Motorola (?) RingEmitterTransistor MN25 / MP 25

[Bernhard]

Hi,

any information about those transistors or substitutes Sanken (?)
Seem to have been used in Pioneer M25 amp.

[jacco vermeulen]

Not likely.

MN25 was a TO3 germanium transistor made by Motorola.
MP25 a Russian made TO5 device (ELORG= elektron org. teknika in Moscow)
MN25 and MP25 were probably the internal Pioneer device numbers, M25 NPN and M25 PNP.
Only ones producing ringemitters were Toshiba and Sanken, production of high power ringemitter transistors started before Pioneer started production of the M25 in '79.
Later production Toshiba ringemitters had the identical MT200 casing and color as Sanken devices.

Pioneer produced the open-style chassis 30 watt class A M22 end of the 70s, followed-up by the partial class A M25.
Both looked practically identical, seen quite a few of these machines in France.

www.visi.com/~jweeks/stuff/pioneer/#series20

[Bernhard]

Thanks,

the matter is, if I get a broken M25 and need to replace output RETs, is there a possibility to get those or use Toshibas or Sankens ?

[jacco vermeulen]

The ringemitter devices used in the M25 and A27 integrated amplifier were TO3 models.
Fat chance that you can find those, MT200 Sanken's will have to do.
Means redrilling the sinks with the MT200 pattern.

[jacco vermeulen]

Here is a picture of the output section of the A-27 integrated amplifier model (found it on a Pioneer series homepage somewhere)
2 NPN and 2 PNP TO3's per channel.
Supposedly the A-27 used the same devices as the M25 did, and much of the circuit concepts of the M25 and C21 preamplifier.
Pioneer used the big casing Sanken multi-emitter devices in the later M series power amplifiers.

[jacco vermeulen]

Later model multi-emitter devices

[jacco vermeulen]

revised casing Toshiba ret's

[Bernhard]

Thanks, so I have to look for a A27.

Your first picture does not load completely.

[jacco vermeulen]

found the homepage i got the picture from again:
http://www.silverpioneer.netfirms.com/a27_amplifier.htm

These amplifiers have collectors value, and you would probably need 2 of the A-27 amplifiers to have enough output devices to repair an M25.
Fixing an M25 with modern Sanken devices will not keep the amplifier original, but a lot easier and big Sankens are very rugged.

The M model is a lovely design, wouldn't mind having one myself.

[Bernhard]

Just got the amp and - huh - all output transistors measure around 0,5 V from case to one pin and another 0,5 V between pins with diode tester.