Are these power supplies unworkable? - UK Vintage Radio Repair and Restoration Discussion Forum

bileaflet_valve · 14th Dec 2014, 11:50 am

Help me get my head round this please, guys.

I attach two power supply circuits from pre-war published designs - both essentially the same as regards the HT arrangement.

But they appear to me to be unworkable, in that one end of the HT secondary is connected to the junction between two capacitors. I am familiar with the conventional way of doing things (full-wave either with bridge or with centre-tapped secondary, or half-wave with a single rectifier).

Am I right in thinking the arrangements as shown are unworkable? If so, what do you think was intended?

Les.

kellys_eye · 14th Dec 2014, 12:08 pm

Voltage doubling.

Cobaltblue · 14th Dec 2014, 12:21 pm

Kellys Eye is spot on it's a voltage doubling arrangement commonly used in the early 1930's by manufacturers that preffered copper oxide rectifiers rather than valve rectifiers such as McMichael and PYE to name just two.

Cheers

Mike T

turretslug · 14th Dec 2014, 12:51 pm

It's a recognised "standard" circuit, a straightforward way to think of its operation is to imagine positive-going half-cycles being passed by one diode into one of the capacitors and charging it, the other capacitor being charged by the other diode by negative-going half-cycles. As the circuit is connected across the capacitors in series, the output voltage is double that of a single diode/capacitor half-wave circuit. The regulation is poor, but it's a simple circuit and lives on where it's best suited- generally high-voltage, low-current applications like 'scope high-voltage supplies. Search "voltage doubler", "voltage multiplier" and "Cockroft-Walton multiplier" for explanation, waveforms and extensions/developments of the basic idea

bileaflet_valve · 14th Dec 2014, 5:48 pm

Thank you, gents! No previous experience of voltage doublers, so I've learned something useful today!

Les.

MotorBikeLes · 14th Dec 2014, 6:02 pm

All the earlier TeleQuipment scopes had voltage doubler HT circuits, most CTVs had the taller ladder version, the quintupler, but often referred to as a "Tripler" in generic speak for the CRT's final anode (EHT) voltage.
My first new CTV, a NordMende 2245 hybrid (F2 chassis) had a voltage doubler for the high voltage rail, BUT the second diode was in fact a thyristor, so contolled the HT rail at a chosen voltage. It was actually fed off an auto transformer winding of the main transformer, so, at 320v was rather less than a conventional doubler on the 220v mains of Germany
If you short circuit the output, you don't get the usual fire and destruction, they just sit there fairly quietly.
Les.

GMB · 15th Dec 2014, 10:09 am

There is a huge advantage to using a doubler for generating your HT. Circuits of this form are intrinsically current limited!

14th Dec 2014, 11:50 am	#1
bileaflet_valve Tetrode Join Date: Jun 2011 Location: Leighton Buzzard, Bedfordshire, UK. Posts: 88	Are these power supplies unworkable? Help me get my head round this please, guys. I attach two power supply circuits from pre-war published designs - both essentially the same as regards the HT arrangement. But they appear to me to be unworkable, in that one end of the HT secondary is connected to the junction between two capacitors. I am familiar with the conventional way of doing things (full-wave either with bridge or with centre-tapped secondary, or half-wave with a single rectifier). Am I right in thinking the arrangements as shown are unworkable? If so, what do you think was intended? Les. Attached Thumbnails

14th Dec 2014, 12:08 pm	#2
kellys_eye Octode Join Date: Jan 2014 Location: Oban, Scotland, UK. Posts: 1,129	Re: Are these power supplies unworkable? Voltage doubling.

14th Dec 2014, 12:21 pm	#3
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,863	Re: Are these power supplies unworkable? Kellys Eye is spot on it's a voltage doubling arrangement commonly used in the early 1930's by manufacturers that preffered copper oxide rectifiers rather than valve rectifiers such as McMichael and PYE to name just two. Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

14th Dec 2014, 12:51 pm	#4
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: Are these power supplies unworkable? It's a recognised "standard" circuit, a straightforward way to think of its operation is to imagine positive-going half-cycles being passed by one diode into one of the capacitors and charging it, the other capacitor being charged by the other diode by negative-going half-cycles. As the circuit is connected across the capacitors in series, the output voltage is double that of a single diode/capacitor half-wave circuit. The regulation is poor, but it's a simple circuit and lives on where it's best suited- generally high-voltage, low-current applications like 'scope high-voltage supplies. Search "voltage doubler", "voltage multiplier" and "Cockroft-Walton multiplier" for explanation, waveforms and extensions/developments of the basic idea

14th Dec 2014, 5:48 pm	#5
bileaflet_valve Tetrode Join Date: Jun 2011 Location: Leighton Buzzard, Bedfordshire, UK. Posts: 88	Re: Are these power supplies unworkable? Thank you, gents! No previous experience of voltage doublers, so I've learned something useful today! Les.

14th Dec 2014, 6:02 pm	#6
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Re: Are these power supplies unworkable? All the earlier TeleQuipment scopes had voltage doubler HT circuits, most CTVs had the taller ladder version, the quintupler, but often referred to as a "Tripler" in generic speak for the CRT's final anode (EHT) voltage. My first new CTV, a NordMende 2245 hybrid (F2 chassis) had a voltage doubler for the high voltage rail, BUT the second diode was in fact a thyristor, so contolled the HT rail at a chosen voltage. It was actually fed off an auto transformer winding of the main transformer, so, at 320v was rather less than a conventional doubler on the 220v mains of Germany If you short circuit the output, you don't get the usual fire and destruction, they just sit there fairly quietly. Les.

15th Dec 2014, 10:09 am	#7
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,094	Re: Are these power supplies unworkable? There is a huge advantage to using a doubler for generating your HT. Circuits of this form are intrinsically current limited!