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Darius Loftin White explained
Darius Loftin White explained
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Old 14th January 2009, 09:22 AM   #81
oldeurope is offline oldeurope  Germany
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Default @ #80

Hi Sheldon,
yes, the output resistance is calculated in the following way:

rout = RkKF II RS II riKF / (n x +1)
rout ≈ riKF / (n x +1)
rout ≈ 60KΩ / (0,5 x 101)
rout ≈ 60KΩ / 50
rout ≈ 1K2Ω

rKB = (riKB + x RkKB)
rKB = (75KΩ + 100 x 1K5Ω)
rKB = 225KΩ

n = RaKB / (RaKB + rKB)
n = 220KΩ / (220KΩ + 225KΩ)
n ≈ 0,5

rout is the output resestance of the cathode follower
RkKF is the cathode resistor of the cathode follower
riKF is the internal resistance of the cathode follower triode, from data book ≈60KΩ
riKB is the internal resistance of the cathode base triode, from data book ≈75KΩ
rKB is the output resistance at the anode of the cathode base triode
RkKB is the cathode resistor of the cathode base triode
RaKB is the resistor between anode cathode base and bootstrap cap =220KΩ
RS is the resistor from bootstrap cap to supply rail =220KΩ
from data book ≈100

Kind regards,
Darius
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Old 14th January 2009, 09:50 AM   #82
oldeurope is offline oldeurope  Germany
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Quote:
Originally #79 posted by kenpeter
Does your 220K resistor present higher dynamic resistance
to the ECC83's plate when so bootstrapped? ...

If so, was that your main intention for this bootstrapping?
Or you had some other important reasons in mind?
Hi kenpeter

The main intention was getting a factor >4 .
Putting two triodes in parallel is not possible because of the miller capacitance.
Influence of Cm at different volume settings

The bootstrap is a kind of "resistance multiplier"
ra = Ra / (1 - vu)

calculation of ra

Ra is the resistor between anode and bootstrap cap
ra = dynamic resistance to the triode's anode
vu is the gain of the cathode follower

comes from

Kind regards,
Darius
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Old 14th January 2009, 05:44 PM   #83
Sheldon is offline Sheldon  United States
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Location: San Diego
Thanks for the calculation Darius. I'll have to draw that up and chew on it for a while. Nice to see you back here.

Sheldon
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Old 16th January 2009, 03:36 PM   #84
oldeurope is offline oldeurope  Germany
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Default @ #76

Hello, I uploaded the articles in an additional blog:
link
This blog is under construction.

Kind regards,
Darius
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Old 18th January 2009, 12:08 PM   #85
oldeurope is offline oldeurope  Germany
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Default blog...

Hello,
please help me and bring the following text into good English. I want to write it in the blog.

In the PC86 RL12T15 schematic update I made the compensation in the same way I did in the ECC83 300B schematic. The advantages of this modification are a more linear adjustment and an enlarged range for the adjustment.

In the Part three Radio News articles Loftin and White made two major modifications, Cgh and C3. C1 and Chb are combined to Cgh and this requires C3, see radio news text. I hate cathode decoupling i.e. cathode bypass caps because of their sonic influence. Please note that the cap divider C2/C3 moves the tapping of R1 to a more left position for compensating hum. This will not be the position for compensating the 'losses' of C2 and making the driver signal floating on the cathode level of the output triode. Adding dotted Cf cuts the 'Ultrapath' i.e. local circuit C2, triode and load.

Thanks and regards,
Darius
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Old 19th January 2009, 11:15 PM   #86
Sheldon is offline Sheldon  United States
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I think you are trying to explain why this change is inferior to the original?

Sheldon
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Old 20th January 2009, 08:34 AM   #87
oldeurope is offline oldeurope  Germany
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Default #86

Quote:
Originally #86 posted by Sheldon
I think you are trying to explain why this change is inferior to the original?

Sheldon
Hi Sheldon,
yes. In later applicationes Cgh is missing too. It is possible to make the hum compensation with C3 and C2 only. And this is the common method today e.g.
http://www.jogis-roehrenbude.de/Lese...Loesch-Amp.htm

#35 C4(=part three Loftin White C2) C5(=LWC3)

Kind regards,
Darius
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