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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Wed 15, 2017 1:15 am 
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Notice that black bobbin, L3 sitting very close to C11. Could there be a problem with that?
Also, is the gain control needed?
And should a star common be better to use? Where would be the best place to ground the commons? Should I ground the input commons at the input?

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Thu 16, 2017 3:11 am 
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I made a new chassis for the BTL box. Just needs a coat of clear lacquer. That idea come from Peter. A real master at finish.
Attachment:
tx10.jpg
tx10.jpg [ 125.06 KiB | Viewed 2858 times ]

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Thu 16, 2017 3:21 am 
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john8750 wrote:
I made a new chassis for the BTL box. Just needs a coat of clear lacquer. That idea come from Peter. A real master at finish.
Attachment:
tx10.jpg

Looking very good!
Did you use a brake?
Did you drill all holes using the stepped drill?

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Thu 16, 2017 5:59 am 
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Pbpix wrote:
john8750 wrote:
I made a new chassis for the BTL box. Just needs a coat of clear lacquer. That idea come from Peter. A real master at finish.
Attachment:
tx10.jpg

Looking very good!
Did you use a brake?
Did you drill all holes using the stepped drill?



I had the box since the 70's. It is preformed and aluminum. I cut it to fit inside the cab and drilled the holes.
The fit is excellent. The big hole in the middle is where the power supply board mounts, on nylon feet.

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Fri 17, 2017 9:23 pm 
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Hello john
Looking good that us the chassis and nice cabinet
I have one those old blunder tongue UHF tv tuners that saving for this project


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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Fri 17, 2017 11:01 pm 
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Mike Toon wrote:
Image

Hi Tom.
Could you please send schematic info for this amp. I want to build it next project.
And, would really like to see under the chassy.
Does that chassis need to be earth grounded :?:
I live in Griffith Park, so not so far away....

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Fri 17, 2017 11:30 pm 
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John, it's Norm's original 6888 transmitter with a doubler PS and no audio amp.
The chassis is earth grounded but the var cap is floating.
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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 12:23 am 
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John:
Here's some vaery basic info about "supressor-grid modulation"

http://www.vias.org/basicradio/basic_radio_17_06.html
Image

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 1:28 am 
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Mike Toon wrote:
John, it's Norm's original 6888 transmitter with a doubler PS and no audio amp.
The chassis is earth grounded but the var cap is floating.
Image



Thanks Tom. Just as Purdy underneath as on top. Beautiful job.
Is there a link for actual part description? Like that var cap.

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 1:41 am 
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Pbpix wrote:
John:
Here's some vaery basic info about "supressor-grid modulation"

http://www.vias.org/basicradio/basic_radio_17_06.html
Image



Thanks Peter. I guess RFC is a choke? So the RF and AF are simply added together?

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 1:45 am 
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Here she is so far :wink: Think I will change the power cord to a 3 cond/ with ground.
Attachment:
tx12.jpg
tx12.jpg [ 173.08 KiB | Viewed 2795 times ]

Attachment:
tx11.jpg
tx11.jpg [ 167.4 KiB | Viewed 2795 times ]

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 3:34 am 
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john8750 wrote:

Thanks Peter. I guess RFC is a choke? So the RF and AF are simply added together?

Well... I'm no transmitter xpert guy... so I can't say exactly ... but typically two frequencies mixed in a tube do create a mix = the sum, the difference and the original two.

But I do know what a modulated radio carrier looks like coming out of the antenna so:
I think, it looks to me more, as though it works this way:
It feeds the audio signal to the suppressor grid to make it more or less positive.. so it's like the audio signal on the suppressor is acting to help increase or decrease the flow of the electron stream from the cathode to the plate... so it's modulating the carrier. More signal/less signal.

Like this:
Image

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 3:46 am 
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Technically dual control tubes do not have a suppressor grid(though is often still called as such), it becomes a second control grid or G3... Some tubes with suppressor can be modulated, but it requires extra circuitry and usually a large amount of audio input, results are generally far from optimum... The 12CS6 is a Hextode but still has two control grids as does the dual control pentodes like 6888, 6GY6, 6HZ6 ect... And lets not forget my current favorite, 9KC6... Requires 9v for heater and a G3 bias supply to really perform but results are excellent... Would have been nice if there was a 6KC6, but it only comes in 9v flavor...

In real life music will look something like this(can't remember what song was playing)...

Image

Apparently it was full of high notes as a 1k tone looks lie this...

Image


Tom


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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 7:49 am 
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Hello john that set looks great
And I will be using the same chassis as mike toon


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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 8:07 pm 
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radiorich wrote:
Hello john that set looks great
And I will be using the same chassis as mike toon



Great Rich. Get goin and have some fun :wink:

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Sat 18, 2017 8:57 pm 
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john8750 wrote:
Thanks Toon. Just as Purdy underneath as on top. Beautiful job.
Is there a link for actual part description? Like that var cap.


The variable cap is what I had, any AA5 cap will do. The toroid coil and cap are overkill as Tom (35Z5) has proven with just a trimmer. I wanted to have a wide range for different xtals and have it look stock.

Also note, the chassis with the 6888 tube as pictured didn't fit the cabinet. I had to re-locate the tube socket under the chassis. It's that tight!


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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Mon 20, 2017 4:06 am 
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Mike Toon wrote:
john8750 wrote:
Thanks Toon. Just as Purdy underneath as on top. Beautiful job.
Is there a link for actual part description? Like that var cap.


The variable cap is what I had, any AA5 cap will do. The toroid coil and cap are overkill as Tom (35Z5) has proven with just a trimmer. I wanted to have a wide range for different xtals and have it look stock.

Also note, the chassis with the 6888 tube as pictured didn't fit the cabinet. I had to re-locate the tube socket under the chassis. It's that tight!



The box is fine for the 12AV6/12CS6 transmitter. But I had to make a new chassy.
I wanted the Mallory box for the 6888. But might go for a design with VFO. Just for fun.

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Mon 20, 2017 4:34 am 
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Finished the wiring today and fired er up. First, I removed the OSC chip and with the tubes removed got no shorts, and checked all components. Switched on. Pin14 IC socket 5.1v, heater supply 25.1vac, and B+ at 179.8v. Then after about 30 seconds, smoke and a burning component smell. Checked around and found that power supply resistor R9 was getting very hot. I isolated the B+, powered on with the same voltage but no overheating resistor. So, checked the B+ circuit to ground, exactly 100ohms. How could that be. The only component connecting to ground is C4. Oh No. The .01 cap was missing from the kit, no problem, I have a few right here. At 100v, just wasn't thinking. Well, it didn't last long before it shorted. Found a 250v and installed it.
Everything back to normal. After a few minutes I switched off and installed the OSC and tubes.
Still 5.1v for the OSC. Heaters at 24.6v. B+ at 171.6v. A little high. I changed R9 1.2k. Then B+ is 157v. All is fine now.
I will try some transmission testing tomorrow.

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Mon 20, 2017 5:53 am 
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How could you wait?

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 Post subject: Re: 12AV6-12CS6 Transmitter(Revised Schematic)
PostPosted: Feb Mon 20, 2017 6:34 am 
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Pbpix wrote:
How could you wait?



I was screwing around with trying to understand the 5 band resistor code. What a PITA. Then it was dinner time.
Very exciting to just get the proper voltages. Will work on it tomorrow.
I called you, but you must have been out katt in around.

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