Replacements for old Valve Radio Power Supplies - Page 1
Forum section: electronics / general

author: GlennSprigg
author_rank: Super Contributor
timestamp: May 25, 2020, 01:55:21 pm
content: OLD valve radios needed either mains power, or 'vibrator' circuits, or actual HV batteries.These days, (we) use battery eliminator units. I (we) can & do build circuits to re-createthe needs for battery radios. Now I don't have a problem building many/various units, toreplace the 'traditional' 'A', 'B', 'C' batteries to power such antique valve radios.The typical construction, is using variable out put voltages, to simulate the tube 'heater'volts, as well as the variable 'Plate' voltages, (and more!), usually attained by variablevoltage regulators, and banks of 'Zenner' diodes for voltage division.The MAIN need/drawback/requirement is for the main Transformer!! One can 'scavenge'one from an old radio, with 'taps' for -45v, Com, +45v, and heater voltages etc....Often, you need even higher voltages to inject into a circuit! However, whenever I findan old 'junk' receiver, I want to rebuild it, and not strip it for parts! hahaha...I just want an old 'tranny' to use for this 'use', as I can't build 'That'

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 25, 2020, 02:14:56 pm
content: Hammond Manufacturing does sell "Classic tube" power transformers. Those will always have the essential windings, like CT-tapped plate voltage, 6.3V and/or 12.6V for the vast majority of heater voltages, and 5V for the rectifier tube, if you prefer those instead of solid state rectifiers.If you require another oddball voltage, you can always use another transformer, say 117/24V to provide that voltage.They even produce output transformers and chokes, in case you require them.All of the "big iron" transformers won't be cheap, but the prices are reasonable considering the sheer amount of steel and copper involved.Have a look:https://www.hammfg.com/electronics/transformers/classicOf course, there are other vintage transformer manufacturers, usually geared towards the "audio phool" community, with prices that will make you wet your pants.

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: May 25, 2020, 03:07:21 pm
content: Is rewinding a transformer an option?I have several from cheap ups units that were beyond repair and they have most of the time (for my models) some low voltage secondaries and another one that can be cut and re-wired with a near 1:1 ratio

author: Shock
author_rank: Super Contributor
timestamp: May 25, 2020, 03:12:22 pm
content: There's also transformer rewinding and restoration if you have enough patience. You can either completely rebuild a transformer or rewind/repurpose an existing transformer or build a new one to spec.You can DIY simple winding tools out of a few bits of wood and a couple of bolts. For counting turns you can modify a cheap or old calculator, Dave did a video on this in Eevblog #962. You can get as elaborate as you like.Check youtube a few people show the general idea of whats involved in power transformer rewinding.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 25, 2020, 04:12:45 pm
content: ClassicTone also makes reproduction transformers.

author: GlennSprigg
author_rank: Super Contributor
timestamp: May 27, 2020, 12:22:44 pm
content: Thanks to all for your replies, and I'll check out those places too.Yea... Years ago, I would rewind any transformer/motor, especially when I worked in the 'bush'.About 10 years ago, I rewound my Bench-Grinder motor, just because I could!! haha...I'm just hoping to find a $25 to $40 power tranny made for the job, to save the work!Here in 'Aussie' Land, especially where I am, we are not 'blessed' with the NUMEROUS places,'meets' etc as people are in the USA! (Makes me jealous!)I've seen some complete replacement units/kits on the Net, but are too expensive.Guess I'll have to trash an old radio with all the max voltages I want.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 27, 2020, 08:22:56 pm
content: My advice, if you allow me one?Don't trash the unit. It is worth something.At the very least you can always restore it cosmetically, and place it in a nice display area.That is what I did with an Atwater Kent radio from the 1920s.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 27, 2020, 08:37:38 pm
content: Quote from: schmitt trigger on May 27, 2020, 08:22:56 pmFunctional is way better than "shelf queens". That's like saying "I have a classic car for sale, the engine and transmission are blown but I waxed it to look like new!"

author: floobydust
author_rank: Super Contributor
timestamp: May 27, 2020, 09:08:25 pm
content: I rebuilt a tube radio battery eliminator, a Perma Power Model A, circa 1947.General Transformer Corp. Model A Perma-Power "For sets using 4, 5 or 6 1.5V tubes"Input 110-120VAC 50/60Hz 5watts, Output: 1.4VDC - 350mA, 90VDC - 13mAAlmost too much work to fix it, selenium rectifiers are a PITA, swapped out with 1N4005.1,500uF 3V caps with 2,200uF 16V electrolytic, 40uF 150V caps with 47uF 200V electrolyticAdding a 1/2A line fuse,on-off switch, three-prong line cord with chassis ground, added bleeder resistors and 1N5377 91V 5W zener to limit Vout until the filaments are warmed up.Adding 10nF cap across the rectifiers to limit their RF switching noise. It is a PITA to get the (unregulated) filament voltage accurate.A consequence of no longer having the output floating, is that shorting the radio's antenna terminal (chassis common) to earth ground can blow up either the filaments or other stuff.To make one from scratch today, I would use two small power transformers, connected back to back. Then you can easily set the heater and B+ voltage. You need very low AC hum and ripple as battery-powered sets expect that. A zener for B+ is OK and an LM317 for the heaters might be best.P.S. check out the 1950 prices lol, $2.10 for a selenium rectifier stack in 1950 is worth $22.34 today, almost 10X.edit: added schematic of the radio that used it, notice each A, B supply should be floating not earth grounded.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 29, 2020, 01:33:13 am
content: If you are talking about +/- 45V, why not try to scavenge one from a used/broken A/V receiver? At least around here, people have been giving away these like crazy. Sure, you won't have the 6.3V, but it should be a start, no?

author: Connecteur
author_rank: Frequent Contributor
timestamp: June 08, 2020, 08:08:36 pm
content: Power supplies are a notorious point of failure, particularly in the oldest radios. Back in those days, copper wire was often stretched to make it fine enough for transformer windings. Because the quality of the copper varied, the resulting wire would be of varying thickness, sometimes disintigrating from corrosion or breaking from thermal expansion. Salvaged transformers are increasingly hard to find, therefore a manufactured equivalent or solid state power supply might be the best option. It depends on the owner's preference for the level of authenticity they want to preserve.

author: GlennSprigg
author_rank: Super Contributor
timestamp: June 13, 2020, 12:05:56 pm
content: Yep.. that can & does happen. Audio output transformers are notorious for failing!They are/were of such low construction quality, that 80% of the old originals now fail.To a 'restorer' that is not insurmountable. Simply 'ReWind it'...As a Side-Note of interest... many years go I ran a 200-Amp mains 3-phase supply to aremote (1 km away) main switchboard. In the end, it was 15 feet short of the Termination!!We stretched it with a Tractor, reducing it by a 'few' amps hahahaha... Shit happens!!

author: bd139
author_rank: Super Contributor
timestamp: June 13, 2020, 01:08:29 pm
content: You can get a wide variety of HT voltages by using two cheap low voltage transformers back to back and doubler circuits. Much cheaper than buying hammond stuff!Say you need 6.3v heater and 200v HT:Fat 120:6 first transformer. Pull the heater winding off it. Then attach a smaller 6:120 on it, use a half wave doubler and then use a C-R-C circuit with empirically determines value of R based on the load to drop it down to the voltage you need. This is near infinitely flexible and damn cheap!