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22nd Oct 2012, 8:43 pm | #1 |
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Join Date: Jun 2012
Location: Milton Keynes, Buckinghamshire, UK.
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Pantry transmitter help for Hybrid
Looking at the various pantry transmitter posts I found the famous EH90 pantry tx "continued"
The cct is attached to post 10 I cannot use an osc. frequency of 1Mhz at home due to other channels encroaching . I have a Spitfire pantry tx and hoped to use the front end which can select any 9kHz position on the M.W. and use this to interface into the EH90 cct. Are there any designers on the forum who can make suggestions I am keen to get a cleaner less distorted transmission and of course get some valve sound!! I attach the spitfire cct Thanks Jim |
22nd Oct 2012, 8:57 pm | #2 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,518
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Re: Pantry transmitter help for Hybrid
Er yes, scrap the whole idea and build one from scratch using valves....
A VFO can be easily built to cover 600-1500kc, run this into a buffer stage, and then onto an "output stage" - if you keep the HT low the output will remain low. You can easily modulate the final stage in a number of ways - Screen grid modulate, using a 12AX7 or similar as the modulator valve perhaps? I might knock something together next week if I get an hour or two.....
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23rd Oct 2012, 1:45 am | #3 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
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Re: Pantry transmitter help for Hybrid
That'll be a bit difficult considering that a 12AX7 doesn't have a screen grid .....
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23rd Oct 2012, 3:19 am | #4 |
Hexode
Join Date: Jan 2007
Location: Welwyn Garden City, Hertfordshire, UK.
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Re: Pantry transmitter help for Hybrid
It's not the 12AX7 that's being modulated, it's a tetrode or pentode that's being screen modulated by the 12AX7!
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23rd Oct 2012, 10:47 am | #5 |
Dekatron
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Location: W.Butterwick, near Doncaster UK.
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Re: Pantry transmitter help for Hybrid
Lets have e few "genuine" low milliwatts circuits posted to keep within the rules.Sure a few would be intrested.
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23rd Oct 2012, 5:21 pm | #6 |
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Re: Pantry transmitter help for Hybrid
Thanks for the replies, maybe another solution for me would be to build the 2 valve tx but I would need to have crystal cut for 1512 kHz. This is the clearest spot on the waveband for me here in Milton Keynes.
How do I go about getting hold of a bespoke crystal? Sean thanks for the offer to design something for me, it would be much appreciated Thanks Jim |
23rd Oct 2012, 6:03 pm | #7 |
Dekatron
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Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
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Re: Pantry transmitter help for Hybrid
Use an L/C oscillator - should be fairly simple.
A crystal for that sort of frequency is going to be expensive in comparison to building a variable frequency oscillator......
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28th Oct 2012, 2:09 pm | #8 |
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Re: Pantry transmitter help for Hybrid
Sean thanks for the offer of maybe finding time knocking up a circuit for a VFO that could interface to the 2 valve pantry transmitter
regards Jim |
28th Oct 2012, 2:28 pm | #9 |
Moderator
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Location: Oxford, UK
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Re: Pantry transmitter help for Hybrid
A much cheaper approach than having a custom crystal made is to look at the frequencies of easily available crystals and check to see if any of them are reasonably clear locally.
You will find it difficult to avoid some frequency drift if you don't use crystal control, though this may be acceptable of course. |
28th Oct 2012, 3:15 pm | #10 | |
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Re: Pantry transmitter help for Hybrid
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28th Oct 2012, 3:16 pm | #11 |
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Re: Pantry transmitter help for Hybrid
Addendum... a 3.6MHz crystal will divide down to 9kHz easily.
Last edited by Guest; 28th Oct 2012 at 3:18 pm. Reason: wrong frequency (twit) |
28th Oct 2012, 3:23 pm | #12 | ||
Nonode
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
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Re: Pantry transmitter help for Hybrid
Quote:
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28th Oct 2012, 3:26 pm | #13 |
Dekatron
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Location: Heckmondwike, West Yorkshire, UK.
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Re: Pantry transmitter help for Hybrid
What's the problem with the 1512 generated by your Spitfire synthesiser?
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29th Oct 2012, 6:37 pm | #14 |
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Re: Pantry transmitter help for Hybrid
Hello Bill,
Thanks for the post, I am no designer and need to rely upon skills from the forum. In post #1, my idea was as you suggest, since the "Spitfire with the appropriate settings will produce 1512 kHz. I thought that if I built the 2 valve pantry tx. as found in "pantry" posts maybe I could dispense with the fixed 1mHz crystal osc. and somehow interface the frequency output generated by the Spitfire. However maybe I need a buffer or matching ccts ? There is an attachment of the Spitfire cct on my post #1 It begs the question why I would want to split the spitfire and add a new mixer amp stage. Well the quality isn't special at all and I would look forward to building a valve project that is very highly praised here on these forums Thanks Jim. |
31st Jan 2013, 11:50 pm | #15 |
Pentode
Join Date: Jun 2006
Location: Malaga, Spain.
Posts: 235
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Re: Pantry transmitter help for Hybrid
This was an UNpraised modulator < 1mW O/P but with a Xtal Search "D & G"
on the forum Very OTT! However the low HT makes it fairly safe both from an operating perspective and regarding possible interference etc. Almost any output type pentode will work well as the oscillator or amp on a 12V plus HT. |