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    Building, troubleshooting and testing of these amplifiers should only be
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Dutch Book

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el156

el156

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Joined 2010
#1
IMG.jpgHi !
Does someone has or knows where to get this book in english?
I can not read dutch....🙁
 
#4
It's a mid '60s book, chances may be slim to find one in English, not counting university libraries.
He'd have to scan and OCR-read about 125 pages, fortunately it's pocket book size.
Surely there must be someone here, willing to clean-up the online translator translation. (the inspecting inspector of the inspector general ?)
 
#8
#9
rjb said:
I have this book, but am not willing to part with it, or scan many pages. Do you have a particular question I can answer?
Click to expand...

Hi !
I also have the book,but in Dutch,and i would like to fully understand the picture of page 7,and as far i can see the best load for 2 EL34 triode connected,425V Va, is Raa 12K ? Can someone explain this graphic for us all ? It is confusing for me,but i think is very interesting!
Thanks a lot
 
#12
No problem, just don't ask me to translate the whole book 🙂

CAPTION:

Output power Wo, distortion dtot, cathode current Ik and input AC voltage Vi in function of the load impedance for two EL34 tubes in triode mode in push-pull class A bias with a B+ of 425V. The left side of the figure shows the case of bypassed cathode resistor; in the (more important) right half of the figure an unbypassed shared cathode resistor of 235 ohms was used.

TEXT:

Very low distortion can be achieved in push-pull finals with class A triodes. 25W pentodes or tetrodes in triode operation can reach below 1% distortion @ 12...15W output power and 425V B+.

Power and distortion depend strongly on the load impedance, as seen in the figure for EL34 tubes. The tubes are run in triode mode and are biased just below the maximum dissipation of 25W.

Below 7kohms load impedance it is possibel to use a shared cathode resistor or two separate ones, and they should be bypassed. Above 7kohms the push-push stage works better with an unbypassed shared cathode resistor. The bias approaches class A as the load is increased; optimal conditions are reached around 10kohms, when output power is 14W at a THD significantly lower than 0.5%.

Finals such as these (e.g. Williamson) were recently very popular and many ~12W output power hifi amps were built to this recipe. Since the inherent distortion is so low, less feedback is necessary than with pentodes or tetrodes of the same power rating. Additionally, the risk of instability is much less in 3- or 4-stage amplifiers where most of the feedback is global and includes the output transformer.

The major drawback of this arrangement is the low efficiency, leading to a costly and heavy power supply and output transformer for a comparatively low output power.
 
#13
kavermei said:
No problem, just don't ask me to translate the whole book 🙂

CAPTION:

Output power Wo, distortion dtot, cathode current Ik and input AC voltage Vi in function of the load impedance for two EL34 tubes in triode mode in push-pull class A bias with a B+ of 425V. The left side of the figure shows the case of bypassed cathode resistor; in the (more important) right half of the figure an unbypassed shared cathode resistor of 235 ohms was used.

TEXT:

Very low distortion can be achieved in push-pull finals with class A triodes. 25W pentodes or tetrodes in triode operation can reach below 1% distortion @ 12...15W output power and 425V B+.

Power and distortion depend strongly on the load impedance, as seen in the figure for EL34 tubes. The tubes are run in triode mode and are biased just below the maximum dissipation of 25W.

Below 7kohms load impedance it is possibel to use a shared cathode resistor or two separate ones, and they should be bypassed. Above 7kohms the push-push stage works better with an unbypassed shared cathode resistor. The bias approaches class A as the load is increased; optimal conditions are reached around 10kohms, when output power is 14W at a THD significantly lower than 0.5%.

Finals such as these (e.g. Williamson) were recently very popular and many ~12W output power hifi amps were built to this recipe. Since the inherent distortion is so low, less feedback is necessary than with pentodes or tetrodes of the same power rating. Additionally, the risk of instability is much less in 3- or 4-stage amplifiers where most of the feedback is global and includes the output transformer.

The major drawback of this arrangement is the low efficiency, leading to a costly and heavy power supply and output transformer for a comparatively low output power.
Click to expand...
Thank you very much! Very clear translation!
 
#16
Guys, the book was translated into English long ago and was available most recently from AudioXpress. English title was: Valves for Audio Frequency Amplifiers (Philips technical library)

Find a used copy on Amazon here: Amazon.com: Valves for Audio Frequency Amplifiers (Philips technical library) (9781882580163): E. Rodenhuis: Books

The book appears to now be out of print. It's one I have in my technical library, and it has some good stuff in it. (The OTL shown on the front cover of the Dutch book for example, IIRC stuff on rimlock tubes, etc.)
 
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