|Restoring my ALPHA 76A HF Linear Amplifier.
( Alfie )
Condition as Bought
had always admired ALPHA Amplifiers for
their performance and reliability but could never find one to suit my
budget, so when an old tired and battle worn ALPHA 76A was offered to me
I jumped at the chance to own one of these legends. It had a hard life
in previous hands as it was used as a contest amp amongst other things
and was in need of lots of TLC. Although the amplifier worked well it
was showing its age with a few dents and dings and broken switches but
nothing that couldn't be fixed, the
front panel was scored and also had the grey sticky paint finish which
would require a paint job and new decals. (Cheaper to fit a new one
which I did ). ALPHA carry a good stock of Legacy Amplifier parts and
offer an excellent service at reasonable cost.
The amplifier as I received it was used for a few weeks to assess its worth for restoration or to use it as it was, then I researched the availability of the necessary bits and pieces that would be needed to make it a good working and bring it back to something of its former glory.
The winter months were spent sourcing the parts required, both new and used to complete the project. ALPHA supplied me with most of the bits including a new front panel and knobs but couldn't supply the now "rarer than hen's teeth " front panel switch mechanism. These parts were sent to me free of charge from a US ham to whom I'm very grateful. With the most of the bits sourced all that was needed now was a little bit of enthusiasm to get started on the project.
all the necessary bits and pieces were at hand it was time to begin the
restoration starting with an almost complete strip down and replace or
repair the parts as required.
ALPHA 76A stripped for further inspection.
Front panel switch assembly.
The switch assembly was in need of repair and as ALPHA could only supply the basic switches and not the selector mechanism so I had to effect a repair to it. The knobs for the switches contain coloured indicator flaps that operate mechanically to change to the appropriate colour when pressed. Some of them were missing and others were damaged and led me to a lot of head scratching. Either I could fabricate something or use a different type of switch knob. As it was my intention to restore it to as near original as possible I laid it to one side while I got on with other jobs that I had parts for.
Repaired Switch Mechanism
waiting for parts to arrive I got on with all the more tedious jobs like
replacing resistors and panel illumination bulbs on the PCB, tidying up
the wiring and removing minor dents in the main chassis.
Timer & Rectifier PCB Chassis Dent Repair
a few weeks and all of the bits needed had finally arrived it was time
to start the serious rebuild. The smaller jobs like fitting new switches
and the repaired selector mechanism etc were tackled first, then fitting
a new front panel and control knobs were carried out.
Finally the tubes, the transformer and all the smaller bits were refitted ready for the switch on.
gave the ALPHA a soak test with HT on for a few hours to allow any
faults to manifest themselves, happily all was well and time now to
apply some RF. The Amp was run into a dummy load and was producing near
full output on all bands thus indicating the tubes were in good
condition and didn't need immediate replacement. The tubes used are a
pair of Eimac 3CX400A7 Triodes in grounded grid and are very expensive
if you can find them.
At a chance meeting at a Radio Rally I purchased a couple of these tubes that had been used in a piece of aircraft ground support equipment. In that role they were not subjected to abuse as the were only used in a voltage stabilising role and looked as if they had just come out of the box.
After a few weeks running the amp with its original tubes I decided to try the recently bought ones. I was very pleased with the results as the tubes were producing full output as per the data sheet.
These tubes were run for a few days then removed to be kept as back ups and the originals re-instated for what I hope will be long service. The final thing left to do was to paint the lid of the Amp to match the new front panel.
All this being done Alfie was placed on the Shack Operating Bench to be used and enjoyed as it should.
The Completed Project