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eHam Forums => HomeBrew => Topic started by: KC9KEP on January 11, 2013, 04:04:58 PM



Title: Class AB1 AM Modulator Project
Post by: KC9KEP on January 11, 2013, 04:04:58 PM
Hello,

I am building a circa 1953 AM Modulator to go along with my 6146B that I had posted
questions about earlier.

I think that it's working fairly well, judging by my power meter and scope trace display.  I have
yet to make a QSO or to get on the air yet (I've just got it operating today).  I have the modulator
connected to my 6146B transmitter and am measuring about 60 Watts output. 
(The modulator is connected to both the Plate Supply to the 6146B and Screen of the 6146B
via a "dropping" resistor.)

One concern that I have; The B+ in the construction article is stated to be around 600VDC,
but my power supply is about 80VDC higher.  I was thinking that perhaps I should have increased
the battery bias supply, but it seems to be working well as it is.
There is a 50 Ohm cathode resistor included in the design that allows the operator to monitor
the cathode current (but I have yet to do so).

Anyway, here are some images.  I am curious to see what others think of this design :-)

http://www.bignick.net/Mod/before.jpg
http://www.bignick.net/Mod/rear_1.jpg
http://www.bignick.net/Mod/under.jpg
http://www.bignick.net/Mod/Temp_Front.jpg
http://www.bignick.net/Mod/front_cab.jpg
http://www.bignick.net/Mod/rear_cab.jpg
http://www.bignick.net/Mod/top_cab.jpg

Scope Trace:

http://www.bignick.net/Mod/scope.jpg

Schematic wiring diagram:

http://www.bignick.net/Mod/Mod_2.jpg

73!

--KC9KEP


Title: RE: Class AB1 AM Modulator Project
Post by: AA4PB on January 11, 2013, 04:13:40 PM
Super! Any 1953 ham would be proud  ;D


Title: RE: Class AB1 AM Modulator Project
Post by: K8AXW on January 11, 2013, 05:56:48 PM
KEP:  Beautiful work!  Homebrew is a hoot, isn't it??



Title: RE: Class AB1 AM Modulator Project
Post by: GW3OQK on January 12, 2013, 07:44:00 AM
ANY and ALL would think that's first class workmanship and beautiful modulation waveform.

How do you cut the big holes? In the 50s I drilled lots of holes with a hand drill and filed the edges. Look forward to hearing your rig on air one day
73, Andrew


Title: RE: Class AB1 AM Modulator Project
Post by: KC9KEP on January 12, 2013, 08:04:07 AM
Thanks for the kind words, guys..

GW3OQK - Most round holes were cut with Greenlee punches.  The large circular hole for the modulation
transformer was cut with an adjustable circle hole cutter. 
(It has an arbor and adjustable "arm" and cutting bit.)

The rectangular hole was cut with a sabre saw with a metal blade, then filed to finish it nicely.

I cover the entire chassis with masking tape before marking and cutting.  After all the holes
are cut, I remove the protective masking tape.

Hope that helps :-)

73

-- KC9KEP


Title: RE: Class AB1 AM Modulator Project
Post by: WD5GWY on January 12, 2013, 08:34:23 AM
Very well done! Wish I had the talent to do as nice work.
My homebrew projects look like a natural disaster in progress!  ::)

james
WD5GWY


Title: RE: Class AB1 AM Modulator Project
Post by: WA7PRC on January 17, 2013, 01:55:51 AM
Nice work, Tom.  I also browsed some of your other HB projects.  VERY nice work.  :)
I noticed we use some of the same techniques.

vy 73,
Bryan WA7PRC