P.C.R. 3 radio - UK Vintage Radio Repair and Restoration Discussion Forum

kalee99 · 19th Oct 2008, 6:00 pm

Hi all,
Just bought this set to restore and was thinking of adding a BFO at the same time. I already have a circuit in mind using a single transistor and a small if unit.
Just wondering if the vast storeroom of knowledge oh here has any ideas or tips on this project?
Thanks,
Paul.

paulsherwin · 19th Oct 2008, 11:53 pm

This was a common modification in the 60s and 70s, when these sets were often converted to general amateur comms receiver use by hard up teenagers. You just need an oscillator running at around the IF frequency, with a control on the front somewhere.

I wouldn't recommend doing this today though. There are lots of mutilated PCRs around, and original unmodified examples are sought after and fetch good prices.

Paul

kalee99 · 20th Oct 2008, 6:40 am

Hi Paul,
You are right I ought not to go drilling holes in the old thing

I guess the kindest thing to do is just a capacitor change and use "as is".
I do seem to remember a long time ago a "stand alone", BFO unit which came in kit form from some supplier or other, and could (supposedly) provide the required beat frequency without any big modifications to the set in use? I guess it was connected by making an inductive connection to a valve by wrapping an insulated wire around a grid lead or some such?
Thanks,
Paul.

davidw · 20th Oct 2008, 9:16 am

Just a thought, I used to resolve ssb on a.m by loosely coupling the output of a signal generator to the aerial (a few turns wound round the aerial lead)and injecting something close to the received frequency(ie.offset by the I.F.) With the careful adjustment of the generator frequency and level readable ssb is achievable. Might be worth a try; certainly,as Paul says, don't go drilling holes in it!!!!

paulsherwin · 20th Oct 2008, 10:22 am

You could build the oscillator in a separate box and run a wire into the PCR, loosely coupling it to the IF chain somewhere. This would be easily reversible.

Paul

kalee99 · 20th Oct 2008, 11:19 am

Quote:

Originally Posted by paulsherwin

You could build the oscillator in a separate box and run a wire into the PCR, loosely coupling it to the IF chain somewhere. This would be easily reversible.

Paul

Hi Paul,
Grand Idea

Now to scrounge a tin box off the wife. and get the soldering iron warmed up. I will post photos of the full job when done.
thanks everyone

Herald1360 · 20th Oct 2008, 12:57 pm

You may want to make the BFO output level variable so as not to swamp the AGC on the PCR (unless it has the option for variable RF gain with the AGC off).

Just poking a short length of unscreened wire from the BFO into an IF can should provide adequate coupling!

Chris

paulsherwin · 20th Oct 2008, 1:08 pm

Quote:

Originally Posted by Herald1360

You may want to make the BFO output level variable so as not to swamp the AGC on the PCR (unless it has the option for variable RF gain with the AGC off).

The PCRs don't have switchable AGC or an RF gain control, and this was another common mod back in the 60s.

They are really just broadcast receivers, intended to allow soldiers far from home to listen to familiar BBC voices. They do have a tuned RF amp so are quite sensitive.

Paul

dave walsh · 20th Oct 2008, 3:30 pm

Paul's completely right about the sensitivity. The PSU on mine is currently u/s but it was a surprisingly lively SW set when in use due to that RF amp, which also made conversion to comms mode a real possibility. There are articles in PW from the sixties. If you do a "PCR receiver" search on here Paul [Kalee] there are two threads Nov/Dec 2007 re restoration/derivations and polite disputes about whether it really was just a "Naafi Set" or not. Lots of interesting links and info!
Hope this helps you. Dave W

kalee99 · 20th Oct 2008, 4:16 pm

Quote:

Originally Posted by dave walsh

Paul's completely right about the sensitivity. The PSU on mine is currently u/s but it was a surprisingly lively SW set when in use due to that RF amp, which also made conversion to comms mode a real possibility. There are articles in PW from the sixties. If you do a "PCR receiver" search on here Paul [Kalee] there are two threads Nov/Dec 2007 re restoration/derivations and polite disputes about whether it really was just a "Naafi Set" or not. Lots of interesting links and info!
Hope this helps you. Dave W

Thanks Dave,
I have just about decided that whatever I do will involve no mechanical alterations to the set. So I will be building a separate BFO and coupling by RF somehow. I have already built a circuit today for such an "add on", BFO working from 9 volt battery and it's working on an existing Ekco set which has a few short wave "spread", bands. I was able to listen to a few hams on 40 meters SSB. So all I need to do now is get stuck into restoring my PCR 111.

I will post photos of the whole lot when I get done.
Paul.

