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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Jan Mon 09, 2017 2:22 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Thanks Guys---was sure relieved, believe me !

Rocco---I am wondering about the bias regulator also as I don't know how many of their radios uses that specific one and what can be used as a sub. Am already searching for the matched pair outputs and have found a couple of their cheaper sets that use them. Stay tuned as I'll post what I find. Glad your problem was only in the audio !

John


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Jan Mon 09, 2017 4:02 am 
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Mitch


Last edited by PBPP on Jan Tue 10, 2017 7:43 am, edited 1 time in total.

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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Jan Mon 09, 2017 7:32 pm 
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Joined: May Wed 01, 2013 10:05 pm
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Location: British Columbia, CANADA
I checked my MA23 again and it does act like a diode so I think it's ok.
It also drops in resistance when heated.

The way it's wired in the circuit I'm thinking it's acting like a thermistor that I've seen in other audio stages.

An MA23 also refers to an NTE109 equivalent (fast switching germanium diode)
there's a data sheet on this page.

http://www.weisd.com/test/GenericParts_ ... id1=MA23(B)


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Jan Tue 10, 2017 3:18 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 4382
Location: Indianapolis, IN
Thanks Mitch---responded in more detail via e-mail.

And thanks Rocco for your info---so it doesn't conduct both directions as you mentioned earlier ? Maybe then, the driver will get it going !

John


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Jan Sun 15, 2017 11:24 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Went ahead and cleaned all the "cosmetics" & pieces this weekend and put all away until I can find the transistors needed...

Pics below...

John


Attachments:
ARF T81H PRTS CLN.jpg
ARF T81H PRTS CLN.jpg [ 192.17 KiB | Viewed 342 times ]
ARF T81H CAB PRTS CLN INS.jpg
ARF T81H CAB PRTS CLN INS.jpg [ 191.36 KiB | Viewed 342 times ]
ARF T81H CAB PRTS CLN OUT.jpg
ARF T81H CAB PRTS CLN OUT.jpg [ 236.3 KiB | Viewed 342 times ]
ARF T81H SPKR BK CLN.jpg
ARF T81H SPKR BK CLN.jpg [ 227.04 KiB | Viewed 342 times ]
ARF T81H SPKR FRT CLN.jpg
ARF T81H SPKR FRT CLN.jpg [ 202.46 KiB | Viewed 342 times ]
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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Mon 06, 2017 1:19 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Bit of good news !

My sister had an old, well-used Panasonic R-1029 which she let me have while I was down there this weekend to take the needed transistors for this set. It has the 2SB176 matched pair outputs and 2SB175 driver which should hopefully get this going !

Since the radio still works, am going to take the driver and outputs from another junk pocket set PCB so it'll still be usable...

Hope to get these transistors in place tomorrow and see how this T-81 sounds with it's own working audio ! Am going to check the MA23 carefully before applying power---haven't looked at it out of circuit, but know the outputs are bad and it may be too if power was reversed...

The IF transistor is still "iffy", so am going to disable the shield lead first since the other had a short.

Stay tuned !

John


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Tue 07, 2017 12:24 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 4382
Location: Indianapolis, IN
Got it together !

Installed the audio transistors from the R-1029 and a good MA23 I found in a junked Panasonic set---all works very well ! Disabled the IF transistor shield and seemed to notice an increase in performance. Went ahead and left the one socketed transistor in place temporarily since all seems fine---may try a better sub in future if I run across one...

Replaced the transistors I'd taken from the R-1029 with off-brand ones out of a junked PCB, treated the volume control with De-Oxit Faderlube, and it also works well !

Pics & more later...

John


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Tue 07, 2017 12:54 am 
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Nice going, John!

You're learning... :wink:

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


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Tue 07, 2017 3:02 am 
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Location: British Columbia, CANADA
Wow, you found another MA23, Impressive!
I don't think there's another MA23 within 100 miles of my location, lol

Just in case you're interested, I put my MA23 under the microscope, with all three legs separated it tests as a regular PNP transistor, they join the B and E together to utilize it as a diode.

Glad you got it going, nice job!


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Wed 08, 2017 2:47 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 4382
Location: Indianapolis, IN
Thanks Guys !

Still no time for pics... Didn't mention that the replacement output transistors had much shorter leads and took some "finagalling" to get them installed ! Since the original battery holder was corroded, installed a 9V style battery clip using Teflon wire to mate with a 2+2 "AA" holder which fits fine...

Rocco--didn't even think that junk set had a MA-23, but since it was a Panasonic of same era, looked it over closely anyhow. The part wasn't next to outputs as usual, but on other side of driver transformer and number couldn't be easily read---thank goodness, though, it was there ! I know they are transistors, but without the actual transistor number, would be hard to accurately match and don't know how critical the specs would be and wanted the audio to perform the best it could...

John


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Sun 12, 2017 4:04 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Finally got the "final" pics taken today in the midst of other projects---took a couple along with the T-81 (AM/FM only) for comparison...

This turned out to be a real gem of a radio !

Hope you enjoy them...

John


Attachments:
1ARF T81H FRT LFT TOP.jpg
1ARF T81H FRT LFT TOP.jpg [ 208.03 KiB | Viewed 177 times ]
2ARF T81H FRT RT TOP.jpg
2ARF T81H FRT RT TOP.jpg [ 191.55 KiB | Viewed 177 times ]
3ARF T81H BK.jpg
3ARF T81H BK.jpg [ 166.33 KiB | Viewed 177 times ]
4ARF T81 T81H DIAL VIEWS.jpg
4ARF T81 T81H DIAL VIEWS.jpg [ 183.18 KiB | Viewed 177 times ]
5ARF T81 T81H COMPARE.jpg
5ARF T81 T81H COMPARE.jpg [ 215.7 KiB | Viewed 177 times ]
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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Sun 12, 2017 7:47 pm 
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Location: Mount Pleasant UT 84647 (from Coventry, UK)
Well done John. A good looking pair of radios.

Colin


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Sun 12, 2017 10:50 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Thanks much, Colin !

Well worth the effort on these !

John


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Mon 13, 2017 4:03 am 
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Awesome job as always John.

Mitch


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Mon 13, 2017 9:48 pm 
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Location: Indianapolis, IN
Thanks much, Mitch...

john


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Mon 13, 2017 10:08 pm 
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Location: British Columbia, CANADA
Looks so shinny and clean John, nice work!


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 Post subject: Re: 1964? Panasonic T-81H AM/FM/SW -- latest arrival (nice)
PostPosted: Feb Mon 13, 2017 11:37 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Thanks much, Rocco---am sure glad it turned out well !

John


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