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Old 16th October 2002, 08:47 AM   #1
up4 is offline up4
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Default the unstable sound from tube pre-amp !

hello everyone...
have anyone suffered unstable sound coming from the tube pre-amp whenever you turned on it ?

I know somebody might say it's "procedure problem", turn on the tube pre-amp and then the power-amp.

isn't there any other solution to get rid of the irritating unstable current sound ?

usually I have to wait 20~ 30 secs to turn on my power-amp...
otherwise....

the sound is like killing a poor chicken ...
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Old 17th October 2002, 08:30 AM   #2
SHiFTY is offline SHiFTY  New Zealand
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You might have some sort of oscillation? Hmmm...

Tubes do take a while to warm up (longer than I thought!)

Otherwise... arrange a relay delay switch?

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Old 17th October 2002, 08:41 AM   #3
up4 is offline up4
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not really oscillation...
I tested it with oscilloscope... it's ok...
well...it at least take 10 sec to be stable....
I think I'll get a delay circuit .... since I always forgot turn on my tube pre-amp first... @@

Quote:
Originally posted by ShiFtY
You might have some sort of oscillation? Hmmm...

Tubes do take a while to warm up (longer than I thought!)

Otherwise... arrange a relay delay switch?

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Old 18th October 2002, 05:18 PM   #4
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Actually.. it is an oscillation.. of the power supply. It may not show in the scope. Perhaps adding some filter to the B+? Or maybe a bad filter?

If that doesn't help then swap out the tubes (do this one first. Easier). I have heard tubes do that. Generally I hear it in the 1 -3 volt tubes in my battery radios.

My 2 cents,
Gabe
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Old 18th October 2002, 06:27 PM   #5
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Are you using a solid state power amp?
If so this warm up instability is normal. You may want to try fitting a timer delay until your valves have reached their operating temp.
It sounds like your diong the right thing by delaying the turn on of your power amp.
Phil.
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Old 18th October 2002, 06:51 PM   #6
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Phil,

Why?

If the inpedance of the power amp is low, while the output impedance is high, this might make sense.

But output impedances of any good preamp should either be universal (low) or adjustable/switchable, if not two separate outputs.

Why?

Thanks,
Gabe
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Old 19th October 2002, 06:25 PM   #7
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Hi Gabe

I just presumed that this is what may be happening here.

By the way Gabe I allways look for your interesting posts.
Great web site too, learned a lot from it. Thanks, keep it up.

Phil.
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Old 21st October 2002, 05:57 AM   #8
richt is offline richt  Puerto Rico
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salute folks

i have a tube pre & power and i suffered a lot of wierd sound
and coloration.

i installed a variac in my system (power & pre).
my stand by mode is 60 v & play mode 117v.

tubes dosnt like to be turned on & off.
plates suffers from temperatue changes.

i am a lot happier with my system & sound more even every
time that i hear music. ( i dont have to suffer the 2 hr wamup)

i hope this info can help!

thanks
richt
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Old 21st October 2002, 09:02 AM   #9
up4 is offline up4
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hi hi ...

sorry... but what is "variac" ???

variable capacitor ???

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Old 21st October 2002, 02:28 PM   #10
richt is offline richt  Puerto Rico
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hi

variac means variable ac voltage.
it is a big rehostat that you can control the voltage from
0 to 120 vac. (it is some kind of dimmer for lamp but wirewound
fot technical use on repair shops)

this is great when you use black gate caps (very epensive)
& expensive tubes on your amp and you apply 117 vac
slowly to make some sort of "soft start"


thanks
richt
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