should I or should I not?

[quaddriver]

I got a silvertone 6200A farm radio....meaning battery powered. back and any battery module long gone, case PERFECT.

I can likely get it running, it needs a volt or two for the filaments (look to be loctals) and 90V for the plates....heck I can make an AC power supply nice and clean and filtered for this using a full wave for smooth-ness and it would easily fit in the back.

should I or should I not? Or just offer this up to the farm radio collectors?

[stusnyder]

wood case or Bakelite? Got a pic? There were 3 different versions thru the years of the 6200's

[quaddriver]

Originally Posted by stusnyder

wood case or Bakelite? Got a pic? There were 3 different versions thru the years of the 6200's

Its probably catalin, but same type of thermo...
Ill grab a pic when I get back to it monday

[DavGoodlin]

I would do it. I have an Air Castle farm set I need to do this for. Find a transformer and rectifier combination to supply a well-regulated source to the tube filaments in particular. Battery tubes use the filament as the cathode and ANY ripple on it will be amplified and objectionable for sure.

My experience with doing this on my Atwater Kent 30 showed that the B supply at 90 volts was easy. The heater supply was impossible to filter adequately so, I ended up getting a rechargeable sealed lead acid battery.

[Electronic M]

Originally Posted by DavGoodlin

I would do it. I have an Air Castle farm set I need to do this for. Find a transformer and rectifier combination to supply a well-regulated source to the tube filaments in particular. Battery tubes use the filament as the cathode and ANY ripple on it will be amplified and objectionable for sure.

My experience with doing this on my Atwater Kent 30 showed that the B supply at 90 volts was easy. The heater supply was impossible to filter adequately so, I ended up getting a rechargeable sealed lead acid battery.

If it can't be passively filtered (RLC), then actively filter it! Get a regulator chip like a LM317 (you'll need to feed it a few more VDC than you want to get out) with a filter cap before it and after it, that will drop the hum by orders of magnitude.

[rca2000]

I would BUILD One. Use a small iso tranny-- rect. then filter the output and send it to a regulator--set for 90 volts. I am sure a zener for 90 volts and a 3055 transistor for the reg would work nicely. 200 mA or less of current should suffice.

for the fils....assuming 1.5 volts...use a 6.3 volt tranny at 1.5 amps or so-rect and filter it with about 6800'10 volt cap...--then get a reg ic--adjust it's output to 1.5 volt and post-filter with about 6800 mf of capacitance

ALL of this could be built into the cabinet--to not be visible from the outside.

Now--if you want to use batteries--use about 4 d dry cells..in PARALLEL. use this to power the fils directly. take the output from them and run into a small DC-DC converter--like used for neon blubs. schematics are readily available on-line. Regulate the output to 90 volts using a zener and 3055 transistor. Then post filter with about 470 mf /160 volts cap. This also could be made right into cabinet.

[quaddriver]

well I was thinking those lines last night and it just so happens I have an LM317 floating around, I was going to yank apart a 500ma power supply to take its transformer and rectifier, probably a 9-12volt unit. for the 90volt I have a bunch of 10w cements in various flavors, experiment on todays line voltage to get down to 90ish and a full wave rectifier - I have a few in 1amp

I might need to plug in a .01uf or so here and there to pass any stray ripple....

[Electronic M]

You know direct rectification will yield a hot chassis....A better way to go is (assuming you are using a step down transformer as part of the filament supply) if the fill xformer is say a a reasonably stout 120V-6V transformer, then get a 120V-9V Stepdown transformer, and connect the 9V winding to the 6V....That will give you around 80Vac isolated on the 120V winding of the 9V step down xformer (being used to step up here).

You will get roughly 80*1.414=113V rectified which is easier to resistively divide down than 120V*1.414=170V...You could also use another LM317 to regulate the B+ and get it down to 90V from 113V.

[quaddriver]

Im not sure I am following, I have not cracked it open to see how it was wired, but what I was thinking (without seeing what the on/off control actually looks like - is it double pole or single?) is thus:

polarity correct a plug, where neutral is tied to the chassis - if in fact the chassis is part of the game (dunno yet, but lets assume yes)

hot to the on off. fused. then the other side of the on off to a 120->6v xformer AND, for arguments sake, ab out 150-200ohms of 10W cement.

Take the backside of the cement to a rectifier...half wave ok, but im thinking a full wave might work, since neutral is fixed, the hot side would be +/- line, minus the effect of the resistor (I need to draw this out to make sure I am not stupid) ahh now I see, the value of '-' from the bridge is not the same as the neutral of the AC line...ok back to the drawing board...but the bucking idea for the xformers is interesting, I have 1000ma capable 6, 9, 12, 15 supplies in a box....many dozens.

[DavGoodlin]

Bypass the Silvertone's two-pole on-off switch on the A and B supply. Then use on-off switch for the A and B supply transformer primaries.

Unless this is set requires an external antenna (and earth grounding of the chassis) , grounding the chassis even using the neutral may not be a good idea since it was not designed for "hot" operation.

The step-down/step-up transformer pair for your B supply as Tom says can be had from common wall-warts. I used a trans having a 70-volt secondary (from a defunct Jerrold channel strip amp) and some resistors/caps for 90, 45 and 22.5 volt "B" supplies as required by the AK. I agree actively filtering with a zener and power tab is better.

The "A" supply for filaments is best done using a standard filament transformer like RCA2000 suggests. I need to try this myself. v

Another method for "hum control" on A supply to filaments is to use a 20 ohm wirewound pot to balance (thus cancel) hum by varying the ground reference like on this set http://www.nostalgiaair.org/PagesByM...7/M0044007.pdf