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Lost 9090 Left Channel Last Week -Fixed!

T

TubeRelic

AK Member
FYI. Problem occurred after playing several hours FM rock station at fairly high volume - 8 - 10 watts. Traced problem to left channel BA312 pre-amp IC on F2544 tone board. This post is to inform this Sansui forum that NTE1433 was found to be a great straight-up replacement for the BA312.

Interesting findings: 1) repaired left channel now plays at 30% - 40% higher volume level according to the output power meter; 2) voice and music sound crisper and cleaner on left channel versus the right side.

As far as getting this '1st ever IC replacement' repair done, I did a little TYDG (Thank you Dear God) this afternoon. Never hurts and makes me feel good to do it. And I'm happier than a hog in a wallow.

Question: should I tweak the pots on the protection board to even out the power meters ? Or just leave it alone for a while to see what may develop... And/or should I go to the extent of replacing the other BA312's (5 or so on 9090 and 5 on 9090DB) before I get too crotchety to do this sort of thing ?
 
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Normally do not use NTE, ECG, RCA replacements, but I have had excellent results with NTE replacement for 3SK45 DG MOSFETS. If it was my 9090 and I got the results you've described with the NTE part, I would buy and install for the R-Chan for a matched set.

I wish I could get an OpAmp upgrade PC board for the BA312 as good as the one I have for the TA7136 I use for SX-750 and other restorations. Upgrading opamps can really make a huge difference if applied properly. I plan on upgrading all 4 opamps in a Kenwood KR-6400 restoration which uses 4558s. If anyone has an opamp upgrade for the BA312 *PLEASE CONTACT ME*!!!!!
 
TI Mentions 4558 In Upgrade List

Does TI (Texas Instruments) make acceptable opamp upgrades? Your 4558 -or at least it contains that numerical designation - is listed as being upgradeable w/ OPA2209. Supposedly quieter, lower quiescent current, greater bandwidth - what's not to like?

Unfortunately for BA312 holders, 7 pin packages seem to be slowly or entirely disappearing except for the NTE1433.

The link here about TI upgrading has another link to a bread boarding hints and tips page. BB a circuit or two of your own design using some of the really neat high quality pre-amp op amps out there and I'll bet you come up with something great.

http://e2e.ti.com/support/amplifier...gn_notes/upgrading-op-amps-in-audio-equipment

Thanks for yr suggestion to install matched pair of 1433's. I tested the addl units I got in mail as far as I cd w/o actually installing, and all seem to test about the same. Tested 3 pins at a time using a component analysis device I bought off Ebay a few months ago under $20. I plan to follow your advice and install the two that match the closest.
 
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