Brian,
In the late 70s and 80s a lot of car radios manufactured by the Japanese before the PLL LSI chips became popular used a lot of these PTO tuned oscillators to cover MW and SW bands. I guess this was primarily done to avoid frequency jumping on bumpy roads!!
I had a unit that was hardly 1.5 X 1.5 x 2 inch assembly that had a shaft with 4 ferrite cores mounted on it. When you turned the shaft, these 4 cores moved in and out of 4 independent coils of 8mm dia and 25mm length. I guess it was a simple and elegant way to maintain the same bandspread and tuning linearity on all the different bands.
JRC took the collins approach to the next level in their NRD-505 receiver in the 70s, this RX had a PLL that utilized a PTO tuned oscillator.
On the internet you find a lot of homebrew PTO projects based on the lipstick idea, I suggest you take a look at the internal construction
details of the collins PTO.
http://www.radiomuseum.org/forum/design_excellence_the_collins_pto.html
73s
Pramod
vu2ttp
--- In HamBrewers@yahoogroups.com, Brian Burns <burnsguitar@...> wrote:
>
> Hello Raj,
>
> ~ You could look up the manual / schematic of Collins 51J4 (old boat anchor) which is a permeability tuned receiver.
>
> I have looked at schematics for commercially made equipment, and Collins is certainly the permeability tuned king. The sort of info I'm looking for is the do-it-myself kind of thing--coil diameter, spacing of turns, slug type etc.
>
> One idea that I've had is to use a ferrite slug and a brass slug in tandem to extend the tuning range of a PTO VFO, without band switching. If the ferrite slug were fully inserted in the coil for the lowest frequency, and as it is withdrawn, the brass slug comes into the coil to raise the resonant frequency, it might be possible to extend the tuning range enough to provide coverage of WARC bands. It's basic design information as a place to start that I'm looking for.
>
> ~ Great guitar homebrewing Brian!
>
> Thanks very much, but I'm afraid that it has gotten rather out of hand! Since I'm trying to set up for one man production of guitars, I would have to call it commercial-brewing (:->)...
>
> I gave guitar making 5 years back in the early 1960's and failed utterly. I returned to it in 1993, and finished up a couple of flamencos from parts that I still had on hand. One turned out spectacularly well, but I didn't know what I had done right!
>
> I took eight orders off that guitar before I realized that I needed to get the process figured out before trying to reproduce it. So, a long period of sporadic research has ensued, and a year ago last November I finally came up with a method of accurately adjusting the frequencies of the natural resonances of the guitar body.
>
> The process is called "voicing" and it consists of moving resonances to positions in the guitars' range that result in the tone you want. This mostly covers bass and mid-range frequencies. Wood selection using mechanical and Q testing, plus body size and bracing pattern design, have the most effect on the treble response.
>
> I have a bunch of photo .pdf's that are notes on the process for my guitar making students. I can send them along to anyone that's interested, as attachments.
>
> Cheers,
>
> Brian
>
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