Brute 75 Repairs and Demo

 This is one of the great hidden treasures at hamfests... the Brute 75. It's a 1-tube grid driven monoband HF amp built by Majestic Communications (Maco) in the mid-70's. It uses a M-2057 tube, but can be fitted with a number of different tubes commonly found, today. Most of these have a built in switchable recieve preamp. It's designed to use low level drive, 5 watts or less. 

These were originally targeting CB. It has a tuned input and a built-in low pass filter, in addition to a Pi-net output stage. These are very clean, spectrally. By scrapping the tuned input and swamping the grid circuit with a 50 ohm carbon resistor, a simple band switch on the tank will allow multiband operation. These are perfect to add power to a QRP station.  With the proliferation of low power rigs, SDR, and others, it's a solid and cheap amp to grab.

As for tubes... the 2057 can be substituted with a 8950 at slightly reduced output. Same with a 6LB6, with a simple change to reduce the fil voltage from 12v to 6v, most have a transformer tap. Simply change the socket, and an 8908 will work perfectly, same goes for a Russian 6P45C swap. It runs 900v on the plate, 450v on the screen, and is biased into near cutoff at -170v on the control grid. 

This one had bad diodes in the hv circuit, a shorted tube, and a bad rx preamp transistor. Here's a couple of vids in the shop and on Studio B, and a few pics...

Built-in low pass filter!

Boomer 600 Repairs

 This is a Boomer 600 broadband HF amp. This type of amp is readily available at swap meets and on the market, and most work really well with QRP rigs, low power SDR rigs, etc. When used with external bandpass filters, they are a great addition to a low power operation.

A friend picked this up at a swap meet, DOA. I found a burned and damaged contact in the T/R relay. Once working, I discovered a SWR issue on the input, due to an input transformer mismatch (possibly as a result of different power transistors than the original design, not sure). I corrected the transformer ratio, altered the input pad, and all was well. 

Next, the 2nd harmonic on the output was only down about 20db. Despite it being used with an external bandpass filter (60dbm.com), I felt this needed to be improved. Using arco trimmers temporarily sub'd into the output tuning stages in place of the fixed values of C as supplied, and the Spectrum analyzer, I was able to achieve around -30 dB. I dialed it in, measured the Arco's, and installed fixed value caps in their place. This helped improve the performance of the downstream bandpass filter. Here's a few pics.

Firebird Amplifier, Gut / Build

 This project started from an old Firebird amp a friend picked up on eBay. It was pretty much junk, but the cabinet had promise. I decided to build a grid driven one or two tube amp in a modified version of the old Firebird cabinet. This would allow operation with low powered SDR and QRP rigs with a power range of 1-5 watts. Stay tuned :-)

Boy, it doesn't look like much, yet. Humble beginnings :-)

I'll cut a piece from this aluminum bar to build a new faceplate.

I'll trim a piece of this to attach t the inner top, and provide an attachment point for the lid.

A piece of 3/8" aluminum u-channel here,xto raise the face plate.

The old rectifier board... I may use this, haven't decided, yet...

Antenna Tuner Project

I've been scavenging parts for a transmatch, for quite some time. A friend recently gave me an old BLJ amplifier parts unit, and the aluminum cabinet seems exactly what I needed for the project. 

I gutted the entire unit, repaired a hole in the lid, and stripped it to it's aluminum base. I riveted the faceplate into the cabinet, I still need to work out a few dings before priming and painting. Here's a few pics, up to this point. Stay tuned...

This is how it started...

The faceplate was originally held in place by only the toggle switches...

There were several layers of paint from 50 years of being repainted...

The hoke in the lid was _very_ rough and had to be cleaned up before a patch was applied...

After the hole was recut squarely, this is a patch of similar material I'll use to repair the lid...

A pic from under the lid...

Lid repaired. I still have to add some flat bar to the lid to stiffen it up a bit.

Kenwood TS-700a #2

This is the 2nd TS-700a in a group I got from a local friend.  These are great rigs, manufactured around 1976 for $700!! Every one of these I've ever worked on, had me chasing my tail with weird symptoms that were ALWAYS traced back to a dirty band switch, a dirty mode switch, a dirty repeater offset switch, and/or dirty toggle switches. As a result, the _first_ step of servicing these rigs is a thorough cleaning and lubrication of all rotary and toggle switches. This one was no exception...

This rig was totally DOA. After cleaning and lubrication as mentioned above, I discovered the MH6P 6pdt relay was totally missing. I replaced the relay, and it came alive and was a serviceable radio. FM was inoperative, and that was traced to a faulty 10.245mhz crystal osc transistor on the FM board (also very common on these rigs...it's usually the crystal or the transistor). A replacement transistor, cleaning of the multi-contact plugs on the crystal osc board, a full alignment, indicator lamp replacements, and it was good as good as new. Here's a few pics and a vid...

Swan 117XC Restoration

 This is another Swan 117-XC power supply restoration. These are solid performers and used to power many of the Swan rigs like the 250, 350, 500, etc. 

Restoration is pretty straightforward... refinishing the cabinet, compounding the front panel, replacing all electrolytic caps, replacing the old "metal-can" style rectifiers, and replacing the 4.7 ohm resistor in the 12v relay supply circuit. Here's a few pics...

Rust to be removed and repainted...

Old caps to be installed...

4.7 ohm resistor measured 22 ohms...

Compounding front panel with Flitz...

New caps installed...

New caps installed...

New diodes in place, and 4.7 ohm resistor replaced.