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 A synchrodyne valve tuner part 1 the test circuit.
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 Return to top of page · Post #: 1 · Written at 10:03:18 AM on 27 May 2018.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 574

Hi all, I had some down time so sat in the workshop and on a prototyping chassis put together the circuit from "Radio and Hobbies" September 1963, a year I remember so well! (steady job, car, girlfriend what could go wrong?)

I'll send a pdf to Brad with the story of how it went, a short story actually as it did not go well, but at least I understand the shortcomings and a way forward to a better solution.

The R&H boys may have gone the next step, but locked into "superhet" thinking and with no advantage in the Synchrodyne design it was never going to happen.

Fred.

The Sychrodyne AM Tuner


 
 Return to top of page · Post #: 2 · Written at 11:49:39 PM on 27 May 2018.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

with no advantage in the Synchrodyne design it was never going to happen

But it lives on as the PLL.


 
 Return to top of page · Post #: 3 · Written at 6:53:59 PM on 29 May 2018.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 5510

Document uploaded.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 4 · Written at 7:09:19 PM on 29 May 2018.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 574

Yes, GTC and that will be part of the fun, making a reactance valve circuit do a PLL action.
No, I am not looking at using any transistors or chips and that's that.
Valves or nothing!
Fred.


 
 Return to top of page · Post #: 5 · Written at 10:28:27 AM on 28 August 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1291

Fred, how's this for an idea to make the Synchrodyne into a practical HiFi AM receiver?

1. Take an ordinary superhet, preferably one with an RF stage.
2. Connect the Synchrodyne circuit to the output of the mixer in parallel with the existing IF, bypassing most of its selectivity.
3. Have the existing AGC control the "RF" stage of the Synchrodyne.
4. Have the AGC switch the audio output between the normal AM detector and the Synchrodyne, so that its output is only heard when it's locked and working properly.

Once it's set up, the Synchrodyne should not need to be fiddled with. You might be able to hang your existing hardware off a suitable donor radio. Maybe make it a plug-in adaptor?


 
 Return to top of page · Post #: 6 · Written at 11:09:17 AM on 29 August 2018.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 377

Hi Fred,

Until now, I have never bothered to understand how an AM Synchrodyne Tuner actually works ... so I always use your Special Projects write-ups to extend my knowledge .... Smile

If I understand the theory correctly ..... in your Fig 3, one would expect to see none, or little, of the Audio signal (modulation signal) riding on the Oscillator RF(blue) signal ..... ?????

.... hence the need to isolate the Oscillator as much as possible ..... ????

Can you see the RF (carrier) signals 'locked' in phase (ie with a change of Scope scale) ....... ?????

Cheers,
Ian


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Cheers, Ian

 
 Return to top of page · Post #: 7 · Written at 12:30:56 PM on 29 August 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1291

Ian. maybe I can explain it simply:

You have two signals at the anode of the mixer bottle, they are the same frequency and in phase.
What you see on the anode is the sum (or difference) of the two signals.
One of those signals is modulated and so the summed signal is also modulated.
When you filter out the RF you are left with the modulation component, i.e. the audio.


 
 Return to top of page · Post #: 8 · Written at 9:26:36 AM on 31 August 2018.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 574

Hi Tinkara, what Ian Rob says is it in a nut shell.
If you mix the station signal and oscillator signal you get selective tuning. Then filter the RF and the AF is left.
The theory then was who needs an IF stage, less valves and coils etc, but in practice does not hold true.

In the paper, fig 2 is swept at RF rate so the jumbling multiple wave shapes are created in the CRO as the time base trys to lock onto the RF and AF varying components. If you remove the AF modulation on the signal you then see steady plain RF waves and can see the phase difference .

In fig 3, this is swept at lower speed and the AF modulation is the sine shape of the RF signals. The blue trace should not be modulated but cross coupling was "squegging" the oscillator and making it look modulated as well, thus showing one of the short comings of a too simple circuit.


Sorry about delay in answer, has sudden heart failure on Monday, ambulance ---hospital...cardiac ward......stabilise…..back home today Friday!


Fred.


 
 Return to top of page · Post #: 9 · Written at 9:59:37 AM on 1 September 2018.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 377

Good grief Fred ..... no apologies required ... I hope that all is okay with you again. I seem to remember that this is not the first of this type of episode for you ..... ???

Take your recovery seriously .... soak up up the TLC .... Smile Smile

Cheers,
Ian


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Cheers, Ian

 
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