4 valve dull emitter circuit? - UK Vintage Radio Repair and Restoration Discussion Forum

Rishtonite · 14th Jul 2020, 8:07 pm

Hello fellow enthusiasts. New member here.
I have a vintage wireless, assumed to be home built.
Built into the top of a gramophone cabinet.

Pictures on my website at www.g4iat.co.uk/wireless/wireless.html

I'm clueless when it comes to valve circuits so would appreciate any help to restore it.

Valves are Marconi 3 x DER, 1 x DE6, square cross-section wiring. Other parts can be seen in photos. I can take more/better photos if needed.

I've spent some time, intermittently, over the last few years, trying to find a circuit.

I have valve data from the National Museum and have looked at the american/world radiohistory website. Magazines like Modern Wireless and also the Practical Wireless Circuits book by Camm.

So far I've drawn a blank. I'd love to get this set working (assuming the valves still function!)

Can anybody suggest a publication that might have some detail?

Thanks

Ed_Dinning · 14th Jul 2020, 8:19 pm

Hi, the coil/tuner unit was a commercially made part sold through the likes of Wireless World etc in the mid 20's. They often were shown with a suggested circuit and were used in sets designed by the magazine.
A lot of looking through the American Radio History site's scanned copies might reveal something

Ed

Rishtonite · 14th Jul 2020, 10:53 pm

Thanks Ed. I have been looking on the American (now renamed World) Radio History site, not found anything yet, but I don't think I've searched Wireless World.
I've searched for terms like dull emitter, de6, der, variometer.

I did find one open circuit resistor. I forget the full details now but I remember it was cardboard with pencil graphite rubbed on it. I put a modern resistor inside the tube to keep it looking original. Might no be so easy if the caps (sorry - condensers!) or the valves turn out to be faulty.

PJL · 15th Jul 2020, 5:09 pm

It looks almost complete (there is a missing intervalve transformer) and untouched so I suggest you just draw out the circuit as best as you can.

The DER valves are 1.8V filament voltage and the DE6 is 6V so you will need various DC power supplies to provide the two LT, HT and grid bias voltages.

Gridiron · 15th Jul 2020, 7:46 pm

The DE6 is not a 6 volt valve, it has a 1.8 volt filament and is a small power valve (not much power! ) and was used with 2 DER's in the later version of the Marconiphone V3, for instance. Don't put 6 volts on the filament you will burn it out!
The set looks to be a home-made set from the mid to late 20's, the RI (Radio Instruments) tuner unit and HF unit were often used by home constructors and were frequently advertised in radio magazines of the period.
Mike.

PJL · 15th Jul 2020, 7:48 pm

Oops! sorry my mistake.

Rishtonite · 15th Jul 2020, 9:01 pm

I have the valve specs from the museum. I also have a Willard 2v battery, but severely caked up. And an Exide Drydex 9v grid bias battery. Obviously deceased.

The missing "intervalve transformer" was taken off the board. I thought it was a choke and seemed to be open circuit. Lots of turns of enamelled wire which I measured and decided was about 42 swg.

Just found it. Marked AJS Choke Unit 1st Stage and has a "Fixed Condenser" attached to the top. Terminals are marked P, HT+, G and LT-.
Also the resistor I mentioned earlier. AJS, 2.0 ohm (I think between LT- and G, presumably to drop the 2v to 1.8v)

I'm working my way through the history site, looking at Wireless World. Hoping to find a plan rather than having to draw my own.

Herald1360 · 15th Jul 2020, 10:26 pm

That AJS resistor between G and LT- sounds more like a grid leak, as does "cardboard with pencil graphite rubbed on it". If it was marked 2Ω rather than 2ω it is probably 2megohms. There was an old convention where upper case omega (Ω)= megohms and lower case omega (ω) = ohms.

A 2ω resistor would almost certainly have been wirewound at that time, too.

PJL · 15th Jul 2020, 11:34 pm

Sounds like an intervalve unit but with a choke anode load with CR coupling to the grid. Choke from P (plate) to HT+, capacitor from P to G (grid), resistor from G to LT- (grid bias). You will need to check if the C is paper or mica as a paper capacitor will be too leaky to use in that position by now.

