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Author Topic: HEATHKIT TUBE LMO  (Read 1559 times)
N3QE
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« Reply #15 on: November 20, 2017, 07:22:03 AM »

The SB series used an Linear Master Oscillator because Collins had a patent on their Plate tuned Oscillator (PTO).

I think you mean "Permeability Tuned Oscillator". It was never awful clear to me that the Collins patents were that general, RCA used permeability tuned oscillators back in the 30's.

Several other pieces of low-end Heath equipment used apparently linear dial tuning scales e.g. HW-16 receiver, but maybe the stability not good enough for SSB? Or 250kc tuning range not seen as wide enough for SSB? HW-16 friction drive turn reducer was certainly an interesting and super-cheap approach. I actually like my HW-16 way more than I like my Heath SSB rigs of that era.
« Last Edit: November 20, 2017, 07:35:03 AM by N3QE » Logged
N2EY
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« Reply #16 on: November 20, 2017, 08:12:00 AM »

The SB series used an Linear Master Oscillator because Collins had a patent on their Plate tuned Oscillator (PTO).

Not true.

First, the Collins units were Permeability Tuned Oscillators.

Second, any relevant patents had long since expired. Check out the Drake TR-3, TR-4, R-4 and T-4 series - all Permeability Tuned Oscillators, same time frame as the SB line.

These LMO units were factory built as they need the stability and precision which Heath thought amateurs could not build.

The real issue was that most hams would not have the test equipment to adjust and align an LMO unit. Some would, of course, but Heathkit was trying to sell kits that could be built with a few common hand tools and simple test gear.

It was cheaper to subcontract out the LMO assemblies to TRW and others, and treat them as components. Same for the bandpass and crystal filters.


Other than the LMO/PTO parts, Heath tried to clone the Collins equipment and did quite successfully.

Clone? Not really.

What Heathkit did very successfully was to design and sell gear that offered performance and features "almost as good as" the Collins S-line, but at a much lower price. The SB-301 wasn't a clone of the 75S-3, nor as good a performer - but at well under half the price, the SB-301 was a real value. Same for the SB-401, etc.

73 de Jim, N2EY
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N2EY
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« Reply #17 on: November 20, 2017, 09:28:11 AM »

Several other pieces of low-end Heath equipment used apparently linear dial tuning scales e.g. HW-16 receiver, but maybe the stability not good enough for SSB? Or 250kc tuning range not seen as wide enough for SSB? HW-16 friction drive turn reducer was certainly an interesting and super-cheap approach.

The HW-16 is a completely different design from the SB series.

The HW-16 dial is indeed pretty close to linear - but note that it is marked in 5 kHz increments, not 1 kHz like the LMOs, and the accuracy....is what it its.

The HW-16 isn't a transceiver in the modern sense - it's a transmitter and receiver in one box. The heterodyne scheme in the HW-16 receiver section isn't the same as that used in the SB series, and the VFO tuning range is much lower in frequency (around 2 MHz). With tunable VFOs, the lower you go in frequency, the easier it is to get really good stability.

One of the MAJOR problems in HF transceiver design is coming up with a heterodyne scheme that works well in both receive and transmit. Things like oscillator harmonics not falling in a bad place are a very big deal - and a scheme that works well for receiving may not work well at all for transmitting. And the more bands involved, and the wider the bands, the more problems. The HW-16 receiver only had to work on receive, and only on three bands, and only on CW.

By limiting the HW-16 tuning range to 250 kHz, they could use a lower first IF (around 5.5 MHz) and a narrower bandpass filter. They could also simplify the design greatly. Note that the HW-16 has only one IF stage, for example.

I suspect that one of the reasons you like the HW-16 so much is because it doesn't use AGC.

73 de Jim, N2EY
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N3QE
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« Reply #18 on: November 20, 2017, 11:53:57 AM »

I suspect that one of the reasons you like the HW-16 so much is because it doesn't use AGC.

Yes, that is certainly a big part of it.

The non-brick-wall shape factor of the crystal IF filter is also very pleasant for long term listening and is useful at CW bandwidths.
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