Freelance 4V Battery Superhet - UK Vintage Radio Repair and Restoration Discussion Forum

Variometer · 14th Mar 2010, 2:59 pm

A few weeks ago, I decided to think up a 4 valve battery superhet circuit. I have never been clever enough to be able to drawn out a circuit, build it and find it works, so I thought I would try a different approach.

The valves I chose were Mazda octals, TP25 (FC), VP23 (IF), HL23DD (Det/1st A.F.), and PEN25 (Output). I chose these because their non-standard bases meant that they can still be obtained cheaply and I have quite a lot of MO valveholders anyway!

I decided to build it in four separate stages. I began with the output stage in the corner of a wooden board that was larger than I would need as I didn’t know how big it would turn out. I tested the output stage by connecting it to a crystal set.

The diode detector/1st A.F. was then added and this was tested by connecting a tuned circuit to it that consisted of the variable capacitor with a 100uH RF choke connected across it. The selectivity was pretty poor, but the volume almost loudspeaker level by this time.

Next, I made the frequency changer and the performance suddenly took off with good selectivity and good loudspeaker strength. The coils in this were two more 100uH RF chokes in the oscillator section and another one in the aerial circuit. I needed to tweak the IF transformer capacitors to get good volume.

Finally, I inserted the IF amplifier valve and after tweaking the IF transformer capacitors, I got excellent volume and selectivity.

The set is powered by a 6 Volt rechargeable battery for LT (dropping resistors in filament legs) and 60 Volts HT from a small mains PSU that I made some time ago. HT current drain is just over 7mA.

Now the circuit is proven, I will eventually move each of the modules from the board (one at a time) and fit them on a polished wooden base.

Problems encountered:
Loud buzz (not mains) appeared when the two audio valves were working. Defied all efforts to cure it, but it disappeared when I fitted the frequency changer stage!

Initially, it wouldn’t work at all when I fitted the frequency changer, but I had simply forgotten to connect the oscillator tuning capacitor up (fixed vanes).

It was all good fun, but I was pretty fed up with it by the time it sprang into life this morning. Will have a rest before transferring it all to the new baseboard.

Bob

Station X · 14th Mar 2010, 3:41 pm

Brilliant job Bob. It would make an excellent teaching aid.

mikelect · 14th Mar 2010, 3:41 pm

Great Stuff Bob, that's the way I like to see things done, no mucking about just get in there and do it

or to the purists the Empirical method

any chance of the circuit ??

Mike

Variometer · 14th Mar 2010, 3:49 pm

Thanks,
The circuit is just a big pile of pencilled notes and crossings out at the moment. I need to sort it all out before I forget what I did. I was intending to write a small book on this sort of thing, but there don't seem to be any publishers about these days in this field!
Bob

Variometer · 14th Mar 2010, 7:02 pm

Here is the rough (very rough) diagram of the frequency changer. Fair amount of experimenting to get it to work OK.
Bob

6.3volts · 15th Mar 2010, 6:45 am

Brilliant result and you must be very pleased. Regarding the 'small book' you want to write-have a look at www.blurb.com. They can produce one or more copies for you. Jonathan

Variometer · 15th Mar 2010, 7:53 am

Hi Jonathan,
Thanks for that. I had a look, but it seems very expensive with prices at £6.95 for 20-40 pages. I believe it is known as POD (Print on Demand), but a pure E-book is more cost effective, as a 16p disk will hold an almost infinite amount of text and images and can be produced on the PC.
I was thinking more about a conventional publisher, but there simply don't seem to be any when it comes to vintage radio!
Bob

Herald1360 · 15th Mar 2010, 1:34 pm

That's getting on for "steampunk". Just add some polished brass......

I like it!

Variometer · 15th Mar 2010, 2:03 pm

There will be some polished brass in it eventually. As I said, it is just at the "proving" stage at the moment. I hope to be able to replace the IF transformers with hom-brew ones soon.
This is a valve radio in my usual style. I have posted it before, but you may not have seen it.
Bob

