Connex 3300HP Galaxy DX55HP circuit EPT360015C
- I got my hands on a Connex 3300HP to repair.
I see that many have problems with this radio, and all those other
IRF520 MOSFET RF output section radios in general.
- I only have worked on a few of these radios, to get them to work in SSB mode.
But I am very familiar with these IRF510 - 540 devices, using them in
shortwave band pirate radio class-E AM transmitters. Letting them transmit
for hours and hours, without burning up.
- I got this 3300HP to work, with 7 watts carrier, with good modulation.
It can be overmodulated and all. Turn down the carrier power to 3 watts,
turn up the mic audio. and it is a "swing machine." Modulation
transistor TR51 does not blow up. I have been doing many "CB whistles"
into it and all. But TR51 gets warmer that it should due to the design.
Before I did this modification, made adjustments, the input current was
about 5 A, swinging up to 7 A or so with modulation.
Then transistor TR51 got so hot, smoked and blew up on me!
(the "smoke test") (and it worked!) (fun!)
------
But, it is, what it is, so I made it work.
on the top of the board, cut the bare jumper wire from TP7 to TP8.
On bottom side of board, add a wire from TP8 to the emitter trace of
TR51. This puts the the IRF520 driver TR44 drain circuit at 13.8 V.
Modulating this driver is not needed. It causes problems.
Looking down at the board, turn VR10/20 fully ccw, and VR11 fully cw
for no gate bias voltage, no bias.
I soldered a .001 uF disc capacitor across TR45 collector to ground.
Easy to do on bottom side of board. This kills the RF from going to the
IRF520's, so bias adjustments can be made.
Put a current meter in line with the 13.8 V going to the radio,
that can measure small current adjustments.
Turn the microphone all the way down, set the voltage at
TP7 to 5.5 V with VR13. (with this radio here, the Receive RF Gain
was modified to set this level.)
Key up radio, notice the input current (maybe around .44 A)
and turn VR11 ccw for an additional .05 A,
then each VR10/20 cw for and additional .05 A each.
I had .58 A or so total.
Turn 13.8 V off, then unsolder the capacitor on bottom
of board that kills the RF.
Power up radio again. Key up in AM mode.
Check your carrier power. This radio here had very low power.
I adjusted driver bias pot VR11 a little ccw and RF output
increased. I got it up to 14 watts. So turn it down for
7 watts of carrier. And check or adjust again for around 5.5 V at TP7.
turn up the mic gain. modulate it. always monitoring the heat at
the side of the radio at the modulation/regulator transistor.
while modulating this radio here, with 7 watts of carrier,
the input current stays steady at around 4 amps,
until you crank it up and whistle, then the current will drop
at peaks.
This all works, and the best that can be done with this design.
"it is, what it is" as they say.
- I got my hands on a Connex 3300HP to repair.
I see that many have problems with this radio, and all those other
IRF520 MOSFET RF output section radios in general.
- I only have worked on a few of these radios, to get them to work in SSB mode.
But I am very familiar with these IRF510 - 540 devices, using them in
shortwave band pirate radio class-E AM transmitters. Letting them transmit
for hours and hours, without burning up.
- I got this 3300HP to work, with 7 watts carrier, with good modulation.
It can be overmodulated and all. Turn down the carrier power to 3 watts,
turn up the mic audio. and it is a "swing machine." Modulation
transistor TR51 does not blow up. I have been doing many "CB whistles"
into it and all. But TR51 gets warmer that it should due to the design.
Before I did this modification, made adjustments, the input current was
about 5 A, swinging up to 7 A or so with modulation.
Then transistor TR51 got so hot, smoked and blew up on me!
(the "smoke test") (and it worked!) (fun!)
------
But, it is, what it is, so I made it work.
on the top of the board, cut the bare jumper wire from TP7 to TP8.
On bottom side of board, add a wire from TP8 to the emitter trace of
TR51. This puts the the IRF520 driver TR44 drain circuit at 13.8 V.
Modulating this driver is not needed. It causes problems.
Looking down at the board, turn VR10/20 fully ccw, and VR11 fully cw
for no gate bias voltage, no bias.
I soldered a .001 uF disc capacitor across TR45 collector to ground.
Easy to do on bottom side of board. This kills the RF from going to the
IRF520's, so bias adjustments can be made.
Put a current meter in line with the 13.8 V going to the radio,
that can measure small current adjustments.
Turn the microphone all the way down, set the voltage at
TP7 to 5.5 V with VR13. (with this radio here, the Receive RF Gain
was modified to set this level.)
Key up radio, notice the input current (maybe around .44 A)
and turn VR11 ccw for an additional .05 A,
then each VR10/20 cw for and additional .05 A each.
I had .58 A or so total.
Turn 13.8 V off, then unsolder the capacitor on bottom
of board that kills the RF.
Power up radio again. Key up in AM mode.
Check your carrier power. This radio here had very low power.
I adjusted driver bias pot VR11 a little ccw and RF output
increased. I got it up to 14 watts. So turn it down for
7 watts of carrier. And check or adjust again for around 5.5 V at TP7.
turn up the mic gain. modulate it. always monitoring the heat at
the side of the radio at the modulation/regulator transistor.
while modulating this radio here, with 7 watts of carrier,
the input current stays steady at around 4 amps,
until you crank it up and whistle, then the current will drop
at peaks.
This all works, and the best that can be done with this design.
"it is, what it is" as they say.
Last edited:
