On Tue, 24 Dec 2024 04:52:04 -0800
"Jim VE7RF via groups.io" <jim.thom@...> wrote:
IOW,? you are closing the barndoor......after the horse has bolted, and every time you trip the VOX on SSB.
The funny thing is that those of us that have been using Drake ALC with amplifiers for years don't seem to have any problems with it when used properly. I have posted here multiple times that there is not significant overshoot with the TR7 unless you turn the mic gain up to 11 and scream into it on key-down. I assume that would be true of ANY rig. But that's not the way proper ALC is meant to be used.
And the ALC time constant in the amplifier has to match the ALC time constant in the xcvr / tx.? Drake had a tech note out about matching the time constants if using a T4XC with a L7....or using a? TR7? with an L4B.? It was? a cap / resistor change.? ?The mic gain in the T4XC is not a PO control....when using SSB.
I would like to see a copy of this tech note. I have gathered a lot of Drake information over the years but no one as aver produced this tidbit. That puts it in urban legend status file for me. I've used a L4B with a TR7 and guess what? ALC works and I get good reports. The only things my minty copy of Single Sideband Principles and Circuits has to say about time constants is that they can be "much faster" in the RF domain, and that dual time constant ALC can be used to "take care of gain variations in the r-f exciter over the frequency band". Also that extra filtering is required to filter IM products outside of the passband if you want to try to use ALC as syllabic compression. We know this also from SM5BSZ's research. But Drake's ALC was not intended as a syllabic compressor and I sincerely hope no one is doing this.
The advantage of using the external, adjustable DCV method is..... the ALC voltage has already been developed, and is sitting there all the time, at a constant level.
Which seems to me to be an invitation to turn the MIC gain up too high. Same with the TR7 SSB power control mod on the HFN web site. If you set it too low you will still be flat topping your amp. Best IMO to set it at the amp. Tune for maximum smoke CW, overcouple the load a tad, set ALC to the peak level you want, and adjust mic gain for proper level. Even a cave man could do it.
Where you would really get into trbl, is when using a TR7 / T4XC on SSB mode, and try and drive an amp that requires very little drive, like most of the SS amps.
That is off topic for the OP's question.
If that 5K @ 7 watt resistor below the chassis in the L4PS / L7PS opens up, you will end up with full B+ on the ALC adjustment pot in the L4B / L7.
There are ways to guard against this. K9SQG has a good one.
In my case, the 7K pot, along with the pair of 50K bleeders was tossed, to reduce heat in the L4PS.? Since the yaesu xcvr already has adjustable PO, it's a non issue.
Again, off topic. What happens with YaeComWood is not germane to the subject of this thread. Drake designed a good system here. Especially with the TR7 where you have a visual indication that ALC is active. When used as intended it does the job. If you want to run without ALC, your amp has the needed headroom not to clip on peaks, and you have the equipment to ensure this, fine. I don't think there is enough margin in the L75 for that to be practical.
--
73
-Jim
NU0C
Jim Shorney