2270 Transistor replacement issues

[camaronut]

Hope to get some clarity here. I know there is plenty of info on this site on replacing the H760 transistor on the 2270 amp boards. So I completed a total recap of the unit and decided to tackle the H760 update. According to a recap list I found on this site I used the listed MJE243GOS-ND transistor. I added wires to each part noting the EBC layout of the part and installed them to the board accordingly. So......I could adjust the DC Offset at each channel at 0mv - no problem. Now when I move the leads between J754 / J756 according to the service bulletin, I can't adjust anything.....its like the outputs were floating all over the place. Adjusting it was impossible. Same on both sides.
So I went back and reinstalled the original transistors and all was well again. I could adjust them both to the suggested 10mvDC. So I kept them in - with hesitation.
So I'm wondering if anyone else has had the same issue and what the corrective action was...
Any help will be appreciated. Thanks!!

 

[bktheking]

Are you adjusting on a dbt or mains?

 

[camaronut]

Are you adjusting on a dbt or mains?

Sorry.....can you clarify...dbt / mains???? I must be having a brain fart!!!

 

[Steven Tate]

He’s wondering if you were testing on a dim bulb tester for protection or if you were plugged into main power. Some people try to adjust on DBT and this can affect the reading. FWIW, I have used the 243G on a 2245 that would not adjust to proper bias and it settled mine down perfectly. But I have seen mixed results in the threads with that part. If your bias diodes are working, count your blessings and keep them.

 

[catrafter]

Doesn't the MJE part have the collector in the middle, TO- 225 package.

Tom

 

[camaronut]

Doesn't the MJE part have the collector in the middle, TO- 225 package.

Tom

View attachment 1118218

Yes it does. Right off the product data sheet.

I went and bought a set of Fairchild KSC2383 - which are supposed to be a direct substitute for the 2SC497 2SC945 2SC984 2SC1211 2SC1213 2SC1364 transistors. I'll try those.
And I was testing straight off the mains.

 

[sregor]

Don't know if this is a factor, but the metal surface on the mje243 should be collector, and may need insulator or insulated hardware.

 

[camaronut]

Don't know if this is a factor, but the metal surface on the mje243 should be collector, and may need insulator or insulated hardware.

Done with mica isolators and plastic screws.

 

[petehall347]

check replacement pin outs with your meter .