Uploaded February 2026 | Updated September 2026, 1 week ago
Shortly after the Monobanders were on the market, hams with the knack converted the Monoband radios to Tri-Banders. Kits were made available while other hams brewed their own. They are somewhat rare as not many survived.
Each Monobander had a unique set of transformers named L2, L3 and L5. The coil L5 is used for the heterodyne circuit and in the case of the HW-12 (80M) there is no L5. The conversion from Monobander to Tri-Bander involves three band switches to select a proper heterodyne crystal and appropriate sets of L2, L3 and L5 and to select taps of on the final Pi Network. A separate switch selects LSB and USB. I found that the switch must be in USB to receive LSB on 80M... the mixing produces a sideband inversion. The VFO operate in the 1.6 MHz range, so it is fairly stable. The IF is 2.3 MHz.
I found one of these converted units on eBay for $50 and the rest is history. The unit I found was filthy and its condition was uncertain. But fools rush in and get the best seats. It was missing the carrier balance pot and had a sticky panel meter. Fixed both of these. The tubes all tested good. I have schematics for the base radio but nothing for the mods.
The biggest task was building the power cable. I had a 11 pin to 11 pin Heathkit cable but the non-A version of the Hot Water radios uses an 8 pin. So, I had to research the pinouts and match the wire colors and then solder on a new socket that plugs into the radio.
The radio is inhaling RF on 20 and 40 but 80 is not so good. I tested the Tx on 4om and get 100 watts on peaks. But no output on tune so something in the tune circuit. (Need to check resistors R1 and R2). To get a tune signal, DC is pumped into the diode ring. The Bias sets OK but other bands like 20M is a 29A whereas on 40M we have the 44DD.
So lots more work but so far pretty promising.
73's
Pete N6
Shortly after the Monobanders were on the market, hams with the knack converted the Monoband radios to Tri-Banders. Kits were made available while other hams brewed their own. They are somewhat rare as not many survived.
Each Monobander had a unique set of transformers named L2, L3 and L5. The coil L5 is used for the heterodyne circuit and in the case of the HW-12 (80M) there is no L5. The conversion from Monobander to Tri-Bander involves three band switches to select a proper heterodyne crystal and appropriate sets of L2, L3 and L5 and to select taps of on the final Pi Network. A separate switch selects LSB and USB. I found that the switch must be in USB to receive LSB on 80M... the mixing produces a sideband inversion. The VFO operate in the 1.6 MHz range, so it is fairly stable. The IF is 2.3 MHz.
I found one of these converted units on eBay for $50 and the rest is history. The unit I found was filthy and its condition was uncertain. But fools rush in and get the best seats. It was missing the carrier balance pot and had a sticky panel meter. Fixed both of these. The tubes all tested good. I have schematics for the base radio but nothing for the mods.
The biggest task was building the power cable. I had a 11 pin to 11 pin Heathkit cable but the non-A version of the Hot Water radios uses an 8 pin. So, I had to research the pinouts and match the wire colors and then solder on a new socket that plugs into the radio.
The radio is inhaling RF on 20 and 40 but 80 is not so good. I tested the Tx on 4om and get 100 watts on peaks. But no output on tune so something in the tune circuit. (Need to check resistors R1 and R2). To get a tune signal, DC is pumped into the diode ring. The Bias sets OK but other bands like 20M is a 29A whereas on 40M we have the 44DD.
So lots more work but so far pretty promising.
73's
Pete N6
