Bendix Aircraft AM

[WU2D]

Well Al,

It looks like we have a couple of Bendix TA-12B's to get on the air! Nearfest was fruitful today and it is good to have friends like Brown NZR. I was thinking of staying pretty close to the original on the modulator (power supply will be AC and not a Dynamotor though) but I like the 6N7, 6F6 and pair of 807 scheme and will stick with it.

Mike WU2D

[Opcom]

Am I missing something or how is Channel 1 tuned? There seems to be no control for that, just 2, 3, and 4. Nice looking set that's for sure!

[WU2D]

We shall see how it fires up. I don't have any knowledge about the radio yet other than what I have read. Apparently a lot of Hams used them in the 50's and 60's as a cheap and stable entry rig.

The TA-12 was developed for aircraft use and was a lend lease item so it was manufactured in great quantities. The radio along with its brother receiver was primarily used in light aircraft and some Canadian Mosquitoes and Lancasters and in the the C-47 and DC-3 post war. It has 4 separate VFO's, an 807 driver and a Pair of 807s in the final. The modulator and dynamotor PSU were on a separate chassis and the mods were a another pair of 807's. It has 4 channel remote control so when each of the 4 channels are preset, you can switch instantly from the cockpit. It was considered a poor mans ART-13. Bendix and Northern Electric in Canada manufactured them in great quantity. They sold for 49 bucks for years and were listed in the Fair Radio catalog up to the early 80's. It was based on a pre-war commercial Bendix design.

[WU2D]

The set is actually a TA-12D model which is later than the A and B which were prewar designs. I like the separate VFO s for each range. The first range 300 to 600 kHz appears to be a variometer type PTO and the three higher VFO's are all conventional Colpitts with variable caps. The lowest range used an outside loading coil so the control is actually re-assigned for tuning duty.  That control is assigned as a loading control on the higher ranges with each getting a separate roller loading inductor. What this arrangement allows is instantaneous 4 frequency operation on any channel from 300kHz to 12 MHz using one in each of the 4 bands and tuning and loading are preset on each. This is a "poor mans compact ART13".

It is interesting to see what parts manufacturers and how many were needed to build a set like this. Exactly 26 it turns out. See list. How many of these do you know? How many are still around?

Mike WU2D

[WU2D]

Now I can see that the low frequency oscillator is a variometer tuned Colpitts not a PTO but a pretty wild design. The other three HFO's are all Hartley's. The fun I am having returning the filaments and relay to 28VDC is epic. They were wired for 6.3VAC on the 807s and 12.6V on the 4 VFO's.

[w1vtp]

Mike

Looks like your Hammy hambone was busy in your TA12d

I will pull off the cover to my VFO section so see what my Hammy did

Al

[w1vtp]

Here's a shot of the back.  That heavy RG-8 coax is leaving town.  Come on!  We're only dealing with 40 watts out!!

Al

[W2PFY]

Here's a shot of the back.  That heavy RG-8 coax is leaving town.  Come on!  We're only dealing with 40 watts out!!

Al

\\

I don't think they had smaller coax in those days all. Maybe Pete will tell us otherwise

[w1vtp]

Here's a shot of the back.  That heavy RG-8 coax is leaving town.  Come on!  We're only dealing with 40 watts out!!

Al

\\

I don't think they had smaller coax in those days all. Maybe Pete will tell us otherwise

Right up tighe against the variometer. Sigh!

[WU2D]

The funny looking deck to the left with the movable spring contacts is the cap bank. The set allows you to put in various fixed caps depending on your loading needs for a particular part of the band and your particular "aircraft trailing antenna". The variometer is for the low band, which you will likely not be using. You have some cleaning and lubing to do Al. Pull the tubes first. Does your set have the original connector? If so you should be in better shape than I as far as artistic conversion goes.

I noticed looking at the manual - which I now have in PDF, that the Modulation transformer is 5700 to 2280 Ohms. So my TCS mod iron being 6K:6K will not be ideal. It would be fine for a pair of 807's modulating a single 807; not two in parallel. It is however ideal as a driver transformer, although a bit large.

Mike

[w1vtp]

The funny looking deck to the left with the movable spring contacts is the cap bank <etc.>  You have some cleaning and lubing to do Al. Pull the tubes first. Does your set have the original connector? If so you should be in better shape than I as far as artistic conversion goes.

I noticed looking at the manual - which I now have in PDF, that the Modulation transformer is 5700 to 2280 Ohms. So my TCS mod iron being 6K:6K will not be ideal. It would be fine for a pair of 807's modulating a single 807; not two in parallel. It is however ideal as a driver transformer, although a bit large.

Mike

OK on the "funny looking deck."  No, I do not have the original connector. I don't anyone does if it was ever put on the air.  That connector is impossible to find.  I'd like to bring it over some time and we can do a little looking and suggesting.  Did you check your email?  I send you some more detailed pics.  Gotta find that schematic that one of my handbooks had on what looks like a perfect fit for mod / ps

On the lubing: I have some Lubraplate and other oils that may work.  Need your expert suggestion.

Al