Thanks; I didn't notice the slight revision in the schematic on the first page. Now I've got my story straight. All I have to do is find a chassis and I'll get started on this thing...

-Dan

How important is it that L3 be 470uH? For some reason I don't have one of those on hand, but I do have a 500uH. Will this work OK or should I seek a 470 instead?

-Dan

I'll send you a complete set of coils

Thanks to Bill Hamre for bailing me out once again! In the meantime, I have a quick question about tube socket wiring:

Here is the picture of the 12CS6 socket pinout from the NJ7P database:

My question is, does the numbering represent the view from the top of the socket, or the bottom? I want to make sure of this before I start wiring sockets backwards.

Also, while I'm at it, I should make sure it's OK that I tie all the grounds to AC ground, as the chassis I'm using is plastic and therefore not very conductive for grounding purposes. I'm using the recommended Radio Shack 7x5x3 box.

Thanks for your help!

-Dan

Dan

Tube socket basing is from the bottom, clockwise. If you forget filament on 7 pin tubes is pin #3 amd #4. Looking inside the tube you can see the filament.

Bill was kind enough to send me one of these kits a couple of weeks ago. I had a lot of stuff going on like work, building a wood shed, finding old radios - stuff.

Since I was working nights this week doing antenna sweeps and I can’t sleep past 9AM regardless, I had some time yesterday to work on this project. I put about 4 hours into it coming and going. I did have the 2 weeks to plan what I wanted to do and did not have to go get any parts - even if I needed them.

I had some nice aluminum chassis parts from an old organ, some even had tube sockets mounted - not the ones I needed. I don't use many 7 pin sockets on the pre-40s radios I collect so I had to drill the rivets out on an old chassis and get a couple of sockets - not fancy but useable.




I cut the doner-organ chassis in half and it was just right. It already had the 2 terminal strips, top and bottom, so that saved some time. These were just enough for my point to point. Remember I'm a 20s-30s radio guy - no printed circuit boards here. But there is nothing like the smell of roasting PC board in the morning - or afternoon.



I did the under side of the chassis first, before mounting the power transformer. Used all of the kit parts except the 1 red surface mount cap - substituted an axel. I eventually moved the 5W resistor to give me more clearance below the chassis and to give it a little air space.



Power transformer mounted topside.



At this point I did have an issue. I have 3CS6s, 4CS6s and 6CS6s, lots of them, but not a single 12CS6. And I was not going to stop or WAIT for one. So my fuse holder became a light bulb socket. I just happen to have a lot of various voltage tubular bulbs like go into 70s stereo receivers. Don't ask why. Anyway I inserted the holder and a 6V .25A bulb inline between the 12AV6 and my 6CS6. The 24 volt filament circuit needed to loose 6 volts. The bulb dropped it a little over 5V according to my VOM. That will do till I get a 12CS6, which are now on the way. Of course the bulb takes a beating on power up for a second or two. When I get a 12CS6. All I will need to do is substitute a fuse for the bulb. This is kind of cool (the bulb gets hot), but I can substitute tubes of various filament voltages by changing bulb values.




The light inside the cabinet I chose is kind if cool also. The cabinet- A choice, perforated metal box that came from who knows what. It needed to be black.




The box did not have a base. A nice piece of mahogany veneered cabinet scrap from the doner-organ (a Baldwin, I think) will do just fine. Put the feet on first so you will not be taking a hammer to your finished circuit.



Use spacers to stand off the assembly from the enclosure base.



Bill, I did not have any square drill bits so I put the on/off onto the mod/volume pot. I have to set it every time I turn on the transmitter, but my source, and old laptop playing MP3s, does not have a fixed output volume either. So it is OK.

Now here is something you just have to do - make the VC trimmer cap accessible from outside of the enclosure. You are going to need to retune every time you change the length or even position of the antenna. By the way, the circuit seems to like an antenna between 4 and 10 feet. Not shorter, of course, but not longer than 10 feet or you can't tune it.




