CB Radio Talk

The amp maker (Fat Boy) recommends a 2-4 watt input dead key. A sponsor of this site (RedMan) claims that much more is safe.

What will this type amp handle, within a reasonable expectation of durability??? (What can it handle and still last for a couple of years???)

I want to push it pretty hard, but not destroy it.

2 watts should be enough to push it without burning it up...Dj

No amp will last if you push it hard, if it does, then you are not pushing it hard enough :D
If you want more watt, should try to get a bigger amp.

Smooth Talker wrote:The amp maker (Fat Boy) recommends a 2-4 watt input dead key. A sponsor of this site (RedMan) claims that much more is safe.

What will this type amp handle, within a reasonable expectation of durability??? (What can it handle and still last for a couple of years???)

I want to push it pretty hard, but not destroy it.

Here's how I set up my 2x SC1446 Fatboy Class C Amp:

As for power input into the Fatboy--- it has a Hi/Lo switch on it, turn it on full power (Hi), and forget it's even there. Then turn radio mic gain all the way down. if radio has variable power on it, turn it to minimum, if not, remove radio cover & lower power output to a watt or so. turn amp on, key radio, and adjust radio power output til wattmeter shows amp doing about 45 watts dead key. Later you may find radio is keying only 3 or 4 watts, but don't go any higher, keep amp at 45 watts out. Then adjust mic gain til you see about 180 watts PEP, or 100-130 swing on a non-peak reading meter.
That's pretty much the instructions for it. 90 watt transistor x 2 = 180 watts output(PEP). divide by 4 for dead key, that's your 45 watts. switch on for amplifier, off to bypass. keep the heatsink unobstructed & be sure amp stays only relatively warm more or less. Use on SSB can be done, but if you want to use an amp on SSB, you're better off with a Texas Star.

2 watts is working great.

But what about bumping the input signal ever so slightly with a 1 pill box which has a variable, setting the input dead key of the 2 x 1446 box at 4 watts and boosting the swing a hair in the process?

I'm getting a 1 x 2879 soon, but it will be a while before I can get a 2 x 2879 or 4 x 2879, etc. I was wondering if I could drive the 2 x 1446 just a little bit in the meantime?

2 watts is working great.
But what about bumping the input signal ever so slightly with a 1 pill box which has a variable, setting the input dead key of the 2 x 1446 box at 4 watts and boosting the swing a hair in the process?
I'm getting a 1 x 2879 soon, but it will be a while before I can get a 2 x 2879 or 4 x 2879, etc. I was wondering if I could drive the 2 x 1446 just a little bit in the meantime?

I got the 1 pill modulator today, and even though I haven't had much time to play with it yet, I did go ahead and try the 4 watt dead key scenario.

Barefoot Radio = 2 watts dead key, swinging to 39 watts PEP on channel 20
Radio + 2 Pill = 250-290 watts PEP

Radio + Modulator at @10:00 = 4 watts dead key, swinging to 80 watts+ PEP on channel 20
Radio + Modulator + 2 Pill = 350 watts PEP on channel 1, 325 watts PEP on channel 20, and 300 watts PEP on channel 40

YOu will never notice the difference between 280 watts and 300 watts.
If you are driving the transistors too hard, heat and longevity will be an issue.
It's your stuff...
preacherman

YOu will never notice the difference between 280 watts and 300 watts.
If you are driving the transistors too hard, heat and longevity will be an issue.
It's your stuff...
preacherman

Well, I do intend to also try dead keys of 2 watts, 2 1/2 watts, 3 watts, and 3 1/2 watts with the modulator on. I want to find the lowest dead key below 4 watts that still gives me the most PEP swing.

I emailed Fat Boy directly, and he recommended an input dead key of 2-4 watts for this 2 pill that I have. I don't believe I'll hurt it with 4 watts, since that's what Fat Boy recommends.

The long range goal of course, is to use the 1 x 2879 modulator to drive a big amp with big pills.

I just wanted to try it with the 2 x 1446 and see what it would do.

I actually like using the modulator stand alone, or using the 2 pill that I have stand alone.

The bottom line:
1 x 2879 Class C does a max of 150 watts, with 40 watts of PEP input and a 2 watt dead key.
2 x 1446 Class C does a max of 300 watts.
Numbers are at road speed with alternator at full charge.

