of the unfortunate shortcomings of the marvelous little FLEX 1500 is
its very low output RF Power. It only puts out 5 watts of PEP power, or
5W of SSB, CW and 1.5W of AM.
There are a few solutions of varying complexity and cost, of course.
1. Just use it the way it is, QQRP.
Incorporate several amplifier solutions on the market to boost to
50W-150W. That makes it a very respectable sounding rig with the
receive capabilites of FLEX and the power of a FLEX 3000.
3. I have
also used a small TenTec 505 amplier left over from the early TenTec
days but it really wasn't designed for this type of use. (I describe
this on another page under Flex Experience)
4. Obtain a Hi Power RF
amplifier that will drive to full legal limit with just a few watts.
Homemade ones are not for the beginner or even mid-level ham and
storebought ones are very expensive, unless you are fortunate to find
an old Johnson Thunderbolt or Heathkit Chippewa.
A Very Easy and Affordable Solution
I was speaking with a friend of mine, Fred, K1NVY about
an old TenTec Triton lV, solid state 100W tranceiver he had had since
the 70's. He asked me if I'd like to take it and play with it as it was
of no longer any use to him. He had done a lot of modification to it
for FSK, it didn't work quite up to snuff BUT, the PA still put out 100W.
and I started talking about the possibility of inserting the meager
output of the FLEX directly into the input of the Triton lV Power
Amplier. What follows is the journey to that end. I can tell you it
works outstanding and there is no reason that this method can't be used
by anyone owning a FLEX 1500 who is yearning for more power.
first thing I did when I got the Triton from Fred was bring it home and
pop the bottom, which gave access to the input of the power amp.
was a small coax jumper between the lo-pass filter, just after the low
level driver, that went to the RF Amplier (PA) Driver Block.
almost have to pinch yourself when you look at this and say, "you mean
all I have to do is plug the FLEX output into the Triton RCA jack on
the back of the PA/Driver block?" In theory that is exactly all that is
needed. In reality, however, a lot has to go into making this happen.
You can't just plug it in because on receive the FLEX would be
listening thru the PA/Driver block. Few signals thru that!
2. All that is really necessary to do this is the addition of a 12vdc SPDT relay to act as an antenna changeover relay.
3. Make sure you cut the antenna permanently from the receive circuit of the Triton. Just cut the wire that goes to the receive side.
Power the relay from any 12vdc source in the Triton and switch it with
the FLEX auxillary N/C contacts so the receive antenna is available to
A suggestion is in order at this point. I made a relay box for the FLEX to expand by 3X the FLEX auxillary relay contacts. I made
3 N/O and 3 N/C sets of contacts using a 12vdc 3P2T relay and closed it
using the 12vdc FLEX source and switching it with the single set of
FLEX auxillary contacts. Having these sets of contacts made this whole
exercise a lot easier. I also switch my amp with a set.
5. Use one of the empty RCA jacks on the back of the Triton to insert the FLEX RF output.
6. Connect this jack to the SPDT relay armature of the new relay mentioned above.
7. The normally closed contact (the up relay position) would connect to the antenna jack.
6. The normally open contact would connect to the PA/Driver module's RCA input.
O'kay that is done. Make sure it closes when you key the FLEX.
Next, you have to have a way to "key" the PA/Driver circuit "ON" so the RF from the FLEX can be amplified 1.
Take one of those N/O relay contacts from your handy dandy new relay
box and connect it to the "KEY" jack on the back of the Triton. Make
sure you have the mode switch on the Triton in CW position.
are almost done. The place where I "Broke into" the RF line coming from
the low level driver should have a load placed back on it to keep
things from self destructing. I put a 47 ohm 2W resistor across it.
There are a few things that you need to do to make sure the rf out of the new "Amplifier" is clean.
the ALC is no longer active, make sure you keep the output at 100W by
lowering the drive on the FLEX. It WILL go much higher and very likely
burn out the finals with continued use at that level or at the very
least cause your signal to go into distortion and splater all over the
AM Operation - I use my setup a lot with AM. Since AM is
100% duty cycle, I noticed that the PA heat sink was getting VERY hot.
So, I installed a fan on the back to keep things nice and cool.
you can see, it is powered continuously by plugging it into the 12vdc
auxillary jack. I drilled holes in the heat sink and fastened the fan
on with small wire ties.
COMMENT: Most solid state rigs utilize
this PA/Driver modular system. If you've got one that is excess to your
needs or one that has problems in ANY part of the rig other than the
PA/Driver Section, try this scheme out for yourself. Also,
theoretically you could do the same thing with any transceiver provided
you put the FLEX output THRU a 0.01uf capacitor into the grid of the
driver tube. You would have to experiment to see how much drive is
necessary. It MAY be too much but an attenuator could be used to crank
it down to an acceptable level.
Have fun with the project BUT DON'T BLAME ME IF IT BLOWS SOMETHING UP