The AM Forum

Greetings,

Been licensed since 1976, but totally new to AM. Recently refurbished/aligned a Hallicrafters HT-37. Have put it on the air paired with a Collins 75S-1 receiver with a homebuilt TR switch. It seems to be working ok, getting good reports on audio.

I would like a little more power (25watt carrier) than the HT-37 alone.

I was wondering if anyone has used a Kenwood TL-922A amplifier on AM?
I checked with Tom Rauch W8JI and he indicated I should be able to use it with a carrier up to 150-175 watts.

Anyone have experience with this amp and the tuning procedure of it? Any help or input is appreciated!

73
Larry
W4PJP
Spring City, TN

Tune for maximum peak power.

There you go.

The TL922 is a good amp for ssb.  Akin to the Sb220.

As such, Tom is right about the carrier level.  It's not really made for high duty cycle modes.   It's not made for 2kw output.  It's made for 1200 watts of output, peak.

I have friends running the 922 with 200 to 250 watt carriers.  But that's the highest I would run.

--Shane
WP2ASS / ex KD6VXI

Thanks Shane!

I guess the amp (voltage) should be set on the CW setting?


Larry
W4PJP

  I run a Heathkit SB-221 - a similar amp - at 200 watts carrier. SSB/CW switch in SSB position; tuned and loaded for 800 watts.
At 200 watt carrier, your peaks at 100% modulation will increase to 800 watts; if your amp isn't tuned for 800 watts your peaks will be clipped and distorted. Problem is, now your amp is very inefficient at the 200 watt carrier level - somewhere around 30% - so your tubes are dissipating much more energy than they would when amplifying an SSB signal. That's why an amp capable of 1200 watts SSB is only a 200 watt amp on AM.
  Nothing you can do about it - it's the nature of tube amps - but an amp like an AL-82, which uses the same tubes but with much better cooling, will give you more headroom. I installed a "booster" fan on my SB-221, significantly increasing the airflow, but I still wouldn't run any more than a 250 watt carrier with it.
  I watch my tubes: a dull tomato red with the SB-221's cooling is fine, but save the bright orange for amps with better cooling.

The more air you can get on tubes in an 'ssb' ratings type of amp, the better. Not after higher power but reliability and long life.

A simple thing that can be done on amps that draw in their cooling air from the bottom is to obtain or make up a short box the amp sits on, and which has a relatively powerful blower inside, like an old rackmount dual squirrel cage type. Those blowers take usually 5-7" of height in a rack. Don't bother with fans because pressure is what's wanted along with the volume.

Cut out the top of the cabinet so that the feet of the amp just sit inside the hole and the amp covers the hole completely.
The whole amp will run way cooler. The Caveat is noise due to the booster blower, and the size of the 'wind chest'.

The SB-220 draws air from the back so this won't work for it. Don't know about the Kenwood.

Hi Larry ...good to see you on the forum ... met you at Mcminn Co. hamfest last July

I hope to be back on the air soon. 73. John

I ran my sb220 on the ssb switch constantly.

The only time it saw the cw switch was at turn on.  It lowered the in rush current.

I always like aded it to the pep value I needed for the carrier level.

Caveat:  I don't do digital modes, including CW 😉

--Shane
WP2ASS / ex KD6VXI

Thanks for all the comments! I hope others will chime in, this topic is not discussed much anywhere…..

John, good to see u at the hamfest….didnt know you were interested in AM!


73
Larry
W4PJP

I have a friend in Idaho that uses his TL922A on AM all the time with either a DX60 or an ICOM 7300.  I concur with all the above on limiting carrier to 200 watts or less for the SB 220.  I have both a HL2200 (last of the SB 220 series) and an Ameritron AL-1500.  Full legal limit (375 watt carrier) on AM from the Ameritron, but I run the Heath at 200 watts AND I have increased flow with the Harbach mod fan cooling.  It would be hard to see the difference on an S meter between the two as I have experienced on 75m AM.

Some Henry amps using 3-500s get more power due to running higher voltages and better cooling with tube chimneys and ducting.

Regards, Good Luck, and 73s - enjoy AM with old and new "Buzzards".

NS7H