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Old 17th February 2012, 02:39 PM   #1
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Default Rectifier tube change ... procedure?

TSE sounding extremely good, but some buzz from both speakers when B+ comes up - the buzz disappears completely after an hour or two playing. Filament noise?

About to try a new rectifier tube (JJ instead of Sovtek). I have ammeters wired in so I can watch the bias, however do I need to turn the trimmers down before installing the new rectifier?

And do I need to recheck my B+?
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Old 17th February 2012, 03:04 PM   #2
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I think that electrolytic caps are old or bad. Try shunting with another of equal or bigger voltage and capacitance than original. Be careful with high voltages inside the set!!!
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Last edited by Osvaldo de Banfield; 17th February 2012 at 03:12 PM.
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Old 17th February 2012, 03:56 PM   #3
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How many hours do you have on the rectifier and the amp? If it is relatively new, you shouldn't need to make any major adjustments. It's worth verifying the bias anyway.
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Old 17th February 2012, 04:10 PM   #4
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Quote:
Originally Posted by rknize View Post
How many hours do you have on the rectifier and the amp? If it is relatively new, you shouldn't need to make any major adjustments. It's worth verifying the bias anyway.
@ Russ. Maybe 100 hours. I can see the bias continually anyway, so will just change the tube and watch carefully.

@ Osvaldo. This is a new build, and still breadboarded so yes I am being careful with the high voltages! I guess if the tube change makes no difference, I will have to start thinking about the caps, however I really need to get on with the casework - and lay out all the wiring/grounds properly before I declare the buzz due to a faulty component.

I blew the pretty little blue LEDs in the ammeters by my ignorance (didn't know they couldn't be wired in parallel and that LEDs don't obey ohm's law.) Noob, but learning.
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Old 22nd February 2012, 11:55 PM   #5
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Alan:
My TSE also buzzes. I minimized it with a parallel motor run cap at C5. The buzzing I think is intrinsic at this point but noticeable to me because my 2-way speakers are BMS-4592 on a tractrix horns (~108 dB?) over JBL 2226's at (97 dB?). Altogether I attribute my situation to higher than usual speaker sensitivity which you might consider, too.
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Old 23rd February 2012, 12:41 PM   #6
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Thanks CD,

I have already installed a motor-run cap - no improvement. Speakers 96-97dB.
Curious thing is, the buzzing becomes inaudible after the amp has been on for about 1.5 hours. Turn it off for a while, and on again, and the buzz comes back.

Just to quantify this, it is audible at listening position, inaudible with almost all music, though just possible to hear during very quiet passages.

Rolled three rectifier tubes: no change.

The circuit is currently sprawled out on a breadboard, so I really need to case it properly before chasing this.

My previous SET initially had grounding issues causing hum, there were a few folk on the Decware forums chasing this, and finally one guy found the fix which was a supplementary large-gauge wire from the pot-ground to input-ground in parallel with the trace already present on the PCB.

Alan
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Old 23rd February 2012, 01:57 PM   #7
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Could this be a mechanical buzz? I know if I get close enough to my SSE, I can here the power transformer buzz. If I then clamp the bells between my fingers it will go away.

Maybe after the transformer heats up from operating, the slight thermal expansion is enough to dampen the vibrations?

Just a thought
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Old 23rd February 2012, 02:13 PM   #8
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Definitely through the speakers, transformer is quiet.
It kicks in as B+ comes up.
I'm puzzled, because it seems a very long time to be a component warm-up phenomenon.
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Old 23rd February 2012, 03:28 PM   #9
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Do you have a scope? How about cooling spray (or an upside-down can of dust spray)? It would be interesting if the temperature-related part has to do with the FETs or even the filament supply to the 45s. It has to be something solid state for the buzzing to go away over the course of an hour. I assume that both channels are affected the same?
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Old 23rd February 2012, 05:37 PM   #10
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Thanks for the input guys. I don't have a scope - but this is 50hz (UK mains).
I am probably trying to be too clever here with the warm-up stuff, the appearance of the buzz is consistent, but it doesn't always disappear (it is still there now after about 4 hours playing). My money is on mains interference from who knows where.

Both speakers are affected equally, and when it disappears both channels are clean.

I will ignore it for now and build the case, getting grounding properly sorted, then see where I am.

Will report back here ...

Alan
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