[DanH6464]

In regard to David's mention of a Schematic...I expected there to be math involved but not ART! lol...and to answer the 35Z3 tube socket question there is no hardware holding it in place. The tube socket does not have any "ears" to screw it to the chassis so it is soldered directly to the chassis. I can't really see coverting it back to a battery set especially with what was involved in modifying this set. I'm sure that purists would disagree with me on this. I'm sure that we can all agree that when you're poor or can't find the parts you need you improvise and make do. I can repect that and even honor it. Seems more appropriate to keep it just like it is. My concern however is..after recapping and re-insulating the wires...being unfamilar with this set up...is it going to go up like a roman candle and set the house on fire???

[morzh]

I would keep the radio in its present shape, get the correct tubes for the AC mod, check the wiring for bad things and try to power (obviously after proper recap and such).

This is in fact much simpler than a transformer radio: you have a string of filaments, no ballast, so the cord needs not be the curtain burner etc.
The rectifier is also straightforward.

I restored one like this for Kirk - I mean, not modded, but similar lineup for an AA5 with no schematic - just check for common sense things.

[DanH6464]

I would really appreciate some guidance on proper tube line up for this modification.

[David]

GEradiomodel115.pdf Size: 202.11 KB  Downloads: 175

Hope this helps the person who made the mods did only what was necessary to make parts on hand work. Print out several copies of the orginal sch. next go to  http://frank.pocnet.net/ look up the tubes you found in the set and print out. Mark the replacement on the sch with corresponding tube pin changes. Since the set did not have a rectifier tube look at the fellowing PDF for a general ideal of a AA5 without a pilot light your set has a 35Z3 the PDF shows a 35Z5GT electrically they are the same just a different base and different pin assigment.  Hope this helps take your time draw every thing out ask question folks here are willing to help. David

[vinzer]

this could a very dangerous radio to use with out an isolation transformer.

[mikethedruid]

First, let's start with a link to the schematic of the 39-70. http://www.nostalgiaair.org/PagesByModel...013302.pdf

First thing I see is that all the filaments were originally wired in parallel to ground rather than in series, so the first thing to look at is the way the filaments have been rewired. To do this properly, first let's look at the data on the tubes you have.

35Z3 AC rectifier... 50L6 audio output amp, replaces the original 1C5.... 12SA7 pentagrid converter would replace the 1A7 of the original... the 12SK7 is used as the IF amp in place of the 1N5... the 12Q7 is used as the 2nd detector, ist audio amp in place of the 1H5. You can find data on all these tubes here http://www.nucow.com/Free%20Tube%20Data%...20data.pdf

I will leave it up to you to check if the pinouts match, and how closely. Please keep us posed on the developments of this project. It is really interesting.

[mikethedruid]

I also found these pages, with typical AA5 schematics. Hope they help.
http://www.wa2ise.com/#aa5
http://www.wa2ise.com/
The latter is the home of the former. Lots of information there you may find either helpful or interesting.

[Arran]

