当時５０MHｚで正式免許になった最大出力は５０Wだった。直線増幅用の半導体はまだ高価だったので放送局出身の４F15Rでオーソドックスなリニアアンプを製作し、ＤＸＱＳＯやコンテストに数年間使用した。９０年代になってからハイパワー免許を意識して4F15Rからプレート損失の大きな５F35RAに真空管を交換し、バイアス電源もシャントレギュレータに変更して動作テストを実施した結果は以下の通り。
Ep 2.0KV, Ip 430mA(Idle 125mA), 860W input, Esg 275V, Ig1=12mA（AB2）,Ig2=25mA,
530W output,η=62%, Gain24dB
なんとか目標の５００Ｗを得たが既に飽和領域にあり、直線領域での実力は４００Ｗ止まりであった。無負荷で２５００Ｖまで試したが、ブローのリスクがあるのでこの球は２ｋＶ以下で使ったほうが良いと思う。プレート同調にスプリットステータ型バリコンを使ったためか、効率は常に６０％をクリアしていた。製作は１９８０年。
The legal power limit of 50MHz was 50W in Japan in those days. Semiconductors
for linear amplification were still expensive, so I made a traditional
G-K amplifier with 4F15R (pull out from the broadcasting station in Matsumoto,
Pd=150W with forced air cooling), and it was used for DX-QSO and a contest
for several years. To be conscious of a high-power license in 1990, I exchanged
a vacuum tube to 5F35RA (Pd 350W) from 4F15R, and also changed the bias
power supply to a shunt regulator. The result is as follows.
Ep 2.0KV, Ip 430mA (Idle 125mA), 860W input, Esg 275V, Ig1=12mA (AB2),
Ig2=25mA, 530W output and η =62%, Gain24dB
I obtained 500W of output finally, but it was already in the saturation
(non-linear) region. Its ability of the linear amplification was upto 400
W. I experimented DC2500V on the anode, but there is risk of blow, so I
think it's better to use this tube with Ep of less than 2 kV. As the split-stator
type of variable capacitor was chosen for the plate vtuning, the plate
efficiency seemed to be always above 60%. Making was in 1980.
