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 Post subject: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Mar Wed 28, 2018 1:50 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5509
Location: Indianapolis, IN
Hello All,

Saw this radio on Ebay and gave it some thought... Kinda plain looking, but unique in the fact that it has bi-directional electric motor tuning---no "wind-up" like the Panasonics in collection, but also doesn't have a manual tuning knob if needed... Not too bad of condition other than the missing battery cover and trim strip on the back. And the seller said it worked well...

It arrived today and does work as well as seller described all across band with really good sounding audio---but can't get my favorite DX oldies station since it's adjacent to a stronger, closer signal and there is enough of a lag when you press button that seeking circuit misses it (drat !)... The bi-directional tuning is neat, though, when pointer hits end of dial and reverses itself---and there are forward and reverse buttons so you can go back and forth within a smaller range if desired. The action is very smooth and quiet and the "feel" of the buttons good. It seems fine with the original electrolytics, but several are those plastic-encased parts which are known for failure. The audio is very good, but maybe just a wee bit "muddy" even with tone in "HIGH" setting.

Seems like a fairly scarce set, even though there was another on Ebay at same time in worse condition---don't think I'd ever seen another before then. Had actually bought the other set first and owner refunded payment when he said he couldn't find it (but still posted that it shipped)---good thing since this one is much better and ended up costing less !

Anyone else have experience with these ? Other than the lack of a manual tuning knob, I'm impressed.

Ebay pic below...

John


Attachments:
arf tosh auto ebay pic.jpg
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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Mar Wed 28, 2018 12:41 pm 
Member

Joined: Nov Mon 26, 2012 1:21 am
Posts: 84
Hello John,
No experience with this set, but maybe there is a "trimmer" or something to adjust the sensitivity of where the auto-tuning stops. I would think that is determined by signal strength.

Sort of a guess on my part! ;)


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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Mar Wed 28, 2018 2:46 pm 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5509
Location: Indianapolis, IN
Thanks Marty,

Found the factory service manual on Radiomuseum... It does have a sensitivity switch on back which works and weaker signals do trigger it correctly when in "D"istant position, but that station is at 1230 kHz and the stronger one at 1240, and you have to hold the seek button for just enough time to start "action" that it bypasses. Even though performance is excellent otherwise, will probably look into it anyway out of curiousity---maybe that tiny delay is not normal ?

John


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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Mar Fri 30, 2018 2:33 am 
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Joined: Aug Wed 26, 2009 1:50 am
Posts: 1416
Location: Mount Pleasant UT 84647 (from Coventry, UK)
Interesting. Maybe you can modify the seek circuit so that it finds your station.


Last edited by Colin Ames on Mar Fri 30, 2018 12:46 pm, edited 1 time in total.

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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Mar Fri 30, 2018 5:57 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 28882
Location: SoCal, 91387
Nice toy you are playing with there , John! I've never seen one of those.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Mar Sat 31, 2018 12:41 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5509
Location: Indianapolis, IN
Thanks Guys !

Colin---think I'll replace the electrolytics anyway, even though it seems to work fine before trying anything else. There is a sensitivity adjustment which is to be made in the "D" (distant) mode that I'll try afterward.

Richard---had never seen one before, either, then two appeared on Ebay... The other was in much worse cosmetic condition with several dents in grille, paint splatters, and corrosion on battery contact...

John


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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Apr Sun 01, 2018 12:48 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5509
Location: Indianapolis, IN
Hello All,

Project completed today...

Disassembled and cleaned---grille had a lot of crud in holes and required a lot of scrubbing with "stubby" toothbrush. The thin felt behind grille really held the water and took a lot of blowing with compressed air to dry completely... Polished the dial & volume control position "windows" with Novus-2.

Replaced all eight electrolytics---one required removal of PCB from chassis for access. Left wiring intact and just handled very carefully. Took a "before" picture of chassis bottom so that wiring could be "re-dressed" properly when done. Notice use of M-F threaded standoffs for chassis support while servicing---the idea came to mind quite awhile back and really helps protect the components during handling...

Noticed no improvement in performance once back together with new caps---the audio quality seems a bit better. Tried adjusting the sensitivity trimpot on PCB and found that it was already set to maximum. Was able a couple of times to get my favorite station, but could hear the "adjacents" slightly in with it---so probably need to remove IFT sealing wax and do a sharp alignment one day...

Project pics below---the last including two of the Panasonic Radar-Matics in collection...

Hope all have a Good Easter !

John


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1ARF TOSH TUNING MECHANISM.jpg
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2ARF TOSH SPKR AND HRDWARE.jpg
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3ARF TOSH CAB CLEAN INSIDE.jpg
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4ARF TOSH SPKR IN CLEAN CAB.jpg
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10ARF TOSH AND RADAR-MATICS.jpg
10ARF TOSH AND RADAR-MATICS.jpg [ 118.34 KiB | Viewed 521 times ]
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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Apr Sun 01, 2018 1:03 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1221
Location: Jackson, TN
Really cool John!

How does the automatic tuning work? Is the tuner driven by motor? If so, what controls the motor, ie transistor?

Thanks, Tim


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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Apr Sun 01, 2018 3:39 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5509
Location: Indianapolis, IN
Thanks Tim !

Basically, when you press a "seek" button, the geared-down electric motor is turned on via switching transistors and as soon as a signal of sufficient amplitude reaches peak at 2nd IF amp output (3rd IFT input) which is coupled to "trigger amp" input, a "brake" transistor is turned on and motor stops. The "reversing action" is mechanical and difficult to describe (but interesting to watch) without studying it more closely... I had thought originally (before viewing schematic) that motor was electrically reversed... If you'd like the service manual pages, I could e-mail them. The Panasonics use "wind-up" motors with a relay that engages "tang" into gear to stop seeking activity.

Do you still have the S-38 ? Think about it once in awhile...

John


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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Apr Sun 01, 2018 4:10 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1221
Location: Jackson, TN
Hi John,

Yup, I can visualize the motor running until the signal strength tells it to stop. The gear arrangement looks like it can slide the pinion one direction or the other to change direction. Pretty clever.

My dad had a little skinny Sony pocket radio back in about 1972 that would auto tune . As I recall, you'd press the button which would wind a motor spring. On release, the tuning would then move upward until a station was found. At that point it stopped until button was pressed again. I believe it was FM. The button was also turned to adjust on/off and volume, so the radio had just one control.

The S-38 has been sittinging on my desk shelf for a few years now. It is getting to the point where I'll need to go back in to deal with a noisy volume control. This is a long term keeper for me due to its cool design and small size, perfect for desk shelf.

Tim


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 Post subject: Re: Toshiba 15M-915 Automatic Tuning radio project...
PostPosted: Apr Sun 01, 2018 4:29 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5509
Location: Indianapolis, IN
Hey Tim,

Glad the S-38 has a good home ! Can still remember when a high-school friend gave it to me back in 1976...

That Sony radio seems to be a desirable set on Ebay---prices always seem high...

Yes, the mechanism is unique on this radio---neat watching those crown gears engage with precision when lever shifts tuning direction...

Thanks for jumping in---good hearing from you...

John


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