Sufficent drive for amp

[boomer111]

4 2sc2879 transistors, converted Twister am, was a 1x4 now straight 4 pill with bias.

From the spec sheet I see the 4 pills need around 20 watts drive peak to saturate.

Using a Stryker 440hp running at around 3 watts dk seeing around 20 peak with mic cut back to get this peak number.

Amp only showing around 50 watts dk and modulated to around 450 using the rat shack meter. ( I have two of them and using the stingy one, maybe 50 watt difference with peak mode and 1/2 watt at radio dk, very close with amp dk.)

Reports say I sound better with this than running radio at 6-7 watts dk and peaking into amp above above 45 with amp dk around 200 watts. Still peak watts from amp with this is just over 500 on said meter.

This amp on a rf spectral analyzer did 620 pep Bird watts with -45 db suppression. With a clean Cobra 29 driving. Not sure of the 29's output but I was assured it was a clean radio.

This amp with same radio did close to 900 in it's original configuration of 1x4 with -21db suppression.

Just trying to drive the amp correctly. I know the out put will not matter at the receive end.

Kinda of bored and just looking for something to do!!

 

[9C1Driver]

You will also have to consider how the amp was built. If you took a comp style class C box that can take drive levels like a Davemade or X-Force 4 pill HD and tamed it down to like a Texas Star 500 then it's quite a different amp then when built. Since it once was a 1x4 class C box you will have to talk to the amp builder you had do the work to it and see what they think. I take it now it's a class AB amp?

 

[psycho]

4 2sc2879 transistors, converted Twister am, was a 1x4 now straight 4 pill with bias.

From the spec sheet I see the 4 pills need around 20 watts drive peak to saturate.

Using a Stryker 440hp running at around 3 watts dk seeing around 20 peak with mic cut back to get this peak number.

Amp only showing around 50 watts dk and modulated to around 450 using the rat shack meter. ( I have two of them and using the stingy one, maybe 50 watt difference with peak mode and 1/2 watt at radio dk, very close with amp dk.)

Reports say I sound better with this than running radio at 6-7 watts dk and peaking into amp above above 45 with amp dk around 200 watts. Still peak watts from amp with this is just over 500 on said meter.

This amp on a rf spectral analyzer did 620 pep Bird watts with -45 db suppression. With a clean Cobra 29 driving. Not sure of the 29's output but I was assured it was a clean radio.

This amp with same radio did close to 900 in it's original configuration of 1x4 with -21db suppression.

Just trying to drive the amp correctly. I know the out put will not matter at the receive end.

Kinda of bored and just looking for something to do!!

With all the fancy words and technical jargon you used, you should be able to figure out how to properly drive an amp.

 

[boomer111]

Supposed to be AB, according to Justin DePolis.

Like I said I am a little bored and want a clean signal. The power output I understand will have little bearing at the other end.

Sometimes a little knowledge is a dangerous thing!

I understand that many myths prevail.

Just want to do the correct thing from technical standpoint.

I have used a external amp for 20 years from a 150 TX Comstar to a Messenger M4V to the Class C boxes. I have never blown one up, so ya I can drive an amp.

Just the builders say one thing and the tech sheet for the transistors says something else.

Psycho....thanks for your help, your a Prince.

 

[mackmobile43]

It's a 600 watt amplifier, make the amp key at 150 watts and the rest will take care of itself, you do not have to key it at 150 watts but that is a safe carrier and if your modulated signal exceeds 600 watts pep then back down on the modulation until it nears that level.

 

[boomer111]

It's a 600 watt amplifier, make the amp key at 150 watts and the rest will take care of itself, you do not have to key it at 150 watts but that is a safe carrier and if your modulated signal exceeds 600 watts pep then back down on the modulation until it nears that level.

Ya I understand this and have run it like that since I accrued it maybe 7 years ago. I was thinking that even at this level I overstimulated the devices.

So your calling these 2879 devices 150 watt level? Why not 400 watt box?

Maybe because of the frequency they are used in as compared to what Toshiba spec sheet rates them at?

In other words how is a 100 watt device doing 150 watts, and not bleeding all over with the extra watts off channel or is it? I know with the driver installed in the box it was all over the band on the analyzer in class C doing 900 watts.

Just questions I am asking. I am not trying to start anything one way or another.

Like I said the myths prevail and I would like to understand the the science of it a little better.

And know I will not get a license. Just can not teach and old dog new tricks.

This does not mean that I do not want to learn.

 

[mackmobile43]

Ya I understand this and have run it like that since I accrued it maybe 7 years ago. I was thinking that even at this level I overstimulated the devices.

So your calling these 2879 devices 150 watt level? Why not 400 watt box?

Maybe because of the frequency they are used in as compared to what Toshiba spec sheet rates them at?

