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 Post subject: Re: ITT 6409A ---very unique radio !
PostPosted: Dec Mon 04, 2017 3:21 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5281
Location: Indianapolis, IN
Well, the suspense got to me and decided to look at that audio output transistor (X9 in schematic) before "hitting the hay"... Applied power, then connected voltmeter to ground and touched positive probe to X9 case---measured 6V !!! Checked rest of transistors and only one other, X7 (audio driver) had a very slight indication on meter. TIN WHISKERS !!! And didn't think they were a problem with quality Japanese transistors ! Removed power and measured resistance from each lead to case on X9---appeared that the "leakage" was to the base element and you could watch the needle fluctuate as though the transistor had a life of its own !

Mystery solved... Now on to replacement...

BTW---didn't mention it before, but the control thumb-wheels are recessed enough into front panel that they don't make contact with surface when radio face down. And they are accessible from back side so you can operate radio while servicing---wonder if the engineers realized this benefit from their design ???

John


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 Post subject: Re: ITT 6409A ---very unique radio !
PostPosted: Dec Sun 31, 2017 8:35 pm 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5281
Location: Indianapolis, IN
Almost a month, but finally replaced the audio output transistors !

Had a good matched pair of same type (2SB176) removed from a junked Panasonic pocket set that I was saving for another project before getting this radio and decided this set was well worth receiving them.

Radio sounds excellent now with plenty of stable clean, audio ! And as mentioned earlier, performance is outstanding across entire band with a low noise level between stations. An excellent set...

Did forget to install those B-C caps I was considering---wonder how much difference they'd make ???

John


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