The AM Forum

I worked a station in CT tonight on 80M CW on the little peanut whilsle I rolled up over the weekend. To be fair I used my one tube Morgan Regen as the receiver so the station would be "Balanced". The Regen hums nicely as you key - sort of a poor mans sidetone? Anyway he came back to my CQ.

The 6AK5 is one serious power tube. I whipped it to the point of putting out over 3 Watts. I am embarrassed to say that i might have exceeded recommended ratings. Poor little thing. I can only imagine how it was heating the 110 ft longwire I strung across the yard. Again I was going for station "Balance".

Kind of mad he said I was hitting S9 but only gave me a 559. COME ON!

Mike WU2D

You should try one of those cryogenic treated 6AK5's! Good for 1 KW till they warm up ;D ;D

You got 3W from a 6AK5? Impressive. I have a bin of them, most the the 6AK5/nnnn ones. I'll have to revisit those little jewels. Would you share your operating conditions?

With NIB JAN 6AK5W/5654's in the penny bin at hamfests its a bargain tube. Another often overlooked penny tube is the 6J6 which loafs at 3W, and also does fine at audio.

Carl

flip her upside down in yer coffee cup.....  should get a watt more out of  'er.


klc

Well, you only need to run 500 of them in parallel and you will have a legal limit CW rig.

6AK5 Maximum Ratings (Design Center Values)

Pentode
Plate Voltage ................................. 180 V
Grid No. 2 Supply Voltage ..................... 180 V
Grid No. 2 Voltage ............................ 140 V
Positive Grid No. 1 Voltage ................... 0 V
Plate Dissipation ............................. 1.7 W
Grid No. 2 Dissipation ........................ 0.5 W
Cathode Current ............................... 18 mA


Let's see I have 380 VDC on the plate...Well I guess that might be a little over the recommended ICAS ratings but the tube seems happy on CW. By the way, at 180 VDC she will do 1 Watt barely. Now remember this is a straight colpitts ECO on 80M so it can not be much more efficient than say 30-40%.

Mike WU2D

Why not use a 6AK6 or a 6C4, both are easily capable of making a little power? ? ?

We need to save the 6C4's for Hammarlund and National oscillators ;D

Funny how great minds (NOT!) run in the same gutter.  I immediately thought of the same thing.  Just have to neutralize the beast.  Maybe push-pull-parallel with link coupled output.

 ;D

Sent CQ tonight in the rainstrorm with the little station and had two answers. The regen had trouble but eventually I sorted it out. This is ridiculousness.

Well I turned down the juice to 300 VDC and decided to try a bunch of different tubes in the little oscillator. Tubes like the 6AK5 and 6AU6 are similar enough that if you tie the suppressor and cathode pins together, you can stick almost anything in the socket.

Here are the tubes I tried: 6AK5, 6AK6, 6AU6 6BA6 6BJ6, 6BZ6/6JH6, 6CB6, 6BH6, 6BJ6, 6HZ6, and the JAN 5769 (6BA6W). I tried several of each type and the A versions.

Who can guess the tube with the most output?

The least output?

The best efficiency?   

WU2D Mike

Most Output - 6AK6 Worst 2.1 Watts Best 2.8 Watts Most 6AK5's, 6BA6W's and a very few 6AU6's could hit 1.8 Watts. 6CB6's and 6BZ6's were around 1.2 W

Least Output most tired 6AU6's. Around 700 to 900 mW.

Most efficient: Again 6AK6 at 30% with the 6AK5's around 28% and 6BA6W around 27%. The 6AU6's were between 18 and 25% depending on the tube. The 6BZ6/6BH6 were lower around 17%, not a great power oscillator.

Mike WU2D

High gm remote cutoff pentodes make poor oscillators except in amplifier circuits ;D

The 6AH6 should be a good performer also, several NOS of those and the 6AU6's I tried in the Champ 300 gave the 6AH6 the edge in power and stability. I needed to get output up in all stages to get the 813 to perform well.

Mike,

Nice looking station,  but I think you should have use a bigger crystal.  The one you have in the set looks a little wimpy. ;D

Fred

Woops messed up on the efficiency calulations because I used the voltage number before I reduced it so the numbers are higher.

Most efficient: Again 6AK6 at 42% with the 6AK5's around 35% and 6BA6W around 32%. The 6AU6's were between 25 and 30% depending on the tube. The 6BZ6/6BH6 were lower around 21%, not a great power oscillator.

The crystal does make the 6AK5 look a bit diminutive. Marketing...