Cossor Model 30. (battery) - UK Vintage Radio Repair and Restoration Discussion Forum

longneck90 · 27th Sep 2020, 3:18 pm

Hello to everyone. I have experimented on this Cossor 30, hoping to provide it with a mains power supply. I am about at the end of my tether with it, and I was hoping a Forum Member, or member's might be able to provide me with some advice as to whether such a thing (provide with power supply minus batteries) was/is possible, or, I am just wasting my time. With a hand wound transformer, and a seperate 9 volts from a independent source, I have actually got it going, but... a constant hum, which I have been unable to eliminate, drowns out the reception. Unfortunately, I don't have a valve tester. What makes this power supply complicated, is, there are 5 different voltages. 2, 4.5, 9, 50, and 120 volts. Any advice will be greatly appreciated and valued. All the Best. John.

deswradio · 27th Sep 2020, 3:27 pm

Sounds as though your mains power supply is lacking smoothing - the radio is presumably expecting clean DC. How are you generating all those different power rails? Sunds like a fun project! Best wishes - Des

AC/HL · 27th Sep 2020, 3:44 pm

Bear in mind that the LT supply is just as liable to produce hum as the HT. It's not really worth bothering with GB as the batteries are practically everlasting.

Cobaltblue · 27th Sep 2020, 3:44 pm

Hi John

First thing is that the 2V filament supply needs to be impeccably smooth DC.

The valves are directly heated as you probably gathered.

The grid bias again needs to be super smooth TBH I tend to use batteries for the GB they will last virtually a decade (unless they are duracell

)

It's not quite as fussy on the HT side a decent Cap resistor Cap is usually OK and the 50V supply can just be tapped down from the HT with another resistor and capacitor.

Have you tried batteries on each supply in turn to see which is causing the grief?

It doesn't sound like valve trouble.

Crossed with Des and Bill

Cheers

Mike T

Techman · 27th Sep 2020, 4:52 pm

I agree - power supply, not valves.

Sideband · 27th Sep 2020, 6:21 pm

You need a very smooth LT supply. I used an LM317 regulator adjusted to give exactly 2V, bridge rectifier (from a 6V supply) and a 3300uF smoothing cap. Pretty much hum-free.

Here's the circuit I used to supply my Bush BA91...2V LT and 120V HT, the latter supplied by a voltage doubler.

The four series diodes across the 2V supply are simply to provide protection if the LM317 goes short.

longneck90 · 28th Sep 2020, 1:43 pm

Hello to all. Thanks to everyone for the advice and information. I forgot to mention that 3 seperate voltages were taken from transformer, to 3 W10's to provide voltages (VDC) of Approx. 120,50, and 9 volts. Another winding from transformer provided 2 volts for heaters. It is only after your combined information, that I now realise that the heater voltage must not be AC, which is the voltage I was using. To Sideband. I have used that circuit in other 'battery' radio's. In fact, the radio I am presently listening to, is working happily for long periods with that battery eliminator circuit. Because of the many dillerent voltages needed for the Cossor, I didn't think I would be able to use it with it.
Thanks again for all the useful information which will greatly help me to decide whether to continue with this project. All the best. John.

27th Sep 2020, 3:18 pm	#1
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Cossor Model 30. (battery) Hello to everyone. I have experimented on this Cossor 30, hoping to provide it with a mains power supply. I am about at the end of my tether with it, and I was hoping a Forum Member, or member's might be able to provide me with some advice as to whether such a thing (provide with power supply minus batteries) was/is possible, or, I am just wasting my time. With a hand wound transformer, and a seperate 9 volts from a independent source, I have actually got it going, but... a constant hum, which I have been unable to eliminate, drowns out the reception. Unfortunately, I don't have a valve tester. What makes this power supply complicated, is, there are 5 different voltages. 2, 4.5, 9, 50, and 120 volts. Any advice will be greatly appreciated and valued. All the Best. John.

27th Sep 2020, 3:27 pm	#2
deswradio Tetrode Join Date: Sep 2020 Location: Lewes, East Sussex, UK. Posts: 66	Re: Cossor Model 30. (battery) Sounds as though your mains power supply is lacking smoothing - the radio is presumably expecting clean DC. How are you generating all those different power rails? Sunds like a fun project! Best wishes - Des

27th Sep 2020, 3:44 pm	#3
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Cossor Model 30. (battery) Bear in mind that the LT supply is just as liable to produce hum as the HT. It's not really worth bothering with GB as the batteries are practically everlasting.

27th Sep 2020, 3:44 pm	#4
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	Re: Cossor Model 30. (battery) Hi John First thing is that the 2V filament supply needs to be impeccably smooth DC. The valves are directly heated as you probably gathered. The grid bias again needs to be super smooth TBH I tend to use batteries for the GB they will last virtually a decade (unless they are duracell ) It's not quite as fussy on the HT side a decent Cap resistor Cap is usually OK and the 50V supply can just be tapped down from the HT with another resistor and capacitor. Have you tried batteries on each supply in turn to see which is causing the grief? It doesn't sound like valve trouble. Crossed with Des and Bill Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk Last edited by Cobaltblue; 27th Sep 2020 at 3:46 pm. Reason: crossed with Des and Bill

27th Sep 2020, 4:52 pm	#5
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Cossor Model 30. (battery) I agree - power supply, not valves.

28th Sep 2020, 1:43 pm	#7
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Re: Cossor Model 30. (battery) Hello to all. Thanks to everyone for the advice and information. I forgot to mention that 3 seperate voltages were taken from transformer, to 3 W10's to provide voltages (VDC) of Approx. 120,50, and 9 volts. Another winding from transformer provided 2 volts for heaters. It is only after your combined information, that I now realise that the heater voltage must not be AC, which is the voltage I was using. To Sideband. I have used that circuit in other 'battery' radio's. In fact, the radio I am presently listening to, is working happily for long periods with that battery eliminator circuit. Because of the many dillerent voltages needed for the Cossor, I didn't think I would be able to use it with it. Thanks again for all the useful information which will greatly help me to decide whether to continue with this project. All the best. John.