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The difference is likely to be the coil voltage. This amplifier only has 6 volts available for low voltage.

Now that the color bands are burnt off, there would be no way to tell without a schematic. It appears to be in a non-critical part of the circuit being used to simply remove RF, rather than in a tuned circuit where its value would be critical. A likely guess would be to start someplace around 10...

The determining factor will be if the tube's anode turns red during use. If it does, it's being hit too hard.

Keep in mind, in the absence of bias switching, that tube is biased in the transmit mode all of the time. Check to make sure it is not developing excessive heat in the receive mode, otherwise that tube is not going to last long. The good news is, these amplifiers operate close to class C so...

Notice the size of that replacement plate transformer. That seems robust for a 6BQ5. It looks big enough to run two 6LF6s. Heavy duty.

Your idea to link the two cathode pins together is exactly what we do when one fails. I don't like to do this in advance, because it will allow twice as much current to flow through each tube and provides no second chance in the event of a severe overload. That's something you do after you've...

The glitch resistor makes a huge difference. I back that up with a cathode fuse when a single stage has a bunch of sleep tubes. One extra step when you're dealing with six tubes in a final like this, is to balance them out with one ohm non-inductive resistors feeding each cathode. The fuse...

The nice thing about the 8950 and the M-2057 are that these tubes give you a pair of 1 amp fusible cathode links on pins 2 and 6. You get two chances to destroy each of those tubes.

I'm thinking an arc inside one of eight finals, cannot be responsible for reducing the output power all the way down to four watts. That sounds more like we may have lost plate voltage on the finals and are looking at the feed through RF from the drivers. There is also the possibility that...

The good news is, you can't turn tube anodes cherry red with a bad power transformer. My first question would be, what tubes turned red, drivers or finals? If only the drivers turn red, check the plate choke feeding DC into the caps of the eight finals. The flash that was seen, may have been...

I have to take this one step further and point out one of my major gripes about Texas Star. I don't think I've ever seen another amplifier attempt to add bias, in the absence of both thermal tracking and any attempt at all, to regulate the bias voltage. These damn things changed their class of...

Sorry to be pessimistic however, forget the Viking. I serviced and built amplifiers for decades and only seen one of these come into the shop. That's because only one person in my area ever purchased one and naturally, it had to come in for service. Their smaller amplifiers were prone to...

Crack a 24 volt AC wall wart apart and pull out the tiny inch and a half transformer. Run that through two diodes and two capacitors to form a voltage doubler and walla, you've got 65 volts of DC to work with. The first picture in my post above, shows this transformer mounted on the deck. I see...

While I wasted a lot of time trying other methods of stabilizing this amplifier, the addition of neutralization only required adding two more parts. The air variable you see in the pictures and a 680 picofarad capacitor that was placed in series with the grounded side of the RF input...

If you ever burn the finals up in this radio, they can be replaced with MRF454, still in production. If you're willing to do a few modifications, you'll also get a noticeable improvement in power output. The link for this modification is below. http://atlas.wireless.org.uk/mods.htm

It sounds like you have already found out that cheap versions of this relay work fine, right up until you try to solder their pins directly into a PC board.

It's been my experience that these relays have a very low tolerance for heat while being soldered into the PC board. A little too much heat and it will melt the contact pin and shift it out of alignment enough to where it either does not make connection or makes one with a little extra...

I do not see where you are claiming that either one of these microphones worked on this radio, just prior to removing the noise toys. Maybe the problem is your setup will squeal with any power Mike because of poor RF ground? One loose coax connector can cause this entire problem.

These amplifiers are a wonderful demonstration of how few parts are needed to make something work , as compared to how many more parts are required to make something work correctly. How many extra circuits can you count here, as compared to a stock unit ?

Easy enough to determine. If you have a brass nut compressing the plates on each end of the rotor shaft, that one can be disassembled. Otherwise, the only way to use this cap, may be to carefully rip out the defective plate with needle nose pliers, and probably say goodbye to low end 80 meter...