Question about a linear

[DaleH1985]

I have a 100 watt linear. Is it safe to hook a radio up to it that pushes 30 watts?

 

[kopcicle]

From the 449?

Short answer, no.
Better answer is what kind of 100W linear?
Small transistor, over rated 100w
Large transistor under rated 100w
Mosfets , could be anything.

Small transistor 2w DC
Large transistor 4w DC
Mosfets, no more than 2w DC. (RM Italy and the like)

Back to the TRC-449. You are fortunate that if it is the 449 AMC, ALC, AM Power all have fairly wide adjustment ranges that can get you down to reasonable output for driving a 100W linear.

 

[DaleH1985]

From the 449?

Short answer, no.
Better answer is what kind of 100W linear?
Small transistor, over rated 100w
Large transistor under rated 100w
Mosfets , could be anything.

Small transistor 2w DC
Large transistor 4w DC
Mosfets, no more than 2w DC. (RM Italy and the like)

Back to the TRC-449. You are fortunate that if it is the 449 AMC, ALC, AM Power all have fairly wide adjustment ranges that can get you down to reasonable output for driving a 100W linear.

Thank you. New to the whole running power thing. I have a peaked and tuned 29 lx I can hook up to it as well

 

[kopcicle]

Just be aware , 100w linears are not created equal.
Generally it's a less is more kind of thing.
If two watts input gets it done 10 watts isn't better.

 

[jessejamesdallas]

Thank you. New to the whole running power thing. I have a peaked and tuned 29 lx I can hook up to it as well

It would work better if your 29 hadn't been tweaked & peaked...Like kopcicle said, it depends on what 100 amp you have...some don't like high dead keys..may need to lower your dk to 1w or 1 1/2w...

 

[W2EKG]

No. You'll be blowing smoke/Pills.

 

[nomadradio]

All amplifiers have a "ceiling", an output level where additional input power gets you no real increase in output.

The question is where that "ceiling" will be for your 100-Watt amplifier. That number tells us what comes out of it. But not what you have to feed into it to get that result.

Small 2-transistor amplifiers from the 70s and 80s would often reach that overload level at 8 or 10-Watt peaks. A radio with 20 Watt peak output would sound terrible. Half of the radio's audio waveform would be clipped off at the input, and not be seen coming out of the amplifier. Made the wattmeter look happy, but would sound terrible.

We got pretty good at adding attenuator resistors to these amplifiers. So long as we had the radio it would be used with, we could cut down the drive level adding resistors to the input circuit and make the two units sound good together.

Some newer amplifiers are built to accept 20 or 30-Watt peaks.

An amplifier that bangs its head against the ceiling at 15 Watts won't sound right with 30-Watt peaks driving it.

Trouble is, very few amplifiers are sold with this specification spelled out clearly. They are NOT all created equal, especially on the input side.

73

 

[2315 Robert]

Agree with JJD and NR, the new 29'a are a quagmire. Lowering the dead key and making it back right is not as easy as it used to be.

 

[AudioShockwav]

Please post a picture of said 100 watt amp.
A picture of insides would be very helpful as well.
73
Jeff

 

[nomadradio]

The type numbers see on the RF power transistors is also a big help. Some of them will accept more drive power than others will.

73

 

[DaleH1985]

The amp is a hooker/bimbo 100 bilinear amp if that helps any

 

[kopcicle]

https://datasheet.octopart.com/MRF455A-Motorola-datasheet-107025.pdf

At anything over 2 watts input and 100% modulation I can ju9st about guarantee you'll be into 1db compression as well as right up against the maximum dissipation of the devices. I'll admit my self imposed limits are conservative but I've never had to replace transistors.

Previous to my learning the difference between enough and too much I destroyed a few of these boxes with nothing more than 5 watt dead key and a clipped audio limiter.

These boxes have little more than a delay for SSB and no, zero, bias circuitry. They are unbelievably bad on SSB and worse yet the usual 12-18 watt PEP will kill them in short order.

What you wanted to know ?

*edit, for technical accuracy , yes they do (most, not all) have about .7 Volts off a diode for rudimentary bias. It does not even resemble the temperature tracking, low impedance voltage source necessary for linear operation.

 

[DaleH1985]

https://datasheet.octopart.com/MRF455A-Motorola-datasheet-107025.pdf

At anything over 2 watts input and 100% modulation I can ju9st about guarantee you'll be into 1db compression as well as right up against the maximum dissipation of the devices. I'll admit my self imposed limits are conservative but I've never had to replace transistors.

Previous to my learning the difference between enough and too much I destroyed a few of these boxes with nothing more than 5 watt dead key and a clipped audio limiter.

These boxes have little more than a delay for SSB and no, zero, bias circuitry. They are unbelievably bad on SSB and worse yet the usual 12-18 watt PEP will kill them in short order.

What you wanted to know ?

*edit, for technical accuracy , yes they do (most, not all) have about .7 Volts off a diode for rudimentary bias. It does not even resemble the temperature tracking, low impedance voltage source necessary for linear operation.

Basically if a peaked and tuned 29 lx would be safe to hook up to it

 

[kopcicle]

Basically if a peaked and tuned 29 lx would be safe to hook up to it

Umm , NO.

Some basic radio math. Even if it makes you're head hurt.
AM output = 4 x your carrier when 100% modulated.
So even if your 29 is just doing 4 watts then

4 x 4 = 16 watts


Where anywhere on the left graph is it possible to input 16 watts? I'm sure you can find a way ( I did) but , poof!

I'll include the first page just for reference.

These curves were produced by the tuned, single ended test circuit referenced above. This does not take into account bias currents and voltages or broad band transformer losses. Note also that the values on the graph are for a single transistor.

This doesn't mean that you can arbitrarily double the input for a pair of transistors. (actually yes it does but that is a further design element). It is however a good guideline.

In figure three the graph extends out to 16 volts but notice that the input curves are for 1, 1.75, and just 3.5 watts.

Even if figure two suggests that 5 watts input can be supplied to the device it only shows curves for 12 and 13.6 volts.

So in summary , Take your radio and plug it into a reliable watt meter and 100% modulate it into a dummy load. If that result is any more than approximately 8 watts you are approaching 1db compression (or well into it) and about to saturate the device.

8 divided by 4 is 2. 2 watts dead carrier is about all you can afford without turning the box into a grenade with a loose pin waiting for a place to happen.

I'll guess that a "tuned and peaked" 29 anything has not only in excess of 5 watts but all kinds of artifacts accompanying the signal as well. (okay I'm jaded and skeptical of any claim to "peak and tune" a radio by all but a qualified tech with all the tools). Again the answer is no, the 29 will smoke this 1970's amplifier design in short order. I'll take the under on this one as in less than 10 minutes.

I refer you to any number of members here for a "lick and stick" variable power modification. I don't have it on this laptop and won't go looking for it right now.

I don't know how many ways to tell you other than just NO. It will work but it's life expectancy would be minutes if not seconds.


Had enough?

 

[DaleH1985]

I greatly appreciate the info. Just learning some of the technical stuff. Looks like I'm gonna stick to the 449 barefoot until I can get a stock 29 or something detuned a bit.