The Trio belonged to HP and was used for many years as a DX receiver for Short Wave Listening. The receiver was in good condition when acquired, and only needed the audio output stage to be rewired. It was set up for head phone use and had no output valve, speaker transformer or speaker. The speaker and transformer are intended to be external, so one was added. An audio output valve was plugged in, the amplifier rewired and it all worked first go.
The receiver drifts quite a bit during warm-up. I would like it to have more RF and Audio gain, but it still performs quite well. The band spreading is good on the higher frequency bands, as the coarse tuning becomes quite touchy. I usually set the band spread pointer to the middle of the 0 to 100 scale, and tune the station with the main tuning knob, and then fine tune with the band spread knob. I don't have a manual which might tell me the correct way, but this works for me. It makes resolving SSB signals easy, but I have to adjust the RF gain as well, and this is where I feel that more RF gain might be helpful, or perhaps the BFO injection may need some modification. It is constructed from sheet steel and so is not very heavy, and painted in grey crackle paint.
The controls are: Tuning, Band spread, S meter Zero Adjust, BFO Pitch, AF Gain ON/OFF switch, BFO/MVC/AVC switch, IF Gain, Band switch, Receive/Standby, ANL ON/OFF switch, Phone Jack.
The valve line-up is: rectifier 5CG4, audio output 6AQ5, detector AGC and audio preamplifier 6AV6, second IF amplifier 6BD6, first IF amplifier 6BD6, mixer 6BE6, RF oscillator 6BE6, RF amplifier 6BD6, BFO oscillator and noise limiter 6AV6.
Here is the circuit.
Thanks to Kurt Brandstetter for the circuit
Ray Robinson VK2NO
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