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Re: Reliability of electronics

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On 31/05/2022 1:03 pm, Phil Allison wrote:
> Trevor Wilson wrote:
> =================
>>>>>
>>>>> 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.
>>>
>>> ** Measured with open base ? Not how they are used.
>>>
>>>> I may still have a few originals lying around.
>>>> If I locate them, I'll measure the breakdown
>>>> Voltages.
>>>
>>> ** If you do, put 100ohms between B and E.
>>> Makes at least a 10% increase .
>>
>> **Will do.
>>>
>>>> Don't forget: It was 1973. High voltage, high power PNP
>>>> devices were very scarce.
>>>
>>> ** SJ types were factory selected from stock, mostly for Vbe matching.
>>> Crown, SAE and Peavey used them all the time.
>>>
>>> Total PITA for repairers, who had zero clue what the types really were.
>>
>> **Yep.
>>>
>>> BTW
>>>
>>> if the Marantz SJs lacked adequate Vce, examples would have commonly failed bench testing.
>>> So I don't buy the idea.
>>
>> **Point taken. When the Japanese devices were installed, the Model 500
>> became reasonably reliable. If I recall correctly, most amps failed at
>> switch on, rather than under use. I could be wrong.
> 
> 
> **  I once used to see a lot of Phase Linear 400 mk2 amps.
>      A revised version of the famous PL400 hi-fi model.
>      Complementary MJ output devices and input op-amps on the pcb.
>     These were all used in PA systems - not a good idea.
> 
>     Saw a lot of blown output stages and many that simply went DC taking speakers with them.
>     Nothing to do with Vce or even SAO limits.
> 
> The first problem was due to overheating of output devices - since owners had to devise fan cool themselves.
> The installed temp cut out was useless, since all TO3s were mounted using thick, pink silicone thermal pads.
> I called the "thermal insulators" as they allowed devices to get 50 C hotter than when mica and grease was used.
> 
> Going DC was due to 5W ww resistors that fed +/- 16V zener regulated rails for the op-amps.
> The resistors were all faulty,  going bright green inside and hence open cct.
> 
>   Did a nice trade in fitting relay speaker protectors in many power amps.
> ( wired the RIGHT way so DC arcs were eliminated)
> 

**Good plan. FWIW: The Model 500 never overheated. Thermostat 
controlled, two speed fan cooled. Output devices were all mica/thermal 
paste mounted. Even after repair (using original output devices) the 
amps failed. Only after the output devices were substituted with 
Japanese types did reliability significantly improve. The amp could run 
all day at 40% max power. Easy. Even into 4 Ohm loads.

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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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