Kris Boomer Upgrades

This is an old Kris monoband amp from back around the late 70's. They were simple grounded grid amps using a pair of 6JU6 sweep tubes. This amp was a dog when I got it...power supply problems, rf sensing problems in the keying circuit, tubes shot, and other issues.I set out to get it running and back on the air. 

Before I would repair the other issues, I had to locate a set of tubes. The 6JU6's are almost unobtainium these days, in new condition. I had been looking at a Russian glass tube that is still available as new, and decided this was a good time to test my idea. The Russian tubes are larger, but have the same tube socket (and are fairly inexpensive!)...I rewired the sockets, repaired all of the other issues, and set it up on 10 meters. With a Radio Shack HTX-10 this little amp now does about 150 watts out on SSB, & about 100 watts out on FM. 

Below are a few pics, including some to show the difference in the physical size of the tubes...

There was a considerable difference in the physical size of the tubes. They were pretty close to the top cover, but with some work around the parasitic suppressors and plate caps, I was able to fit it all inside.

Craig 4201 23 Channel CB Base Station

This is a Craig 4201 23 Channel CB Base Station that a friend found on eBay, and purchased it for another friend as a gift. He brought it to me for a quick checkup before delivering it, but when we opened the box, it was broken and bent. Considering it was a fine specimen from around 1977, I decided to see if I could straighten and repair it. The main PCB was cracked, the channel selector had been smacked around, the bottom was bent, the faceplate was cracked, side panel banged in, and more. 

I couldn't help myself...so first I got it working electrically. I found 2 of the synthesizer crystals to be bad... so I found a couple online, got and installed them, and padded back on frequency. The PCB crack was repaired, and a full alignment and tx tuneup was in order. Once it was running, I started repairing the cosmetic issues. In the end, it turned out pretty darn good and another piece of radio history from the '70's lives again :-) Here's a few pics...

Here's a little video of the completed radio, receiving signals off the air... It sounds good, and was taken to it's final home. The person he gifted this to is now a ham radio operator, but this was the same exact model of the first CB radio he ever had. 

 

Xeron Mini-Max Sweep Tube Amp

This is a repair on an old Xeron Mini-Max Sweep Tube Amp. This was built back in the early 80's, as best as I can tell. It originally used 12GB3 sweep tubes, this one had been converted to 12DQ6B tubes, and used 4 of them. This is a grid driven amp, with about +700vdc on the plates, +150vdc on the screens, and about -35 on the control grids. The input is swamped with a 47 ohm load, and is tuned. The output is a conventional Pi-network for one band, with the plate tune adjustable external & the plate load internal and set for an output load of about 50 ohms. 

These are neat little amps, probably mostly designed for AM operation. I've used it with a HTX-10 10m mobile QRP rig, and found it to be decent on SSB if the bias was adjusted accordingly. AM with 100% modulation yielded about 500w pep output, and about the same on SSB with the bias adjusted for that mode. Operation on FM, due to duty cycle, had to be held to about 120 watts output. CW operation in the SSB mode provided adequate break-in delay. 

This one had a toasted power transformer. These amps are kinda prone to that, as it's cramped quarters inside for a decent transformer and adequate cooling. A larger transformer on an external chassis solved that problem. Here's a few pics of the repairs & mods ...

Ripped all the "guts" (seen below) from the chassis with the "new" larger transformer, and rewired a cable for remote connection to the mini-max...

 

Comparing old transformer (left) to new transformer (right)

Cable and quick disconnect installed and ready to go...

Testing things out, adjusting bias, checking voltages,  tuning input coil, etc...

External bias adjustment installed by someone in the past...

Tuned input (now with pink wax installed to "lock it down")...

Internal load control in output Pi-network, I drilled hole in cover to allow for external adjustment...

All finished up and running great. Pretty strong for a little sweep tube amp!

Cobra 21LTD Classic

I'm a sucker for old CB radios. This one isn't sooo old, probably around 25 years or so, but it was pretty rough. It was in a box of junk radios. I didn't take before pics, but I should have. The S-meter was broken, it had been connected to a DC source via reverse polarity, was missing the microphone, had a couple of "noise toys" installed that were causing all sorts of problems, and practically everything that could be turned inside, had been turned. All the pots were dirty, the ribbon cable for the channel selector indicator had a bad solder joint, etc. 

So, I removed all the aftermarket junk, replaced the S-Meter, replaced the bad lamps, repaired the damage from being connected to 12vdc backwards, fabricated a power cord for it, cleaned all the pots, found a mic and wired it up, gave it a complete alignment and a few extra tweaks. Wow, there was a real radio in among all that :-) The little red push button isn't connected, I left it in to plug the hole int he face of the radio. I scrounged around for a mounting bracket and mounting hardware, gave it a bath, and here it is...

Royce I-600B CB Restoration

This is a Royce I-600B CB that was in a tub of junk radios. My dad had one of these in one of his service trucks back in the 70's, so I couldn't help be try to revive this one from the dead. it was pretty nasty, and had a variety of problems... no RF output, poor receive sensitivity, no power cord, and a microphone that was questionable at best. 

After a bit of poking around, I discovered the final RF amp to be blown. A suitable replacement was found among other junkers in the tub, and the transmitter was back online. After a full alignment, receive sensitivity was up to .15uV for 10db, not shabby for a 40+ year old AM CB radio. The mic actually worked, despite it looking so grungy! A good bit of scrubbing, and the radio didn't look too bad. It brought back fond memories of working with dad during my early teens. Here's a few pics of the "restoration"...

 Out with the old bad part...

In with the old good part :-)

 Man, that was one dirty microphone!