drive for 2 pill

[tvrc18]

What would be the safe drive for a 2 mrf454 amp on ssb? My 2510 PEP is about 20 watts on side band is this to much?

 

[mackmobile43]

20 watts shouldn't hurt it a bit, should see about 150 watts or so at 13.8 volts.

 

[9C1Driver]

Should be a real nice SSB combo. I assume it's a nice AB amplifier?

 

[tvrc18]

Yes it is ab1 I believe, a Magnum by Palomar. It looks alot like the Cobra xl series inside. I think I may need to drive it with less power however. Inside it has a 25 amp fuse. My feedline has a 20 amp and I blew the 20 amp last night on medium power. If my Turner mic is turned up to much it does seem to peak every now and then just above 20 watts from my 2510. It shows about 200 watts on medium and hi is just a tad more. This is a PEP reading from a radio shack meter so I don't believe it is 100% accurate. The old data sheet for the 454 does not seem to state max input power. I am thinking it may be over driving a little with 20 watts.

 

[VA3ES]

I'm not sure how you are measuring your power, but you'll need a reasonably accurate PEP reading watt meter.

A 2-pill MRF454 amp likes to see about 10W CW power for about 150W output. If this amp is based in the famous Motorola EB63 App note, then it is a true AB amp. This amp will deliver almost 200W output with only 5W drive.

In any case, the MRF454 likes to see no more than about 5W input each pill (CW).

 

[tvrc18]

Would that be about 10 watts PEP for ssb?

 

[eagle1911]

10W PEP is the recommended maximum input yes, but quite often some of the input power is lost in the input circuitry of the amp. When you select low or medium power, for example, the input signal is cut back by the input circuitry in the amp so that the output is lowered. The only time that close to the full 20W of input would reach the transistors is if the amp is set to full power. This will most likely not destroy the transistors, but it will likely push them into saturation which will cause your signal to become distorted.

 

[VA3ES]

10W PEP is the recommended maximum input yes, but quite often some of the input power is lost in the input circuitry of the amp. When you select low or medium power, for example, the input signal is cut back by the input circuitry in the amp so that the output is lowered. The only time that close to the full 20W of input would reach the transistors is if the amp is set to full power. This will most likely not destroy the transistors, but it will likely push them into saturation which will cause your signal to become distorted.

Quite so. But even at saturation, the distortion might be manageable. If your amp has a variable input, I'd use that to keep the distortion at a minimum. You know you're over driving when your signal sounds "crunchy". Every 2-pill, MRF454 amp I have ever seen, was a "lo-drive" amp, designed for a barefoot standard CB radio. (4W AM, 12W PEP SSB).

 

[tvrc18]

Thanks for the input. I will probably just run the amp om the medium setting. That seems to give about 50 watts more than the low setting. I will also turn down my 2510 a little to about 10 to 15 watts PEP. I got concerned when the 20 amp fuse blew on the supply line. I also have a 2 transistor amp with 2879's and it shows on the data sheet about 10 watts per device as max input. That is probably more than the 454's can take without over driving them. I would rather drive them in their comfert zone so they last and give that clean signal I want.

 

[VA3ES]

Thanks for the input. I will probably just run the amp om the medium setting. That seems to give about 50 watts more than the low setting. I will also turn down my 2510 a little to about 10 to 15 watts PEP. I got concerned when the 20 amp fuse blew on the supply line. I also have a 2 transistor amp with 2879's and it shows on the data sheet about 10 watts per device as max input. That is probably more than the 454's can take without over driving them. I would rather drive them in their comfert zone so they last and give that clean signal I want.

Yes, that 2-pill 2879 amp is the preferred way to go! It will handle the full output from the 2510 with no problem. In fact, I run a 4-pill 2879 amp on occasion.

 

[tvrc18]

Well I turned my 2510 down to about 12 to 15 watts PEP on ssb and the amp seems to like that. On low I was seeing about 150 watts and medium was 180 and high almost 200. Not much difference between medium and high. Not sure what that meens but that should be a safe way to go. With the 2510 putting out about 20 watts the amp was putting out maybe 50 watts more on high but I bet is was distorting at that setting.

 

[VA3ES]

Well I turned my 2510 down to about 12 to 15 watts PEP on ssb and the amp seems to like that. On low I was seeing about 150 watts and medium was 180 and high almost 200. Not much difference between medium and high. Not sure what that meens but that should be a safe way to go. With the 2510 putting out about 20 watts the amp was putting out maybe 50 watts more on high but I bet is was distorting at that setting.

There ya go!

 

[AudioShockwav]

Sounds like you are right in the ball park.....
Can we get you to snap a few pictures of the inside of that amp?
How does it compare to this amp?

73
Jeff

 

[tvrc18]

Yea it looks pretty close to that amp. It may have a few less components that that one. I will try to get a picture of it and see if I can figure out how to load them.

 

[AudioShockwav]

Take your picture, and upload it to your computer, it should be in your documents folder or downloads folder somewhere, then when you make your post, scroll down a bit and you will see a grey box that says "manage attachments" click on that, and a box will pop up, Click on the grey box that says " chose file " this will open another box that will show your my Doc`s folder....look around, find your picture and click on it.
Click on "upload" it will take a min or so to upload to the forum, close the manage attachment box, finish your post, hit submit, and there ya go.

73
Jeff