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Old 24th November 2004, 11:23 AM   #1
GeirW is offline GeirW  Norway
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Default Distortion+low volume..

Gday.

I recently read a article about the effect faulty tubes can have,
(can`t remember where, or how serious the article was.)
my problem is related to this one:
http://www.diyaudio.com/forums/showt...596#post509596
The volume pot does very little from 1-50%
but from 50-100% it`s realy takes off, and around 65% the sound
beggins to distort very heavy.
(In the beginning i thought this could be related to
a. the former owner haven`t used it at full,
and that it could possibly be "burned inn".**
or b. there is wrong ohm out/wrong ohm load at the speakers)
(** it have, at a certain ratio)

The article pointed out, if there was faulty tubes
(in the powerstage), it could show symtoms like this.
To try pinnpoint the problem, it was adviced to change
place of the tubes or replace.
I did change place of the two el84,
and the result was crispyer hight`s, the volume pot did function
better at 1-50%, but the distortion began at 55% turn.

(ps. Am not sure about this, since it`s not function.
to my knowledge, all tanberg products, (atleast tube)
do have a knob for adjusting overall gain.
this is using the same pot as volume, (2 deck)
can that have something to do with it.?))
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Old 24th November 2004, 11:49 AM   #2
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The output tubes may have low emission due to their age.
I'd replace them with new tubes.
Is the volume control original? It may have been replaced with a higher value, causing the output level to be too low when the control is below the 50-60% position.
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Old 24th November 2004, 12:26 PM   #3
SY is offline SY  United States
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One more thing to check- if the volume control is not original, make sure that the replacement isn't a linear taper.
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Old 24th November 2004, 01:09 PM   #4
GeirW is offline GeirW  Norway
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Gday.

Will have to ivestigate that.. it looks to me that it have been
replaced.
TnX. for your answers.
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Old 25th November 2004, 05:28 AM   #5
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Quote:
- if the volume control is not original, make sure that the replacement isn't a linear taper
Wouldn't that have the opposite effect - i.e. too sensitive at lower settings?
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Old 25th November 2004, 01:04 PM   #6
GeirW is offline GeirW  Norway
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Gday.

After looking at the schematic for it, it turns out that
it is one el84 pr.channel. (strange arrangement
if you look at the schematic and the signal out
is infact true stereo on one out.)
The "changing tube" thing i tried
and the diff, turned out to be "gas" = one faulty 84.
So wrong "pot/values" seems more to be the case.

btw: Am attach the amp. part of the radio.
It seems like in time, the pot is wired to one.
(i like it like this, but i assume it`s then to small values,
1 mono pot. wired for stereo.)
(on the shematic each channel have there own volume)
I reckon he have done the same with the out`s.

ps. if you miss anything from the pic. give a shout.
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