener as plain silicon diode voltage drop tends to wander a bit as the temperature changes.
This power supply has 3 valves so it warms up as time goes on.
If I used silicon diodes the drift in the HT voltage would be slow but it would mean regular re-calibration of the VFO in the BC-221 and more annoying with my TS-174 which is a VHF version of the BC-221.

All good.
Cheers, Robert.

[usradcoll1]

Originally Posted by QQVO6/40

Attachment 282836

Greetings all.

I have an Australian designed and built Y-1 external power supply for the very capable BC-221 wartime frequency meter.
Circuit of the Y-1 power supply below.As part of the HT voltage regulator there is 2 x 1.5 Volt in series and they are in series with the cathode of the 6J7G shown as V3 on the circuit.
The 6J7G is the regulator valve that drives G1 of the pass valve the 6V6G shown as V2 on the circuit diagram.

The setup, as is, with the batteries in place works quite well to power my BC-221 meters.

What I was wondering is if it is possible to replace the 2 x !.5V torch batteries with a string of diodes or a zener diode.

The batteries are only used as a reference voltage and I believe do not supply any current to the circuit.

I have another Y-1 power supply that many years ago somebody neglected to remove the batteries. Oh what a mess. Recoverable with quite a bit of work.

With my advancing years I would hate to forget to change the batteries in my pristine Y-1.
And so to my query about a simple mod.

Thank you in anticipation.
Cheers.
Robert.

It seems to be a rather involved regulator circuit! The Surplus Radio Conversion Manual shows a circuit using a gas type regulator, 0D3/VR150.
I have a few BC221's that uses that design. I also incorporated a simple neon lamp modulator so it can be used a signal generator.
Dave, USradcoll1

[Jez1234]

A TL431 IC with a suitable Zener across it (anything from say 4V7 to 15V should be fine) to protect from overvoltage should work very well. They are very stable and can be set with a couple of resistors for 3V.

[bill knox]

Hi All

I have just bought at an auction a BC221-M that is in fantastic condition with no signs of corrosion or exterior work being done in the past, the batteries have been removed and a valve regulator (a VR150) style PSU has been installed, someone in an earlier posting said they have several BC221s that use this type of PSU, is there any chance of a copy of it. The PSU fitted has 2 of those lovely Selenium rectifiers, you know the ones, they never go wrong, do they!!!!!!!!!, they will have to go and be changed by 4 1N4007s

Also in the BC221 is a few sheets of paper setting out how the valves can be changed for FET transistors and then changing the PSU to a single battery which will regain the portability of the BC221.

I just cannot believe the condition of the overall unit, there are a couple of Sprague Capacitors they I may try replacing, but if I do it will be by restuffing the original cans, the only two things missing are two of the valves, I think that they are a 6K8 and the other is a 6SJ7 (I think that is right) and I have already ordered them and asked for them to be American metal style.

This is the first one of these that I have had so if there anything else that I have to do will someone put me on the right track.


Bill

[QQVO6/40]

G'day.

Thanks to all those who have offered some thoughts on my ideas of removing the 2 torch batteries from the regulator circuit.
I have 4 of these power supplies so I am not going to do radical changes to any of them. Inserting a string of 5W Zeners in place of the batteries is a logical step which is easy to remove if not needed any more.

I am quite familiar with the 3 volumes of the Surplus Conversion Manuals.
Having done quite a bit of work undoing the damage caused by people following the instructions outlined in those infamous books.

Hello Bill.
I hope you have the calibration book that comes with the SCR-211 also known as the BC-221.
It needs to have the same serial number as the instrument itself.
The books were calibrated against the instrument. If you have a book with a different serial number the numbers will be wrong.
You can draw up your own book if you have the time and only need a few specific calibration points.
Ok we have established book and serial numbers match. Important! Good!

You would be advised to replace the 3 bathtub caps as they are paper and somewhere along the way they will fail if not already.

Do not fiddle in any way with the inner workings of the tuned circuits around the 6SJ7. If you do it will change the calibration of the instrument.

