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Someone once gave me a Yaesu FT-101E for free because it had beat finals. I later gave it to a friend that had a pair of 31JS6Cs tubes and a small variac. Can you guess what we did the light the filaments? It's probably the only Yaesu around with a variac bolted to the back where the DC to DC...

He's waiting for someone to wave a magic wand over the top of his 12 volt filament winding.

That's funny because your diagnosis is most likely incorrect. The odds of an open filament winding in a Siltronics, are very unlikely. These transformers almost always fail with a short and if it's an open, it's almost always going to be in the primary. Don't get mad at us because you cannot...

So, is it a 6X4 or 35Z5?

If your calibrate side reads lower than it did into the 50 ohm dummy load, the antenna impedance (or input to the amplifier) is below 50 ohms. If the calibrate side reads higher than it did into the 50 ohm dummy load, the load impedance is above 50 ohms. It's all about RF voltage and you get a...

Just screw a 12 volt transformer to the back of the radio and call it a day.

The only thing that complicates the use of an internal driver, is decoupling the DC from the final stage and some basic shielding between the two stages.

Eric, I took the time to investigate everything available on this topic before posting. Including going to the FCC website and see if any certification number had been issued for the BLA-703. I can't find anything listed anywhere for that model number. Can you provide it? On the other hand, I...

The only Russian Surplus military tube amplifier that I have that still runs reliably, is one that I built for a pair of GI7bs, that required a GS35b to be installed in order to make it reliable. I understand that others have had a better experience with them. Mine were all extremely gassy. I...

The most reliable sweep tube tester that I had was an old two tube, cathode driven 6LF6 amplifier. Pulled one tube socket to install a 9 pin 6LQ6 socket. Aligned the tank circuit so the plate tune could hit resonance on a single tube. Switching to a variac as the filament transformer, allowed...

They also tend to have a lot less harmonic content, without any additional filtering required to achieve those specifications. I won't run a 12 volt linear as a base station because it's simply too difficult to get a clean signal with good IMD characteristics. To meet good IMD specifications at...

Not exactly true. Especially with a pair of 2SC2290s as the drivers. You'll need a pair of that match the six finals. Then you have to consider the layout of the board and the location of the driver stage. Is it symmetrical to the other three push-pull stages? If it's not, the difference in RF...

This amplifier detects and blocks out of band operation electronically. It does not use filtering to achieve this. Therefore, it can sharply cut the amplifier off just below 28 mhz.

The BLA-703 does not have an FCC ID number affixed to its back like the BLA-600... Meeting FCC specifications for second and third harmonics while locking out 11 meters, does not imply FCC type approved equipment. Broadband solid state amplifiers do not typically require individual input...

Assuming it has a standard 120 plug on it, you can't have anything larger than a 20 amp breaker at the box. I would try the lowest fuse that holds reliably under normal operating conditions. That will offer the most protection if accidentally operated outside of safe conditions. I don't think I...

The difficult part is understanding why when you place the Mitsubishi part in a Toshiba circuit, it produces less than half of the output. If the person doesn't know the input match is off by more than 3 to 1, they may never overcome this problem.

The problem I see is the manufacturer won't mention how many transistors are being used to reach this power level or, what type they are. The price indicates they must be the cheapest switch mode transistors that will work. Advertising the part number might complicate marketing the amplifier as...

I think the biggest reason these 2SC3240 transistors have not seen widespread use in the amplifier market, has to do with its 0.4 ohm input impedance. This is 3.6 times lower than the 2SC2879 and a big enough difference to make the part perform very poorly in a 2SC2879 circuit. This transistor...

I consider the 811A as an obsolete tube out of production many years ago. It's replacement is the 572B.

They have not made an accurate equivalent of the original RCA 811A tube, in over 30 years. The 811A tube became completely worthless as soon as the six radiator fins were removed from the anode and replaced with a flat fold on each side. That is not the way the original tube was constructed and...