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xrhonda91
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Post subject: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Thu 05, 2017 2:44 am |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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egg
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Thu 05, 2017 3:45 am |
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Joined: Jan Tue 31, 2012 1:55 am Posts: 3831 Location: Mountains of Mourne. Ireland.
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Very nice John... no duck + cover markings!
Greg.
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fifties
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Thu 05, 2017 9:10 am |
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Joined: Jan Thu 01, 1970 1:00 am Posts: 27043 Location: SoCal, 91387
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Slick looking radio there, John! I like the top facing slide rule dial. Yeah, so many of the '60's Japanese made Transistor sets are now dead, and normally requiring just changing the usually 4 Electrolytics to get them going again.
Interesting that it's a 3-bander, kinda unique for that size set.
_________________ \\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////
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xrhonda91
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Thu 05, 2017 1:27 pm |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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Thanks Guys !
Greg---didn't even notice the lack of Conelrad markings ! Hmmm... The seller said he found it in a box of his things while unpacking---think I'll contact him and see where he got it ! But it does have the label on back cover...
Richard---more than four in this set and a little more "packed" inside than the AM/FM...
Hope to get to it this weekend !
John
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xrhonda91
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Fri 06, 2017 3:09 am |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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Doesn't look good...
Pulled cover and checked power input with VOM---30 ohms forward with speaker noise & 700 ohms reverse... Looks like a shorted audio transistor...
But it is clean inside, though...
John
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fifties
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Fri 06, 2017 4:34 am |
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Joined: Jan Thu 01, 1970 1:00 am Posts: 27043 Location: SoCal, 91387
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I wouldn't assume anything until the Electrolytics have been changed out.
_________________ \\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////
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xrhonda91
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Fri 06, 2017 4:10 pm |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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Hey Richard, hope to pull the PCB tonight...
I heard back from the seller and he said that he had it packed away so long he'd forgotten where he got it !
John
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Colin Ames
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Fri 06, 2017 7:06 pm |
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Joined: Aug Wed 26, 2009 1:50 am Posts: 1343 Location: Mount Pleasant UT 84647 (from Coventry, UK)
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That's a nice looking radio. Hopefully all it needs is caps.
Colin
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Rocco53
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Fri 06, 2017 9:40 pm |
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Joined: May Wed 01, 2013 10:05 pm Posts: 1479 Location: Rayleigh, BC, CANADA
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Good catch John. Glad to see you found the 3 band version of that. Hopefully the SW band performs well on that set too.
_________________ Rocco
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xrhonda91
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Sat 07, 2017 2:24 am |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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Thanks Guys !
Does look like a audio output transistor issue causing fault...
Rocco---was yours the 3-band ?
John
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Rocco53
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Sat 07, 2017 10:15 pm |
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Joined: May Wed 01, 2013 10:05 pm Posts: 1479 Location: Rayleigh, BC, CANADA
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xrhonda91 wrote: Rocco---was yours the 3-band ?
John No, it's just a plain T-81 (AM/FM) same as your first one. I just noticed, my radio is not working anymore (no audio) on either band, gonna dig into it this weekend. John, it should be easy locating a shorted audio transistor. hope that's all it is with yours. Check the headphone jack as well for bent contacts.
_________________ Rocco
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xrhonda91
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Post subject: Re: 1962 Panasonic T-81H AM/FM/SW -- latest arrival (nice) ! Posted: Jan Sun 08, 2017 4:21 am |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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Colin Ames
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Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) Posted: Jan Sun 08, 2017 5:31 am |
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Joined: Aug Wed 26, 2009 1:50 am Posts: 1343 Location: Mount Pleasant UT 84647 (from Coventry, UK)
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Well that's a shame. Are the transistors specific to this set, or would other radios from the same era possibly provide replacements?
Colin
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xrhonda91
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Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) Posted: Jan Sun 08, 2017 5:47 pm |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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Colin---The converter & IF transistors (2SA70) appear to be special, shielded Matshusita parts. Considering how well the "plain" T-81 performs, think that they must be something special... They are not used in any of the other Panasonic sets that I know of...
Am going to play with it a bit more today...
Mitch---Haven't even looked to see what subs might be for the 2SA70, but it appears to be a unique part...
Thanks !
John
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50sTransistorRadios
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Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) Posted: Jan Sun 08, 2017 6:20 pm |
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Joined: Sep Sat 29, 2012 6:32 pm Posts: 789 Location: 13760
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I hate when I spend a bunch of time on a radio and it ends up not working anyway due to some unobtainable part (or a fault I just can't seem to locate). Do you use a power supply with current limiting, or do you just use an ammeter when you suspect a problem? (The power supply I use has adjustable current limiting, so I can keep excess current draw from cooking something).
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xrhonda91
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Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) Posted: Jan Sun 08, 2017 7:14 pm |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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Matt, typically just use batteries. When I noticed the voltage drop when switch turned on, then used ammeter to determine current draw...
John
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metzman
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Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) Posted: Jan Sun 08, 2017 7:49 pm |
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Joined: Nov Wed 14, 2007 11:37 pm Posts: 1418
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Get a refund. It's not worth fussing with.
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xrhonda91
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Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) Posted: Jan Sun 08, 2017 11:59 pm |
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Joined: Oct Mon 26, 2009 10:02 pm Posts: 5249 Location: Indianapolis, IN
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Metzman---these radios are real gems when working, so worth a little effort... And they look great, too !
A bit of good news this afternoon !
Found that the "bias regulator" transistor was the "current sucker"---erroneously thought I'd disabled the entire output stage by pulling the 5.6 ohm emitter resistor... After disconnection, current dropped to just a few milliamps.
Decided to go ahead and pull the converter transistor (X3) and install a socket for experimentation. After removal, checked junction resistances and found significant leakage to grounded shield lead---tin whiskers ??? Bent the shield lead over and placed into socket---still no oscillation. Looked around in my transistor drawer and found a clipped-out Delco DS-38 which I think was used as an RF or converter in an old car radio. Plugged it in, applied power, and checked with scope---now oscillating fine !!! Got out the signal tracer and RF probe and connected to the collector pin---several stations were heard fine though there were some oscillations at various points on the dial. Moved probe to detector diode input and WOW---many stations came in fine including my favorite low-power DX station I use as a benchmark !!! Excellent sensitivity & selectivity without any adjustment---but there were still some oscillation issues mid to low dial. The signal sounded pretty good, but seemed to have a bit of distortion probably due to degraded IF transistor. Continued into the audio preamp & driver circuits with the tracer and there was significant amplification each stage, but somewhat more distorted. SW also seemed to work fine with just a short test lead as antenna. At least there's hope !
Pretty excited now to get this done !
John
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ARF T-81H PCB TOP RECAPPED X3 SOCKET.jpg [ 200.02 KiB | Viewed 2236 times ]
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Colin Ames
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Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) Posted: Jan Mon 09, 2017 12:06 am |
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Joined: Aug Wed 26, 2009 1:50 am Posts: 1343 Location: Mount Pleasant UT 84647 (from Coventry, UK)
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Rocco53
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Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice) Posted: Jan Mon 09, 2017 2:15 am |
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Joined: May Wed 01, 2013 10:05 pm Posts: 1479 Location: Rayleigh, BC, CANADA
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I knew you wouldn't give up that easily John, you can't stop now.
Today I also found my bias regulator is shorted in both directions (34 ohms) and an audio driver transistor is open. Using my signal tracer I'm getting good strong audio just before the driver on both AM and FM.
Looks like anything close to a 2SB173 will work, I tried a few subs already, but not sure what to do about the "bias reg"
_________________ Rocco
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