14th Mar 2010, 2:59 pm	#1
Variometer Retired Dormant Member Join Date: May 2008 Location: Preston, Lancashire, UK. Posts: 428	Freelance 4V Battery Superhet A few weeks ago, I decided to think up a 4 valve battery superhet circuit. I have never been clever enough to be able to drawn out a circuit, build it and find it works, so I thought I would try a different approach. The valves I chose were Mazda octals, TP25 (FC), VP23 (IF), HL23DD (Det/1st A.F.), and PEN25 (Output). I chose these because their non-standard bases meant that they can still be obtained cheaply and I have quite a lot of MO valveholders anyway! I decided to build it in four separate stages. I began with the output stage in the corner of a wooden board that was larger than I would need as I didn’t know how big it would turn out. I tested the output stage by connecting it to a crystal set. The diode detector/1st A.F. was then added and this was tested by connecting a tuned circuit to it that consisted of the variable capacitor with a 100uH RF choke connected across it. The selectivity was pretty poor, but the volume almost loudspeaker level by this time. Next, I made the frequency changer and the performance suddenly took off with good selectivity and good loudspeaker strength. The coils in this were two more 100uH RF chokes in the oscillator section and another one in the aerial circuit. I needed to tweak the IF transformer capacitors to get good volume. Finally, I inserted the IF amplifier valve and after tweaking the IF transformer capacitors, I got excellent volume and selectivity. The set is powered by a 6 Volt rechargeable battery for LT (dropping resistors in filament legs) and 60 Volts HT from a small mains PSU that I made some time ago. HT current drain is just over 7mA. Now the circuit is proven, I will eventually move each of the modules from the board (one at a time) and fit them on a polished wooden base. Problems encountered: Loud buzz (not mains) appeared when the two audio valves were working. Defied all efforts to cure it, but it disappeared when I fitted the frequency changer stage! Initially, it wouldn’t work at all when I fitted the frequency changer, but I had simply forgotten to connect the oscillator tuning capacitor up (fixed vanes). It was all good fun, but I was pretty fed up with it by the time it sprang into life this morning. Will have a rest before transferring it all to the new baseboard. Bob Attached Thumbnails

14th Mar 2010, 3:41 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Freelance 4V Battery Superhet Brilliant job Bob. It would make an excellent teaching aid. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

14th Mar 2010, 3:41 pm	#3
mikelect Retired Dormant Member Join Date: Sep 2003 Location: Wrexham, North Wales, UK. Posts: 799	Re: Freelance 4V Battery Superhet Great Stuff Bob, that's the way I like to see things done, no mucking about just get in there and do it or to the purists the Empirical method any chance of the circuit ?? Mike

14th Mar 2010, 3:49 pm	#4
Variometer Retired Dormant Member Join Date: May 2008 Location: Preston, Lancashire, UK. Posts: 428	Re: Freelance 4V Battery Superhet Thanks, The circuit is just a big pile of pencilled notes and crossings out at the moment. I need to sort it all out before I forget what I did. I was intending to write a small book on this sort of thing, but there don't seem to be any publishers about these days in this field! Bob

14th Mar 2010, 7:02 pm	#5
Variometer Retired Dormant Member Join Date: May 2008 Location: Preston, Lancashire, UK. Posts: 428	Re: Freelance 4V Battery Superhet Here is the rough (very rough) diagram of the frequency changer. Fair amount of experimenting to get it to work OK. Bob Attached Thumbnails

15th Mar 2010, 6:45 am	#6
6.3volts Pentode Join Date: Nov 2009 Location: Welshpool, Powys, UK. Posts: 121	Re: Freelance 4V Battery Superhet Brilliant result and you must be very pleased. Regarding the 'small book' you want to write-have a look at www.blurb.com. They can produce one or more copies for you. Jonathan

15th Mar 2010, 7:53 am	#7
Variometer Retired Dormant Member Join Date: May 2008 Location: Preston, Lancashire, UK. Posts: 428	Re: Freelance 4V Battery Superhet Hi Jonathan, Thanks for that. I had a look, but it seems very expensive with prices at £6.95 for 20-40 pages. I believe it is known as POD (Print on Demand), but a pure E-book is more cost effective, as a 16p disk will hold an almost infinite amount of text and images and can be produced on the PC. I was thinking more about a conventional publisher, but there simply don't seem to be any when it comes to vintage radio! Bob

15th Mar 2010, 1:34 pm	#8
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Freelance 4V Battery Superhet That's getting on for "steampunk". Just add some polished brass...... I like it! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

15th Mar 2010, 2:03 pm	#9
Variometer Retired Dormant Member Join Date: May 2008 Location: Preston, Lancashire, UK. Posts: 428	Re: Freelance 4V Battery Superhet There will be some polished brass in it eventually. As I said, it is just at the "proving" stage at the moment. I hope to be able to replace the IF transformers with hom-brew ones soon. This is a valve radio in my usual style. I have posted it before, but you may not have seen it. Bob Attached Thumbnails