In the olden days, the maximum power for hams was a kilowatt DC input to the plate circuit of the final amplifier stage (if accurate enough measurement was used).
Easy, simple....
Then, sometime in the late 60's I started hearing that if one is using a G-G amplifier, the driving power shows up at the output of the amp. I didn't really worry about that then because I didn't need to with the equipment I had. But I heard advice that, to be exactly legal, you had to take that into account.
Fast forward to today....
In another discussion I rcently read comments that implied that that rule had been changed to include the power into the grid circuit, unless I misread that and it was an example of a "trick" question on an exam.
Those last two comments seemed to say that somehow the 1 KW DC input to the plate circuit of the final stage rule had been changed. So I set about to collect License Manuals to find out exactly when the rule changed and what it was changed to.
The last hamfest I was at I picked up a License Manual from the mid-70's, and at that time the rule was exactly as it was in the earlly 60's, e.g, DC input to the plate circuit of the final amplifier stage. So I'm scratching my head trying to figure out why there were concerns about the driving power to a G-G amp appearing at the output. Seems that the way the rule is written, that's legally immaterial.
Was there a time between the "1 KW DC input to the plate circuit of the final amplifier" times and the "1500 W Peak Output power" times when the rules said something else?
Historical question only...no real practical implications today.
Went from 1 kW DC input directly to 1500W PEP output. That some drive power in GG amps appears as part of the output power is immaterial either way. Today, you'd be measuring that as part of compliance. In the old day, there was no output power limit, only input power, so if somebody could produce a 99% efficient amplifier they could have run 990W output.
Actually, under the old rules only carrier power was measured as "DC input," with no PEP limitation, so a 100% modulated AM station could run 4kW PEP input power without exceeding the regulations.
At the time I got my novice ticket (1974), the regulation was worded something like, "all DC power to the final stage, exclusive of power used solely for heating the cathodes [e.g., filament current]."
So on my novice test, it had a problem with all of the voltages and all of the currents. The correct answer was (EP x IP) + (EG x IG) + (EC x IC).
I believe that two of the wrong answers were just EP x IP, and another one which added in the filament voltage times filament current.
There might have also been a trick answer for kids like me who hadn't taken algebra yet, which would have been (EP + EG + EC) x (IP + IG + IC). Fortunately, when I tried to do a practice problem that way, my Elmer told me that it wasn't right.
At the time I got my novice ticket (1974), the regulation was worded something like, "all DC power to the final stage, exclusive of power used solely for heating the cathodes [e.g., filament current]."
So on my novice test, it had a problem with all of the voltages and all of the currents. The correct answer was (EP x IP) + (EG x IG) + (EC x IC).
I believe that two of the wrong answers were just EP x IP, and another one which added in the filament voltage times filament current.
There might have also been a trick answer for kids like me who hadn't taken algebra yet, which would have been (EP + EG + EC) x (IP + IG + IC). Fortunately, when I tried to do a practice problem that way, my Elmer told me that it wasn't right.
That's the rule wording I was looking for. I'll check that License Manual again for the wording and get back.
I didn't find the old rule, but I did find the new regulation adopted in 1983, which contains a "grandfather" provision for AM, which quotes the prior regulation more or less as I remember it:
"the power input (both radio frequency and direct current) to the final amplifying sta[g]e* supplying radio frequency power to the antenna feedline does not exceed 1000 watts, exclusive of power for heating the cathodes of vacuum tubes."
*--the quoted article has the word "state", but I believe this is a typo.
A license manual from the 1970's through 1983 should have the prior regulation, but the language quoted in this "grandfather clause" is more or less as I remember it.
And here's a quote (sorry, no link) for the 1974 NPRM which would give novices 250 watts (up from the previous 75):
"250 watts input power to the transmitter final amplifying stage supplying radio frequency energy to the antenna, exclusive of power for heating the cathode of a vacuum (tubes), within the limitations of § 97.67."