Rishtonite · 16th Jul 2020, 10:01 pm

Quote:

Originally Posted by Herald1360

That AJS resistor between G and LT- sounds more like a grid leak, as does "cardboard with pencil graphite rubbed on it". If it was marked 2Ω rather than 2ω it is probably 2megohms. There was an old convention where upper case omega (Ω)= megohms and lower case omega (ω) = ohms.

A 2ω resistor would almost certainly have been wirewound at that time, too.

That's really useful to know and maybe explains why I thought it was o/c.
Yes It's a large omega, same font height as the 2.0
Your advice also matches an advert I found describing the unit.
I'm glad I mentioned it and very grateful of your advice.
I'll add some pictures and scans to my web page (which I have revised)
http://www.g4iat.co.uk/wireless/wireless.html

Rishtonite · 16th Jul 2020, 10:09 pm

Quote:

Originally Posted by PJL

Sounds like an intervalve unit but with a choke anode load with CR coupling to the grid. Choke from P (plate) to HT+, capacitor from P to G (grid), resistor from G to LT- (grid bias). You will need to check if the C is paper or mica as a paper capacitor will be too leaky to use in that position by now.

Thanks. I have a bench psu with variable current limit so I can apply some volts. I also have a capacitance meter.
I'm trying to gather as much information as possible before applying any voltage to the complete set.
There's certainly information scattered in the 1920's wireless magazines but I haven't yet found anything close to a complete circuit.
I suspect I also need to read something like the Camm book to understand how it's supposed to work. The first thing I ever built was with germaniums. I've never really studied valve circuitry.

ms660 · 17th Jul 2020, 10:00 am

Don't apply a filament voltage and HT voltage with the valves in place unless you have first connected a suitable grid bias supply and made sure that the grid bias voltage is reaching the grids.

Lawrence.

Rishtonite · 17th Jul 2020, 12:30 pm

Quote:

Originally Posted by ms660

Don't apply a filament voltage and HT voltage with the valves in place unless you have first connected a suitable grid bias supply and made sure that the grid bias voltage is reaching the grids.

Lawrence.

Thanks for the advice. I still feel I'm a long way off that stage.
I do appreciate that I need to be very careful about powering up as, especially for the valves, it would not be easy to find replacements if anything went pop.

PJL · 17th Jul 2020, 12:30 pm

I would be inclined to replace the valves with less valuable Mullard PM series 2V types.

Rishtonite · 18th Jul 2020, 9:52 pm

Quote:

Originally Posted by PJL

I would be inclined to replace the valves with less valuable Mullard PM series 2V types.

Thanks for the suggestion. I'll see if I can find any.
I'm still accumulating information about the set.
I have no desire to rush and then regret something later.
I'll look up what other makes/valves might be suitable.

And to answer another query - quote - You will need to check if the C is paper or mica - According to the advert for the AJS choke it's mica.
But I'll be checking all the components individually before any volts are applied.

14th Jul 2020, 8:07 pm	#1
Rishtonite Triode Join Date: Jul 2020 Location: Darwen, Lancashire, UK Posts: 11	4 valve dull emitter circuit? Hello fellow enthusiasts. New member here. I have a vintage wireless, assumed to be home built. Built into the top of a gramophone cabinet. Pictures on my website at www.g4iat.co.uk/wireless/wireless.html I'm clueless when it comes to valve circuits so would appreciate any help to restore it. Valves are Marconi 3 x DER, 1 x DE6, square cross-section wiring. Other parts can be seen in photos. I can take more/better photos if needed. I've spent some time, intermittently, over the last few years, trying to find a circuit. I have valve data from the National Museum and have looked at the american/world radiohistory website. Magazines like Modern Wireless and also the Practical Wireless Circuits book by Camm. So far I've drawn a blank. I'd love to get this set working (assuming the valves still function!) Can anybody suggest a publication that might have some detail? Thanks

