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The datasheet for the Toshiba 2SC2879 also says that its maximum specifications are provided at 25° c. This is fairliy common albeit, impractical to achieve. The Mitsubishi part is still easily found online for sale. Some places have it priced very economically too.

In the case of this particular S-827, we sold it to a school bus company in Florida. We cut them down and tuned them for VHF low band. I can only assume because of the area that it was a severe lightning storm. The customer sent the antenna back to me claiming that only the coil was damaged and...

Your lightning protection advice, is spot on. The only thing I will add is that the S-827s DC grounded loading coil will protect you from nearby lightning strikes however, it most certainly will open right up under a direct strike. I've got one that took a direct strike and the coil burned open...

The specific bipolar RF transistor I was referring to is the Mitsubishi 2SC3240. It has a collector dissipation of 270 watts! Superior to the original 2SC2879.

The 2879 was designed to monopolize the 100-watt transistor HF market in 12 volt equipment. It's price point and durability made that goal very easy to achieve. They literally destroyed Motorola's market in just a few years. Mobile HF radios are still using 12 volt 100 watt transistors and the...

As a side note, mine blew up the drivers again about 2 years ago and I won't even consider fixing this piece of garbage again. The original drivers used in the non D version, are absolute garbage. No wonder why they abandoned this part on the newer version. The problem is, when you send the old...

Another thing I just thought of is the shifting output power alone, regardless of the reason for it, is going to cause the resonant load impedance to change, and therefore the amplifier will tune in a different spot anyway. The only way to prevent a shift in output power from changing the...

That symptom supports a shifting part value.

Look at the symptom again... "They both exhibit a strange issue where dead key, after keying for a short time, starts to drop from about 250W down to 100W. After a little while, it climbs back up to regular output and stays for a while." A capacitor failing from too much RF current will not...

Neither the screen Grid or control grid voltages are regulated on this amplifier. The screen grid looks to have the same positive voltage that feeds the relays and is not likely to be moving around. However that method of a resistor and diode or just the resistor on the final stage to establish...

Good bass hammers two senses and smell is not one of them.

Amplifiers with "Clip" warning indicators, help keep a lot of unwanted DC off of those voice coils. That helps you keep the bass set to the point where you can feel it, but not to where you can smell it yet.

The thing I like most about Prime Minister is he would much rather talk to you about our radio hobby then his fame or fortune. An accurate description of him, would be too normal to be wealthy and famous. He doesn't care if you're rich or flat broke, what shade your skin is, he'll talk to anyone...

I've spoken to the gentleman in question many times over the years. He's built everything from LDMOS, to a grid driven tetrode. I can't say whose amplifiers he did or did not build however, I can certainly vouch for the fact he knows how to build amplifiers. Clean work too, no expense spared.

It turns out you can teach an old dog new tricks.

How do you do that when the standard transformer has its 6 volt filament winding internally wired in series with its 37 volt bias winding? I don't see how there is the isolation available to use a voltage doubler, when that winding is already referenced to a positive ground power supply. Maybe...

If I had to make that relay work, I might try spinning some more magnet wire on the solenoid to bring up its DC resistance or, stretching the spring a tiny bit to reduce its mechanical resistance. In one case, I've even swapped the solenoid from the original relay to the replacement, in order to...

That often relates to an unregulated screen supply where secondary emissions are driving the screen voltage higher. Using a low impedance screen supply or the addition of a shunt regulator, keeps tetrodes much more stable over wider operating conditions and temperature. Prior to adding the...

Oh wow! I completely overlooked the fact that this is an older unit with the 6AQ5 tube. That will not be an easy relay to replace. Later versions only had 6.6 volts of AC to work with from the filament winding.

Sorry, it sold almost immediately.