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 Post subject: Fisher 50R trouble
PostPosted: Jan Tue 14, 2020 4:44 am 
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Joined: Aug Sat 09, 2014 7:41 pm
Posts: 10
Hi-

My Fisher 50R tuner recently developed a nasty problem -- the output volume is very low and the quality is scratchy and thin. This applies whether selecting AM, FM, or "TV" (the aux choice on this model). I have replaced a few resistors and caps and all now seem to be in spec. I have tried several different 12au7's (known working) and none improved the situation. The pic attached may be of help in diagnosing (my soldering work is not very good but the connections all test fine).

If anyone has any ideas, I'm all ears. Thanks to all.

Attachment:
Attachment-1.jpeg
Attachment-1.jpeg [ 771.87 KiB | Viewed 214 times ]


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Tue 14, 2020 5:34 am 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 11445
Location: Mountains of Mourne. Ireland.
Don't worry about the neatness of your soldering no matter what folks here say. lol

Clean all that dirt from around the tube socket with some IPA or whatever else that you have on hand. Use small acid brushes (eBay) or cut up some old or cheap toothbrushes.

Look out for solder blobs in the chassis!

Clean tube pins (lightly scrape with a sharp X-Acto knife) also check the sockets.
Watch: Cleaning Vacuum Tubes Pins.
http://www.youtube.com/watch?v=UHhNCr2fYoU&t=2m12s


Greg.
oh... IPA info, and... cleaning carbon potentiometers...
viewtopic.php?p=3101699#p3101699


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Tue 14, 2020 5:51 am 
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Joined: Aug Sat 09, 2014 7:41 pm
Posts: 10
Thanks. Cleaning the crud is on my list. The sound I describe as scratchy does not change as I turn the volume pot. Perhaps a better description of the sound is thin, no bass at all. Somewhat like listening to an old land line phone, even like the sound from someone speaking into an old candlestick phone.


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Tue 14, 2020 6:08 am 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 11445
Location: Mountains of Mourne. Ireland.
SOP (standard operating procedure) is to replace all the electrolytic and paper capacitors as a first step.
Resistors can fail open or short, alongside their value changing.
A good close visual inspection can often reveal circuit troubles and suspect components.
For suspect dry joints, touch them up (reflow) with your soldering iron.

Sams Photofact Set-231 Folder-7 service manual for model 50R (eight-pages) can be downloaded from Tom Bavis' website, in DjVu format.
https://tinyurl.com/tom-bavis-hi-fi

I use this DjVu reader (safe download from sourceforge.net) works great.
http://antiqueradios.com/forums/viewtop ... 9#p2746819


:) Greg.
If you are using a Windows computer, here is a direct link to the DjVu reader .exe file.
https://sourceforge.net/projects/djvu/f ... rror=netix

Save it to your desktop, open it and follow the installation instructions.


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Tue 14, 2020 6:20 am 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 11445
Location: Mountains of Mourne. Ireland.
Here are a few informative restoration videos...
viewtopic.php?p=3113804#p3113804

As the above videos are long, it's best to save them to your computer...
viewtopic.php?p=3128591#p3128591

Greg.


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Wed 15, 2020 1:35 am 
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Joined: Aug Sat 09, 2014 7:41 pm
Posts: 10
Thanks again for the videos and the link to the Sam's sheet, which I actually already had and have been using. To be clear, I've had this tuner for roughly six years and did a re-cap right after buying it. Until recently, it had worked fine. The problem does seem isolated to the audio amp section. Reception appears to be fine - I can tune in the usual stations in my city. But even using the aux input (marked "TV" in this model) the audio sounds as I've described -- very low, and with a frequency range that somewhat resembles an old telephone. So I ask myself, even after replacing some of the audio section parts, verifying the specs on the original audio section parts, triple checking components, what am I missing? What else in this machine could have this effect on AM, FM and aux output?


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Wed 15, 2020 2:04 am 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 11445
Location: Mountains of Mourne. Ireland.
Have you compared your Voltage and Resistance readings to the ones on the schematic page of the Photofact.

Greg.
photos, for curious minds. lol
https://www.ebay.com/itm/233451329826


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Wed 15, 2020 4:04 am 
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Joined: Nov Mon 02, 2009 7:01 am
Posts: 4104
Location: Lincoln City, OR 97367
Greetings to junkjer and the Forum:

You refer to this unit as a tuner. I therefore presume that it has a line level output to drive an amplifier of some sort? If that presumption is correct, then I have a dumb question:

Have you tried any other source directly into the amplifier input used by the tuner? In other words, are you sure that the problem is actually in the tuner?

If on the other hand, the Fisher 50R is actually a RECEIVER with its own audio power amplifier section, then disregard all above.

Regards,

_________________
Jim T.
KB6GM


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Wed 15, 2020 4:40 am 
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Joined: Aug Sat 09, 2014 7:41 pm
Posts: 10
Jthorusen-

The 50-R is a tuner. It has a 12AU7 audio amplification stage that requires further external amplification. I normally have its output go into a homebrew pre-amp (using a Korg Nutube) and then into a restored Dynaco SCA-35 (which I could not have accomplished without the online help of St. Gillespie, who deserves the title I give him in jest). The pre-amp plugs into the SCA-35's Spare (aux) input. While working on the 50-R I have been using the direct Tuner input on the SCA-35 rather than going through the pre-amp because the Tuner input is easier to reach than the pre-amp inputs. Just now I swapped out the pre-amp for the 50-R's output into the SCA-35's Spare input and what do you know... the tuner sounds beautiful as always.

So Jthorusen - thank you for the slap in the head with a large sock filled with obvious. Or, what ought to have been obvious to me.

Now, of course, I have to dig into the SCA-35 to see what's up with the Tuner input.

Thanks also to everyone else for their suggestions.

I will now see about changing my handle here to "dumb-as-a-rock."


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 Post subject: Re: Fisher 50R trouble
PostPosted: Jan Wed 15, 2020 1:31 pm 
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Joined: Nov Mon 02, 2009 7:01 am
Posts: 4104
Location: Lincoln City, OR 97367
Greetings to junkjer and the Forum:

I'm glad you are on the right track. I suggest that you not be too quick to change your handle.... if I had $50 per hour for every hour I have wasted looking for a problem in the wrong place, I would be an extraordinarily wealthy man. :D

Good luck,

_________________
Jim T.
KB6GM


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