14th Jul 2020, 8:19 pm	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,196	Re: 4 valve dull emitter circuit? Hi, the coil/tuner unit was a commercially made part sold through the likes of Wireless World etc in the mid 20's. They often were shown with a suggested circuit and were used in sets designed by the magazine. A lot of looking through the American Radio History site's scanned copies might reveal something Ed

14th Jul 2020, 10:53 pm	#3
Rishtonite Triode Join Date: Jul 2020 Location: Darwen, Lancashire, UK Posts: 11	Re: 4 valve dull emitter circuit? Thanks Ed. I have been looking on the American (now renamed World) Radio History site, not found anything yet, but I don't think I've searched Wireless World. I've searched for terms like dull emitter, de6, der, variometer. I did find one open circuit resistor. I forget the full details now but I remember it was cardboard with pencil graphite rubbed on it. I put a modern resistor inside the tube to keep it looking original. Might no be so easy if the caps (sorry - condensers!) or the valves turn out to be faulty.

15th Jul 2020, 5:09 pm	#4
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 4 valve dull emitter circuit? It looks almost complete (there is a missing intervalve transformer) and untouched so I suggest you just draw out the circuit as best as you can. The DER valves are 1.8V filament voltage and the DE6 is 6V so you will need various DC power supplies to provide the two LT, HT and grid bias voltages.

15th Jul 2020, 7:46 pm	#5
Gridiron Heptode Join Date: Apr 2010 Location: West Midlands, UK. Posts: 663	Re: 4 valve dull emitter circuit? The DE6 is not a 6 volt valve, it has a 1.8 volt filament and is a small power valve (not much power! ) and was used with 2 DER's in the later version of the Marconiphone V3, for instance. Don't put 6 volts on the filament you will burn it out! The set looks to be a home-made set from the mid to late 20's, the RI (Radio Instruments) tuner unit and HF unit were often used by home constructors and were frequently advertised in radio magazines of the period. Mike.

15th Jul 2020, 7:48 pm	#6
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 4 valve dull emitter circuit? Oops! sorry my mistake.

15th Jul 2020, 9:01 pm	#7
Rishtonite Triode Join Date: Jul 2020 Location: Darwen, Lancashire, UK Posts: 11	Re: 4 valve dull emitter circuit? I have the valve specs from the museum. I also have a Willard 2v battery, but severely caked up. And an Exide Drydex 9v grid bias battery. Obviously deceased. The missing "intervalve transformer" was taken off the board. I thought it was a choke and seemed to be open circuit. Lots of turns of enamelled wire which I measured and decided was about 42 swg. Just found it. Marked AJS Choke Unit 1st Stage and has a "Fixed Condenser" attached to the top. Terminals are marked P, HT+, G and LT-. Also the resistor I mentioned earlier. AJS, 2.0 ohm (I think between LT- and G, presumably to drop the 2v to 1.8v) I'm working my way through the history site, looking at Wireless World. Hoping to find a plan rather than having to draw my own.

15th Jul 2020, 10:26 pm	#8
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: 4 valve dull emitter circuit? That AJS resistor between G and LT- sounds more like a grid leak, as does "cardboard with pencil graphite rubbed on it". If it was marked 2Ω rather than 2ω it is probably 2megohms. There was an old convention where upper case omega (Ω)= megohms and lower case omega (ω) = ohms. A 2ω resistor would almost certainly have been wirewound at that time, too. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

15th Jul 2020, 11:34 pm	#9
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 4 valve dull emitter circuit? Sounds like an intervalve unit but with a choke anode load with CR coupling to the grid. Choke from P (plate) to HT+, capacitor from P to G (grid), resistor from G to LT- (grid bias). You will need to check if the C is paper or mica as a paper capacitor will be too leaky to use in that position by now.

17th Jul 2020, 10:00 am	#12
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: 4 valve dull emitter circuit? Don't apply a filament voltage and HT voltage with the valves in place unless you have first connected a suitable grid bias supply and made sure that the grid bias voltage is reaching the grids. Lawrence.

17th Jul 2020, 12:30 pm	#14
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 4 valve dull emitter circuit? I would be inclined to replace the valves with less valuable Mullard PM series 2V types.