SMPS using a TV horizontal output valve - Page 1
Forum section: electronics / projects

author: Circlotron
author_rank: Super Contributor
timestamp: May 18, 2021, 05:30:17 am
content: I wonder if anyone has ever made a switch mode power supply using a TV horizontal output valve / sweep tube? The way they are meant to be used is not all that different from a power supply, and seeing many of them will tolerate a +6kV pulse on the anode, you could have a duty cycle of >90% and consequently good transformer utilization and lower DC output ripple. Driving the control grid positive say 10V or so during the on-time wouldn't hurt either. Interesting to see what kind of frequency it could run at, given a suitable driver. I expect given the cathode current limits of available valves and using a 340VDC buss things might top out at about 50 watts max. Actually, no reason you couldn't use a voltage doubler and a 680VDC buss and double the available output for a given valve. Of course, this isn't meant to be a practical solution to anything in this day and age, just an experiment to see what could be done.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 18, 2021, 08:06:50 am
content: Tektronix did for a number of EHT supplies. Typical circuit is a blocking oscillator or class C oscillator, same as the TVs they came from. Control usually by grid or screen bias.I've done it personally, not so much for power delivery purposes but as an audio experiment years ago:https://www.seventransistorlabs.com/tmoranwms/Elec_Compound2.htmlAs you can guess from the linearity (of the final version at the bottom), it sounds pretty good, given that it's only a few watts due to the "class A" output network.Tim

author: SeanB
author_rank: Super Contributor
timestamp: May 18, 2021, 10:16:12 am
content: Tim, wonder if a pair of CRT's could be repurposed into drivers for an ES speaker then, seeing as your anode voltage would be in the kilovolt range. Would need a big enclosure, but you can use the CRT aquadag connections as the output coupling capacitor for this.

author: Terry Bites
author_rank: Super Contributor
timestamp: May 18, 2021, 12:22:00 pm
content: The EHT and HT boost come from from the line output transformer. So its an HV SEPIC conceived in the 1930s and used unti the 1970's.So yes thought of before. Tube SMPS date at least back to the 1940's.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 18, 2021, 01:59:17 pm
content: Quote from: SeanB on May 18, 2021, 10:16:12 amHah, nah, beam current too low. Similarly 6BK4C and friends -- same ratings as CRT, for obvious(?) reasons. Regular receiving tubes aren't bad, honestly -- EL34, 6BG6 for example, you don't need all that much voltage to get a fair amount of power, AFAIK. Especially so on smaller ones (ESL headphones?). Higher voltages (over 1kV or so?) really need transmitter types AFAIK, or you find a specialty triode like 2C53?Aquadag coupling capacitor, that's a new one.Tim

author: CaptDon
author_rank: Super Contributor
timestamp: May 18, 2021, 03:12:11 pm
content: A little off topic but relates to your Horizontal Output Stage, have you ever seen the absolutely bizarre 'two SCR' horizontal output section that RCA used in the old XL100 series of 19" portable color T.V.'s??? It was a go-or-blow circuit!! You really had to use the RCA sourced SCR's. If you tried the ECG replacements POW out went the main line fuse. It was a commutating circuit (SCR's with a D.C. supply voltage) that often failed to commutate!!

author: PKTKS
author_rank: Super Contributor
timestamp: May 18, 2021, 04:40:52 pm
content: Not sure if you mean like "doing yourself one..."or just wondering what is already available..As a matter of fact I was an active TV repairmanover the 70s 80s ...And I have over 10.000 service manuals and stuff ...All TVs are SMPS "FLYBACK" class based...All TVs "FLYBACK" sets in the 70s are TUBE based..PL509 PENTODE is a rather typical H-drive ...it handles up to 7kV of raw spikes just ordinarilyThey ALL operate at nominal 15.750 Hz andthe output stage holds above 1KV typicalbut overall output power is rather low...Things changed in early 80s with high voltage BIPOLARtransistors being used instead of classic PENTODE + DIODEtubes in the HORIZONTAL and HT stage...My bench stuff attached..Paul

author: Circlotron
author_rank: Super Contributor
timestamp: May 18, 2021, 11:16:53 pm
content: Quote from: CaptDon on May 18, 2021, 03:12:11 pmI’ve never actually seen the circuit but I have heard of SCRs being used in horizontal output stage. SCR forced commutation circuits are for the most part a lost art. They got the attention of some very smart minds back in the day.