 I rather resent the current fashion of using "purist" as a pejorative, as though to denounce or belittle sound preservation and workmanlike restoration techniques. It's been my experience that it often easier to put a radio, or anything, back to original, or at least start over from scratch, then it is to try to get into the head of whoever modified the set. From what I can see they left all of the original coils in place, the only thing missing is the original output transformer which was supposedly mounted under the chassis, other then the tube shield bases being removed from the 1N7G and 1A7G sockets. It would not take that much to convert it back into a battery radio again, if you forget about the Philco style tube shields, although you could probably find an unmolested chassis to restore instead.
  The question is did this thing ever work after they did all these mods to it, and if it did how well did it work? I've never actually seen a farm battery radio converted to AC operation using AC tubes, that was successful. Most I've seen are borderline hack jobs, to outright hack jobs. I think that most people who wanted to run a battery set on AC either bought a power supply like a Sears Power-Shiftr or an Electro where you could plug your battery cables into the supply, or they built a home brew one. I have a plan for a home brew one out of a Radio Craft/Radio Electronics magazine from the 1940s, although there are obviously more modern designs now. This isn't to say that it could not be done properly, but I would pretty much ignore whatever this last guy did to it and treat it like a clean slate. To make everything work properly you would have to change more then just the B+ circuitry and the filament wiring from parallel to series string, things like resistor values and biasing would need to be changed, for example. I'm also not sure if an oscillator coil designed for use with a 1A7G would work with a 12SA7, the antenna coil would be fine, and the IF transformers I think would be the same.
  I don't really know how one would get away with just soldering a tube socket in place, unless it had metal ears that they then soldered to the chassis, if it was held in place by attempting to solder the socket tie points to the chassis then they were shaking hands with danger doing so with a rectifier tube. What do we normally have with a 35Z5 or 35Z3? Well we have the hot side of the AC power line going to one end of the tube heater and also to the plate pin, if that socket decides to shift, and one of those pins touches the chassis, look out! So I would get a socket that does have mounting ears and rivet or mount it in with machine screws and nuts, or find one of the types that uses a locking ring, which are harder to find. I'm sure that someone here could provide you with either type, at least an octal one.
Regards
Arran
 

[DanH6464]

I'd like to start by thanking everyone for the much needed and heeded information and advice from everyone. I am very new to this hobby/obsession and to quote my girlfriend I'm "eat up with it" lol. Arran it most certainly was not my intention to offend by using the word purist. Having not been involved with this activity for decades like some on here, I am forced to educate myself through the literature I can find and the kindness of strangers on forums like this. A lot of people who post on these forums give the unseasoned eye the impression that it would be in poor taste to make a wire substitution with something not made by a blacksmith and insulated with seventy year old textiles. It has been my experience that those inflexible few are but a small percentage of the growing number of passionate people involved in breathing life back into these magic boxes that pull words and music out of the air with glowing globes of glass and magic. I started this endevor because I wanted to restore my grandparent's 1934 Philco 45L lowboy which has had a prominate place in my home my whole life. It holds a lot of wonderful memories of my childhood in the 60's. Not wishing to cause it more harm than good, I bought two basket case radios, a hairs breath from the landfil for thirty dollars to learn on and make my bones before tackling the heirloom. My other basket case is a 37-93 with a hole in the top you can put a fist through and a speaker with about two square inches of cone left. Both of these have been quite the learning experience. One of them I think lived in a swamp and the other is a puzzle that is absolutely facinating. There is much more about this chassis and set up that I don't know then what I know. I'll ride the train for a while until it looks like it's going off a cliff and then at that point I'll make a different plan...perhaps with a different chassis. I've now kind of become attached to this redhead of a radio so I'll keep everybody posted on what happens. I'm making a wire diagram of what's in place and compare it with the info from David and mikethedruid and compare with the tube info then go from there. I am definitely open to anyone's suggestions here and thanks again to everyone

[mikethedruid]

Dan, don't worry about the "purists." We each have our techniques for bringing these old radios back to life. Some people go to the trouble of stripping the guts out of the old wax and paper caps, and stuffing them with new poly caps; I don't. I replace the original caps with their poly cap equivalent, and don't try to hide the changes. I feel that unless this is a museum restoration, it is better to leave clear evidence of MY repair work, for the next guy to be able to see what has been done over the years. Also, I suppose it is just habit. When I started repairing these old sets, they were not considered "antiques." A lot of people just considered them "old junk," which made them cheap to buy and learn on for a budding EE like myself. I simply put in the modern equivalent and didn't worry further. As for your set's conversion, if the tubes were carefully chosen, and the job done correctly, there is no real reason why a farm set so converted should not work as well as it originally did. I will be very interested to see how far your set varies from the original schematic, and how the new B power supply is wired.

[David]

AidsToWarTimeServicing1945.pdf Size: 3.23 MB  Downloads: 154

I downloaded this around 2 years ago, gives one a idea of the effort folks made to keep radios going during WWII.  David

[7chip7]

Thank you for that link Dave, makes sense , the document could be handy for replacing a tube you don't have with one you do have, especially AC DC sets
thanks again
Chip