Help identifying a hb pw mobile tx?

[kf6pqt]

thats a lotta acronyms!

So, we've got a 6ag7 driving a 2e26, modulated by a 6l6, which is driven by (what I'm assuming is) a BC-375 carbon-mike transformer.

As you can see, I've scanned the label which came off of the mod tranny... sadly said label crumbled as I took it out of the scanner.

Now, of course I havent traced out the circuit into a schematic... but does any body recognize this thing? As to what article it may have been from, etc?

Thanks,
Jason kf6pqt

[kf6pqt]

Of course, I cleaned it...

[kf6pqt]

oops, one attachment per post...

[kf6pqt]

...

[kf6pqt]

tank coil

[kf6pqt]

rear, says "300" on it, assuming B+

[kf6pqt]

mod tranny label:

[kf6pqt]

Its much purtier now...

[kf6pqt]

A lot of the aluminium work looks like it was scavenged from a bc-375 TU.

Thanks for lookin',

Jason kf6pqt

[W1GFH]

Coil looks like 80M (or 160?). Wow. Nice haul!

Check this out:

http://smg.photobucket.com/albums/v652/ranickel/Top%20Band%20Goes%20Mobile/

These were built in great quantities by hams in 50s and 60s. Or...could be this one...

http://www.geocities.com/CapeCanaveral/Hall/8701/ham/m62.gif

Or this one (a 2E26):

http://www.geocities.com/CapeCanaveral/Hall/8701/ham/m60.gif

[kf6pqt]

I forgot one pic, has this odd coil-in-a-can... I'm guessing its the oscillator coil...

[WU2D]

Jason,

It looks like a sommabwhachamcallit...

I can not see the oscillator tube but lets say it is the tube near the 6L6 metal. It would drive the 2E26 final to about 15 Watts Input on AM. A 6AG7?

In that case it would be a 6AG7 driving a 2E26.

The 6L6 is a conventional class A plate modulator because you have a transformer. If the mystery tube turns out to be the oscillator, I guess you could drive the 6L6 with a carbon microphone and a step up transformer with no mic pre amp.

Is there another tube like a 6SL7 or 6SJ7 mic preamp hiding, that we can not see? 

I wonder if it is wired for 6V or 12V fillament?

Mike WU2D

[kf6pqt]

Yes, its a 6ag7, and there are no other tubes. I'm betting that with only three tubes, its wired for 6v.

-Jason kf6pqt

[The Slab Bacon]

Somehow I dont think a trip throught the dishwasher did that open frame mod tranny any good. Hmmmm...................

[kf6pqt]

More like a spritz with the hose. Then it cooked in the 86 degree sun all day, being rotated/inverted frequently. On top of that, we're having Santa Ana winds, which are like having a million hair-dryers pointed at you from the east. (wind that blows the wrong way, originating from the desert, rumored to make people go crazy.)

Those poor water molecules didn't even have a chance!   

[WU2D]

Jason,

Now you need something to drive the 6L6 from the microphonium. We need to get this thing in the car and your car is 12V so that is the first thing to fix.

 The 2E26 takes 6.3V at 0.8 A and the 6L6,6.3V at 0.9 A - close enough to wire them in series. If you want to get relegious, put a 68 Ohm 1 Watt resistor across the 2E26 fill.
I would ground the 2E26 fillament and bypass the other side to ground and then feed the 6L6 and bypass both sides.

The 6AG7 is 6.3 at 0.65 A. Can you shoehorn another 6V tube in there? The good old 6SN7 is 6.3V at 0.6 A - again close enough wire them in series and now you have two stages of amplification before the 6L6 and 12V fills. The 6N7 is another great old buzzard metal tube and it has a common cathode.

Mike
 

[W1GFH]

Excellent. Put a big arse loadink coil on a CB whip and run mobile from truck. The summit of Mt. Wilson is only a 25 min. drive. Let me know when you get it up and running, we can sked on 75M.

[kf6pqt]

Thanks Mike, but how does the BC-375 carbon mic transformer figure in?

Thanks,
Jason kf6pqt

[The Slab Bacon]

Mike,
         That is a very similar circuit to 7w piss-weaker that I built some years back. 6AQ5 osc,
2E26 final, mod by single ended 6V6 with 12AX7 mic/speech amp. Makes about 7w outpoot with pretty good audio. I actually built it to be a dedicated driver for my junkston T-bolt.

One little trick that i did was the mod tranny. At that time I didnt have any small mod transfomas, so here is what I did. I had a nice 10-12w push pull audio outpot transfoma. I left the speaker leads unhooked and taped off. I fed the B+ into the normal primary center tap as normal. Then I hooked 1 plate lead to the plate of the 6V6 modder, and the other plate lead to the plate / screen feed for the 2E26. An autotransfoma if you would. It worked ok-fine and sounded quite good.

Just a thought to ponder as mod trannys of assorted sizes are getting a bit harder to get these days. But there are still tons of old tube audio stuff being thrown out.

                                                                                 The slab Bacon

[Todd, KA1KAQ]

Neat looking rig, Jason - you certainly have the packrat gene, helpful in finding the cool stuff others miss.

Slab is right, be careful with water around the old components. Hosing isn't so bad as you can better direct the water where you want it. The dishwasher thing has always made me nervous with old gear, since it can easily cause more damage than good on anything beyond bare metal parts. Of course, having the scorching sun available out there sure helps drive any excess from the chassis once you're through.

Keep us posted on how things go. That first contact with it should be a blast.

[kf6pqt]

The 2E26 takes 6.3V at 0.8 A and the 6L6,6.3V at 0.9 A - close enough to wire them in series. If you want to get relegious, put a 68 Ohm 1 Watt resistor across the 2E26 fill.

Mike, whats the ohms law math to figuring that out? I stink at math, thats why I had to go to work on computers and not be an engineer!

The summit of Mt. Wilson is only a 25 min. drive.

Joe, there is so much RF up there, no receiver that I own would likely work while near the top of that hill!

[Carl WA1KPD]

The dishwasher thing has always made me nervous with old gear, since it can easily cause more damage than good on anything beyond bare metal parts.

How true.

I once put just the outer cabinet of a light color wrinkle paint transmitter into the dishwasher because it was so filthy and stained that i could do little with my toothbrush and cleaners (Besides it made my toothbrush taste terrible)

An hour later it was done and I opened the washer to see a clean shiny BARE metal cabinet with my beloved  wrinkle paint in a pile in the dishwater filter...

[WU2D]

Jason,

No math. We want 6.3 volts on the 6L6. We know we need 900 mA to make the 6L6 fil light up. The 2E26 only draws 800 mA.

That means we are shy 100 mA.

Now the Ohms law: R = E/I or 6.3 / 0.1 = 63 Ohms

Mike

[kf6pqt]

Thanks Mike!

[WU2D]

Jason,

Now some math.

We have 6.3V and 800 mA on the 2E26

R = 6.3/.8 = 7.875 Ohms

We have 6.3V and 900 mA on the 6L6

R = 6.3/.9 = 7 Ohms


How do we make a 7.8 Ohm resistor look like 7 Ohms?

Going back to the formula 1/R = 1/R1 + 1/R2

 Call R the 7 Ohm Resistor and call R1 the 7.8 Ohm resistor. We want to solve for R2

R2 = (R x R1) / (R1 - R)

R = 7 x (7.875) / (7.875 - 7) = 63