Hi all,
I am interested to make a small tube FM radio, preferably stereo...any ideas one where I can start? reading materials, schematics, etc...
thanks
Byron
I am interested to make a small tube FM radio, preferably stereo...any ideas one where I can start? reading materials, schematics, etc...
thanks
Byron
Here's someone who did a nice job on a Dynaco FM3:
http://mpbarney.googlepages.com/dynacofm3
His links will also take you to the original schematics and manual, the study of which might prove useful. The FM3 was a very good tuner; when restored and minimally upgraded, you get 90% of the audio performance of a 10B at 5% of the price. Spend the rest of your effort on a good antenna.
http://mpbarney.googlepages.com/dynacofm3
His links will also take you to the original schematics and manual, the study of which might prove useful. The FM3 was a very good tuner; when restored and minimally upgraded, you get 90% of the audio performance of a 10B at 5% of the price. Spend the rest of your effort on a good antenna.
Byron,
Before you spend a single red cent, make darned sure your test bench has the requisite instrumentation for doing a proper sweep alignment of VHF superhet circuitry. If your bench is not up to snuff, SY's suggestion of overhauling a Dyna FM3 is the only realistic option. Heath worked around the alignment issue, for this specific case.
Even if your bench is stellar, you still face HUGE hurdles. 10.7 MHz. IF transformers intended for use with tubes are as scarce as hen's teeth. 🙁 It may be possible to use BJT IF trafos in a parafeed setup. What about using tuned filters, instead of IF trafos? More than 1 knowledgeable person has stated that much of the good sound tubed tuners yield is connected to transformer coupled IF stages.
Get past the IF trafo issue and you have to source a suitable 3 gang variable capacitor for the VHF front end. Perhaps another member can suggest circuitry that uses varicap diodes and the low voltage 6GM8 for the front end.
Before you spend a single red cent, make darned sure your test bench has the requisite instrumentation for doing a proper sweep alignment of VHF superhet circuitry. If your bench is not up to snuff, SY's suggestion of overhauling a Dyna FM3 is the only realistic option. Heath worked around the alignment issue, for this specific case.
Even if your bench is stellar, you still face HUGE hurdles. 10.7 MHz. IF transformers intended for use with tubes are as scarce as hen's teeth. 🙁 It may be possible to use BJT IF trafos in a parafeed setup. What about using tuned filters, instead of IF trafos? More than 1 knowledgeable person has stated that much of the good sound tubed tuners yield is connected to transformer coupled IF stages.
Get past the IF trafo issue and you have to source a suitable 3 gang variable capacitor for the VHF front end. Perhaps another member can suggest circuitry that uses varicap diodes and the low voltage 6GM8 for the front end.
Eli, if I were scratch-designing, I'd probably use tubes in the front end and in the sections after the demodulator. No reason not to use solid state in between, which solves the IF problem.
All moot, of course- there's really not much on the radio I care to listen to.
All moot, of course- there's really not much on the radio I care to listen to.
Here is one that use a low IF (around 300kHz) so that you need no specialised IF transformers, and it uses a pulse count detector, so no quad coil needed.
Very neat & elegant design for simplicity, But it won't strech to stereo.
PCD FM tuner
Very neat & elegant design for simplicity, But it won't strech to stereo.
PCD FM tuner
SY said:
SY,
So, are you suggesting a trafo coupled BJT IF strip? FETs will oscillate if tuned circuits are used at both the I/P and O/P, which forces the use of supposedly bad sounding ceramic filters.
Mouser stocks BJT 10.7 MHz. IF trafos. Look here.
Actually, I'm thinking of using the BJT IF trafos "reverse" (step up) connected and parafeed wired. Mouser also stocks the requisite J.W. Miller RF chokes, which can stand tube B+. 🙂 A 4 tube strip with a 6BZ6 followed by 3X 6AU6s would be employed.
FWIW, I'm partial to the 6BN6 as a combined limiter/2nd detector.
Eli Duttman said:
All you have to do is buy a GE/Westinghouse table top radio from the era and gut them out. Do they have Salvation Army Stores in Canada?
The Sencore SG-165 will help you with alignment -- the prices are all over the lot for these sometimes they go for $10, sometimes for well over $100.
http://cgi.ebay.com/SENCORE-SG165-A...52|39:1|66:2|65:12&_trksid=p3286.c0.m14.l1318
Wow! Thanks for the info guys...but it seems a little too complicated for me. For now, I think I will just make a small tube amp and speakers and go from there with a vintage sansui or something..
I may go for something like this after I get a little more experience and understanding.
I really just want a small, good sounding unit for the porch, and was intrigued by an old tuner i saw yesterday at an antique store 🙂
I may go for something like this after I get a little more experience and understanding.
I really just want a small, good sounding unit for the porch, and was intrigued by an old tuner i saw yesterday at an antique store 🙂
Here is a good site as well:
http://philsvalveradiosite.co.uk/philsvalveradiosite/severnvalvehfsuperhet_1.htm
Shows how to use transistor IF transformers with valves.
http://philsvalveradiosite.co.uk/philsvalveradiosite/severnvalvehfsuperhet_1.htm
Shows how to use transistor IF transformers with valves.
