Date: Tue, 18 Dec 2012 15:19:00 +0200
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From: phl@netikka.fi
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Subject: Re: LF: FT-241A xtals?
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Hello Dimitrios,

Yes lets share ideas and progess, hope I managed to get any crystals  
(very odd way of ordering and I don't know if I actually got any yet).  
There is already one mighty fine built example on the net, but no  
schematic provided:

http://www.cchidgey.pwp.blueyonder.co.uk/500_KHz.html


On a side note there seems to have been a goldrush after those X-tals  
because now there is suddenly only one channel available within the  
band giving 473.6kHz but this is very close to NDB SA lower sideband  
at 473.5kHz.

BR

Paul-Henrik, OH1LSQ


Quoting Dimitrios Tsifakis <dtsifakis@gmail.com>:

> I am glad you found the eBay seller and your project is about to be
> revived. A VFO, as David G4DMP mentioned before, is also another valid
> option. It shouldn't be too hard to make a VFO stable enough for 472
> kc, even if it is a valve one! As a test, I built a VFO for 7 Mc using
> a 6C4 oscillator and a 6AG7 as a BA - it was perfectly good for CW
> work.
>
> I hope we can exchange more technical information about both projects
> here. Maybe this will be a source of inspration for others that have
> considered the possibility of using valves for a 472 kc transmitter.
>
> 73, Dimitris VK1SV
>
>
> 2012/12/18  <phl@netikka.fi>:
>> What a coincidence Dimitros!
>>
>> After answering to your posting I did a search on Ebay for FT-241 crystals
>> and found the same seller - an order has already been made :)
>>
>> Many thanks for bringing up this subject - I had lost hope already.
>>
>>
>>
>> Paul-Henrik, OH1LSQ
>>
>>
>> Quoting Dimitrios Tsifakis <dtsifakis@gmail.com>:
>>
>>> Hi Paul-Henrik,
>>>
>>>> Yes, the same thought has been on my mind for a long time now. The
>>>> problem
>>>> is that fundamental X-tals for this frequency band are nearly
>>>> unobtainable.
>>>> I have even tried to custom order some new ones for me and a couple of
>>>> friends but never succeeded - the quantities would need to be much larger
>>>> for this type of crystals. (They use a different kind of cut as compared
>>>> to
>>>> crystals for say 3500kHz which can still be ordered custom fairly easily)
>>>>
>>>> Hopefully people with a stash of suitable vintage X-tals will wake up
>>>> when
>>>> the new band opens for real and put some up for sale if they don't want
>>>> to
>>>> use them themselves.
>>>
>>>
>>> I bought a few crystals from this ebay seller:
>>>
>>>
>>> http://www.ebay.com.au/itm/FT-241-CRYSTALS-Many-to-choose-from-You-pick-/260897401407?pt=LH_DefaultDomain_0&hash=item3cbeb26a3f&_uhb=1#ht_4373wt_1188
>>>
>>> There seem to be a few left. They are sold as-is, but I found that the
>>> majority of the ones I bought worked OK. There may be other sellers on
>>> eBay.
>>>
>>>> I'd say go for it - I have built a couple of "MO-PA" transmitters for
>>>> 80/160m, they are really pleasant and rewarding projects with a distinct
>>>> sound of their own. This is especially true if you also key the
>>>> oscillator.
>>>
>>>
>>> I have built recently a similar transmitter for 40 m, using a 6CL6 and
>>> an 807. When I keyed the oscillator together with the PA, I couldn't
>>> get it to behave properly, so I added a switch to leave the oscillator
>>> on and key only the cathode of the PA. I only key the oscillator when
>>> I want to draw some attention with the home-brew sound!
>>>
>>> In general, I have had difficulty sourcing a HV transformer suitable
>>> for an 807. In the past, I found that one can build a voltage doubler
>>> or quadrupler, with modern electrolytics, it is a viable alternative.
>>> The 6.3 V for the filaments I found I can get from a 6 V transformer.
>>> Hint: it's easy to add extra turns on a toroid type transformer :-)
>>>
>>> 73, Dimitris VK1SV
>>
>>
>>
>>
>>