I noted the Syncrodyne AM tuner in a back issue of Radio and Hobbies.
I also found references in Wireless world and other magazines showing designs of various complexity.
So the question is, has anybody in VR ever made the RH version or any type of valve Syncrodyne (or Homodyne) tuner?
While I am doing 10 other things I might knock up the RH version for fun.
Fred.

I wanted to build the Homodyne really bad but could not obtain the parts, but just happened by coincidence to later (1974) to see kit for it in a shop window in Wellington NZ. Bought it back to Bris where it did not work well due to lack of selectivity on crowded AM band (more suitable for sparse station spacings in NZ?)

Hi NV, sounds like a barrel of fun, RH note the Q of the tuning coil is low so the selectivity may be pretty bad.
Just what I need to separate the only music station 1172 2CH from the high power adjacent station 1224 2RPH!!
Not to worry probably just needs a good front end with a couple of RF stages first to sort out the stations BEFORE the homodyne frequency convertor thingy stage.
I still don't see how it demodulates so I guess I have to build at least the simple RH circuit and see what it does.
Cheers, Fred.

In my experience with the particular NZ 'Homodyne' unit, you could get the perfect AM audio fidelity (flat to 10 kHz) on the odd strong station (rarely) in Brisbane (Bill Hurrey's Jazz-Fusion show on 50kW 4QR where they used Ortofon moving-coil cartridges.)(there being no FM to speak of in Bris at that time )

The other tuner I had that can do this was a Sansui TU-X1 which was designed around 1979 and was another example of synchronous AM detection (rare in the 1970s I guess.)

Funny enough, I bought the TU-X1 with only FM in mind as I was DX'ing Chicago in Milwaukee with large high gain Channel Master 4408 FM antenna.

When I bought the TU-X1 on ebay around 2005 got into a bit of a bidding war & paid over $500, but wanted it badly as was told its FM was better than both the Sansui 9000 and 9090 which also had hot FM tuners.

Then one day I thought since I paid so much, I should try the AM (this flagship 35lb 'supertuner' had a separate AM section under a central chassis partition, you turn it upside down to see the AM.) Discovered the AM didn't work! (after all that money!) Turned out it used a National Semiconductor LM1496 synchronous detector chip that was blown. These were nearly obsolete by that time but found one & installed it with a socket. The AM sound was breathtaking, it sounded like FM. Its secret, apart from synchronous demod, was also no IF coils (not sure how they did this, you might want to search for a schematic because it also had good selectivity!)

I understand by the time of AM Stereo, synchronous detection was used more often, but these probably still used IF coils, so not as pure as the Sansui or Homodyne sound?

Synchronous demod for vision has been used in almost all analogue colour TVs because their inherent linearity eliminates cross-modulation between the vision and sound carriers .

There is a wide choice of parts and they often come with IF amps and AGC.
They usually use a lumped filter at the input and a tuned circuit at the IF frequency.

Should be easy to make a nice high-performance synchronous AM radio tuner using one of these just by adding a mixer-oscillator in front of it.

only music station 1172 2CH

It's 1170.

It's 1170

unless your dial is out of alignment

Very funny you lot, I think I had 702 on my brain and tacked a 2 onto the 1170, or its just old age!
Fred.

As I recall, that article in EA/RT&H featured a schematic and circuit description of the Homodyne, but it was kind of impossible to build as it used a special chip (Signetics?) and other specific parts, but then article concluded saying "a kit for it is available from New Zealand", again not much help as ordering from overseas was not the fashion back then. Not sure of the date of the article, but the one I later found - by serendipity - in NZ in 1974 was already built (somebody got bored/disillusioned with it quickly?)

Ahhhhggggggggg, CHIP? puleese NV that's far too new age for me!

When I get to it I'll use a VALVE and then get into all sorts of trouble!
Funny when you think about it the complex chip is long gone but the old school valves are easy to get.

I went through my valve box and found some pentagrids, 6CS6 and 6BE6 so will try those for the mixer and I have plenty of 6EJ7/6EH7 for the rest.

I've got the guitar amp to make first, just cutting up metal for the chassis, but I might fool around and prep up some oscillator and tuning coils.

Fred.

OK, then, might I suggest a valve design as follows:

Conventional mixer/osc, say a 6BE6

A broadly-tuned IFT (overcoupled by tuning at the inner slug settings and damped to get about 15kHz at the 3db points)

6EH7 for the IF

Similar broard and flat IFT

Diode detector, used just for AGC.

6BE6 as Synchrodyne detector

Conventional 9kHz notch filter.

Half a twin triode as a cathode follower.

Other half set up to mute the audio if needed when detector is out of lock and/or AGC is too low.

Hi Ian, ta for that, sounds like a plan.
I'll knock up the mixer first of all and sort the tuning and oscillator coils.
Fred.

Hi Fred.
For revenge, I suggest that you build the guitar amp inside a fish tank

Wayne.

Wayne, you are funny.
How about:
The only fish I like are the ones on a plate with chips...............nuk nuk nuk.

Fred.