Be aware that it takes a lot of experience and skill to successfully build a 100MHz radio front end, and 10.7Mhz IF strips. It would be better for a novice to radio circuits to get an old tube tuner and play with that (replace wax caps and such, but ceramic and mica caps rarely go bad, so don't touch 'em).
Heathkit made a simple FM only table kit radio that would make a good starter for modifying. It was a series string heater, but has an isolation transformer for safety. Change that out to something more normal, like a 6.3V parallel heater, full wave B+ supply, and delete the small audio amp to free up room for more IF stages or stereo decoding.
Heathkit made a simple FM only table kit radio that would make a good starter for modifying. It was a series string heater, but has an isolation transformer for safety. Change that out to something more normal, like a 6.3V parallel heater, full wave B+ supply, and delete the small audio amp to free up room for more IF stages or stereo decoding.
6bn6
I am using two 6BN6 in the limiter,
see pictures and schematics.
Kind regards,
Darius
Eli Duttman said:
I am using two 6BN6 in the limiter,
see pictures and schematics.
Kind regards,
Darius
Hi..
I would like some input whether the following plan is feasible. Using a working IC-based superhet FM receiver, i would like to replace the IF-amplifier and quadrature detector part with tubes.
The working FM receiver schematic is below:
The part that says FM tuner basically contains the RF amp+local oscillator+mixer and it outputs IF signal. What do we usually call this? It's a self-contained module. For now, i will call it FM front-end.
So basically the plan is below:
From the front-end output, signal goes to a ceramic 10.7MHz filter and fed to 4 stage of 6N23P-based IF amplifier stage. No IF-transformers are used to couple the stages. From there, it goes to a 6BN6-based limiter+quadrature detector to extract the audio signal which goes to power amp (or the LA3361 stereo decoder) and also fed back to the front end's AFC input.
So as you can see, basically i want to the place the LA1260 IC with tube-based circuit. Does this make sense? Will it work?
If the plan is feasible, can i use the same 10.7MHz tank connected to pin 5 of LA1260 for the 6BN6? Any other concerns i should be aware of?
I would like some input whether the following plan is feasible. Using a working IC-based superhet FM receiver, i would like to replace the IF-amplifier and quadrature detector part with tubes.
The working FM receiver schematic is below:
An externally hosted image should be here but it was not working when we last tested it.
The part that says FM tuner basically contains the RF amp+local oscillator+mixer and it outputs IF signal. What do we usually call this? It's a self-contained module. For now, i will call it FM front-end.
So basically the plan is below:
An externally hosted image should be here but it was not working when we last tested it.
From the front-end output, signal goes to a ceramic 10.7MHz filter and fed to 4 stage of 6N23P-based IF amplifier stage. No IF-transformers are used to couple the stages. From there, it goes to a 6BN6-based limiter+quadrature detector to extract the audio signal which goes to power amp (or the LA3361 stereo decoder) and also fed back to the front end's AFC input.
So as you can see, basically i want to the place the LA1260 IC with tube-based circuit. Does this make sense? Will it work?
If the plan is feasible, can i use the same 10.7MHz tank connected to pin 5 of LA1260 for the 6BN6? Any other concerns i should be aware of?
You can't just run a cascade of untuned IF amplifiers. Each stage will have relatively low gain at the IF frequency (because you have no L to accomodate stray C), and the whole IF strip will oscillate at some frequency of its own choosing. You can't amplify 10MHz with grounded cathode triodes. You need pentodes or cascodes, with at least single-tuned IFTs or preferably double-tuned IFTs. Or possibly LTPs, which is what IF chips often use.
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did you do any searches on here or the internet - there's lots of designs out there:
http://www.diyaudio.com/forums/tubes-valves/127487-fm-tube-radio-design.html
http://www.diyaudio.com/forums/tubes-valves/127487-fm-tube-radio-design.html
@DF96
How about 2 IF amp stages using 6J1P? It will be like this:
Mixer Output (IF signal) -- ceramic filter --> 1st 6J1P IF amp stage -- 10.7MHz IFT --> 2nd 6J1P IF amp stage -- 10.7MHz IFT --> 6BN6 limiter+detector
Each IF transformer will be using a pair of typical BJT IFT wired back-to-back. Something like this 42IF123 IFT: 42IF123-RC Xicon | Mouser. HT will be kept around 100v to reduce risk of damage to the IFT.
@Bigun
Yes, there are lots of design but i'm looking to use as much existing parts as possible, including the front end, which means i'm limited to 10.7MHz IF amp stages. Most of the designs i found use much lower IF.
How about 2 IF amp stages using 6J1P? It will be like this:
Mixer Output (IF signal) -- ceramic filter --> 1st 6J1P IF amp stage -- 10.7MHz IFT --> 2nd 6J1P IF amp stage -- 10.7MHz IFT --> 6BN6 limiter+detector
Each IF transformer will be using a pair of typical BJT IFT wired back-to-back. Something like this 42IF123 IFT: 42IF123-RC Xicon | Mouser. HT will be kept around 100v to reduce risk of damage to the IFT.
@Bigun
Yes, there are lots of design but i'm looking to use as much existing parts as possible, including the front end, which means i'm limited to 10.7MHz IF amp stages. Most of the designs i found use much lower IF.
That might work. You have the necessary RF test equipment, and experience in building radio systems? If not, start with an AM radio.
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