SSE left channel dead.... - diyAudio
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Old 24th February 2010, 02:17 AM   #1
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Default SSE left channel dead....

Didn't really expect any problems with my recently finished SSE (KT88Triode), but this one has got me stumped. I have no output from the left channel. The right channel plays loud and clear.

This is what I have done so far for troubleshooting:

1. Measured: B+ @424, Plate @ V21=418v, R27=40v, R20=1.76v
2. RCA inputs and speaker terminals are correctly wired with no shorts or opens. Audio source (CD player) has L & R signals.
3. Tested both Hammond 125 ESE OPT's on right (T2-PRI) channel, and both work. Neither one will work on the left (T3-PRI) channel.
4. Exchanged KT88's l-r. r-l; no change. Both tubes are known to be good.
5. 12AT7 is NOS Phillips. I have no tube tester, but both sides light. I assumed finding 1.76v at R20 means things are ok on the front end. I don't know how to run any other tests on the CCS.
6. All resistors and capacitors are spec'd value and installed correctly.
7. All joints on PCB checked, especially around V21.
8. The circuit is basic triode connected; no UL, no NFB, no volume control, no extra switches, wiring etc. Grounding as per schematic. Have aux. motor run cap and Triad choke.

What have I missed? This is not my first tube project and I expected it to work right off. At least it didn't smoke or make funny noises or blow up!

I searched the archives, and other builder's problems were more basic than this one appears to be. So I'm sending out my SOS to the experts, and thanking you for any help.


Right channel only (for now)....
"The Cat"
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Old 24th February 2010, 03:17 AM   #2
rknize is offline rknize  United States
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1.76V is about right. I would say it is most likely that you have a short at the RCA jack or at the speaker terminal. When you swapped OPTs, did you leave them on their respective speaker jacks? If so, then you can rule that out. What happens when you measure the resistance at the RCA jacks (with the amp off)? Another possible spot for a short is at or near R25/R26.
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Old 24th February 2010, 03:35 AM   #3
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Quote:
Originally Posted by rknize View Post
1.76V is about right. I would say it is most likely that you have a short at the RCA jack or at the speaker terminal. When you swapped OPTs, did you leave them on their respective speaker jacks? If so, then you can rule that out. What happens when you measure the resistance at the RCA jacks (with the amp off)? Another possible spot for a short is at or near R25/R26.
Russ,
Thanks for the reply.
Triple checked the RCA's. They are insulated from the chassis and have the outer shells going to ground on board. The "hot" sides are not shorted or open. Each RCA measures 220K to ground. Speaker jacks have also been checked and rechecked. Nothing wrong with them. R25/26 check out ok.
Frustrating!
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Old 24th February 2010, 05:45 AM   #4
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You said you checked the tube pin solder joints. Did you measure the resistance from the socket pin to the relevant components on the PCB? Sometimes a cold solder joint is not very obvious.

One user a while back had a really weird issue with the coupling caps. I can't quite remember the details, but he sent the board back to George and he found the issue. I think the wires were too large for the holes, or something like that, and the solder joint wasn't complete through the PCB.

Do you own a scope? It would be a easier to find the issue that way.
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Old 24th February 2010, 05:53 AM   #5
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Russ,

Bingo!!
I resoldered every pin on V21 and now have two channels!!
Nothing "looked" bad at all, but who knows.
Thanks for burning the midnight oil with me. The little amp sounds great.

Regards,
"The Cat"
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Old 24th February 2010, 07:33 AM   #6
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Glad to hear it was a simple fix!
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Old 27th April 2010, 01:18 AM   #7
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Default mine too

SSE completed this past Saturday. Pretty much stock parts list. Iron - 6K7VG and Edcor XSE15-8-5K OPT's Had a day and a half of glorious listening. Spent all day at work today looking forward to more. Come home, power up, no left channel. No sparks. No smoke. No noise. Just silence. Swap in known good power tubes, no joy.

One clue. On power up a couple of times yesterday, a low "scratching" noise could be heard, on both channels (I think), for a few seconds. Then everything was nominal.

Bad 12AT7 tube?
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Old 27th April 2010, 01:31 AM   #8
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Could be the 'AT7,or perhaps a crummy solder joint. The solder joints between the sockets and board might get stressed a bit from thermal cycling,re-flowing them is worth a shot.
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Old 27th April 2010, 02:15 AM   #9
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Quote:
Originally Posted by DigitalJunkie View Post
Could be the 'AT7,or perhaps a crummy solder joint. The solder joints between the sockets and board might get stressed a bit from thermal cycling,re-flowing them is worth a shot.
Way ahead of you.
Even though I never make cold joints , I went ahead and reworked all the left channel stuff.
Still no joy.

Anyway, ordered a replacement 12AT7 (and a spare). While I wait, anything else I can do to narrow down the list of suspects?

Thanks in advance.
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Old 27th April 2010, 03:14 AM   #10
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DIY Rule #1: Connections! Connections! It's the connection 90% of the time.

Check all the terminal strips for tightness and full insertion of the leads.
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