Smooth Talker wrote:The long range goal of course, is to use the 1 x 2879 modulator to drive a big amp with big pills.

I just wanted to try it with the 2 x 1446 and see what it would do.

I actually like using the modulator stand alone, or using the 2 pill that I have stand alone.

The bottom line:
1 x 2879 Class C does a max of 150 watts, with 40 watts of PEP input and a 2 watt dead key.
2 x 1446 Class C does a max of 300 watts.
Numbers are at road speed with alternator at full charge.

What's goin' on down there in Mississippi ?? Just a quick post since I read your thread. As a reminder for the pill wattage ratings. I used RF Parts transistor comparison chart as reference.

The 2SC2879 is rated for 7W input and 120W output.
The SD1446 is rated for 7W input and 70W output. (X2 = 140W AVG)
What you will "see" on the meter will vary a little, depending if you are a PEP or RMS guy.

I have varied the input to my 2 pill and found that 4.5W input works good for my particular set-up. Some will tell you 2W, others 4w---I've even heard people say 10W. You see the maximum input is 7W but I'd keep it lower. Did you see a couple of posts back the directions I received to properly configure the 2 pill Fatboy. It's not the 300W that the sell sheet claimed but still a good little modulator. I've read here where many like to use a 3 pill as a driver, that the 2x 1446 might be a little on the low side, but that might not be entirely true.

Here's the transistor spec sheet: [Please login or register to view this link]

The goal will always be to use the 1 x 2879 modulator to drive whatever amp I own at the time, better than the radio could alone.

Using a radio with a 2 watt dead key and a 39 watt max PEP swing, I feed the output of the radio through the modulator and into my other amp. Without modifying the radio any further, I can set the modulator for:

1 watt dead key swinging to 50 watts PEP

2 watt dead key swinging to 70 watts PEP

3 watt dead key swinging to 80 watts PEP (This is the level of drive I have settled upon. Fat Boy said 2-4 watts, so 3 is safe.)

4 watt dead key swinging to 90 watts PEP


I could also drive a High Drive Amp with:

a 5 watt dead key swinging to 100 watts PEP, up to 10 watt dead key swinging to 150 watts PEP, and anywhere in between.


The advantage I see is an improved amount of swing on my watt meter. I actually dead key lower and swing higher when using the modulator, than when not. (I understand why it's swinging higher, but not why it's dead keying lower? I do like it though.)

The swing from dead key to talk power is also a harder faster swing. I have heard from many sources that the more swing you have, the better. The amount of power isn't supposed to be as critical as the amount of modulation swing. My understanding is that the radio drives the amp, and that the modulation comes from the radio.

How does a modulator work? What does it do, and how does it do it?

Smooth Talker wrote:The goal will always be to use the 1 x 2879 modulator to drive whatever...... How does a modulator work? What does it do, and how does it do it?

"Their really isn't a difference between an amplifier and a modulator. Both take a signal and boosts its level. But what makes the difference is how they do it. A 'linear'' amplifier is a class A,B,AB and the input to output ratio will make a straight line on a graph (hence the name 'LINE-ar'). So if you put 2w into a linear amp and got 40w out then 3w in would give you 60w out.

A "modulator" is usually, but not always, a class C. A low level in will give a low level output since the the input must first bias the RF transistors on ( a.k.a.-- turn the transistors on). There is no DC voltage to do this, so the input signal must do it by itself. the higher the input power is after this 'turn on' the higher the output will be (but not in a linear fashion). So the same amp with 2w in/40w out above that is linear, may only give 20w out with 2w in if is class C. Then at the 3w input level it may give 50w out. The amp is not linear in its input to output ratio.

"Modulators" are used to push bigger amps because of its non-linear characteristics. It often possesses a low carrier and high swing, the perfect combination to 'push' a bigger amp. The Texas Star mod-v is one such amp. It is class C and designed to push a larger amp (DX1600). The guys there were careful not to call it a modulator, but yet named the amp in a fashion that "modulator" was implied. It was designed to "modulate" a bigger amp-------basically "a small driver".

Both of the amps I currently have are Class C. Almost all Fat Boy amps are Class C.