The ARRL book "Single Sideband for the Radio Amateur," published in 1962, makes reference on page 14 to an FCC letter addressed to ARRL concerning power limits. The Commission opinion says, in part, "The maximum DC plate power input to the radio frequency tube or tubes supplying power to the antenna system of an SSB transmitter, as indicated by the usual plate voltmeter and plate milliammeter, shall be considered as the 'input power' insofar as Sections 12.131 and 12.136(d) are concerned ..."
So it's clear that only plate power input is concerned. The fuss about grounded-grid amplifiers is that since the driver stage is in part "supplying power to the antenna system", then the driver stage plate power input must be included as well as the final stage plate power input.
Pity the rule change to 1500w peak output didn't include that same grandfather clause for AM!
It did! That's exactly what I was quoting from! The regulation I quoted states that it expires on June 1, 1990. I don't know if that deadline was subsequently extended.
The ARRL book "Single Sideband for the Radio Amateur," published in 1962, makes reference on page 14 to an FCC letter addressed to ARRL concerning power limits. The Commission opinion says, in part, "The maximum DC plate power input to the radio frequency tube or tubes supplying power to the antenna system of an SSB transmitter, as indicated by the usual plate voltmeter and plate milliammeter, shall be considered as the 'input power' insofar as Sections 12.131 and 12.136(d) are concerned ..."
So it's clear that only plate power input is concerned. The fuss about grounded-grid amplifiers is that since the driver stage is in part "supplying power to the antenna system", then the driver stage plate power input must be included as well as the final stage plate power input.
Anyway, that's the way I always heard it ...
Apparently, that's apparently what the reg was in the 1960's. When I first read that, I was a bit surprised, because when I took the novice test in 1974, you definitely had to add in the other powers. I had assumed that it had always been that way since time immemorial, but based upon what you and others have quoted, the regulation must have changed in the early 1970's.
I always supposed that the reason for the regulation as I learned it was that with some creative engineering, one could construct a final "amplifier" stage whose own DC power input was negligible, but which would allow the power from the previous stage to pass through. So one could have a 10 kW "driver" stage going into the 100 watt "final" stage. I have no idea why the regulation was worded as it was, but this was my hunch.
In the olden days, the maximum power for hams was a kilowatt DC input to the plate circuit of the final amplifier stage (if accurate enough measurement was used).
Easy, simple....
Then, sometime in the late 60's I started hearing that if one is using a G-G amplifier, the driving power shows up at the output of the amp. I didn't really worry about that then because I didn't need to with the equipment I had. But I heard advice that, to be exactly legal, you had to take that into account.
Fast forward to today....
In another discussion I rcently read comments that implied that that rule had been changed to include the power into the grid circuit, unless I misread that and it was an example of a "trick" question on an exam.
Those last two comments seemed to say that somehow the 1 KW DC input to the plate circuit of the final stage rule had been changed. So I set about to collect License Manuals to find out exactly when the rule changed and what it was changed to.
The last hamfest I was at I picked up a License Manual from the mid-70's, and at that time the rule was exactly as it was in the earlly 60's, e.g, DC input to the plate circuit of the final amplifier stage. So I'm scratching my head trying to figure out why there were concerns about the driving power to a G-G amp appearing at the output. Seems that the way the rule is written, that's legally immaterial.
Was there a time between the "1 KW DC input to the plate circuit of the final amplifier" times and the "1500 W Peak Output power" times when the rules said something else?
Historical question only...no real practical implications today.
As you can see, measuring PEP R.f. power took care of all the ambiguities.
While it IS true that R.F. drive in a GG amplifier is added to the R.F. signal out, the fact is that drive power also increases the DC plate current by a proportionate amount, so the "tradition" of adding drive power to DC derived PEP output was probably a bit bogus.
Needless to say, under the old rules, folks running hgh level A.M., where the efficiency of a Class C amplifier could push 90% (with a few tricks) had a bit of an advantage. You could LEGALLY run well over 1500 watts PEP with an asymmetrically modulated heavy iron rig.
With the new rules, SSB operators got a big break, while A.M. operators took it in the shorts.
Eric
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Legacy legal power limit rule
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