I have not had anything to do with changing one of these beautiful instruments to solid state. Why bother? Just to make it portable? I use other solid state stuff for that.
I have a friend who has an SCR-211 that was in absolutely pristine condition and used it regularly.
Did the solid state conversion and it drove him demented trying to get it to behave. He worked on it on and off for nearly 2 years before giving up on it.
Went and bought another SCR-211 original valve one with power supply and just tossed the solid state one towards the back of his shed.
Personally, I wouldn't change them.

Cheers.
Robert.

[ex seismic]

Bill,
I run one of mine off some Li-Ion cells and voltage converter modules from ebay. It seems happy enough.
Gordon

[QQVO6/40]

G'day all.

You would have to choose which inverter to buy very carefully.
Get the wrong one and you will end up with birdies all over the place.
Bear in mind the SCR-211 generates a lot of harmonics as a prime objective.
I am guessing Gordon you may have scored a good one but anyone contemplating this idea to keep in mind the aforementioned thought.


I do have in my collection an SCR-211 with a genuine 6 Volt vibrator power supply. It is an army one intended for field use. The supply uses a synchronous vibrator and is very heavily filtered to keep the hash confined to the supply.

Below is a pic of the Y1 240V mains power supply.

Cheers all.
Robert.

[ex seismic]

Robert, not much choice for the high voltage module, there seems to be only one type around at present on UK ebay. I think it needed a bigger output capacitor to reduce the HF hash from it.

[Craig Sawyers]

This is exactly the unit I have https://www.royalsignals.org.uk/photos/bc221ak.htm

Note the rather rare power supply that fits inside the battery box.

There is a link on that page to a schematic - not dissimilar to the Y1 - but uses an 85V regulator valve/tube as the voltage reference.

Craig

[Craig Sawyers]

Incidentally my daughter lives in Newcastle NSW!

Craig

[QQVO6/40]

Greetings all.

I have not abandoned this thread.
I have been thrown some serious health issues that have prevented me from taking part in any radio related tasks.
I just escaped from hospital last Tuesday after major surgery for kidney cancer.
Another "I". Have decided to shelve the power supply for a while to get on top of my health issues.
Not permanently.

Craig, is it ok for me to PM you?

Cheers all.

[Craig Sawyers]

Of course Robert. In the meantime the schematic of the unit I have is here https://www.royalsignals.org.uk/phot...su-diagram.jpg

Craig

[FrankB]

Bill, If you replace the selenium rectifiers, you will need to add a dropping resistor.

I have several of the LM freq meters I picked up over the years. One with mil PS and one I added a commercial PS to. Voltage regulation is critical. I allow mine to warm up 1/2-1 hr minimum for stability.
Having the freq book with the unit with the ORIGINAL MATCHING serial number is crucial.

Those freq books were all individually hand typed and calibrated to NBS standards, and matched to each LM unit. (One heck of a long, hard job from what I see in mine!).

The LM also makes a good VFO by adding a freq counter to it. IIRC there was an article in QST on this, or possibly in one of the Surplus Handbooks series. There are many articles in QST, 73', Ham Radio, amd CQ magazines on the LM freq meters/BC221.

[Julesomega]

Originally Posted by bill knox

.. a few sheets of paper setting out how the valves can be changed for FET transistors and then changing the PSU to a single battery which will regain the portability of the BC221.

Bill - if you still have those papers I'd love to see them, to encourage me in my forthcoming project to convert a Type D wavemeter to semicons

[G6Tanuki]

The BC-221 was, in most instances, calibrated automatically by a special 'computer' invented by Philco. The individual calibration-books were printed on a modified typewriter which is why they _look_ like they may have been manually produced.

See http://jproc.ca/ve3fab/bc221.html and a description of/some pictures of the Philco machine are shown in https://nzvrshome.files.wordpress.co...nzvrs-30-2.pdf

A BC-221 is rather useful; I remember in the 'sixties a local ham had a BC-221 as the VFO for his 80-Metre transmitter [813 as a final, modulated by a pair of 807s]