JHGibson · 20th Oct 2008, 9:05 pm

You can get the effect of a BFO by causing the last IF amp to go into oscillation. Hallicrafters used this simple, cheap method by wrapping a turn of insulated wire around the anode lead, then continuing the wire and wrapping it one turn around the grid lead. The end of the wire then goes to a switch which grounds the wire. When the switch is closed, the wire only induces a neglegible few pf's of capacity to groumd.at the anode and grid. With the swich open, these few pf's are in series from anode to grid and the the IF goes into oscillation.
As usual with these simple BFO's, the AGC line will need to be earthed.
John.

Stockden · 20th Oct 2008, 10:08 pm

Quote:

Originally Posted by JHGibson

You can get the effect of a BFO by causing the last IF amp to go into oscillation.

I'm pretty certain that I've got an old PW article somewhere that modifies the PCR in just this way. IIRC it includes a pot so you can get variable selectivity up to the point of oscillation and then a BFO effect. If you're interested in a copy Paul, let me know and I'll dig it out and scan it.

Hugh

kalee99 · 21st Oct 2008, 7:15 am

Quote:

Originally Posted by Stockden

I'm pretty certain that I've got an old PW article somewhere that modifies the PCR in just this way. IIRC it includes a pot so you can get variable selectivity up to the point of oscillation and then a BFO effect. If you're interested in a copy Paul, let me know and I'll dig it out and scan it.

Hugh

Hi Hugh,
Yes thanks

I would like a look at that circuit. I am still very much at the development stage and am looking at as many ideas as possible.
Thanks again,
Paul.

Stockden · 21st Oct 2008, 5:53 pm

Paul,

I've attached scans of the 2 page article as promised. They're not as good as I'd hoped so let me know if you'd like me to have another go.

Hugh

dave walsh · 21st Oct 2008, 6:07 pm

Hi Hugh. Which PW is it please? I'm sure I will have it. Dave W

Stockden · 21st Oct 2008, 6:12 pm

Quote:

Originally Posted by dave walsh

Hi Hugh. Which PW is it please? I'm sure I will have it. Dave W

Unfortunately it comes from an era when PW didn't date the pages of the magazine, so the publication date is unknown (to me at least). However, it refers to a 1965 article which was "long out print" so I'd guess it was somewhere between 1966 and 1969.

Hugh

dave walsh · 21st Oct 2008, 11:07 pm

I've only got up to February 1967 so far but the article mentioned at the end of the one supplied by Hugh[ie June 65] is very comprehensive, including a Product Detector/BFO combination. As Paul isn't planning to be too invasive with his set however this may be "interest only". Dave W

paulsherwin · 22nd Oct 2008, 12:06 am

I think I remember Hugh's article. It would be from 1968 or 1969 if I'm right.

Paul

JHGibson · 22nd Oct 2008, 8:29 pm

You can also get the last IF to go into controlled oscillation by breaking the earth end of the screen by-pass capacitor wire and inserting a 10K pot there. Withe the pot at zero ohms you get normal receiver operation. As you turn the pot up you get controlled feed back which will improve selectivity somewhat. With the pot increased still more, the IF will start to oscillate and acts as a BFO. This all comes about because the screen grid becomes less effective and the plate to grid capacity increases.
John.

Herald1360 · 22nd Oct 2008, 9:27 pm

That very article brought back some early radio tinkering memories- I used the screened cable feedback and pot IF gain idea in it on an old radiogram to resolve the strange Donald Duck noises that I had figured must be SSB. I don't recall having the knowledge then about how to short out the AGC line, so it must have been a strong signal!

ISTR I did it before we moved away from Worcester which was late '66 or early '67, though.

Chris

19th Oct 2008, 6:00 pm	#1
kalee99 Rest in Peace Join Date: Dec 2004 Location: Newcastle Upon Tyne, Tyneside, UK. Posts: 420	P.C.R. 3 radio Hi all, Just bought this set to restore and was thinking of adding a BFO at the same time. I already have a circuit in mind using a single transistor and a small if unit. Just wondering if the vast storeroom of knowledge oh here has any ideas or tips on this project? Thanks, Paul.

19th Oct 2008, 11:53 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: P.C.R. 111 radio This was a common modification in the 60s and 70s, when these sets were often converted to general amateur comms receiver use by hard up teenagers. You just need an oscillator running at around the IF frequency, with a control on the front somewhere. I wouldn't recommend doing this today though. There are lots of mutilated PCRs around, and original unmodified examples are sought after and fetch good prices. Paul

20th Oct 2008, 6:40 am	#3
kalee99 Rest in Peace Join Date: Dec 2004 Location: Newcastle Upon Tyne, Tyneside, UK. Posts: 420	Re: P.C.R. 111 radio Hi Paul, You are right I ought not to go drilling holes in the old thing I guess the kindest thing to do is just a capacitor change and use "as is". I do seem to remember a long time ago a "stand alone", BFO unit which came in kit form from some supplier or other, and could (supposedly) provide the required beat frequency without any big modifications to the set in use? I guess it was connected by making an inductive connection to a valve by wrapping an insulated wire around a grid lead or some such? Thanks, Paul.

