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Author Topic: Tuned Grid Tuned Plate Oscillator question  (Read 5217 times)
G8HQP
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Posts: 595




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« Reply #15 on: November 07, 2017, 05:41:18 AM »

Quote from: K6KV
I want however to respond to what I believe is some misinformation.   The TPTG circuit is not like a Hartley because there is no inductive coupling between the plate and grid tuned circuits.
Inductive coupling is not necessary for an oscillator to be a Hartley, however common is this misunderstanding. In amateur and technician books you are likely to see inductive coupling in all Hartley oscillators, but this is not essential.

Quote
It's also not necessary to tune the grid tank carefully; I speak from experience that it can be tuned a long ways to either side of resonance.
If the anode circuit is sufficiently inductive, then I guess you can sometimes get enough phase inversion from that and the feedback capacitance.
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K6KV
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« Reply #16 on: November 07, 2017, 08:47:54 AM »

Thank you for the reply; we can agree to disagree.
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K6KV
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« Reply #17 on: November 07, 2017, 09:21:53 AM »

Sorry, I wanted THIS to be my reply, but the web site timed out! 

Thank you for the reply.  In your favor, while every Hartley schematic I've seen shows inductive coupling, that is not what his 1915 patent shows.  Instead it describes a capacitor connected across a series connection of two non coupled inductors.  Wikipedia shows schematics of both the patent drawing and a "modern" Hartley, and (wrongly in my opinion) calls them equivalent.   

It's probably safe to say that the modern "Hartley" configuration is clearly superior.  Hartley was fortunate to have it attributed to him. 

As to "sometimes get enough phase inversion", my measurements show inversion to be the preferred state; indeed it is near perfect over a wide range of mistuning between the plate and grid circuits.  If you are interested in the AWA Journal article I mentioned please let me know at my call letters at ARRL.org.  It contains several tests and measurements. 
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G8HQP
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« Reply #18 on: November 07, 2017, 12:06:13 PM »

The Wikipedia entry for the Hartley oscillator does not seem to be very well written. It simply asserts, without any meaningful discussion, that the coupled and uncoupled Hartley versions are essentially the same. If we could rerun the last century again it might be better if the more popular 'coupled Hartley' acquired a different name (e.g. like the Clapp version of the Colpitts oscillator) - but now we are stuck with things as they are.

Thanks for the offer of your article, but the TGTP oscillator is not actually one I am likely to use.
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K1ZJH
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« Reply #19 on: November 07, 2017, 12:08:55 PM »

An amplifier was explained to me many decades ago as a failed oscillator.

Carl

I prefer to think of it as an example of why tuned triode RF amps should be neutralized. LOL.
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