[Bob Andersen]

Hi guys.

I picked up a Philco 643 recent that needs a little help. Here are some pics: http://www.flickr.com/photos/70039806@N0...649036115/

1. I'm going to refinish the cabinet and I'm trying to figure out what color paint was used on the sides, top and trim. I've seen 'Van Dyke Brown' mentioned in this forum. Do you think that's right for this model?

2. This set was modified long ago from battery to AC operation and the entire output stage was replaced. It used to 30 & 19 tubes driving the output transformer. Now, there's an 80 rectifier in the 19 socket and a 6V6s in the 30 socket. I think the old battery connector has been modified to hold another 6V6 but I'm not sure since it was empty when I received it. I haven't powered the set up or reversed all the mods. yet so I'm not sure if it even works.

So, would you recommend restoring to the original schematic or trying to decipher the mods and get them working?

Thanks, and happy new year!

Bob

[Ron Ramirez]

Hi Bob, and welcome.

I recommend Extra Dark Walnut for the top, sides and trim. It does not have the greenish tint that the Van Dyke Brown has, yet still has the desired dark color. Remember, Medium Walnut for the front panel.

If that chassis has been as heavily modified as I suspect it has, I would suggest you try and find a 640 or 650 chassis, which is a true AC chassis, and install it in your cabinet instead; perhaps saving that butcher job chassis for parts.

Maybe Brian (BDM) will chime in here. Who knows, he may well have a spare 650 chassis, or might be able to steer you in the right direction. One thing, though; if you install a 640 or 650, you'll need to replace the escutcheon with one with a window for the shadow meter above the dial since the 643 did not use a shadow meter.

This is a shame. The 643 was Philco's top of the line farm set for 1936.

[Bob Andersen]

Hi Don,

Thanks for the great info. I've noticed other posters using Mohawk toner instead of stain. Does toner work better? I've never used it before.

Yes, it is a shame about the chassis, but I'm not giving up just yet. The RF and IF stages look to be all original and in great shape. The guy who did the AC mod actually did a pretty good job and used a solid transformer. He even left a note inside "Rewired 10-29-1939 by F.E. Francisco W8OUD" That area of the chassis was pretty bare to begin with. It's really just the output stage that's ugly. I think I'll reverse engineer it and draw up a schematic. I'll work on the cabinet while I ponder the chassis.

Thanks again for the help.

Bob

[Ron Ramirez]

Don's my evil twin brother - I'm Ron

When I mentioned colors, I was referring to Mohawk toning lacquer. Sorry for not being more clear about that. Toning lacquer is very similar to what the original finish was, which was lacquer with aniline dyes mixed in to give it a transparent color (or opaque color as in the case of the top, sides and trim on sets like your 643B).

Well, good luck to you in your reverse engineering. I hope it works out OK. Please feel free to jump in here anytime if we can be of help.

[Bob Andersen]

Yeah, I meant Ron.

Time to put my BSEE degree to work. Too bad I switched to programming 15 years ago and forgot a lot...

I''l let you know how it goes.

[AI2V]

The audio stage was probably rewired for use with a 6F6; the 6V6 didn't gain much radio use until after 1940; it doesn't really matter since the wiring for both is the same and the output power is roughly the same in general use.

As a cheap and common alternative I sometimes use the cooler running 6K6 in these audio stages; these are the long lived audio tubes used in the 1950's TV's. All three, the 6F6, 6V6, and 6K6 use the same wiring. If you want slightly higher volume (and heat) a 6L6 will also work.

[Bob Andersen]

Thanks for the info - I didn't realize they all had the same wiring. I assumed 6V6s might be used because I found one rattling around loose in the box my radio arrived in.

[Arran]

If it were me I would put the set back to original, after making a close inspection to see whether all the hard to replace parts are there, or find another battery chassis of the same model. One good part is that you have the basis to build an excellent battery eliminator with that added power transformer, I would remove it and set about building an A, B, C supply out of it on a different chassis. It's not the worse AC conversion that I have seen but it is still amateur looking, with some its very difficult to tell. Not to run down ham operators but this is typical of much of the mod work I have seen, we know this since he autographed the set with his name and call sign, for some a ticket for Morse code also implied a degree in electronic engineering.
Happy Christmas
Happy New Year

[BDM]

Yikes! Someone got there money from that set. My 650 parts chassis is basically parts. It's resurrected two 650 sets

[Bob Andersen]

It turned out to be worse than I thought. All the original 1XX tubes have been replaced with 6XX tubes. I wouldn't be surprised if the biasing was tweaked too. After verifying the there were no shorts and so on, I did fire it up. It kinda works, but I'm guessing the identity of the missing tube and who knows what else might be wrong! So for the time being, I'm just going to restore the cabinet and keep my eyes open for a suitable replacement chassis. At least my 37-10, 38-10 and 39-30 are all working to perfection

[Arran]

Most battery type tubes from the thirties and forties are fairly inexpensive, barring anyone changing tube sockets, putting it back to original is mostly a matter of following the original 643 schematic step by step and replacing the resistors and condensers one by one along with the wiring. I would be surprised if the coils were changed.
Best Regards
Arran

[Bob Andersen]

Thanks for the input and you're right about the coils. I agree in general, but as Ron pointed out, this is a top of the line set. It covers 4 bands and uses 7 tubes. So, I'd need to track down those 7 tubes, remove the added AC trans and filter caps, undo the wiring changes and restore any other modified or bad components. Plus, I think the audio transformer has been replaced along with the speaker. Certainly possible, but I don't have the funds or time for that right now

[Bob Andersen]

Well, it's been about a year since my last post and I've got some good news! I finally have all seven tubes and will be attempting to restore this set to it's original DC design

I'll start a new thread under Electronic Restoration when I dig into it. I'm sure I'll need some advice.

[Image: http://farm5.static.flickr.com/4061/4331...5be6_b.jpg]

[Bob Andersen]

After many months of searching, I finally found an unmodified chassis It looks to be all original except for the power/volume control.

Now I can really see how extensive the AC modifications really are. Note that I've removed the power transformer on the AC modified chassis on the right.

[Image: http://farm7.static.flickr.com/6139/5919...9776_z.jpg]

[Image: http://farm7.static.flickr.com/6021/5919...180b_z.jpg]

[TA Forbes]

That's some great news. The 643 is one that I would like to find too. Let me know If you need an escutchion for it, as I have several of the larger non shadow meter variety that are in nice shape.

Agree with the advice about a power supply for your radio that will run off of AC. I have one that provides proper and adjustable A, B, and C voltages, and makes it convenient to listen to your battery sets. Agree with Arran in that battery sets are usually cheaper and in better condition than their AC powered cousins.

There are also several people out there who make batteries for your battery sets by combining modern dry cell batteries and packaging them in retro labelled containers. Although I do not have any of them, I think it would be both neat and practical (in the case of a power outage) to have battery power available.