Old amps

 

I now use an Alpha 89 as my main amplifier, with an Alpha 91B for backupĀ  and SO2R operation. Both were purchased used from fellow Frankford Radio Club members.

But for 30 years we used a double rack of six glass-tube amplifiers that also had a long heritage in the Frankford Radio Club. They likely were built in the 1950s or ’60s.

The green amp in the middle on the right is a single-bander for 160 meters using a 4-1000A in grounded grid. This was the first amp in the set that I acquired around 1984 from N3AD.

Soon after the other five were acquired from N3RS when Sig switched to Alphas.

The three on the left are grid-driven pairs of 4-400’s, single banders for 40, 20 and 15 meters.

Top right is an all-band pair of 3-500z’s in grounded grid that was dedicated for 80 meters (I added a single-band input circuit).

Bottom right is a single 4-1000 in grounded grid for 10 meters.

At lower left in the double rack is the screen supply for the 4-400 amps. In a separate short cabinet just visible on the left was the high voltage supply, using an old pole-pig power transformer. The voltage was a bit low for the 4-1000’s so a big variac was used to raise the primary voltage a bit. Still, the 4-1000’s only put out about 1200 watts.

These amps generated a lot of heat — in fact I installed a blower in the attic with a vent in the hamshack ceiling to exhaust the heat during contests.

The fans and blowers used to cool the tubes also generated a lot of noise in the shack.

Around 1988, when operating a contest from a basement hamshack at our Bear, Delaware, QTH, the operating table was on one end of the room and the amps about 15 feet behind at the other end of the room, to get some separation from the heat and noise. I used a mirror to keep an eye on the tubes in the amps, in case something went out of resonance. Suddenly I saw flames coming out of the power supply! I killed the power and was able to extinguish the flames and the only damage was to the pole pig transformer itself (a different one that had a switched primary to give higher voltage for the 4-1000s). Ran low power for rest of contest.

In 2007 I purchased the Alpha 89 from another FRCer, K3NZ (now SK). This became my mainstay for general DXing and contesting, and it got rid of the heat and noise problems of the double-rack, which I had fondly dubbed my “poor-man’s autotune Alpha” for years. The rack had the big advantage that I could change bands instantly without having to re-tune, and was still used for SO2R in the all-band DX contests.

A few years later I acquired the 91B from W2OX (another FRCer, and it was previously owned by FRCer K3OO). This became the backup amp and is used for SO2R. When the hamshack room had to be cleared out to allow installation of new hardwood flooring around 2014, the double rack was moved to my electronic-workshop shed, where it remains pending possible refurbishing. I’ve pondered modifying the 10-meter amp for 6 meters.

Before acquiring these amps, I had built a homebrew amp using a pair of 813 tubes around 1983. It put out about 700 watts on CW on 160, 80 and 40 meters. My first 83 countries on 160 meters were worked before this was built, using 100 watts or less.