Nomad's plate choke cured my10-20M amp woes.

[Naysayer]

11M test just now showed over 400w AM from a 1970's 23 ch CB barely powered by a 12v, 2 amp bench supply. Amp still on work table so I was only using one plate transformer (1800 400mA). That's a best ever for 27Mhz especially given I did not even tweak Tune, Load or RF Input, just took a good guess and as the first try I used a 6A mains fuse. There's much more potential here. Tickled silly to see it working above 40M. These 4cx300a tubes are amazing for their size. Time to put the bottom cover back on and prepare for a full power test and maybe even use if it holds together. It was a good day.
Neil, nyc

 

[nomadradio]

Rock on, Neil! Gotta love it when a plan comes together.

73

 

[Naysayer]

I was too fast to conclude total success. There was overall improvement but the same general pattern of too much C in pi network for 10-20 meters remains.

This picture is an abomination but I’m hoping to rule-out inductance as an impediment to 10-20 meters. The last round of testing showed highest PO on 10-15M without any Tune Cap connected. On 20M, it’s too close to call if min Tune C is helpful or not.

I will eventually ‘graduate’ to vacuum variable for the Tune C but product selection complicated by how to mount. I’ve never seen a vacuum variable IRL yet from what I see online, it’s the mounting system that’s difficult to acquire/fabricate. Not knowing how to mount makes it hard to commit to a Vacuum device. I’ve got lot’s of room but I find almost nothing on how to mount / associate matching clamps/brackets for a given product line. The little squat Comets for example: How do they mount? I see no mounting holes just a hockey-puck lookin’ device.

Anyway I’ve not yet tried the roller in the pic yet. I’ve got so much to write this time of year it takes away from doing anything . Maybe the picture is good for a New Year laugh.

 

[Naysayer]

The picture (above) of an external roller looks absurd and was a last resort. Fortunately, I don't need to pursue that route b/c the fixed inductors are working. It was the T-R relay compartment that precluded 10-20 meter operation (when reassembled). I did sample the input swr with the roller attached (as pictured) and it worked very well. The SWR dip was sharp/narrow when adjusting, not easy to find by Hunt & Peck.

The primary problem with low output on 10-20 meters was caused by the T-R relay compartment as those bands worked with the bottom cover removed. Over the past several months, I did repeated tear-downs to re-wind inductors, test input swr and reassemble. Each time I thought I had it licked after seeing large gains on bench while the bottom tin was removed. Premature claim of success b/c after I replaced the cover, Kaput! It took awhile for me to recognize it was the cover.

Chassis made from 3 aluminum boxes bolted together. The middle box contains Soft-Start and T-R relays (3 SPDT 12A relays glued together: 1 for Input, 2 for Output). It’s a narrow rectangular box 12" long 2.5" wide and 2" deep. Like a big capacitor.

I replaced the 8x cable w/ RG316 and reduced center core exposure; Wrapped copper sheet around Input relay (isolation?). Removed push-on Blade terminal connectors and soldered the RG316 directly to relay terminals. Also removed the COR keying board & wires (keying Buffer since repaired).

I’m waiting for a new set of machine screws & tap to re-thread the bottom cover fasteners. Soon I’ll test my better-targeted fix. Worst case, relocate/replace T-R relays. I can better target my efforts.
neil, nyc