ALC overshoot spikes are minimal if ALC is used as intended. ALC is not a speech processing system nor a hard limiter. It is there to catch those occasional higher peaks. Thus the instruction with the TR7 to adjust mic gain so the ALC LED only flashes on occasional peaks. In bench testing a TR7 some years back with a peak reading Wattmeter I had to hit it pretty hard to generate significant overshoot peaks. The conclusion was that if you are seeing significant overshoot then you are overdriving your audio. I have been using amp ALC for years with L4B, L7, NCL-2000, and now an Alpha 76 and it works as desired if used as intended.
73
-Jim
NU0C
On Tue, 24 Dec 2024 00:31:05 +0000
"Thomas W9TAB via groups.io" <electron@...> wrote:
AGC in the Drake amp is developed from the transmitters ¡°input¡± to the tube(s)
When you key the transmitter it doesn¡¯t see the AGC signal until it goes through the comparison circuit then develops the required negative DC voltage to pull back the RF coming from the transmitter.
So there is a reoccurring front end RF spike that is pulled back by the AGC circuit each time you key the transmitter as the AGC voltage disappears during receive.
AGC control process is ¡°Sample, compare, voltage generation, then transmitter output reduction¡± each time you key the transmitter.
If you set the AGC voltage to cut the transmitters output to 60watts (In the example of my L7) I get 1000watts carrier out.
Looking at the output on a scope the signal is nice and clean with a two tone audio for a test signal and transmitting into a dummy load.
Tom W9TAB
On Dec 23, 2024, at 2:04?PM, Tony N5DIM <tony@...> wrote:
?Thank you everybody for the info. I will definitely check and use the information in the manual. Also scored the speech processor today also. Merry Christmas and 73. Tony N5DIM
On Dec 23, 2024, at 9:34?AM, Jim Shorney via groups.io <jimNU0C@...> wrote:
?
I don't see an advantage to that. Adjustable ALC is right there in the amp and you are adjusting it to what is happening at the amp, not to an arbitrary value.
On Mon, 23 Dec 2024 16:47:22 +0000
"Thomas W9TAB via groups.io" <electron@...> wrote:
You can also ditch the ALC in the amp and use an adjustable negative low voltage source to the radio.
Several simple circuits are out there, some using a 9vdc battery and a potentiometer and others using a Walwart.
The amps ALC setting not only varies with band selection but also changes when you switch from CW to SSB
Tom W9TAB
--
73
-Jim
NU0C
Jim Shorney