Yamaha A1 restoration 2021

[Hifibythekg]

TR137,138 have KSC2383 rotated so that curved side is against the big heat sinks.
Output transistors were also replaced and now have MJ21193/4G on both channels.

 

[avionic]

Yes.
TR 139,140 have KSA1013

What were the original transistors ?

 

[avionic]

TR137,138 have KSC2383

What were the originals.

 

[Hifibythekg]

Sanken 2SA 747A and 2SC1116

 

[Hifibythekg]

Just checking

 

[Hifibythekg]

TR137/8 were C1213
TR 139/140 were A708

 

[Hifibythekg]

Can’t be sure whether the TR 139/140 A708 transistors were original though.

 

[Hifibythekg]

For what it’s worth, some readings of the originals by a cheap transistor tester.
Originals:
c1213
uF680 and b121
uF675 and b142

a708
uF623 and b218
uF657 and b172

Was having problems adjusting Idling Current hence their removal. However, lots of components have since been replaced.

 

[Hifibythekg]

Good morning, especially to @avionic !

Have just checked my records and have seen that the KSC2383 that I put into the board at TR137 and TR138 was an 'O' not a 'Y.' You had recommended 'Y.'
Can see that hFE is a different classification.
Datasheet shows:
'O' 100-200
'Y' 160 - 320
Do you think that this is the very likely cause for the inability to adjust Idling Current above 3.1mV ?

KSA1013 at TR139 and TR140 is a 'Y' designation, so just leave it in place?

Any other suggestions, or just order and install the two of KSC2383YTA ?

 

[Hifibythekg]

Received my KSC 2383Y transistors.
Which two should I install at location TR 137 and TR138?
They measure:

1.
hFE 272
uF 620

2
hFE 217
uF 617

3
hFE 217
uF 622

4
hFE 272
uF 616

5
hFE 272
uF 617

 

[Hifibythekg]

Original C1213A measured

hFE 121
uF 680

hFE 142
uF 675

 

[Hifibythekg]

Ksc2383 ‘O‘ replacements, and with which idling current adjustments still had issues, measured:

hFE 166
uF 631

hFE 166
uF 627

 

[avionic]

TR137 and TR138 was an 'O' not a 'Y.' You had recommended 'Y.'

Not really relevant for this part of the amplifier circuit.

 

[Hifibythekg]

Thanks Avionic, yes, I guess the VR’s deal with this?
Should I try the higher or lower pair first? There’s a difference of 50 hFE...
FWIW the, possibly original, 2SC1213A transistors measured:
hFE: 121
uF: 680

hFE: 142
uF: 675

 

[Hifibythekg]

Just to recap, no pun intended, TC004’s are now in the Drive board, OT’s are now MJ21193/4G, and TR 139/140 are the KSA1013YTA.

 

[mbz]

Should I try the higher or lower pair first? There’s a difference of 50 hFE...

as above, hfe is not relevent so go with any in post #410

 

[Hifibythekg]

Cheers, appreciated.

 

[avionic]

Thanks Avionic, yes, I guess the VR’s deal with this?
Should I try the higher or lower pair first? There’s a difference of 50 hFE...
FWIW the, possibly original, 2SC1213A transistors measured:
hFE: 121
uF: 680

hFE: 142
uF: 675

Doesn't matter.... Put the original transistors back in..

 

[Hifibythekg]

Thanks for the advice.
Any test I can do prior to replacement to ensure that they don’t have issues after working next to those heat sinks for 40 years?
After all the ‘false dawns’ of thinking I’ve finished this repair I’m becoming increasingly risk averse..

 

[Hifibythekg]

A-1 has been playing music loudly and beautifully for a couple of days but .... eek!

Just had a random burst of ‘static-ish’ sound through the left speaker of my main sound system. Can’t risk these huge vintage speakers for a minute so have disconnected the amp.

What’s the most likely culprit?

The sound was like two pieces of soft cardboard being scraped but amplified.