DC PSU Chokes - UK Vintage Radio Repair and Restoration Discussion Forum

Wendymott · 10th Mar 2024, 11:41 pm

Hi peeps. After my purchase of the Codar AT5 tx's. Although I now have a lab Farnell E350 psu, I want to make a self standing PSU for the AT5. The original Codar PSU states 16 uf X 2 caps and a 10H 100 m/A choke.
Did I read somewhere that the Mod transformer could be used. As I have two AT5's that would not be a problem. However, is it true that the laminations are organised differently from an audio transformer.
I purchased 5 X 100 uF @ 450V from Farnell, and I have approx 12V P/P ripple on a HT of 300V from the Radford Labpack psu.
A lot of questions there, but I am sure one answer

Ed_Dinning · 11th Mar 2024, 4:46 am

Hi Wendy, In a transformer the lams are interleaved
In a single ended op trans and a choke the lams are all stacked together , normally with a few thou air gap or paper packing. A tapering air gap is used in swinging chokes.

Ed

Radio Wrangler · 11th Mar 2024, 6:04 am

The inductance of the mod transformer, if designed for comms will be suitd for frequencies down to about 600Hz. For a power supply you'll need more inductance to be good at 100Hz.

Mod transformers of the smaller style with single-ended modulators can run the DC bias currents in oposite directions and so get an easier ride as far as saturation is concerned. Mod transformers of larger size intended for push-pull modulator amps get some cancellation of the modulator DC bias, but none of the RF side of things. So there is some value, but a lot of the core is filled with wire you won't be using in a choke. You could use primary and secondary windings in series to build more inductance, but you get more ampere-turns of flux, and you run into saturation limits.

So a choke designed as a choke can make advantage of the full core capabilities. Done optimised as a transformer, it won't be so good unless you are very lucky.

Dismantling the clamp and changing the inert shim thickness gives you a little wiggle room.

David

Bazz4CQJ · 11th Mar 2024, 7:01 am

Quite surprisingly, I still have 2 or 3 of the 10H chokes bought in RSC when they were in the Grand Arcade in Leeds c1970. At the time, I thought those chokes and transformers they sold were definitely budget items, but 50 years later, none have failed

.

B

Wendymott · 11th Mar 2024, 12:20 pm

Hi peeps.. Thanks for the replies. Bazz do you wish to let one escape from your collection ? . RSC I remember well, my father bought the "Linear Diatonic" and the larger amps for his dance school business. A Long shot I know, but if anyone has a mains transformer from one of those, gold "sheckles" could be traded,

10th Mar 2024, 11:41 pm	#1
Wendymott Octode Join Date: Jun 2013 Location: Huddersfield, West Yorkshire, UK. Posts: 1,796	DC PSU Chokes Hi peeps. After my purchase of the Codar AT5 tx's. Although I now have a lab Farnell E350 psu, I want to make a self standing PSU for the AT5. The original Codar PSU states 16 uf X 2 caps and a 10H 100 m/A choke. Did I read somewhere that the Mod transformer could be used. As I have two AT5's that would not be a problem. However, is it true that the laminations are organised differently from an audio transformer. I purchased 5 X 100 uF @ 450V from Farnell, and I have approx 12V P/P ripple on a HT of 300V from the Radford Labpack psu. A lot of questions there, but I am sure one answer __________________ Should get out more. Regards Wendy G8BZY

11th Mar 2024, 4:46 am	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,198	Re: DC PSU Chokes Hi Wendy, In a transformer the lams are interleaved In a single ended op trans and a choke the lams are all stacked together , normally with a few thou air gap or paper packing. A tapering air gap is used in swinging chokes. Ed

11th Mar 2024, 6:04 am	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,917	Re: DC PSU Chokes The inductance of the mod transformer, if designed for comms will be suitd for frequencies down to about 600Hz. For a power supply you'll need more inductance to be good at 100Hz. Mod transformers of the smaller style with single-ended modulators can run the DC bias currents in oposite directions and so get an easier ride as far as saturation is concerned. Mod transformers of larger size intended for push-pull modulator amps get some cancellation of the modulator DC bias, but none of the RF side of things. So there is some value, but a lot of the core is filled with wire you won't be using in a choke. You could use primary and secondary windings in series to build more inductance, but you get more ampere-turns of flux, and you run into saturation limits. So a choke designed as a choke can make advantage of the full core capabilities. Done optimised as a transformer, it won't be so good unless you are very lucky. Dismantling the clamp and changing the inert shim thickness gives you a little wiggle room. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

11th Mar 2024, 7:01 am	#4
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,935	Re: DC PSU Chokes Quite surprisingly, I still have 2 or 3 of the 10H chokes bought in RSC when they were in the Grand Arcade in Leeds c1970. At the time, I thought those chokes and transformers they sold were definitely budget items, but 50 years later, none have failed . B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

11th Mar 2024, 12:20 pm	#5
Wendymott Octode Join Date: Jun 2013 Location: Huddersfield, West Yorkshire, UK. Posts: 1,796	Re: DC PSU Chokes Hi peeps.. Thanks for the replies. Bazz do you wish to let one escape from your collection ? . RSC I remember well, my father bought the "Linear Diatonic" and the larger amps for his dance school business. A Long shot I know, but if anyone has a mains transformer from one of those, gold "sheckles" could be traded, __________________ Should get out more. Regards Wendy G8BZY