20th Oct 2008, 9:16 am	#4
davidw Heptode Join Date: Sep 2006 Location: Woodbridge, Suffolk, UK. Posts: 643	Re: P.C.R. 111 radio Just a thought, I used to resolve ssb on a.m by loosely coupling the output of a signal generator to the aerial (a few turns wound round the aerial lead)and injecting something close to the received frequency(ie.offset by the I.F.) With the careful adjustment of the generator frequency and level readable ssb is achievable. Might be worth a try; certainly,as Paul says, don't go drilling holes in it!!!! __________________ Dave G1AGK. My perception is my reality!

20th Oct 2008, 10:22 am	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: P.C.R. 111 radio You could build the oscillator in a separate box and run a wire into the PCR, loosely coupling it to the IF chain somewhere. This would be easily reversible. Paul

20th Oct 2008, 12:57 pm	#7
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: P.C.R. 111 radio You may want to make the BFO output level variable so as not to swamp the AGC on the PCR (unless it has the option for variable RF gain with the AGC off). Just poking a short length of unscreened wire from the BFO into an IF can should provide adequate coupling! Chris

20th Oct 2008, 3:30 pm	#9
dave walsh Dekatron Join Date: Jan 2006 Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex. Posts: 5,817	Re: P.C.R. 111 radio Paul's completely right about the sensitivity. The PSU on mine is currently u/s but it was a surprisingly lively SW set when in use due to that RF amp, which also made conversion to comms mode a real possibility. There are articles in PW from the sixties. If you do a "PCR receiver" search on here Paul [Kalee] there are two threads Nov/Dec 2007 re restoration/derivations and polite disputes about whether it really was just a "Naafi Set" or not. Lots of interesting links and info! Hope this helps you. Dave W

20th Oct 2008, 9:05 pm	#11
JHGibson Retired Dormant Member Join Date: Apr 2003 Location: Salt Spring Island, BC, Canada Posts: 368	Re: P.C.R. 111 radio You can get the effect of a BFO by causing the last IF amp to go into oscillation. Hallicrafters used this simple, cheap method by wrapping a turn of insulated wire around the anode lead, then continuing the wire and wrapping it one turn around the grid lead. The end of the wire then goes to a switch which grounds the wire. When the switch is closed, the wire only induces a neglegible few pf's of capacity to groumd.at the anode and grid. With the swich open, these few pf's are in series from anode to grid and the the IF goes into oscillation. As usual with these simple BFO's, the AGC line will need to be earthed. John.

21st Oct 2008, 5:53 pm	#14
Stockden Heptode Join Date: Mar 2008 Location: Forest of Dean, Gloucestershire, UK. Posts: 648	Re: P.C.R. 111 radio Paul, I've attached scans of the 2 page article as promised. They're not as good as I'd hoped so let me know if you'd like me to have another go. Hugh Attached Thumbnails

21st Oct 2008, 6:07 pm	#15
dave walsh Dekatron Join Date: Jan 2006 Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex. Posts: 5,817	Re: P.C.R. 111 radio Hi Hugh. Which PW is it please? I'm sure I will have it. Dave W

21st Oct 2008, 11:07 pm	#17
dave walsh Dekatron Join Date: Jan 2006 Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex. Posts: 5,817	Re: P.C.R. 111 radio I've only got up to February 1967 so far but the article mentioned at the end of the one supplied by Hugh[ie June 65] is very comprehensive, including a Product Detector/BFO combination. As Paul isn't planning to be too invasive with his set however this may be "interest only". Dave W

22nd Oct 2008, 12:06 am	#18
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: P.C.R. 111 radio I think I remember Hugh's article. It would be from 1968 or 1969 if I'm right. Paul

22nd Oct 2008, 8:29 pm	#19
JHGibson Retired Dormant Member Join Date: Apr 2003 Location: Salt Spring Island, BC, Canada Posts: 368	Re: P.C.R. 111 radio You can also get the last IF to go into controlled oscillation by breaking the earth end of the screen by-pass capacitor wire and inserting a 10K pot there. Withe the pot at zero ohms you get normal receiver operation. As you turn the pot up you get controlled feed back which will improve selectivity somewhat. With the pot increased still more, the IF will start to oscillate and acts as a BFO. This all comes about because the screen grid becomes less effective and the plate to grid capacity increases. John.

22nd Oct 2008, 9:27 pm	#20
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: P.C.R. 111 radio That very article brought back some early radio tinkering memories- I used the screened cable feedback and pot IF gain idea in it on an old radiogram to resolve the strange Donald Duck noises that I had figured must be SSB. I don't recall having the knowledge then about how to short out the AGC line, so it must have been a strong signal! ISTR I did it before we moved away from Worcester which was late '66 or early '67, though. Chris