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Re: Reliability of electronics

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On 31/05/2022 10:59 am, Phil Allison wrote:
> Trevor Wilson wrote:
>> =================
>>> Designed in 1963, it used, unusual for the time,
>>>> full complementary symmetry outputs. Unfortunately, the Voltage rating
>>>> on the output devices was marginal.
>>>>
>>>
>>> ** The model 500 dates from 1973.
>>
>>> Each channel used 8 x TO3 transistors with SJ prefixes ( SJ2404 and 2405)
>>> So specially selected types made by Motorola.
>>>
>>> https://www.hifiengine.com/manual_library/marantz/500.shtml
>>>
>>> Rated power was 250W at 8ohms, so 8 devices should be plenty.
>>> Weight was 83 pounds - which is absurd.
> 
>> **If you've downloaded the service manual, you can see the complexity of
>> the beast. SOA adjustments are very comprehensive. The fault with the
>> amp lay with the VCEO of the output devices. There was very little
>> margin for mains fluctuations.
> 
> **  That assertion makes no sense.
>   Facts:
>   1.  Output transistors do not operate in Vceo mode.
>   2.  They are only exposed to * half* the DC supply at idle or moderate volumes.
>    
> 
>> Marantz finally solved the problem by
>> specifying 200 Volt, Japanese output devices, rather than the Motorola
>> ones originally fitted.
> 
> ** MJ numbered power BJTs all exceed their Vceo ratings on test.
>     They way exceeded the ( higher) Vcer rating too - as it almost matches the Vcb rating.
> 
>     SJ numbers have no published ratings.

**Correct. All the US built Marantz models used Motorola devices with an 
SJ prefix. Even some of the early Japanese ones used Motorolas as well. 
Very unusual. I measured a few back in the day. As I recall none of the 
Model 500 output devices exceeded 160 Volts. I may still have a few 
originals lying around. If I locate them, I'll measure the breakdown 
Voltages. Don't forget: It was 1973. High voltage, high power PNP 
devices were very scarce.

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Thread

Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-30 17:24 +1000
  Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-30 19:33 +1000
  Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 16:01 -0700
    Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 10:35 +1000
      Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 17:59 -0700
        Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 11:31 +1000
          Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 18:52 -0700
            Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 12:00 +1000
              Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 20:03 -0700
                Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 13:45 +1000
                Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 21:02 -0700
                Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 14:05 +1000
                Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 14:08 +1000
                Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 14:18 +1000
                Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 21:32 -0700
                Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 21:26 -0700

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