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60 watt Modulator near complete




 
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N4LTA
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« on: August 01, 2020, 01:20:00 PM »

I have pretty much completed my dual 807 modulator. I need to re check all the wiring and tighten all the screws.

Thanks to all for  the help and suggestions.

It uses a 12AU7 as a balanced line amp and has adjustable bias for each 807

I need to add the binding post outputs and test it. I have a 100 watt resistor and  large heatsink due Monday.

Lots of clean up work and testing remain. The power supplies have had basic testing for voltage but no active tubes have been energised.

Pat
N4LTA


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N4LTA
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« Reply #1 on: August 01, 2020, 01:21:38 PM »

A few more photos.


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KI4YAN
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« Reply #2 on: August 01, 2020, 09:03:37 PM »

That looks to be an excellent job. Starting on the RF side next?
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N4LTA
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« Reply #3 on: August 02, 2020, 09:37:31 AM »

Yep

I have some 3C24s . I'd like to use a pair of them running about 900-1000 volts. Can't find much info on them except the Eimac data sheet.

I'd like to find an example circuit that was actually built by someone. The grid connection comes out the side with the plate on top. Not sure how critical layout is for these triodes.

Pat
N4LTA
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Patrick J. / KD5OEI
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« Reply #4 on: August 02, 2020, 10:57:24 AM »

Looks great! They oughta make 807s again - like 6l6 anyway. The Chinese could be asked to place a cap on a 6L6GC and put it in a ST bulb. Oh what a miscgenation.. but very pretty.

Now as to 3C24's, they are the same as VT-204s and also called HK24Gs.

See the manual for the BC-604 transmitter where two are modulated by a low power 811 amplifier.

http://www.bunkerofdoom.com/mil/BC640AB1943.pdf

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K1JJ
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« Reply #5 on: August 02, 2020, 11:42:36 AM »

Yep

I have some 3C24s . I'd like to use a pair of them running about 900-1000 volts. Can't find much info on them except the Eimac data sheet.

I'd like to find an example circuit that was actually built by someone. The grid connection comes out the side with the plate on top. Not sure how critical layout is for these triodes.

Pat
N4LTA

Pat,

I have a hand-drawn schematic of a single 3C24 plate modulated by a pair of 3C24s that I built back in the 90's.  It was during the TPTG  Sideband Eliminator craze when some of us were building one tube self-oscillator rigs. It finally worked pretty well for a one tube transmitter.  I will dig it out and post it when I take some pics of my newest single 3-500Z project.

You will be able to get a general idea of what is involved to make it a standard  plate modulated rig.   It put out about 90 watts and I used an amazing (crazy) plate voltage of close to 2KV IIRC.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
N4LTA
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« Reply #6 on: August 02, 2020, 01:23:06 PM »

I'd love to see it.  Did you have to lay out the tube in an unusual way? Did you neutralize it - I would think so.

BTW - I got a 1642 SE this week. You are right - it is big and heavy.

Pat
N4LTA
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WU2D
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« Reply #7 on: August 05, 2020, 09:49:50 PM »

The Sino 807 for only $$$26.99.95, you can have one of the only modern manufactured 807's!


* SI-807-2.jpg (18.23 KB, 208x500 - viewed 71 times.)
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Patrick J. / KD5OEI
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« Reply #8 on: August 06, 2020, 04:01:33 PM »

aHa! I didn't know those were made. 811s and similar things yes.
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