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Old 7th January 2004, 05:55 AM   #21
barossi is offline barossi  Germany
diyAudio Member
 
Join Date: Oct 2003
Location: Hamburg area
Unhappy Ultrapath

Hello,

the ultrapath capacitor is in the signal path, isn't it?

Greetings Barossi
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Old 7th January 2004, 07:42 AM   #22
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by fdegrove
While I do absolutely believe you on this, it's a pity no hard facts seem to be publicised regarding this.
Well, while mostly dead in modern science and engineering, there is still something called the empitical methode, which is usually apropriate in such cases.

Sayonara
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Old 7th January 2004, 07:52 AM   #23
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Ultrapath

Konnichiwa,

Quote:
Originally posted by barossi
what exactly does the Ultrapath capacitor.
It closes the current loop for the circuit containing the Valve and output transformer. Commonly this loop is closed via the Powersupply and cathode capacitor.

Quote:
Originally posted by barossi
I have huge Leclance 50uF/500V + 20uF/500V (i think MP's) Cans on stock. I think i will use them.
I think the 20uF would be fine for the E55L and the 50uF could be used on a self bias 6S33 with +B = 270V and Rk = 330R + 10R.

Quote:
Originally posted by barossi
After switching on the Amp the 6C33 the operating point at 200mA will reach at about 20min. What could i do against this problem?
Switch to any of the available forms of self bias. I prefer the version where the Bias Voltage is generated with a resistor in the negative supply line but you could go Ultrapath too, as shown here:

Click the image to open in full size.

Quote:
Originally posted by barossi
Hello,

are there any "rules" for the ultrapath capacitors?

Greetings Barossi
Yes, as large as possible with as high a quality as possible. The balance bewteen these two conflicting requirements (good quality capacitors rarely come in large values) will limit the values.

Quote:
Originally posted by barossi
the ultrapath capacitor is in the signal path, isn't it?
Yes, it is so instead of the normal PSU capacitor and cathode bypass capacitor which otherwise would complete the current loop. The only downside - virtually no supply noise rejection with this circuit.

Sayonara
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Old 7th January 2004, 08:13 AM   #24
barossi is offline barossi  Germany
diyAudio Member
 
Join Date: Oct 2003
Location: Hamburg area
Default RESULTS!

Hi folks,

i just build the small circuit:

Lundahl LL1660/18mA connection ALT S; 1:1,125
Valvo E55L with 250Ohm, G2+G3 was connected to anode, G1 as Grid! First without Ultrapath!

I used a Heathkit voltage supply ( 0-400V), Heather 6,3V AC

I tuned the power supply, so that i can measure 5V at the cathode. Than the voltages are UB= 243V, Uanode=222, Ukathode= 5V. That gives me I=5V/250 Ohm= 20mA.

Now i have a problem, Thorsten you said:

<<<<<So actual +B is 160V plus 20mA * IT DCR, the cathode bias esistor should be 250 Ohm and ideally I'd provide a clean supply and use the "ultrapath" cathode bypass connection with a nice juicey big oil or film cap.

Anode impedance of the E55L looks a little above 1KOhm and gain around 30, so theoretical voltage swing before the bias is exceded is 300V P-P, that is well over 6db input overload margin, excellent.

So, I'd try 250 Ohm Cathode Resistor and 160V on the Anode for starters. Then move a little up and down with the Anode voltage by adjusting the regulator or droppwer resistor for the frontend and listen.>>>>>>>>

What's wrong? G2+G3 was connected to anode, G1 as Grid!

Greetings Hauke
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