Use a tube radio to test it. Ya, I know, it's from the 40s. Those dang TRF sets are heavy.


Russ

I think that I overloaded somethin on the site. It would not let me attach the "finished" picture. So here it is. By the way, it sounds very good.

That is my cell phone providing modulation.

Russ

Hello Russ,
Well that little transmitter turned out very nice.
I don't know how many parts that I've saved from those old organs .
Rich

Yes, they are free - on the way to the landfill. It is a win win for everybody.

Russ

Russ

Looks nice from here. Believe you are the first to show a transmitter built using this transformer.

Bill - You should have 12CS6 tubes. They aren't common but Tom should have sent you a bunch.

Norm,

Everybody ran out at the same time including 35Z5 and Tom Bavis. Russ originally thought he had one. So, 35Z5 gave me a source which I gave to Russ. I'm buying the excess from Russ.

Bill
------------------------------------------
EDIT: P.S. I had bought all they had at Kutztown too! I had taken all the ones Norm sent to Kutztown but the two tube kits sold like hotcakes there thanks to Hergi! Wyatt even got one even though he had brought his own homebrew AM broadcaster to Kutztown.

The unit is now hooked up to an old Windows 2000 laptop playing MP3s.

Russ
-------------------------------------------------
I threadjacked the above from a PM from Russ just to give lurkers ideas on where to get the music for the AM broadcasters.

Hi Russ

L2 must be reduced in value if you want to use a long antenna, a 680uh works well at 1000Kc on 35-40ft...

Very nice build, it's great to see some of these are being assembled...

Tom

Thanks. I might try that some day. But honestly the 10ft works fine for me. I might even cut it down some. It seems more important that it is vertical. I might try an extendable whip. Coverage is good in my shop.

I think the most important part of antenna placement is that it doesn't run near any AC wiring... I tried mine along a baseboard and had so much hum it wasn't usable, run vertically beside a window and across the curtain rod, it has virtually no hum and have good coverage anywhere in the house... The one in the garage is connected to a mostly horiz antenna in the attic and has no hum unless it is raining...

Tom

They aren't common but Tom should have sent you a bunch.
by Norm
---------------------------------------------------
Yes he did. They are the ones I ran out of. I never really bought a batch of those tubes on my own except for Kutztown and they all sold at Kutztown. All tubes were from Norm, 35Z5 or Tom Bavis shipping directly to one member here or another.

When I built the 6GY6 two tube transmitter I made this antenna for opeeration at 1000 KHz.


The telescoping antenna measured from ther base to the top is 39"
The coil came from a beyond repair antique radio and the big variable capacitor came from a vacuum tube operated FM tuner. I found a small ferrite rod inserted inside ths coil improved the output signal. Also that coil of wire was needed to permit proper operation of the antenna as it would not work right with the cap connected via short wire to the coil.

So, is that coil and cap taking the place of L2 and VC1 in the schematic on page 1 of this thread? I cant tell, is the roll of wire before the coil or after? The sum of your coil with a core and wire must be the inductance needed for that ant. Do you know the value (max) of that vc?

Russ

Not sure about this schematic as I built it for the 6GY6 two tube transmitter.

Vc1 stays in circuit and the coil in the picture is now L2. I'll post a schematic of the circuit.



Now you will have to experiment with the value of L1 and VC2 to get max signal out. That circuit did increase the output quite nicely (nearly put the S meter on my SP-600 at 80 on the DB from 1 uV scale) and also made the output a true sine wave.

Not sure about the wire coil, but it has to be there. Maybe someone with more experience can explain why I needed a length of wire between the variable capacitor and coil instead of just a short wire. Unfortunately all I know about the capacitor is it came from a vacuum tube operated FM tuner. VC1 is what comes with the kit. I mounted mine on the coil to make it easier to adjust.

Here's a picture of the antenna fully extended

Bill,

THe tubes are going out to you Priority Mail today.

Russ