PM24M valve - UK Vintage Radio Repair and Restoration Discussion Forum

telstar · 22nd May 2023, 4:07 pm

Hi. Can I use a PM24M valve to replace my o/p valve PM24A in my Philips 834A Super inductance radio, or will some components have to be changed?
Cheers
Mike

HamishBoxer · 22nd May 2023, 4:30 pm

The A runs at twice the anode voltage.

Robert Gribnau · 22nd May 2023, 5:38 pm

The heater current of the PM24A is 0,275 A, while that of the PM24M is 1A or even 1.1 A.

So besides handling other differences, you have to be sure that the power transformer can provide this extra 0,725 A or even 0,825 A of heater current.

Cathovisor · 22nd May 2023, 5:48 pm

It will need adaptors to do this, but I have heard of PC86s being used to replace the PM24A - I think I've seen this done in a VE301W before now as the o/p valve in a 301 is quite similar to a PM24A.

Robert Gribnau · 22nd May 2023, 6:25 pm

Perhaps you were thinking of this?

https://www.jogis-roehrenbude.de/Roe...uration/VE.htm

There a PL95 (an output pentode) was used (with an adapter and some other adaptations) to replace a RES164 (an output pentode, like the PM24A).

The PC86 (a triode with modest maximum anode dissipation) was used (with an adapter and some other adaptations) to replace a REN904 (a triode).

Cathovisor · 22nd May 2023, 9:21 pm

I'm pretty sure the PC86 was the output valve - after all, we've used EF80s for that job in TVs! Does sound about right though.

PJL · 23rd May 2023, 9:12 am

Is the original valve missing or faulty? If it is grid leakage then I have had success with the spark generator cure on a PM24A.

Sideband · 23rd May 2023, 10:39 am

Quote:

Originally Posted by telstar

Hi. Can I use a PM24M valve to replace my o/p valve PM24A in my Philips 834A Super inductance radio, or will some components have to be changed?
Cheers
Mike

Mike, you have a PM.

telstar · 23rd May 2023, 2:59 pm

Quote:

Originally Posted by PJL

Is the original valve missing or faulty? If it is grid leakage then I have had success with the spark generator cure on a PM24A.

The output is very weak. It looks like that it was an original valve

Sideband · 23rd May 2023, 10:02 pm

I've offered Mike a good used PM24A. I'm never likely to use it....my 274A uses a PM24M which I was able to replace with an extremely good used type.

The data on the PM24A (middle photo) shows a mutual conductance of 2mA/V. The Avo reads......2mA/V (Mike ignore the 'Replace' marking....that's for rectifiers). The top scale is marked in mA/V. Not bad for an 89 year old valve!

22nd May 2023, 4:07 pm	#1
telstar Octode Join Date: Dec 2003 Location: Leeds, West Yorkshire, UK. Posts: 1,592	PM24M valve Hi. Can I use a PM24M valve to replace my o/p valve PM24A in my Philips 834A Super inductance radio, or will some components have to be changed? Cheers Mike

22nd May 2023, 4:30 pm	#2
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: PM24M valve The A runs at twice the anode voltage. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

22nd May 2023, 5:38 pm	#3
Robert Gribnau Heptode Join Date: May 2017 Location: Konongo, Ghana Posts: 514	Re: PM24M valve The heater current of the PM24A is 0,275 A, while that of the PM24M is 1A or even 1.1 A. So besides handling other differences, you have to be sure that the power transformer can provide this extra 0,725 A or even 0,825 A of heater current. __________________ Robert

22nd May 2023, 5:48 pm	#4
Cathovisor Banned Join Date: Dec 2022 Location: Peterborough, Cambridgeshire, UK. Posts: 418	Re: PM24M valve It will need adaptors to do this, but I have heard of PC86s being used to replace the PM24A - I think I've seen this done in a VE301W before now as the o/p valve in a 301 is quite similar to a PM24A.

22nd May 2023, 6:25 pm	#5
Robert Gribnau Heptode Join Date: May 2017 Location: Konongo, Ghana Posts: 514	Re: PM24M valve Perhaps you were thinking of this? https://www.jogis-roehrenbude.de/Roe...uration/VE.htm There a PL95 (an output pentode) was used (with an adapter and some other adaptations) to replace a RES164 (an output pentode, like the PM24A). The PC86 (a triode with modest maximum anode dissipation) was used (with an adapter and some other adaptations) to replace a REN904 (a triode). __________________ Robert Last edited by Robert Gribnau; 22nd May 2023 at 6:33 pm.

22nd May 2023, 9:21 pm	#6
Cathovisor Banned Join Date: Dec 2022 Location: Peterborough, Cambridgeshire, UK. Posts: 418	Re: PM24M valve I'm pretty sure the PC86 was the output valve - after all, we've used EF80s for that job in TVs! Does sound about right though.

23rd May 2023, 9:12 am	#7
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: PM24M valve Is the original valve missing or faulty? If it is grid leakage then I have had success with the spark generator cure on a PM24A.

23rd May 2023, 10:02 pm	#10
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,571	Re: PM24M valve I've offered Mike a good used PM24A. I'm never likely to use it....my 274A uses a PM24M which I was able to replace with an extremely good used type. The data on the PM24A (middle photo) shows a mutual conductance of 2mA/V. The Avo reads......2mA/V (Mike ignore the 'Replace' marking....that's for rectifiers). The top scale is marked in mA/V. Not bad for an 89 year old valve! Attached Thumbnails __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman..... Last edited by Sideband; 23rd May 2023 at 10:08 pm.