Linear Amp - Page 1
Forum section: electronics / rf-microwave

author: cbjr
author_rank: Newbie
timestamp: January 06, 2024, 08:40:57 am
content: I was given an old REDI KILOWATT linear amp. Cannot find any info on line, There are two toggles and a xmit LED on the front. One of the toggles is labeled PWR on/off, the other is not labeled at all, Does any one know what this switch controls, or for that matter any info al all on this amp?

author: A.Z.
author_rank: Super Contributor
timestamp: January 06, 2024, 09:33:09 am
content: could you post some photos of the amp ?

author: pienari
author_rank: Regular Contributor
timestamp: January 06, 2024, 09:49:30 pm
content: From inside please.Size of the amp tells something.There might be 1pcs MRF455 inside.

author: CaptDon
author_rank: Super Contributor
timestamp: January 06, 2024, 09:56:41 pm
content: Not a clue. Looks like a homebrew P.O.S. Try the switch and see? Does it control a transmit/receive relay? Some amps don't switch automatically and have a manual T.R. switch. Maybe it selects input drive power level or output power level. Those low budget amps really suck when you look at them on a scope. They can barely make any forward modulation since they are already totally balls out at dead key and when you watch the wattmeter it actually goes down with modulation instead of slightly up. Not to even mention the fact that if the wattmeter shows 100 watts out about 10 of those watts is 2nd and 3rd harmonics. I crack up when I hear CB'ers call these things 'modulators'. The switch could even be for AM/SSB selection for the bias circuit.

author: A.Z.
author_rank: Super Contributor
timestamp: January 07, 2024, 08:09:02 am
content: if the amp uses an rf sense to switch on automatically when the PTT is depressed, common with CB amplifiers, then the switch may just insert an electrolytic capacitor to delay the release in SSB mode, or either it may insert an attenuator at the input to reduce the drive power and, in turn, the output power, but without seeing the inside or having a schematic, one may just guess

author: cbjr
author_rank: Newbie
timestamp: January 07, 2024, 11:24:53 am
content: Context: This amp was given to me, along with the radio it was used with (Lafayette Mico 723). No other info. The original label on it was trashed but I got the name "Redi Kilowatt" off it. I can find no info of this company. one switch is labeled on/off and the other was blank from factory, this switch is the one pictured with all the resisters attached. I haven't owned an amp before and would like to get this one going, I know it is probably low wattage but I don't need much, just a little punch through. any info appreciated.

author: A.Z.
author_rank: Super Contributor
timestamp: January 07, 2024, 02:21:45 pm
content: hi/lo power

author: iMo
author_rank: Super Contributor
timestamp: January 07, 2024, 02:47:12 pm
content: OMG, the wiring..It could be the (SSB/AM)/FM switch (changing the bias of the PA transistor there).

author: A.Z.
author_rank: Super Contributor
timestamp: January 07, 2024, 03:17:20 pm
content: oh ... and are you sure it's "Redi Kilowatt" and not "Reddy Kilowatt" ?https://en.m.wikipedia.org/wiki/Reddy_Kilowatt

author: cbjr
author_rank: Newbie
timestamp: January 07, 2024, 04:04:08 pm
content: Yea, It was Redi, it didn't make a difference anyway, no info either spelling.

author: cbjr
author_rank: Newbie
timestamp: January 07, 2024, 04:07:04 pm
content: Yea, I know the wiring is a rats nest, but I wanted to find out all I could before desoldering and cleaning it up!

author: rfclown
author_rank: Frequent Contributor
timestamp: January 07, 2024, 04:58:26 pm
content: Not sure why you'd think a "company" made that amp. Looks home brew to me. Googling "SD1076" indicates a 70 watt transistor.

author: A.Z.
author_rank: Super Contributor
timestamp: January 07, 2024, 05:42:36 pm
content: Quote from: rfclown on January 07, 2024, 04:58:26 pmand that, by the way, does NOT mean that the amplifier will offer a 70W output nor that the output will be "clean"

author: cbjr
author_rank: Newbie
timestamp: January 07, 2024, 06:58:30 pm
content: Because it was a commercial label on it, and I am the one who peeled it off!

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 07, 2024, 08:07:50 pm
content: Quote from: cbjr on January 07, 2024, 06:58:30 pmIts commercial in the sense that some CB'r made a one pill and sold them in very small quantity. Being that its designed for the AM CB, it probably does about 30W out in class A.

author: A.Z.
author_rank: Super Contributor
timestamp: January 07, 2024, 08:21:09 pm
content: assuming it works in class A, and I strongly doubt it, CB amps usually are class C critters; anyhow... with a good antenna, say having 7dBi of gain, like a resonant dipole correctly installed (horizontal, at 0.62 Lambda), 30W vs 5W will definitely make a difference

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 08, 2024, 12:31:30 pm
content: Probably not a SSB switch. The radio it is attached to is just AM

author: A.Z.
author_rank: Super Contributor
timestamp: January 08, 2024, 12:55:04 pm
content: Quote from: Wallace Gasiewicz on January 08, 2024, 12:31:30 pmas I wrote, the switch, which is connected to a bunch of resistors, probably inserts them as an attenuator to the amplifier input, so reducing the drive power and, in turn, the output power, in such a case it works as a "hi/lo" output power selector

author: CaptDon
author_rank: Super Contributor
timestamp: January 09, 2024, 10:01:40 pm
content: If the UP side on the switch is really facing up, and since switch contacts usually close opposite of the handle position it looks like when the bat handle is up it inserts a pair of 62 ohms resistors in parallel (31 ohms) in line with the two coax cables. If the handle were in the down position the circuit would be a pass through from the one coax to the other. If that circuit is on the input to the amp (which I assume it is) then the 'down' pass-through could be for use with a standard 3.5 watt output C.B. and the 'up' position would lower the drive level to the amp and may be selected if you were driving the amp with a 20 watt output 'tweaked' C.B. set. Unless the unit is damaged I guess it is working. Don't see anything smoked although any numb-nuts could have easily fried the transistor from excess drive or too much V.S.W.R. on the output side.

author: CaptDon
author_rank: Super Contributor
timestamp: January 09, 2024, 10:08:09 pm
content: Good for a signal increase of about 1.5 'S-units' on your friend's receiver. If the watt meter shows downward deflection with modulation the amplifier is crap and will sound like crap. Modulation adds to the R.F. output and the watt meter should always deflect slightly upwards. (Unless the radio driving the amplifier is also crap with poor modulation characteristics)