Marantz 2265B Preamp transistors

[Vintage Audio Projec]

Don't know if this is in the right section but here it goes:

As I am a lot at home now because of the Covid-19 it's time to do some stuff that is on the "to do" list.
One of those things was to refurbish my marantz 2265B receiver a little bit.
It has the usual intermittent contact problems etc.... normal for something that is 40+ years old. Hasn't been touched as far as I can see (yes it is older then me, got it for free a few years ago).

So I cleaned every switch/pot and replaced al the electrolytic capacitors in the power supply/preamp/phono pre/output amp.
I left the tuner electrolytics in.
I checked DC offset of the output amps and checked the bias. I also cleaned the DC offset and bias trim pots.


Then I used a test transmitter to adjust the RF section. The discriminator Transformer coil was a little bit of, as do some of the RF stages.
Reception is a lot better now

I also replaced al the fuse lamps as they where all gone.


So after this process al of the switches and potmeters work again like they should. Sound is a lot better. Look a lot better also.

There is one thing that remains.
When the receiver is turned on and still cold one channel is down in volume/distorts. Putting some more volume makes it become good again.
I checked the RCA connectors as they have a pre/main output so you can put an equalizer or something different in between the pre and output amplifier.

So after some reading it looks like some of these japanese transistors can go "bad" and develop some weird intermittend problems.
So I was thinking of replacing some of the small transistors on the preamp and at the input of the main amp.

The transistors are:


2SA798 (double PNP transistor)
2SC1345 (NPN)
2SA722 (PNP)

I could maybe do the phono stage as wel:
2SA872 (PNP)
2SC1885 (NPN)
2SA912(PNP)

So most of these are (ofcourse) obsolete.
Any ideas about replacements?
The double PNP is a difficult one.
For the phono input having lower noise is nice but the noise is not a real issue.

 

[rayma]

Instead of just replacing transistors at random, try freeze spray, tapping with a pencil, etc.
At least localize the problem to just one stage of one channel. That should be easy.

 

[PRR]

> channel is down in volume/distorts. Putting some more volume makes it become good

IME, 99 out of 100, that's a bad connection in connector, switch, or joint. I'd even say 999 out of 1,000 (I've done a lot of sound).

And some of those old Japanese transistors are as good as it gets.

I'm not saying it can't be bad inside a transistor, but odds are it isn't.

 

[Vintage Audio Projec]

> channel is down in volume/distorts. Putting some more volume makes it become good

IME, 99 out of 100, that's a bad connection in connector, switch, or joint. I'd even say 999 out of 1,000 (I've done a lot of sound).

And some of those old Japanese transistors are as good as it gets.

I'm not saying it can't be bad inside a transistor, but odds are it isn't.

That was my idea also, before I cleaned everything it had a lot of these problems.
But I keep searching and it's only when it's cold.
When I turn the volume up it suddenly goes away.
After the volume pot there are the pre-main RCA connectors with an inbuild switch. so when you don't use this feature they are automatically connected.
You could say they are normalised like a patch bay.
But I do use them putting a crossover in between to cutoff the sub at around 50Hz and send the sub to another amplifier.

So I tought those RCA's with inbuild switches are the problem, I cleaned them as good as I can.
Maybe I should find some to replace them.

 

[Mooly]

I agree with PRR, the clue is it fixes itself temporarily as you turn up the volume. Look at the speaker output path and check all contacts (headphone socket??) on route to the output terminals.

Is this unit to old to have a speaker relay... they are the number one cause of this issue across all makes and models.

 

[hirscwi]

The 2265 does have a relay. Replacements are still available. These are known failure point.