Specifications

by WA1RNE on February 11, 2005 Mail this to a friend!
K2WH, any idea what happened?? I was trying to create another post and my computer hung, but I don't think it had
anything to do with these posts....
ALC Adjustment Procedure
by KB8ELK on February 11, 2005 Mail this to a friend!
I think it is important to point out to the casual observer that all amplifiers are not created equal, and have their own tun
ing
chracteristics and requirements.
Depending upon the class of amplifier, and it's configuration, and component configuration, the drive level requirements
vary widely.
Consider the drive requirements of an SB-220 vs an AL-1500. When is ALC neccessary or even appropriate ?
The questions are :
Do you really know how to LOAD your amplifier ?
Can you tell when it's over driven ?
ALC is a bandaid for those who can not answer the above questions.
KB8ELK
RE: ALC Adjustment Procedure
by W4CNG on February 11, 2005 Mail this to a friend!
I use NO ALC. I know how to drive, load, and tune my Amplifier on HF. My Bird-43 Wattmeter with the 1000 watt 2-
30Mhz
slug in the unit is necessary to do the job correctly, while not exceeding the grid current specs, and the Plate current
specs while tuning the proper knobs for maximum RF output. I know this because I was brought up in the old school
where you had to know how to tune things up after you learned the theory and took your test using a pencil and paper to
calculate the answers to the one answer per question with no multiple chance answers to select from. For you book
learned folks, good luck getting it right before you blow up your expensive tubes in your amplifiers.
Steve W4CNG
ALC Adjustment Procedure
by WA1RNE on February 12, 2005 Mail this to a friend!
Here's some interesting information about ALC use from a well known HF amplifier OEM, Alpha Radio Products. This is a
quote from Alpha's manual concerning the use of ALC with their Alpha 87 amplifier.
One of the key take-away's is, you cannot predict the dynamic characteristics of the transmitter's ALC system from one
tranceiver to the next - unless of course, you measure it and/or obtain the specifications from the OEM. Attack and Decay
times will vary as well as the control voltage range and threshold level.
So, allthough you can adjust the amplifier's ALC level using a procedure such as K0BG's, Alpha's, etc., you should be
able to limit splatter and distortion products but you may not end up with a transmitter/amplifier that is truely optimized for
maximum average power on SSB.
I believe Alpha's guidelines are a good reference, which also includes cautionary statements around monitoring grid
current which is another indication as to whether an amplifier is being over-driven. This will also ensure longer tube life.
Other OEM's usually state this as well.
From the Alpha 87 manual:
"ALC is a system used in transmitters which is similar in operation to AGC
in receivers. When the signal at some reference point in an amplifier chain
exceeds a preset level, a bias voltage is generated and used to reduce the
gain of a preceding, low level driver stage. The effect is to more or less
limit drive and output to the preset level.
ETO does not generally recommend the use of ALC from amplifier to tranceiver
**because smooth, distortion free operation requires that the characteristics
of the ALC bias source be matched to those of the controlled stage.