The AM Forum

I got a call from a friend about this, and long story short, I met some 20-year-old kid at a scrapyard in Camden, NJ at 7:00 a.m.  His side-hustle is paying more for than the yard would for stuff that scrappers bring in, then selling stuff online.  He didn't know what this was, but he knew enough.  It was feet from being shredded :)

The scrapper started to pull the transformers apart, and I looked around and luckily found all the pieces.  Copper tank coil was of course gone.

It's interesting, has two large power supplies, modulator, and what looks like a high-frequency amplifier with a 3E29.  Then the finals are 2x813.  It's in really good shape-just dust everywhere.  Now I want to know who built it!  It looks like 40's construction with some 30's parts.

Could the 3E29 amplifier be for 6m?

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The 3E29 tube is your IPA or intermediate power amplifier that drives your push pull 813 tubes. It looks link coupled throughout so to make it work you would need to acquire coils for all the bands you are interested in.  There are too many plates on the variable cap for it to work on six meters efficiently if it would work at all? What is on the deck second from the bottom? (Picture please)

You have everything there to restore that rig if you want to get into changing coils for each band? If it's not for you, maybe you could find and interested party that will actually make it work rather than tear it apart for parts. That would be a real shame!! If I were younger, I would restore it.

The high voltage power supply would probably be 1500 to 2300 volts judging from the era.

Best of luck....Terry

3rd picture down you can see where the coil plugs in.
Regards,
Gary

Wow, what a find.

Relating to the output coil assembly, looks like a B&W HDVL Output Tank and B&W JVL Grid Tank.

See text and images here:
http://amfone.net/Amforum/index.php?topic=9518.0

Another good resource:
http://amfone.net/Amforum/index.php?topic=20517.0

I like that the OM who built this decided to recess mount the panel mater(s) on the RF deck, and cover with a chassis grounded metal screen. Back then it was common to place the plate current meter on the B+ side. With B+ on this created a huge safety hazard. Imagine setting the meter zero adjust with a metal screwdriver.....The OM must have been nailed once or twice, and decided to fix that issue once and for all. Back then it was more common to just "don't do that"! The Heathkit Chippewa Amplifier had the plate meter on the B+ side...a 1960's design, with 3400v B+!

One of the photos may be the modulator deck. If so, that will give you an idea of the RF power, and B+ this thing ran. Those tubes paired up could be 45's, 2A3's, 6A3's, or 6B4's as an audio driver, and perhaps TZ40's as the modulator. If so, I figure about 1250V B+ and 200W DC input to the RF stage. If there are separate, and larger modulator tubes, then go from there.

Did those transformers shown separately come from this rig? Heck, Gary, Wz1M could rewind them from the rocking chair!  :P

Would be interesting to see if you can find the history of this rig. Perhaps a family member is still around. Might find that somebody's grandpa built it and used this rig to pass traffic during a critical time or event. This rig could have been on the air before WW2 began.

Jim
Wd5JKO

Thank you !! for saving that wonderfull piece of transmitter history, It looks so original, very cool.
what an interesting history it must have. Fantastic find !!
It's beautifull, Thank you for saving it, and sharing the pictures with us.
AG5UM

They sure worked mighty hard to get ~160 watts out in those days!  Running  1/4, 1/2 or a full gallon really meant something back then.

Are the chassis' made of galvanized steel or are they aluminum... or something else?

T

Wow good job!

Junk yard rescues forever!

Is the HDVL coil set the largest  "kw-sized" one? I may have some of that stuff here, if you are going to restore it, and it should be restored, but shipping would be quite delayed for reasons.

Gents, thank you.  Have no fear, I saved it for a reason!  The decks are from the Top:
PA
3E29 amplifier
PS + audio amplifier
Huge PS + Modulator
PS (with the loose iron)

The only thing missing on this unit (besides some coils) is an oscillator.  

So the external VFO would feed this.  Is the 3E29 a bold choice for that time?  I read in the data that the tube has a 15 watt capability - so makes me wonder what kind of VFO he had.

n
All the meters are recessed and I was wondering the reason for that.  The downside it's it's difficult to read them with the screen in the way :)

The loose iron was removed from the bottom deck and I guess the scrapper forgot to grab them - lucky me!

Yes, the final tank is HDVL, and I have some laying around, I think for 10m, 80m and maybe 40m.

I drew the diagram out for the modulator, and it really helped finding a 1940s Thordarson transmitter guide from Bunker of Doom website.  The modulator tubes I have to figure out, guessing something in the 8xx numbering due to the length of the plate leads and the bases.

Here are pictures of the bottom side of the PA unit, and the top view of the PS/Modulator.  The modulator transformers are UTC VM-4 and S-9, and that's great because there's plenty of docs available on the "VariMatch" transformers.  The tube pictured is a 242 I stuck in there just to figure out what bases those are.

