Here is a derelict Pride KW-1. And that's the only kind of KW-1 I have ever seen. This one was cheap, since it was missing the small transformer, had a blown (substitute) HV transformer, and the power-supply pc boards were just gone. The relay board was typical, burned in places and missing various foil traces. The board with the dummy-load resistors was just gone.
The plate choke was a bit on the large side. The Load control was a bit on the small side.
The fan was a commercial "Rotron" brand replacement. Sketchy TIG on the adapter plate. This blower has a recangular outlet. The original one had a round flange. It works, so that's one less thing I need to replace.
This is the origin of this amplifier's nickname, the "Havana Taxi".
Like a 50 or 60 year-old american-made car in Cuba. Fewer and fewer original parts every time it gets repaired.
This amplifier ends up with only the chassis, Tune control, tube socket, meter and coax sockets still original. Oh, and the serial number plate.
I put it back together as a DX300, with a stripped-down relay board. Has no preamp, and only the 10-meter input coil.
Fortunately a proper Load control is no big deal. Not original, but sufficient for 10 meters.
The new HV transformer is a toroid type from Antek Inc. It says it's rated for 400 Watts at 50 Hz. At 60 Hz, it's closer to 500 Watts. This is the largest transformer of this type that will fit, and costs a LOT less than a custom-made copy of the original. The output voltage from two 400-Volt secondaries requires a voltage doubler circuit, rather than the full-wave bridge used in the original setup. No big deal to do this with the HV boards we sell. You do need to use bigger filter caps than the original 100uf parts. Six 220uf caps provide the same filtering using this circuit.
Like I said, it just barely fits.
The smaller transformer to the right of the blower is for the heater/relay and bias voltages. That's the one I get asked about the most. This one is Antek type AS05T240. Costs half what ARF Parts wanted for the original until they ran out forever.
Just one problem. It provides only 240 Volts AC, not 500 Volts center tapped like the original. Our low-voltage board adapts to use this transformer by boosting the original 40uf bias-filter caps to 150uf parts. The tube's screen voltage is slightly reduced, but not enough to worry about.
Mounting it may be done more than one way. This time I used a flat bracket of 1/8-inch aluminum.
The only reason a bracket this thick fits under the cabinet top without interference is that there is a gap that thick built into the rear half of the chassis. They used this gap to clear the heads of hex bolts. Came in handy for me.
A steel "L" bracket can be used for this, but not this time.
One of the two 25-ohm 30Watt resistors is the surge limiter, between the HV transformer and the voltage doubler. The other one is a "glitch" resistor between the high-voltage output and the tube's plate choke. Just didn't want to leave that out.
The original "hair pin" parasitic suppressor choke is now a more-conventional type, with a bracket to hold the tube in the socket. The new plate choke is the one we make and sell on FleaBay.
So now it's a somewhat cut-down DX300. The tube's heater voltage comes from the small transformer, but it's not 6.3 Volts AC like the original. This one is six Volts AC. Six point zero. Doesn't sound like a big difference, but it's a part of what made the Pride a hot rod. The tube is rated for six Volts, not six point three.
Leaving out the band selector enables one feature that can be handy. The bias control is mounted where the "Band" knob can be mounted to it by an extension shaft. This puts a carrier-control knob on the front panel. Handy if your radio doesn't have a carrier-power knob on it.
So, the high voltage is only about 2250 Volts DC instead of 2450 or so. Not a big difference, but this reduces the max peak power a bit. And the lower heater voltage reduces the peak power a bit as well. This box will comfortably show 500 Watt peaks with a good tube, but won't deliver the 600 or more you may see with the stock components.
At the very least it does demonstrate the substitute transformers will work, even if the performance is compromised by ten or fifteen percent.
And if the front weren't so butt-ugly I would probably try to sell it.
73
The plate choke was a bit on the large side. The Load control was a bit on the small side.
The fan was a commercial "Rotron" brand replacement. Sketchy TIG on the adapter plate. This blower has a recangular outlet. The original one had a round flange. It works, so that's one less thing I need to replace.
This is the origin of this amplifier's nickname, the "Havana Taxi".
Like a 50 or 60 year-old american-made car in Cuba. Fewer and fewer original parts every time it gets repaired.
This amplifier ends up with only the chassis, Tune control, tube socket, meter and coax sockets still original. Oh, and the serial number plate.
I put it back together as a DX300, with a stripped-down relay board. Has no preamp, and only the 10-meter input coil.
Fortunately a proper Load control is no big deal. Not original, but sufficient for 10 meters.
The new HV transformer is a toroid type from Antek Inc. It says it's rated for 400 Watts at 50 Hz. At 60 Hz, it's closer to 500 Watts. This is the largest transformer of this type that will fit, and costs a LOT less than a custom-made copy of the original. The output voltage from two 400-Volt secondaries requires a voltage doubler circuit, rather than the full-wave bridge used in the original setup. No big deal to do this with the HV boards we sell. You do need to use bigger filter caps than the original 100uf parts. Six 220uf caps provide the same filtering using this circuit.
Like I said, it just barely fits.
The smaller transformer to the right of the blower is for the heater/relay and bias voltages. That's the one I get asked about the most. This one is Antek type AS05T240. Costs half what ARF Parts wanted for the original until they ran out forever.
Just one problem. It provides only 240 Volts AC, not 500 Volts center tapped like the original. Our low-voltage board adapts to use this transformer by boosting the original 40uf bias-filter caps to 150uf parts. The tube's screen voltage is slightly reduced, but not enough to worry about.
Mounting it may be done more than one way. This time I used a flat bracket of 1/8-inch aluminum.
The only reason a bracket this thick fits under the cabinet top without interference is that there is a gap that thick built into the rear half of the chassis. They used this gap to clear the heads of hex bolts. Came in handy for me.
A steel "L" bracket can be used for this, but not this time.
One of the two 25-ohm 30Watt resistors is the surge limiter, between the HV transformer and the voltage doubler. The other one is a "glitch" resistor between the high-voltage output and the tube's plate choke. Just didn't want to leave that out.
The original "hair pin" parasitic suppressor choke is now a more-conventional type, with a bracket to hold the tube in the socket. The new plate choke is the one we make and sell on FleaBay.
So now it's a somewhat cut-down DX300. The tube's heater voltage comes from the small transformer, but it's not 6.3 Volts AC like the original. This one is six Volts AC. Six point zero. Doesn't sound like a big difference, but it's a part of what made the Pride a hot rod. The tube is rated for six Volts, not six point three.
Leaving out the band selector enables one feature that can be handy. The bias control is mounted where the "Band" knob can be mounted to it by an extension shaft. This puts a carrier-control knob on the front panel. Handy if your radio doesn't have a carrier-power knob on it.
So, the high voltage is only about 2250 Volts DC instead of 2450 or so. Not a big difference, but this reduces the max peak power a bit. And the lower heater voltage reduces the peak power a bit as well. This box will comfortably show 500 Watt peaks with a good tube, but won't deliver the 600 or more you may see with the stock components.
At the very least it does demonstrate the substitute transformers will work, even if the performance is compromised by ten or fifteen percent.
And if the front weren't so butt-ugly I would probably try to sell it.
73
