The AM Forum

Reading about the ...
6-meter Heathkit HA-20,
It sounds interesting. (pair of 6146's) Wondering how it would perform with my HT-40 Hallicrafters driving it on 6 mtrs. ?? Anyone ever operated the HA-20? I like my little HT-40 its fun but it needs a Linear....Homebrew time? or Heathkit to the rescue?

The HT-40 seems to have a number of write-ups with complaints of its questionable circuitry design.
Sweep tube output; modulation to maybe, if lucky, to roughly 80%; oscillator issues, power supply issues, and other stuff I don't remember.

The HA-20 amplifier was designed to mate with the Heath HX-30. Drive requirements for the amplifier are from 2.5 to 20 watts. Pair of 6146's in the final.

The real issue is, who you going to contact  :D  seems everyone on 6 meters today is running FT8. During contests, you might find a few stations running AM or CW although, here in the metro New York/New Jersey area, I haven't heard an AM station, even during band openings, in the last several years.

I'm figuring that, with a pair of 6146B's in the HA-20, you'd be looking at around a 25-watt carrier. I've never owned an HT-40, but I suspect that that isn't a whole lot more than you're already getting from your "barefoot" HT-40.
If you just like running the vintage gear for its own sake, which for many of us is part of the fun, an HT-40/HA-20 lashup would be cool, but in terms of actual effectiveness, that HA-20 is probably a non-starter.

If you wanted to go the homebrew route, you might consider a pair of 4CX-250s. Rugged, compact, and capable of sufficient gain and plate dissipation to give you a nice 100-watt carrier from a low-powered transmitter.
Or, a single 4CX-400A or Russian GS-36B, both quite similar. I've got a Dentron Clipperton-V, originally a 2-meter amp with a single 4CX-250, converted to 6-meters (not sure if it was a factory conversion). I replaced the 4CX-250 with a 4CX-400A for greater plate dissipation, and it gives me a comfortable 100-watt carrier with less than 5 watts in.
Build or buy something similar, and I think you'd be very happy with it.

I see the Heath HA-20 in Chuck Penson (WA7ZZE) Heathkit book,
he says :
In the HA-20 a pair of 6146's "produce 125 watts input PEP SSB or about 75 watts on AM"??
Other info from other sources say 70 watts PEP?
So, I was wondering since my DX-100's run 2-6146's.....
I've had the same experience on 6-meters as Pete, not many people on 6 meters, but I have a few friends I could talk with on 6-meters.
Your KD1SH modified Dentron sounds very interesting, I'll have to look that up and see, sounds good. I'll look at that idea.
All I have for 6-meter AM:
My Hallicrafters HT-40 and a Yaesu FT-625RD. Both low power. So the Heath sounded interesting,
Thanks for the comments and suggestions.

There is a Cathode-driven 4CX250B design for 6-meters in the 2004 edition ARRL's "RF Amplifier Classics".
Although this is a modern "new" ARRL type book, its a  Fun book.
Like all of us here, I have many, many of the old and even very, very old, handbooks and manuals, books, etc. Lots of inspiring designs out there.

With your DX-100's pair of 6146B's running at a very ideal 80% efficiency in plate modulated class C, somewhere around 100 watts of carrier is about right, given a DC input of 125 watts.
Since a linear amplifier properly tuned and loaded for AM will be at somewhere around 35% efficiency, at carrier level, I figure that your 75 watts DC input would give you right around 26 watts of carrier output. That would imply a peak, at 100% modulation, of right around 100 watts, the expected 4 X the carrier.
I've seen a few HA-20's around at hamfests. Nice looking little amp. Pretty sharp looking, like a lot of Heathkit stuff.

I have that book, too, and I liked that amplifier design. Cathode-driven, but not a classic grounded-grid configuration, giving good gain for low-powered transmitters. My Dentron Clipperton-V uses a similar configuration.
I may build an amp based on that concept myself, someday, though probably with a pair of 4CX-400A's.
Yes, having a library of ARRL "East Coast" handbooks is great, along with Bill Orr's "West Coast" handbooks as well.