The chassis are all steel.

Looks like I have a good project.  Not much rust, plenty of mouse crap and dust...really great shape!  I just need to figure out the interconnections, then we'll start working on it...and the biggest piece I have so source is an oscillator - maybe it's time to look for one of those Millen jobs (?)

Thanks all for the comments.  
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My guess is that the original tube was more likely an 829B tube that looks identical but has more plate dissipation than the 3E29. The 3E29 was a WW2 radar & radar jammer tube whereas the 829B was always an RF or audio tube depending on its application. Your rig looks like a late thirty's or very early forties build so if a 3E29 would have been original, I would have thought that some of the parts and practices would been reflective of late forties or very early fifties workmanship. Just my opinion, but it may sound convincing on the Antiques Radio show? If nothing else, now you know that an 829B will work in there and if you ever need either tube, I have them around here somewhere.

BTW, if you can measure your modulator filament voltage, that would go a long way to figure out what tubes may have been in use there.

In this transmitters case it looks as if it's only for high voltage safety not TVI. Old timers often talked about people being killed when they had there hands on the meters, that often were directly in the plate circuit with 2-3 thousand volts on them. I have heard that the path was though the metal zero adjustment screws on them. I never checked to see if there is voltage on a meter at that point but maybe tomorrow, I'll hook a D cell up to one side of a meter and see if it reads anything? On many older BC-610 transmitters the plate meter and mod meters are mounted on Bakelite to isolate them from ground. One modification that was made is exactly what is done on your rig with the recessed meters with screens in front of them. In my case, I am still living dangerously with my BC-610D since the are as original. I just keep my hands off of them and if I ever have any guests about, I warn them about it. If kids are there, I don't operate it. When I am not around, everything is locked.    

It looks like the filament transformer is right under the meter, maybe if luck is with you, you can see the voltages printed on it?

Since the tubes have plate caps they could be 805's, 810,s maybe 203Z's. I know the first two have ten volt filaments but I don't know about the 203z?   Over & out for tonight.......

A very manly transmitter!

Well I've cleaned up the PA deck and moving down to the RF preamp with the 3E29.  I'll replace the 3E29 with the 829B.  Does the builders' choice of 829B indicate he was working in the VHF range?  The finals are 813s, so imagine the op was doing HF.  I measured the tuning capacitors on the input/output sides and each section of each cap is 100pf. 

I'm now hunting for references to coil building (calcs, winding).  On the input side I have a bunch of 5-pin coil forms, and on the output side I'm imagining I could use the B&W JCL/JVL series....and on the input side why wouldn't the MCL (25 Watters) work?

This project is taking awhile but I'm getting there!
73

What is the length of the porcelain jack bar on top of the 813 tube area that is mounted atop the plate tuning capacitor? I think I know what it is but perhaps my eyes are fooling me? No matter that your may be taking longer than you expected to get to some point on your restoration because after all, it is your time ;D ;D

The 3E29 may have been something that was used or just had on hand. I don't think it was on VHF because there are too many plates for one on the plate tuning cap for it to work on VHF. Perhaps running on the low end of 5 or 6 meters would have been possible but I doubt it?

The coils on the input most likely would be the ones with the link in the center of the coil for push pull operation. I'll have to study that a bit further since my knowledge of the model types are a bit rusty.  You are correct with the  B&W JVL series but I'm not sure about the JCL? I think the CL part of it means Center Link where the other type is a Variable Link. Maybe someone else knows about all these links? 

 

Thanks for the response!  The jack bar is 10 1/2" B&W HDV series.  I have a couple of HDVL (center link) coils for 10 and 40 meters, and I think 80m though it needs some repair.

Actually, I did look up the B&W coil nomenclature since I have a huge box of them on-hand.  The J "junior" series are 75 watts, and the M are "baby" 25 watt models.
VL is Variable Link (you can bend the inside coil back and forth)
EL is End link
CL Center link.
The CL coils have a center tap for a bias voltage (use all 5 pins of the socket)

I'll post the schematic of the RF amp later today; I'd be working with the CL coils since there's voltage applied to each.
Thanks for the help!  Looking forward to getting this cleaned up and experimenting.

That is a good save! Well done!

A better way to adjust the link rather than bending them, would be to put a 100-250 variable cap in series with one end of the link to ground. You could use combinations of switched fixed caps along with the variable. I did that with my other BC-610 on the output links where you are quite often trimming up the final plate current. By just setting the link to max coupling and using the variable cap in the link, it felt like I was tuning a pi net circuit. I should do that on my newer BC-610D but I got lazy!