[Phlogiston]

Ok, I have some answers.

The freq is 1mhz.

Hum is very dependent on antenna tuning - good tune less/no hum.

I might still have the schematic, or possibly 35Z5 has it.

I think the tubes are 12V versions - using a 6V was the reason for the bulb/resistor.

Here is my post from that other site:

Well I took out the light bulb ( I kind of miss it) and swapped in the 12 volt tube in place of the 6CS6. Then I swapped out L2 for the 680 uh coil. By the way, I am using the 1000kH x1. The unit tunes to a 10 foot ant now with better range. although what I had before was fine, now you can hear it outside on the truck's radio. Adjusting the VC is easier with peaks not as sharp.

Russ

[35Z5]

I suspect Russ used this schematic... Designed using a $3 transformer Norm found at Electronic Gold mine, supplies long depleted...

[Image: https://s18.postimg.org/k1r0x9sah/12cs612av6snip.jpg]

[sam]

I have been studying the circuit Sam posted and I can see several things l like about it. One in particular, and that is the tuning cap is not connected to B+. That had bothered me, since that is a pretty large part to have that kind voltage on it. Then, there was the isolation issue. With this circuit, the tuning cap can be mounted directly to the chassis to ground. Really simplifies things. I am mocking up a potential layout.  I will post some pics of the idea and see what you all think. I want to avoid feedback, hum and noise.

hey tim
I checked .could not make it hum or buzz
I don't have an antenna I either put wire post to post.  or far away still picks up good or it I touch
transmitter post and it comes in loud and clear .
only if I put in kitchen it gets static 

sam

[TV MAN]

Got most of my parts in. Doing an initial mock up. Still drawing and redrawing the underside. Will try to post a sketch when I get I am satisfied with the layout. Like the schematic Sam posted. I may mod the power supply slightly to simplify. So, doing some planning and sketching. I don't know how sensitive these are to layout. I have seen some that had wires and such criss-crossing and going all different ways (not my style) and others that were very neat, like those posted here. 

   

[TV MAN]

Filament question: My PT has a 12v center tapped secondary (6-0-6), so I ground the center tap, send 6v to the 6888. That's one half the sec. winding. Any problems sending the full 12v (the 2 outside taps) to use a 12AV6 tube? I have plenty, and they have a very low filament current draw. If this isn't good, then I can use a 6AV6 and power it off the same 6v winding. I don't want to create a hum issue nor a smoke issue. I have a rough layout sketched, so when I get it cleaned up I will post and see what your opinions are.

[35Z5]

Assuming the other half of 12v winding isn't being used, I'd use the 6AV6 and maybe a dial lamp so there would be a more even load on transformer... A 6AQ6 has 150ma heater and would readily replace the 6AV6...

[TV MAN]

Tom, it might be better to use a 6v tube. Anyway, I have done a rough sketch of my proposed build. I am sure I will adapt some minor changes as needed, but this is an overview of how I plan to build. Comments or suggestions welcome. Here is a list of things I may change: I may add an LED indicator light, put the input on the front, near the level control instead of the back, and may make some changes around/about the antenna coil. There is quite a bit of room as far as height under the chassis, so some things that look like they are on top of each other, like the line cord and input jack, there is actually an inch or so of space between.

EDIT 3-25-18: I found a wiring error on my 1st diagram. Here is a corrected layout. I turned the 6888 tube to move the plate closer to the antenna tuner, but I may turn it back the way I had it first. I also may move the C5 to connect to pin 5 of the 6888 instead of the oscillator to simplify. I may mount the Osc to a PC board as well as to support the antenna coil, L1. I didn't show the filament wiring as I'm not sure how I am going to run it yet. This is from the schematic Sam posted.

   

[TV MAN]

Another filament question. I have decided to use all 6v tubes for now. Concerning center taps and such, would it be well to ground one side of the heaters to the chassis, ground the filament center tap, and connect each side of the transformer to separate tubes? This means I would run the 6888 from one side of the transformer, and the 6AV6 on the other side. Again, this is a center tapped 12v (6-0-6) secondary. It wouldn't be very balanced current wise, but would this accomplish the same thing as a grounded center tap in a 6v filament transformer? I found some information about center taps here: http://www.valvewizard.co.uk/heater.html  But, it doesn't really answer this question. Any suggestions?

[35Z5]

Since you have the CT xformer I'd probably ground it and one connection for heater... This is the arrangement in UHF converters I've repurposed into xmitt... Also I have a xfomer from a GE remote speaker xmitt, it has a CT on the 6v winding with each side of heaters fed separately...

Honestly I'm yet to see a difference in either method, unless one of the tubes has H-K leakage you won't... In the event of H-K leakage, the CT ground version with each heater fed separately should be better... Of course unless you were using 12v tubes, impossible to do so in this application... Well not impossible just not  practical...

Of course you could use DC on heaters, again not really practical but necessary when using oddball TV tube.

[TV MAN]

I have been reading and studying, drawing and redrawing. I haven't heard anything either way, bad or good about my proposed layout. I think the biggest things are to eliminate hum, feedback and static, which I have tried to do by separation, grounding, etc. So   Let the construction begin! 
I have the bridge installed, and power transformer wiring in place. I am changing the value and size of a few caps due to space, or lack of. I am going to use 250v poly caps, since they are smaller. Should be plenty of breathing voltage wise, and slightly smaller output filter caps. I will use the specified 47 uf input cap, and going to try 22uf output caps. Figure they should be adequate since this is a full wave PS. I am debating on my line caps - schematic calls for .01, which I have, and are rather large. They would fit, but ... again, big. I may try .001 and see what I get. I don't know how much difference the size of that cap would make in filtering noise, RF, etc. 
   

[TV MAN]

I am reviving my thread since the weather has turned colder and my work season is over. I sat and studied things last night for awhile. Kinda hung on the mounting of the osc and coil. I have some coils that I got from China in different values, (they look like resistors) and an antenna coil. I think I have an idea of how I am going to mount things. Probably making 'work' out of this... I want to get it running and have something to so I can enjoy those old radios that I am restoring.

[EdHolland]

Half the fun of coils is making your own. I have been playing with this website's calculator recently, working out how to make resonant circuits to cover the range needed with a given variable capacitor:

http://www.66pacific.com/calculators/coi...lator.aspx

Then you can go to work with some magnet wire and have exactly what you need.

Cheers

Ed

[Radioroslyn]

The next thing you know he'll be buying a grid dip meter....

[morzh]

I thought about buying one....but them it is not a very precise tool.

[Radioroslyn]

I suppose if you din't have a way the calculate the L/C ratio there great for ball parking it. Have used them when home brewing some ham gear to determine the resonance of transmitter tank coils among other things. Kinda handy.