Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > aus.electronics > #35552

Re: Reliability of electronics

Show all headers | View raw

On 31/05/2022 11:52 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.
> 
> ** 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.

Back to aus.electronics | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web