Linear Amplifier Tuning Long Winded Walk Thru

Even though I have already done a few already, but as requested by many, a long winded walk thru or talk thru on Linear Amplifier tuning. I think I covered all the bases in the video, but a quick recap:
It's your amp, know what what does what. Know what the Final Tune is, Final Load, Driver Tune and Load if it has it, Input Tune if it has it. Variable and what it does if it has it. Until you know what is supposed to do what, stay out of it.
Know what you are supposed to drive it with. Pretty much all CB amps are made for 4 watt drive or less. Also know what you are going to expect out of the amp. For the most part, normal sweep tubes, like 6lq6 and 6lf6 and family do about a hundred watts out per tube. Driver tubes don't count at all in the output formula. Hence a Palomar 300A with 2x4 tubes, I would expect to see around 400 watts output. D+A Phantom 500 with 4x6 tubes, I would expect to see 600 out. Blackcat JB-76 with 2 output tubes only, I would expect to see 200 watts out. With the smaller 'Baldy' type sweep tubes like in the Browning One Eighty, I would expect to see about 35 watts out per output tube. Again, when tubes normal or baldie, are used as driver tubes, that doesn't count in the equation. With transmitter tubes, from small to large, I expect to see out approximately half the plate dissipation for dead key, and twice the plate dissipation for peak swing watts. Example, a single 3-500z tube has 500 watts dissipation. Hence, I would expect to see around 250 watts dead key and a thousand watts out peak swing, per tube. Of course, any box or tube can be pushed harder, driven more, or voltage upped to do more, and any box or tube will do less if the tube is weak, the box isn't built well, driven properly, or undervolted.
With a CB box, start with all the controls centered. Hook up a wattmeter, make sure you have a good SWR on the output, then apply drive and:

Tune the output, final or Plate TUNE first. The is the most important control. The Plate Tune tunes the Tubes. If this is not tuned for max output, the watts created by the final tubes stays right in the tubes instead of going out. Also, do this as quickly as possible as again, don't leave all the watts in the tubes.

Next tune the output, final, or Plate Load. This does interact with the Plate Tune, but it moreso tunes the watts going out to the antenna or Load. That's why its called load. The load it where the output watts go at the very end of the coax. Same reason a Dummy Load is called that. So again, tune the final Tune first, then the Final Load.

After that is all tuned up, give it a rest for 30 seconds or so to cool down. Tubes get hot fast when not tuned all the way up, so let them cool a bit, then tune the Driver Tune and Driver Load, if you amp has them. Do them as fast as you can. Once you can't squeeze any more watts out, go back to the finals and retune, and back again to the drivers. Once you can't squeeze any more watts out:

If your amp has an Input Tuner, this maybe internal if it has one, you want to tune this for lowest Input SWR. Input SWR has almost nothing to do with the watts going out. This is the tuning of the watts coming from your radio and going into the amplifier, that's why its called Input. I would guess that only half of CB amps actually have an Input Tuner. I would guess that a third don't have any kind of Input network of circuit at all. I would guess another 3rd it has a network, but it is fixed, not adjustable, and with the last 3rd, its adjustable. So, if your amp has an adjustable one, if your radio has an SWR meter, with the amp on. tuned up and running, tune the Input tuner for lowest SWR on the radios wattmeter. If your radio doesn't have an SWR meter, put your SWR meter inbetween the radio and Input of the amp and then tune the Input Tuner for lowest SWR.

2 things I didn't get to as this is purposively basic aka for dummies. One is overcoupling and the other is tuning for peak, RMS, dead key or modulation. With those people are all over the place, and I just don't want to go there.

[keithweiss]

Great explanation Doc! I really like those Black Cat amps. But most CB guys refused to tune them according to the manual. Most amps are grounded grid. That gives a fair gain and a low input impedance. The Black Cats were grid driven. That gave a high input impedance, but a very high gain. On most amps that are grounded grid, you tune for the maximum output, as you pointed out. But if you did that with a Black Cat you would pop the circuit breaker (on the base amp) or ruin the tubes. That’s one reason they had a minimum of adjustments. You adjust to the line and that was about all you had to do. The high input impedance with high gain made for an exceptionally loud amp. I used to get a lot of compliments on the loud volume of my setup. People asked how I got that big swing. I guess that’s why people called them a modulator amp.
I’m a ham operator too, but CB has always been more fun than ham!

[mikesradiorepair]

With the Palomar amplifier your using in the demonstration your showing here the trimmer capacitor on the underside of the amplifier is adjusting the impedance match between the input of the amplifier and the "driving" transceiver. The goal with all the controls on a amplifier is to adjust for the best impedance match from one stage to the next. Be it from driving transceiver to driver input, driver stage to the input to the output stage or output of amplifier to your antenna system the goal is to match input impedance to output impedance of each stage. The better you match each stages input / output impedance the more efficient the system works. As you say, know your equipment. If you have instructions for your amplifier follow them. Also, as you say NEVER detune your amplifier. Your amplifier is still making the same amount of power, It's just now burning up that unwanted power internally. because you have created a impedance mismatch between stages. If you want less power out then reduce the drive power.

[joeyTRX]

Great video. Thank you for posting...Excellence at

[mikesradiorepair]

I wouldn't say by a long shot that Bird Watt metes are the best or that Watt meters are relative. I have power meters that are orders of magnitude more accurate than a Bird Watt meter. The big takeaway is that as far as tuning goes it doesn't matter how accurate your Watt meter is. The accuracy of the meter isn't important when your tuning a amplifier. The maximum power your meter shows is. Accuracy counts when you want to know exactly how much power you are transmitting. Honestly you don't need to know the precise amount of power you are transmitting out of a amplifier to make sure it is properly tuned. The reading on the meter is arbitrary. Your just peaking for maximum deflection.

[animalcorvair]

never did like the 350z 300a is a better amp