Thrift store 2270

[goldswimmerb]

Hey guys, so by a stroke of luck I found a 2270 at a thrift store. It seems to be properly biased and the DC output is minimal, however I wanted a second opinion here. I am planning to recap it since the capacitors all appear original, but looking at it these output transistors definitely are not, right?

Should I replace these outputs or are they fine? Im probably not going to do too much to the power amp boards, just a good recap on the tone, preamp, phono and power supply.

More pics just for fun:

The serial number is 82986, is there anything service bullitens wise I need to look for?

 

[Jailtime]

The Motorola SJ are original, the OnSemi MJ aren't. The MJs are good outputs though.

 

[goldswimmerb]

The Motorola SJ are original, the OnSemi MJ aren't. The MJs are good outputs though.

Figured, should I replace the right channel (Motorola) with onsemi? The left side has almost no DC offset while the right has 75mv

 

[gregj]

So what was the price

 

[Rapscallion]

A 2270 at a thrift store? Man you must be living right!

 

[Jailtime]

Figured, should I replace the right channel (Motorola) with onsemi? The left side has almost no DC offset while the right has 75mv

Might as well, good original Motorolas would be hard to find. Replace the differential pair transistors while you're rebuilding the amp boards, will help stabilize the DC offset.

 

[Steven Tate]

Fantastic find! I am curious about those outputs. The most common OnSemi replacements in the 2270 are either MJ21193/94 or MJ21195/96. I notice on the data sheet that the Mj15024/25 has less gain than the others. I wonder if this has a measurable effect on performance.

 

[No1Smitty]

So what was the price

A 2270 at a thrift store? Man you must be living right!

These !

 

[goldswimmerb]

Fantastic find! I am curious about those outputs. The most common OnSemi replacements in the 2270 are either MJ21193/94 or MJ21195/96. I notice on the data sheet that the Mj15024/25 has less gain than the others. I wonder if this has a measurable effect on performance.

The left channel has considerably lower DC offset (since it was likely adjusted after the swap) but sounds much harsher, any ideas why? I noticed with some high notes there was considerable distortion. Not sure if it's caused by the onsemis or dirty controls.

 

[goldswimmerb]

These !

It wasn't super cheap. Cost $300 but came with a WC-22 in pretty great shape.

 

[EastPoint]

Replace all the outputs with either of those MJ sets. It’ll run better and sound better.

 

[goldswimmerb]

Replace all the outputs with either of those MJ sets. It’ll run better and sound better.

I figure as much. Not sure why they'd use a lower gain transistor in the output, makes the high end distort like crazy. I don't even need a scope to tell me that.

 

[goldswimmerb]

Fantastic find! I am curious about those outputs. The most common OnSemi replacements in the 2270 are either MJ21193/94 or MJ21195/96. I notice on the data sheet that the Mj15024/25 has less gain than the others. I wonder if this has a measurable effect on performance.

Are the onsemis a drop in replacement (aside from biasing) and offset?

 

[EastPoint]

Yes.

 

[goldswimmerb]

Finally got around to working on this guy. Replaced all electrolytic caps in both amplifier boards, as well as a few other components. The parts I used are listed below with the mouser numbers as well.

C751: Cornell Dubilier Orange Drop 100v 1uF 598-225P10591YD3

C753: TDK 1000pF 50v C0G 810-FA18C0G1H10200
C754: TDK 470pF 50v C0G 810-FA18C0G1H47100
C759 and C760: Nichicon UKZ 47uf 25v 647-UKZ1E470MPM1TD

C761: Nichicon Muse Bipolar 25v 33uF 647-UES1E330MPM

I also swapped a few resistors and diodes,
H762 and H763 were upgraded to BZV85-C15 T/R Diodes as that was the closest modern part I could find. 771-BZV85-C15T/R

And R757 and R759 were upgraded to 1% metal film types.

I also added two UF4004 diodes as flyback diodes since this unit seems to lack them.

As you can see I'm pretty much following the excellent guide leestereo has done. His servicing was pretty thorough so I don't think I'll deviate too much except for a few boutique parts here and there. Didn't have to touch this one's differential pair as the offset and bias seemed rock solid.

I also swapped both output pairs over to MJ21195/96 since the previous owner had one set as OEM and one as Mj15024/25 with the bias set incorrectly. Will probably keep the transistors handy though in case I come across a unit with bad outputs in the future.

I used that orange drop capacitor just because I have a thing for brightly colored film caps, I don't know why, but I love WIMAs and those orange drops. I think it has to do with the fact you can see them from the vents in the case so you know the amp was serviced.

 

[goldswimmerb]

Just another update, I actually finished this guy a week or so ago, feeling defeated after I goofed on my 2325 so I figured I would go ahead and update my 2270 post. I realized after I finished I did not get completed pictures for every board. Oh well...
Heres what was done on P800 (Power Supply)

S1B-01-02 diodes in H801, H803 and H811-H813 positions were upgraded to UF4005 soft recover type diodes. Mouser No: 512-UF4005
C801, the main filter here was upgraded to a Nichicon UPW 1000uf/63v 105C rated capacitor. Mouser No: 647-UPW1J102MHD
C802 and C804 were upgraded to 680uF/63V Nichicon UPW capacitors, 105C rating sees to be a must here since the original caps plastic coat had shrunk. Mouser No: 647-UPW1J681MHD
C805 was upped to a 10uf 50V UPW type, Mouser No: 647-UPW1H100MDD
C803 was also visibly fatigued, likely due to its proximity to hot components. It was upgraded to a 470uf/35V UPW, Mouser No: 647-UPW1V471MPD
C806, 807 and 808 are all part of the relay circuit, they were all replaced with UPW types as well since the PSU is generally toasty.
C806: 22uf/50V - 647-UPW1H220MDD
C807: 220uF/35v - 647-UPW1V221MPD
C808: 47uf/25v - 647-UPW1E470MDD

And the notoriously hot R801 (I think?) was replaced with a TT Electronics 150Ώ/7W Mouser 756-W22-150RJI. This was definitely a later model since R801 was actually on my PSU board rather than chassis mounted.

I replaced the relay with an OMRON MY2-DC24 since the old relays always like to put up a fight.
Unfortunately only have a before picture for this board.
Ill try to keep updating this post as I find motivation...