In other words how is a 100 watt device doing 150 watts, and not bleeding all over with the extra watts off channel or is it? I know with the driver installed in the box it was all over the band on the analyzer in class C doing 900 watts.

Just questions I am asking. I am not trying to start anything one way or another.

Like I said the myths prevail and I would like to understand the the science of it a little better.

And know I will not get a license. Just can not teach and old dog new tricks.

This does not mean that I do not want to learn.

Allow me to burst your AB bubble gently, biasing does not equate to a clean signal, that's what output filtering does.

Biasing either turns on the transistor or keeps it turned depending on the bias circuit.

 

[boomer111]

It was just reminded, a negative feedback circuit was installed.

Still wondering about my questions though.

 

[AudioShockwav]

In other words how is a 100 watt device doing 150 watts,

The Data sheet for the 2879 is 100 watts @ 12.5 volts, as the voltage increases the Po will go up be it 13.8 volts or even 14.2 as some Auto systems run now days.
As you move down in frequency Gain will start to go up.
Min Power gain is 13 Db, Typical Gain is 15Db
Also As I am sure you understand, as drive goes up Po goes up.
If you look at the power chart at the bottom you can see, @ 12.5 volts, 10 watts pep input will net Approx 130 watts PO.
This is all based on the Test Jig that was used...these are Typical numbers, not Maximum .
Why did the builder call it a 600 or a 900 watt amp...because it sell`s better that way.
depends who built it.
a 4X2879 amp built by another builder calls it a 400 HD.
The only way to answer the question with out a doubt is to use the exciter and drive the amp, while watching it on the analyzer until the output starts showing things getting out of hand, and back up.
Many things influence what that point is, how it is built, how it is tuned, class of operation, how well it is regulated, how clean the exciter is .....

73
Jeff

 

[boomer111]

The Data sheet for the 2879 is 100 watts @ 12.5 volts, as the voltage increases the Po will go up be it 13.8 volts or even 14.2 as some Auto systems run now days.
As you move down in frequency Gain will start to go up.
Min Power gain is 13 Db, Typical Gain is 15Db
Also As I am sure you understand, as drive goes up Po goes up.
If you look at the power chart at the bottom you can see, @ 12.5 volts, 10 watts pep input will net Approx 130 watts PO.
This is all based on the Test Jig that was used...these are Typical numbers, not Maximum .
Why did the builder call it a 600 or a 900 watt amp...because it sell`s better that way.
depends who built it.
a 4X2879 amp built by another builder calls it a 400 HD.
The only way to answer the question with out a doubt is to use the exciter and drive the amp, while watching it on the analyzer until the output starts showing things getting out of hand, and back up.
Many things influence what that point is, how it is built, how it is tuned, class of operation, how well it is regulated, how clean the exciter is .....

73
Jeff

Ok this is more information that I can deal with. I guess to run the amp the way I was intending it would need to be putting out 200 to 300 pep watts at - 35db. which is the legal limit for the ham 1500 watt amps. This would be 50 to 70 pep for each device. This would require around 2 pep watts input for each device. A far cry from what my Stryker 440 is doing. Even when tuned down to 2 dk watt drive.
And I do understand that the design has to be taken into account so my numbers really mean nothing other than being off the spec. sheet.

Well at least I took the driver out..

Thanks AudioShockwav this is what I was looking for for answers.

 

[mackmobile43]

The more stages you combine the less efficient they become so drive requirements may increase.

 

[boomer111]

This I was unaware of too, yet another piece of the puzzle.

Thanks!

 

[Cookie Monster]

Supposed to be AB, according to Justin DePolis.

Like I said I am a little bored and want a clean signal. The power output I understand will have little bearing at the other end.

Sometimes a little knowledge is a dangerous thing!

I understand that many myths prevail.

Just want to do the correct thing from technical standpoint.

I have used a external amp for 20 years from a 150 TX Comstar to a Messenger M4V to the Class C boxes. I have never blown one up, so ya I can drive an amp.

Just the builders say one thing and the tech sheet for the transistors says something else.

Psycho....thanks for your help, your a Prince.

 

[Cookie Monster]

I found this old thread Googling Commstar TX150. I came across one years ago, I never tried it and have no information for it. Any idea of what amperage a power supply would be required for it? I've had it for years with my gear that has been stored for 20 some years.
I just purchased an IMAX 2000 5/8ths and dusted off my old Uniden HR2510 with Astatic mic and Im itching to get it up. It's been way too long since I DX'd.

 

[9C1Driver]

What amp do you have, a 4 pill Tail Twister or a 1x4? If you like talking SSB a comp style class C box is not the way to go. You will also need at least a 75 amp power supply to feed four 2879's and maybe more if it's a 1x4.