Would a member fluent in technical German please have a look at this link? - diyAudio
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Old 9th April 2012, 12:10 AM   #1
bst is offline bst  United States
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Default Would a member fluent in technical German please have a look at this link?

I was browsing Jogi Gittel's outstanding website Jogis Roehrenbude - Roehrenradios, Roehrenverstaerker und vieles mehr, and came across this design for a neat little 6-watt EF86 -> EL84 amplifier. I'd like to build a pair of these amps, but need to know if there are any pitfalls in the implementation.

I tried running the article through the translation program PROMT, but it couldn't translate several technical terms, and some of its algorithms gave very humorous results (e.g., the prefix 'EL-' was translated as 'tablespoon'...).

I was never very fluent in German, and what little I knew has gone virtually unused for over thirty years. If a member who IS fluent in technical German would read through this article, and advise of any special considerations, I'd be very grateful.

Thanks in advance for your time.

ETA: The direct link to the article immediately follows the pictures and schematic below:


Click the image to open in full size.

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6-Watt-HiFi-Röhren-Verstärker mit EL 84

Last edited by bst; 9th April 2012 at 12:13 AM.
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Old 9th April 2012, 12:39 AM   #2
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The schematic doesn't lie. An EF86 voltage gain block is needed to make up for the tone control losses. 5 W. from a Full pentode EL84 is about right.

The sort of tone control setup shown is, all too often, nasty. Do you really need tone controls? FEW recordings benefit from their presence.

C13 is known, for good reason, as a death capacitor. Eliminate it and use a proper 3 wire power cable, with its safety ground connection.

Use proven, high performance, signal grounding technique. That means either a well thought out bus or a "star".

A satisfactory B+ PSU that can power both channels can be made by Greinacher doubling the O/P of a Triad N-68X isolation trafo.

Better open loop linearity can be obtained by regulating EL84 g2 B+.
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Old 9th April 2012, 01:59 AM   #3
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You can copy/paste the link in google translate and it will translate the whole page:
Looks like this.
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Old 9th April 2012, 06:40 AM   #4
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Hello bst,
I´m a native German. You asked for a translation of possible pitfalls, or in other words: useful hints the author gives:
The circuit is proud of its wide range tone control and a feature you will find in many if not all 1950s German radios. "Gehörrichtige Lautstärkeregelung". That is someting similar to a loudness. The volume pot has taps that are loaded with tone control componenents. As Eli says: not very Hifi.
Keep the power choke away from the output transformer.
Mount the rectifier to the chassis to cool it.
By and large the ciciuit looks like it has been inspired by a 1950s Saba radio. Even the font and details like the killer capacitor (we call it arson capacitor).
Many of the components can be gained from such a radio with the standard European EL84 circuit. That may make the cicuit popular over here. I don´t know about the US.
And the "EL" issue. In German recipes EL in fact stands for "Esslöffel" which is a tablespoon.
Good luck with your SE amp. Any German language or German radio questions left, just ask.
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Old 9th April 2012, 06:56 AM   #5
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Quote:
I'd like to build a pair of these amps,
Don´t do it! It´s a lousy design, probably taken from an old Funkshau magazine of the fifties and addressed to the absolute beginner of that time.
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Old 9th April 2012, 07:57 AM   #6
AJT is offline AJT  Philippines
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schematic seems readable, it's got a tone control and a loudness contour circuit as well...

Click the image to open in full size.
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Old 9th April 2012, 12:04 PM   #7
bst is offline bst  United States
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Quote:
Originally Posted by grommeteer View Post
And the "EL" issue. In German recipes EL in fact stands for "Esslöffel" which is a tablespoon.
Aha! That makes perfect sense. This goes to show the perils of translating; even from one common language to another.

I lived in Bitburg in the mid-1970s, and rented half a house from a lovely couple who had two young children. At Christmas, I wrapped a couple of small toys, and took them downstairs to give to the children as presents.

When I handed them the packages, and told them each it was a 'gift' just for them, the children backed away and hid behind their parents' legs.

It wasn't until I was reminded that 'gift' was German for 'poison' that I realized my blunder. This misunderstanding was soon corrected, but it was a reminder to think twice before speaking.

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Thanks for your reply, and your offer of help in the future.
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