Watts are Relative, + Keying Circuit Tips

Just playing with my junker Maco 300 as I now have decided to keep my almost mint one with M-2057's. So, I got good tubes in the junker, recapped and thought I would have good output once I fired it up. Nope. Almost no output and a horrible Input SWR. Also, sometimes the keying relay will chatter like they do when you hook up the coax Input and Outputs backwards.
Let's go with the watts issue first. Watts are always relative including Bird watts. One of the many issues that effects watts is the load or antenna impedance. In this case, with the Maco 300 inline, but on standby, the watts go straight thru the amp and out to the antenna, or in this case, dummy load. The dummy load is a perfect 50 ohms, and by the way rated at 6kw so 4 watts in is not going to make it heat up and change the impedance, so the wattmeter will read fairly accurately as the load is perfect. However, with the amp on, the watts from the radio no longer go out the amp into the dummy load. The watts now go thru the input tuning circuit and then into the input or grid of the driver tubes. The radio's 'Load' is now the driver tubes. Won't make much difference what the Load is on the output side of the amp to the radio now. So, now that the radios watts are going to the driver tubes, the SWR is now the impedance of the input tuning circuit and driver tubes. However, because this amp had a problem, (short) in the input tuning circuit, the radios watts are grounded out and not even making it into the driver tubes. This is a very common problem with amps, the watts are not making it into the tubes. A quick and easy way to tell this is to have a SWR meter between the radio and amp. This will show the Input SWR of the amp when the amp is keyed down. I've seen people for maybe 50 years now say or ask why their SWR shoots up when they have the amp on even though the antenna has a perfect match. Well, to repeat myself, the watts from the radio now drive the amp so they do not even make it nowhere near the antenna or output. Since this amp has a short in the Input, the SWR has actually gone to 99-1 and then infinity on the digital Watt/SWR meter. Also, notice on the wattmeter that my watts drop way down on the wattmeter too. This is because the watts are now shorted out, or at least pretty close to a dead short. This same thing can, and does, happen with an open circuit too. However, with a short, the watts drop and the SWR goes sky high, but with an open, the watts and the SWR both go sky high. Also, it does not have to be a dead short or open for this effect to happen. 50 ohms is a perfect match, but 49 or 51 is pretty darn good. How about 40 ohms or 60? 25 or 75? The same effect is happening but won't be anywhere near as dramatic. One of the things I think of when someone ways they are getting way more watts out than the amp is capable of is whats your SWR? I've told the story of a Dentron and I was using an elbow in the coax and the elbow opened and my watts shot up. I unkeyed immediately because I knew something was wrong and found the bad elbow. Another one was I was demoing an Alpha on a 1500 watt dummy load and the watts kept going up and up and then I smelled a burning smell. Fried the dummy load and the Ohms where going up so it was showing fake watts on the Alpha. Resonance and harmonics are factors too, but in the Army I was taught the KISS method, so I'm not getting into that at this time.
The other thing happening besides no output and high inputs SWR is that the relay sometimes will chatter like its hooked up backwards. Yes, it is all hooked up correctly. What is happening is the Input short is shorting out the watts coming in as soon as the relay kicks in. Then, since the watts coming in are shorted, the relay unkeys. Then since the relay is unkeyed, the watts are back and the relay kicks back in. This is happening over and over again, maybe 50-100 times a second. It is not the keying circuits fault. The new Nomad keying circuit is working fine, however, when those watts are shorted out, there is not enough watts coming in for the keying circuit to read, so it unkeys the relay.
Going to wrap this one up, but watts are relative, and always check your input SWR when running an amp. 99-1 SWR LOL.

[@spaceflight1019]

You've got a real enigma there! You're just going to have to trace the RF input circuit with a meter to find the short. It wouldn't surprise me if the relay issue is a result of the input circuit problem. I will guess that there is an input sub circuit whose job is to make the input impedance close to 50 ohms.
You are spot on about the accuracy of wattmeters. They are only accurate with a resistive load. Since an antenna is a combination of inductive and capacitive reactances some meters read low and others read high. But just for reference, 4 watts into a 50 ohm resistive load equals 14.14 volts. If you are designing a keying circuit for an amp you have to keep that in mind.

[@tramdr]

You had me at enigma.

[@spaceflight1019]

@@tramdr Calling it a "mystery" would have been too predictable.

[@bblod4896]

The keying circuit is not getting a strong enough signal to latch the relay correctly. I notice that if the power into my amp is too low, the relay chatters.
Thanks for the lesson.

[@tramdr]

Thanks for the info

[@Udx1977sls]

Hey tram doc what model is that workman meter thanks buddy hope you are doing well sir

[@UDX-21]

Semes like a Reverse -Preamp to me. LOL

[@tramdr]

LOL