Search results

If the original D&A tubes with the double strapped, black anode cap are still good, they are far superior to anything you are likely to find in the Varmint. About the only exception would be if the Varmint had Amprex 6LF6 tubes made in Holland. That particular plant made the most reliable 12...

If you can cut one side or lift one side of the zener and the voltage on the output of the 22k resistor approaches =150 volts, the zener is responsible for loading the resistor all the way down to =5 volts. NOTE: While this test is safe to do in this amplifiers negative bias circuit, do not...

It may have started life as a 36 volt zener. After a tube meltdown and likely internal tube arc, it's now acting like a 700 ohm resistor. These devices are fragile to overload and typically turn into low value resistors when they are overloaded.

A working 36 volt zener will appear as an open circuit and only begins to conduct like a short, when you reach anything above 36 volts. Everything above 36 volts gets dropped across your 22 k resistor, while the regulated 36 volts remains across the diode. Since you've disconnected the brown...

The resistor in question is supposed to be 22,000 ohms. At 23,000 ohms it's well within tolerance. I've also looked at another unit and it is the correct value. Your picture shows the only thing this resistor is feeding right now, is the diode with no other connections at that point and you were...

I've recently tested two models of inexpensive digital signal generators. One that tops out at 6 GHz with 20 miliwatts (easily boosted with a $15 pre amp) and the other tops out at 1 GHz with a whopping 200 miliwatts of RF! You don't even want to know what these things can do when set to a .1...

I forgot to add, the blue wire you are questioning is the AC transformer secondary, for the bias voltage. It's feeding the diode half wave rectifier and filter cap. The side of the diode with the wire from the transformer, should show about 105 volts AC, to ground.

Work on it without the tube installed until you get the negative bias voltage correct at the tube socket. If you have -150 at the bias filter cap, it can only be an open 10k 1 watt resistor or, a short across the zener diode. The possibly of the short can be inside the zener or, the circuit it...

I also noticed as soon as those two big 5G signals showed up on 614 MHz. and 745 MHz. that was the end of anyone using an 800 MHz. scanner in town. The intermod wipes all receivers out on this band, unless it has a tunned, narrow bandwidth front end.

One thing I'm learning about trains, is they are becoming a new source of interference. Here in Connecticut, the trains have some type of digital transmitter operating around 217 MHz. Every 18 minutes, all of my VHF high band TV channels would lock up in a pulsed sequence that was repetitive...

Operation within the transistors rated specifications, becomes much more important when they are run in the biased, linear mode. Bias causes a portion of the transistors dissipation, to be consumed at DC, rather than RF. All bias power can therefore only be dissipated as added heat within the...

One simple trick that works on many HF rigs, is injecting line level audio into the radios carrier or drive control circuit. If these are potentiometers, it's easy to inject through a coupling cap to block DC. If the audio lacks high frequency response, look for high value bypassing caps...

I'd have my hands in that top drawer, like I were a kid with a cookie jar today.

I remember buying 10 of those tubes from RF Parts and handing the UPS man a $100 bill. It was overpayment by one penny. The year was 1984.

I can honestly say tube amplifiers and the maintenance of them, are definitely more within Scott's abilities, then our solid state VDMOS venture was. The minute I heard about Harbach, I was surprised that Scott had not already arranged for a seamless transition of the business. Being as...

These are impressive numbers that were commonly achieved with the original part.

Another alternative us to just figure out which plate is bent and bend it back. If it's burnt and melted, use needle nose pliers to remove the plate it hits on the rotor side. As long as the amp tunes before the load cap is fully meshed, the missing plate didn't mater and it's removal will make...

I believe that's 10 Micro Henry's at 500 miliamps.

I have no doubt the amplifier does the numbers you say and more. However, you can achieve longer tube life on an oxide coated cathode, by not undervolting the filament. This is because this type of cathode is dependent on reaching a high enough temperature to produce a protective Cloud over the...

If you can get the Chinese 3CPX1500A7 for reasonably less than you can get an Eimac 3CX1500A7, I might go for it. The reason is the higher breakdown voltages are exactly what this tube benefits from in terms of reliability. This tube is noted for grid arcs and arcing between the cathode and...