The radio will routinely show 28 Watts PEP with the stock final. You have to change more than JUST the final to get significantly more than that from a 2SC1969.
The larger final requires more drive. Altering the driver stage to do this gets you another 10 Watts PEP, more or less. Change the driver transistor, some resistors in the final and driver's input circuits and you're up to about 40 Watts PEP. About 7 or 8 years ago, we worked out a setup that sounds like this. It also involved changing some capacitors and a coil, to get more power out of the larger driver, and INTO the larger final. This got us up to a predictable 45 Watts PEP.
Only did about a dozen and a half of them. Out of those, a handful of units showed 50 Watts PEP or a bit more. We use Bird "A" elements for CB radios. Makes readings a bit stingy.
Experience tells me that if 20% of the radios we modified this way would deliver 50 Watt peaks, that someone could dig further into the circuitry and optimize some capacitor values to make that 50-Watt mark achieveable most of the time, instead of "some" of the time.
Justin appears to have done exactly that. Looked at the circuit, altered component values to maximize power output.
You'll never see this from a modern-day "SSB" radio, CB or "10-meter" with a single final. But an AM-only radio uses a voltage step-up transformer to modulate the final and driver. This roughly doubles the peak voltage FED INTO the final and driver. If you fed steady direct current into this radio's power stages, 28 Volts DC would get you a 45 to 50-Watt carrier. But not for long. A steady carrier that large would be very brief. Since every (28-Volt) voice peak is followed by a (zero-Volts) voice VALLEY, the stress on the final is averaged out, and it will deliver 40-plus peak Watts. Since this remains only 10 to 12 Watts AVERAGE power, the final will take it just fine. Modern SSB radios do NOT contain that step-up transformer, and will only give you about half as much PEP per transistor.
We only did a dozen and a half of the "45-Watt" mod. About that time, the price of two-transistor linears dropped in half, more or less. I couldn't recommend doing it unless the radio would be run barefoot ONLY. For only about double what we charged for our "45-Watt" mod, you could get a (roughly) 200 Watt linear. Spending the same money on an amplifier would get you Watts per dollar. Spending it on the radio would get you "Dollars per Watt". Kinda like comparing "Gallons per Mile" to "Miles per Gallon". That mod ceased to be a good deal, so I stopped recommending it.
Linears got cheaper, stayed cheap, and the price of radio parts and labor only goes up. Haven't done one of those in 3 or 4 years now.
Out of the dozen and a half of that mod we did, a handful of radios DID show 50-plus Watts PEP. Since the wimpiest would still deliver 45 Watts, that was the claim we made for it.
I have no doubt that if Justin looked deeper than I did, he could work out what separated the "45-Watt" radio from the "55-Watt" radio, and optimized his setup. A claim of 50 Watts is perfectly believable from my first-hand experience. I would also predict that his "50-Watt" claim is what he can expect from the average radio. Odds are that at least half the units he does this to will deliver a little more.
There's nothng magic or mysterious about it. Just plain, boring engineering.
It IS a 'hot-rod' setup, mind you. A stock radio could probably stay keyed for minutes at a time with a shorted coax, before blowing a final/driver. A "hot-rod" may tolerate it only for seconds. You do sacrifice some of your safety margin in exchange for the added performance. You just have to treat the SWR like the "red line" on the tach in a race car. Ignore it and something will blow.
And one more detail, not so technical. What a radio's owner reports is colored by ego. Who wants to admit he spent big bucks for a mod and was disappointed? I agree with your skepticism of claims a guy makes about his own equipment. Might be affected by ego, might not. Kinda like asking a fisherman about the size of a fish he caught.
I have no such axe to grind. Don't have any radios Justin has reworked. I get my labor free, don't need to. No, I haven't SEEN his setup, but there is no technical barrier to it, and only a ten percent difference between his claim and what we were seeing. Gotta figure his setup would look very familiar if I saw one. It's just (reverse) engineering, not magic.
73
