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!

Dave's Hamfest!

Like many of you, I tend to collect things that I don't use. Being a builder, I also seem to collect lost of gear and parts that I never use. I've recently gotten the itch for a Flex radio, so I decided the best way to do this painlessly was to 'thin out' some of my excess radio goodies.

So, I've been cleaning out the workshop, utility room, garage, & attic a bit, and selling off the excess radio stuff to build my 'Flex Fund'. There's way too much to list here, but I put it on my website so I could easily update it as it clears out. Check out my load of hamfest stuff on my Dave's Hamfest Page at http://www.wb4iuy.net/hockaday/ .




Dave WB4IUY
www.WB4IUY.net

Ford Escape Cats...

 The latest JoCo Inverted Drill Press improvised to drill out a hardened stud on the rear cat of a Ford Escape...