OK, I finally got on the radio with a trusted friend and got some reliable feedback.

1x2879 sounds great.

2x1446 sounds great.

With both amps on at the same time, there is a slight buzzing noise the whole time I'm keyed up. He said it sounds like a mosquito buzzing around your head. Neither amp does this by itself.

***However, I have found an unexpected benefit to having the modulator in the chain, without even having it on.

With the modulator off, but between the radio and the 2 pill amp, my total dead key power out of the 2 pill amp is lower, but it still swings to the full talk power I see when the modulator isn't in the chain. I have a greater amount of "swing".

With the modulator off, the 2 pill dead keys 10 watts on low power and swings to 200 watts.
With the modulator off, the 2 pill dead keys 35 watts on high power and swings to 290 watts.
This is a much lower dead key than what I had before inserting the modulator into the chain.
But the talk power stayed the same. My needlework is much greater now.

How can the modulator help my needlework, without it even being turned on?

First things first...you are "way" too obsessed with your meter.
10 miles down the road no one can tell you the difference between
swinging to 250 and swinging to 300.

With that said, having the 1 pill in line even with it off has a small
amount of parasitic loss on the signal going to the two pill. Since
the two pill still swings to full output, that tells you that you have
more pep from the radio than you need to see full output on the amp.
It won't hurt anything...that's just what it tells you. You are seeing a
lower dead key because it is pulled down just a touch by having the
signal go through the connections, coax and relay on the 1 pill.

Hope that makes sense.
preacherman

I mentioned this in another duplicate post he'd just recently written------He's run both amps ON, together, at the same time----and is hearing buzzing (or is it sizzling?) noises.

Isn't the output of the (1x) 2SC2879 "a little high" (120 Watts) for the (2x) SD1446's ? That 2 pill 1446 amp is low drive with 2-4 Watt input (5W max) and he's dumping all that wattage into it. I'd think that would be a problem.

I don't have any problems running either one separately. I only got a negative report when I ran them together.

Anyway, my question is, is it better to dead key lower or higher, assuming that either way I still swing to the same talk power?

If you are talking local and you want people to see a lot of
"swing" then by all means run a low dead key. It will make
your audio a little louder. If you want to cut off some lips
and squash a few ducks ...a bit more carrier will help.
As has been mentioned before...if your amp swings to 300,
then a dead key from the amp when it is on hi of about 70-80
watts will get you the best of both worlds. If you spend any time
on the bowl, you will see more guys "maulin" it than with 4 s-units
of swing.

You won't hurt your amp either way as long as you don't get carried away.
preacherman

[/quote]having the 1 pill in line even with it off has a small
amount of parasitic loss on the signal going to the two pill. Since
the two pill still swings to full output, that tells you that you have
more pep from the radio than you need to see full output on the amp.
It won't hurt anything...that's just what it tells you. You are seeing a
lower dead key because it is pulled down just a touch by having the
signal go through the connections, coax and relay on the 1 pill.[quote]

Good info. My dead key power is actually being cut more than in half, but still swinging just as high. The needle on my watt meter looks like a windshield wiper when I go from dead key silence to speaking. The only difference is the modulator (off) and an extra 3 foot jumper.

So if you have a Palomar 600 that's 1 sd1446 driving 4 1446 what type of dead key to run amp

Harley75 wrote: March 12th, 2023, 5:54 am So if you have a Palomar 600 that's 1 sd1446 driving 4 1446 what type of dead key to run amp

Rule of thumb is if the amp has a driver transistor, it is a low input. Most amps on AM like to swing so I would drive it with 2 to 4 watts DK swinging to 15 to 20PEP. Those 1446 transistors are pretty hearty, they are more sensitive to output SWR than input wattage.

3’s

Greg

There are so many different ways to do it but stick to the 2-4 watts so it will live.
Get a bigger linear if you want to have more power.
Make sure the SWR is good that will help lots.

WW1

a twist on the subject, modulation gain and swing can have alot to do with your actual voice.
talking loud or clear or close to the mic or far away, direction ,, or projecting your voice in a mono-tone way can keep your needle up. (feeds the voltage), some guys expect the mic to do all the work, well experienced radio , audio operators know differently.