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Old 3rd March 2003, 10:59 PM   #21
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Default CES BELGES QUAND-MEME.

Hi,

Quote:
My damned amp
I stand with EC8010 in that I doubt very much that this amp was intended for hi-fi use.

Foes,

You're only 15' away from where I live..Landen...if you want I can take a look at it.

BTW,decreasing the feedback will only make matters worse. As Jorge suggests, either put the volctrl at the front or junk it alltogether.

Cheers,
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Old 4th March 2003, 04:36 AM   #22
Foes is offline Foes  Belgium
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EC 8010, I hate you (i joke), you are not very sympathetic with my poor amplifier. Well, i will avoid to show you the internal design.
I Will first try to follow Jorges advices. Thanks Jorge.
I like this forum.
But... anyway exept this feedpot in the feedbak why does it seems so old fashioned ?
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Old 4th March 2003, 10:10 AM   #23
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Default Is the amp old fashioned?

Well...

The valve choice for one thing. Even if you can use EL84s instead of EL41s why were these latter valves even considered in the first place? They were being replaced by EL84s in commercial equipment by the mid to late 1950s at best. This EM80 is also an old choice - the EM81 with the better display was being used in valve tape recorders in preference to EM80s by the 1960s. Incidentally, the option of using EL90s in the output is a bit strange - it is not a direct equivalent of the EL41/EL84 series (it has similar characteristics to the 6V6/6BW6 series) and to use it without alterations to the bias in the output stage is a bit naughty. Ideally, the whole circuit should be looked at if you use different output valves as the difference in HT consumption would alter the overall HT voltage and thus affect the working conditions of the other valves.

Other issues...probably a newer hifi amp would use ultra-linear or triode operation in the output stage for greater fidelity rather than normal loading. Some use of direct coupling to reduce phase shift and enable greater feedback maybe?
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Old 4th March 2003, 02:34 PM   #24
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Hi Bournville!

In your first post in this tread you say that maybe the inclusion of the pot inside the feedback loop it is a designer option!

For me a design option is the type of tubes ,to use triode ,ultralinear or straight pentode loading...in this case everyone can have diferent choice no one is wrong.

In the case of the pot even if it was a choice...its tottaly wrong...a fatal mistake...sorry!

regards

Jorge Santos

PS: By the way my prefered output stage configuration is straigt pentod! i'm not a fashion folower!
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Old 4th March 2003, 03:27 PM   #25
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Default STRANGE AMP.

Hi,

Could it be one of these?

SPARKAUDIO

Cheers,
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Old 4th March 2003, 07:10 PM   #26
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Jorge,

I agree with EC8010 and fdegrove that the amp was probably not designed for hifi audio work but perhaps for guitar, PA or some other purpose. If this is the case, the output transformer may not be of good enough quality for the reproduction of the frequency range normally associated with hifi jobs, but still improvements might be able to be made.

I agree with you about removing the pot, R5 (470k) will be providing the grid bias, and the pot could go at the input of the amp. However, I agree with fdegrove that Foes should not reduce the feedback, but instead perhaps increase it to help improve linearity and reduce distortion.

You may not be able to increase it much, as the amp was not designed to take large amounts of feedback, but likewise if you reduce it you might find hum and potential instability become problems.
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Old 4th March 2003, 07:26 PM   #27
Joel is offline Joel  United States
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Quote:
Originally posted by bournville
...R5 (470k) will be providing the grid bias...
No, it isn't. The cathode resistor is providing the bias. There is no voltage drop across R5.
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Old 4th March 2003, 07:28 PM   #28
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Sorry,

I meant to say grid leak...
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Old 4th March 2003, 08:23 PM   #29
Foes is offline Foes  Belgium
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Hi !
This is the link to te website of dared whitch develop all these new concepts in hifi...

http://www.daredtube.com/
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Old 4th March 2003, 09:43 PM   #30
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Default The Amp that come from Est!

Hi Bournville

I admit that the choice of tubes maybe a little esoteric

But with the pot at the input this amp will became similar to the Jolida 302.

I don't know why you think that this was amp is for PA or instruments!

Regards

Jorge Santos
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