Pantry transmitter help for Hybrid - UK Vintage Radio Repair and Restoration Discussion Forum

jmedley · 22nd Oct 2012, 8:43 pm

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

Sean Williams · 22nd Oct 2012, 8:57 pm

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.....

julie_m · 23rd Oct 2012, 1:45 am

Quote:

Originally Posted by Sean Williams

Screen grid modulate, using a 12AX7 or similar as the modulator valve perhaps?

That'll be a bit difficult considering that a 12AX7 doesn't have a screen grid .....

Amraduk · 23rd Oct 2012, 3:19 am

Quote:

Originally Posted by ajs_derby

Quote:

Originally Posted by Sean Williams

Screen grid modulate, using a 12AX7 or similar as the modulator valve perhaps?

That'll be a bit difficult considering that a 12AX7 doesn't have a screen grid .....

It's not the 12AX7 that's being modulated, it's a tetrode or pentode that's being screen modulated by the 12AX7!

HamishBoxer · 23rd Oct 2012, 10:47 am

Lets have e few "genuine" low milliwatts circuits posted to keep within the rules.Sure a few would be intrested.

jmedley · 23rd Oct 2012, 5:21 pm

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

Sean Williams · 23rd Oct 2012, 6:03 pm

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......

jmedley · 28th Oct 2012, 2:09 pm

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

paulsherwin · 28th Oct 2012, 2:28 pm

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

Quote:

You will find it difficult to avoid some frequency drift

But no more than the average local oscillator! In serious mode... Take a look at huff & puff oscillators http://www.hanssummers.com/huffpuff.html

28th Oct 2012, 3:16 pm

Addendum... a 3.6MHz crystal will divide down to 9kHz easily.

Andrew2 · 28th Oct 2012, 3:23 pm

Quote:

Originally Posted by merlinmaxwell

Quote:

You will find it difficult to avoid some frequency drift

But no more than the average local oscillator! In serious mode... Take a look at huff & puff oscillators http://www.hanssummers.com/huffpuff.html

I use a homebrew Huff & Puff osc for my 160m rig and it's great. The only trouble is they don't always come up on the same frequency at switch on. It depends on the stability of the oscillator. In my case, switching the rig on in a cold shack will bring the osc on at 200 Hz high, but it will stay there all day if I don't retune!

AC/HL · 28th Oct 2012, 3:26 pm

What's the problem with the 1512 generated by your Spitfire synthesiser?

jmedley · 29th Oct 2012, 6:37 pm

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.

boiss · 31st Jan 2013, 11:50 pm

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.

22nd Oct 2012, 8:57 pm	#2
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	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..... __________________ Engineers make things work and have spare bits when finished

23rd Oct 2012, 10:47 am	#5
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	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. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

23rd Oct 2012, 5:21 pm	#6
jmedley Rest in Peace Join Date: Jun 2012 Location: Milton Keynes, Buckinghamshire, UK. Posts: 109	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
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	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...... __________________ Engineers make things work and have spare bits when finished

28th Oct 2012, 2:09 pm	#8
jmedley Rest in Peace Join Date: Jun 2012 Location: Milton Keynes, Buckinghamshire, UK. Posts: 109	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

22nd Oct 2012, 8:43 pm	#1
jmedley Rest in Peace Join Date: Jun 2012 Location: Milton Keynes, Buckinghamshire, UK. Posts: 109	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 Attached Thumbnails

28th Oct 2012, 2:28 pm	#9
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,970	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, 3:16 pm	#11
Guest Guest Posts: n/a	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, 3:26 pm	#13
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Pantry transmitter help for Hybrid What's the problem with the 1512 generated by your Spitfire synthesiser?

29th Oct 2012, 6:37 pm	#14
jmedley Rest in Peace Join Date: Jun 2012 Location: Milton Keynes, Buckinghamshire, UK. Posts: 109	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
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 235	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.