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Old 29th June 2003, 04:50 PM   #1
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Default Amp with 300B and ECC99 - your opinion?

Please express your opinion about my design.

Chris

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Old 29th June 2003, 10:34 PM   #2
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Hi Chris,

If you don't mind, there are a few details that seem rather odd to me.

Keep in mind I didn't do any math on your design, just hunches...you know the kind of things that jump at you when you're used to look at circuit diagrams.

So here goes:

- The filter chokes seem low in value.

-I'd feel happier if you could fit some 500VDC caps for the B+ iso
the series arrangement.

- The filter caps in the heater supply seem extremely low.

On a more "tweaker" level:

-I'd up the first coupling cap to 0.47uF and the second to 0.68uF.

-I'd put some extra bypass caps in // with the 10uF Mundorfs,
even thinking of tripling their value in the process. (the Mundorfs
may not need bypassing)

- I'd increase the filtering, reservoir caps substantially.
in the B+ supply.

-If money no object I'd even endow the ECC99 with a dedicated
regulated B+.

-And have a dedicated supply for the heaters of the ECC99 and
300B, the ECC99 needs 6.3V and the 300B 5V so I reckon the
heater supply drawing isn't quite finnished?

-You can probably drop or lower the value of the gridstopper
resitor on the second half of the ECC99 and use the 1K on the
300B instead. If you have a scope you may find the exact value
for the job.

-I see you use a ripple cancelling technique on the output which
is fine if implementig correctly, again a scope will help to fine
tune the values of the caps.

-The 100K volpot, if yor aiming for a high-end design get the best
you can do there as well, I personally like stepped attenuators
with a constant impedance.Particularly in that position.

Passive component choice is a matter of personal preference, I like as honest to source as I can come best but YMMV.

If you like what this amp does I heartily recommend the Loftin-White for an SE amp as a next step up, you could of course use a choke iso a resistive load or even a CSS all of which should, in theory at least, bring more linearity and better sound.

Subjectively that's not always the case so listening test may be the decisive factor, as they should be anyway.

Hope it helps,

P.S. Hope I haven't missed out anything blatantly obvious...I usually do. nad sorry for the long rant.
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Old 29th June 2003, 10:48 PM   #3
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Quote:
The filter caps in the heater supply seem extremely low.
4.7 mF means 4.7 milliFarad Frank. So they are 4700 uF.
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Old 30th June 2003, 12:17 AM   #4
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Hi,

Quote:
4.7 mF means 4.7 milliFarad Frank. So they are 4700 uF.
I knew it, I just knew it...

Does anyone else actually use that kind of spec in diagrams?
I'm used to the more convential uF expression.
Milifarads...crickey!!!.

O.K. thanks Jean-Paul...

I'll do some " kastijding":



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Old 30th June 2003, 01:15 PM   #5
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Smile Thanks for your advice.

Thanks for your advice, Frank.
Of course there are 3 different heater circuits, sorry I'm was too lazy!!!
Stepped attenuators should be better, but first I will check an Panasonic pot.
Chris
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Old 7th July 2003, 10:38 PM   #6
Joel is offline Joel  United States
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Why are the chokes such a low value?
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Old 8th July 2003, 12:11 PM   #7
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Quote:
Originally posted by Joel
Why are the chokes such a low value?
10 mH means 10000 uH.
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Old 8th July 2003, 12:16 PM   #8
Joel is offline Joel  United States
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Quote:
Originally posted by hugoland
10 mH means 10000 uH.
Yes, I'm aware of millihenries. I ask again, why are the chokes such a low value?
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Old 8th July 2003, 01:53 PM   #9
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Isn't it standard to use chokes at 10-12 mH?
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Old 8th July 2003, 02:03 PM   #10
Joel is offline Joel  United States
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Quote:
Originally posted by hugoland
Isn't it standard to use chokes at 10-12 mH?
Oh my, no. 10 to 12 HENRIES would be a good place to start. 10mH will have a reactance of 7.5 ohms to the 120Hz hum. 10H on the other hand will look like 7536 ohms. See?

reactance=2*Pi*L*F
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