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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 26 Apr 2011, 15:11 
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Joined: 23 Feb 2011, 16:31
Posts: 79
Location: Berlin / Germany
Hi Miguel,
one question about your main capacitor. Do you have dangerous voltage
between ground and the stator of this adjustable capacitor?
This open design fascinates, but can not
be dangerous to touch?

Greetings
Joe


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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 30 Apr 2011, 17:42 
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Joined: 14 Feb 2010, 13:13
Posts: 715
Location: Lisbon, Portugal
Hi Joe!

Questions regarding safety are always good questions. The answer is NO, there are no HV points accessible to the user, the upper chassis area is completely safe.

And now...

The project is complete! Tracking the RF frequencies (FM oscillator, Local Oscillator and Mixer) was a real pain. I spent so many hours working on it! But it worth every minute.

If you look at the Meissner schematic, you won´t find all the components values required for the RF stage. Many calculations, tests and some experience drove me to right values. I consider the following information very precious, so if you pretend to go on with this project please take note of these:

LOCAL OSCILLATOR:
78MHZ - 98 MHZ
COIL = 0.08uH

VARIABLE CAPACITOR @ 78MHZ = 52pF
@ 98MHZ = 33pF
----------
RF FRONT-END
88MHZ - 108MHZ
COIL = 0.06uH

VARIABLE CAPACITOR @ 88MHZ = 55pF
@ 108MHZ = 36pF

----------
MIXER
COIL = 0.14uH
----------

MAIN AIR-CORE VARIABLE CAPACITOR
15pF + 15pF + 15pF (with trimmers at least on 2 sections)
----------

If you cannot get 15pF variable capacitors, you can play with the total effective capacitance in order to get the 15pF swing. But doing this sacrifies a little bit the receiver´s selectivity, but still with great performance.

Now the radio will get a nice exotic wood cabinet, so the next stage is to make some dust! LoL

If you decide to get into this very nice, but not for the beginner project, please feel free to place any questions you may have right here. I´ll try to help you as much as I can.

Cheers!
Miguel


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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 01 May 2011, 12:32 
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Joined: 14 Feb 2010, 13:13
Posts: 715
Location: Lisbon, Portugal
CrazzyAbtTubes wrote:
I think that is one of the nicest tube radios I have ever seen, I really like the fact that you can see all of the tubes, I like that better than seeing it in a cabinet. :P

I'm not sure if you mention this Miguel, but this tuner capable of Stereo FM?

Hi! Sorry for the delay, but I just got the answer.

Yes, this circuit is compatible with a stereo decoder, because it´s capable of pulse counting. You will only need 3 more tubes (12AU7) and other components.

Attached is a simple Stereo Tube Decoder by Heathkit Model PT-1, which looks OK to me, though i´m not going into this for my project (perhaps for another one later).

Attachment:
ac11mpx.jpg

Have fun!
Miguel


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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 30 Jul 2011, 08:06 
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Joined: 14 Feb 2010, 13:13
Posts: 715
Location: Lisbon, Portugal
I have been fighting against some small frequency drift when the receiver gets hot (about 30 minutes of use).

There has also been the need to re-tune the received station each time I turned it on.

I replaced all ceramic capacitors with NP0 types and it helped.

But the main cure was with main variable capacitor. I had to do very well all grounds and ensure that there was almost no resistance to chassis.

I used a thick copper strap on one side and a large silver plated film on the other.

The is no more drift at all, neither on start-up or running hot.

There is also a bonus! The receiver´s selectivity and also sensibility has improved a lot! :)

So be sure to do very well all ground points on this little wonder FM radio!

The sound is suberb!!!

Some ideas come to me from time to time, encouraged from these radio projects. So there will be another FM project soon (later as i´m currently working on a KT88 amplifier).

I´ll be aiming to BOB! LoL (Best Of Best), regarding distoriton, sensitivity, limiter and stereo output! A nice piece of art for your living-room :)

Miguel

CT2JUT @ IM58KQ


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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 24 Feb 2012, 13:13 
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Joined: 14 Feb 2010, 13:13
Posts: 715
Location: Lisbon, Portugal
Hi!

I would like to share with you how happy I am with this radio, that has been working for almost one year.

It sounds so good, I almost can´t believe how can a single 50C5 tube sing so well!

This means that in a near future i´ll start another one, but this time with AVC, stereo and pherhaps a more refined RF front-end stage.

I like 7 pin miniature tubes very much, and have lots of them over here, so they will be used.

Stay tuned! :)


Miguel


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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 17 Jan 2013, 14:26 
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Joined: 11 Jan 2013, 09:13
Posts: 16
Location: Barrio Garay, Almirante Brown, Buenos Aires, Argentina
Very Nice. I'm planning to make one of my own, but with my own circuits and coils (handwired).
Cordially Osvaldo.

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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 17 Jan 2013, 20:55 
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Joined: 14 Feb 2010, 13:13
Posts: 715
Location: Lisbon, Portugal
That´s quite a challenge Osvaldo!

Building IF transformers from zero stage... Do you realise all the calculations with core permeability, wire gauge, spacing (mutual conductance), bandpass, losses, tuning, ressonance, etc...

I would get some from an old unit or at eBay (every now and then they appear).

Otherwise that will be a very long term project.

If you need help, let me know...


Cheers,

Miguel


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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 18 Jan 2013, 07:12 
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Joined: 11 Jan 2013, 09:13
Posts: 16
Location: Barrio Garay, Almirante Brown, Buenos Aires, Argentina
Yeah!, I have done some HF equipment when starting ham radio, and also I have some valuable sets like in the photos.

I'm planning to use fiberglass PCB, ceramic sockets, and copper strip for coils. Also I'm wondering if I can do copper slug-tuned RF stage, like in old TV tuners where a aluminium or brass screw adjust the inductances of coils, in place of ferrites. Copper or brass don´'t have hysteresis loss.


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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 03 Jan 2021, 12:33 
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Joined: 14 Feb 2010, 13:13
Posts: 715
Location: Lisbon, Portugal
Hi everyone!

Time really flies... I can't believe it has been 10 years since I started this project.

Along the years I've been aquiring more knowledge and experience so this radio has been updated.

Now it has AGC and AFC.

It's amazing how it sounds. I just can't understand why does it sound so good. It's even more enjoyable than my Williamson amplifier. Can you believe this?

Audio chain is 6AL5, 6AV6 and 50EH5 tubes.

This radio certainly deserves a MPX stereo decoder, but as I ran out of space on the chassis it'll be done with the MC1310 integrated circuit.

Keep watching for more updates!

Miguel


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 Post subject: Re: Hi-Fi Tube FM Tuner
PostPosted: 17 Jan 2021, 11:41 
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Joined: 14 Feb 2010, 13:13
Posts: 715
Location: Lisbon, Portugal
This is the latest run before going into stereo conversion.

It sounds so sweet in mono, I hope it goes well into stereo...

Look here: https://youtu.be/PciRsVngTMU

What do you think?

Thanks for watching!

Miguel


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