eHam Forums => Amplifiers => Topic started by: W4HIJ on June 29, 2011, 01:39:36 PM

Title: An amp behind an amp??
Post by: W4HIJ on June 29, 2011, 01:39:36 PM
I have a Flex 1500 as my main radio. Yes, I know it's QRP but it's the best " bang for buck" I can afford right now and I absolutely love it's RX performance. I have built a small solid state amp that runs anywhere from 30 to 50 watts depending on the band when driven with the 5 watts from the rig. I may have some spending cash coming my way and I've been thinking about possibly getting an AL-811 to go with what I already have so I would have extra power when I need it.  Anyone see any issues with daisy chaining two amps behind the rig like this? I'm working on the rig doing automatic band switching on the little amp so it's almost like I would just have a 50 watt transceiver driving the 811.
 Please no suggestions of getting another rig, I don't want anything but an SDR and the next Flex up is out of my price range. I just need to know if my plan is feasible and if there are any major "gotchas" I need to worry about.
Tnx and 73,
Michael, W4HIJ

Title: RE: An amp behind an amp??
Post by: W8JI on June 29, 2011, 02:51:13 PM
Every radio is a series of amps behind amps. The only problem is distortion sometimes is much worse with two amps in tandem then one alone, or it can even reduce distortion if the distortin from each subtracts. :-)

As a general rule if the solid state amp you have is more than 5-10 dB better than the AL811 or your radio, it will have negligable impact.

I just measured an AL811, and at 200 watts per tube PEP output the peak distortion products were about 35 dB weaker on normal voice. This data was from peaks stored over a two minute period.

There probably is no harm at all if the solid state amp is pretty clean for odd-order IM.

Title: RE: An amp behind an amp??
Post by: W7TZ on July 06, 2011, 02:29:03 PM
I have a friend doing exactly what you want to do using the Flex1500 and it works just fine. Just do a little experimenting and find the sweet spot for driving the big amp. Also, make sure the impedance is a good match between all units.


Title: RE: An amp behind an amp??
Post by: W8JI on July 07, 2011, 04:01:21 AM
Any working amplifier will appear to work.

How it ACTUALLY works depends entirely on the perfromance quality of the driver amplifier. :-)