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Old 25th May 2006, 11:48 AM   #1
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Default Help on PP EL 34 from Claus Byrith

Hello All,

Anyone used the amp from Claus byrith as integrated amp?
http://www.lundahl.se/claus_b.html

Is possible?


Is possible to use 3.4 K pp OPT?

Thanks to all,

Maurizio.
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Old 25th May 2006, 12:49 PM   #2
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I am familiar with Byrith's schematic and yes, I believe what he says in that article should work. He definitely improved on the Mullard 5-20 but I believe he could have gone further.

His design would have been better, in my opinion, if he had replaced the 12AX7/ECC83 with a more linear tube for the phase splitter and also if he had used a constant current sink (CCS) in the tail of the phase splitter.

You cannot use a 3.4 k plate-to-plate load output transformer for EL34s in ultralinear mode, that's too low. You ideally need 6.6k but Byrith got away with 5k. (The 3.4k impedance you mention is good for EL34s in pentode mode, class AB1, with 400v B+.)
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Old 13th June 2008, 02:04 PM   #3
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Default Suppose...

...you wanted to use 6550s for more power instead of EL34s?

what changes would be required?

my calculations indicate an output transformer with 8K plate-to-plate resistance.

i think the driver circuit could remain unchanged.

thoughts?

i know this thread is quite old, but my curiousity got the best of me...

yes, I am a noob....
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Old 13th June 2008, 08:16 PM   #4
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Gleaning on my tube data (1958) for the 6550 tube in UL p-p fixed bias with 40% taps with 450V B+ shows 3300 Ohms A-A for 70W o/p; whereas the Svetlana C version shows 4000 Ohms A-A for the same power transfer and it doesn't stop there.

The original 3300 Ohms Z is too low for the best of todays tubes and many of us who still use the NOS 6550A version will immediately notice this tube can be punished electrically harder than any of todays made variants, even top notch KT88's.

Another snag with the 6550 versions is a lower grid leak resistance (50K) is required which will load the drivers into producing higher distortion; in contrast with the more recent tube makes i.e Svets suggest grid leaks around 100K and higher for auto bias. This is a large difference.
I haven't measured the output Z of the LTP used in the 5-20 esp at higher audio frequencies, but the ECC83 used to drive the orig Mullard 20W amp with EL34's will have a sweat driving any 6550 version and with such high driver anode load resistances compared to the grid leak values is a cue for a lousy performance. Needless there is a Kit around.

richj
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Old 13th June 2008, 08:38 PM   #5
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The nice thing is that the topology is sound even if some of the design choices aren't. So you can still use the circuit boards and layout info while fixing some of the design issues. A CCS in the long tail will require an outrigger board, though.
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Old 17th June 2008, 07:20 PM   #6
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This is another design I'm considering.

http://diyaudioprojects.com/Tubes/KT...Pull-Tube-Amp/


It looks like changing to KT88 from KT77 is as simple as a resistor in the constant current source (a National Semiconductor LM317 voltage regulator IC).

a IC......I know, I know, I'm a heretic.....

Thoughts?
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Old 17th June 2008, 08:04 PM   #7
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A mediocre CCS with terrible overload recovery. Pretty construction, lousy concept.
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Old 7th November 2009, 05:28 PM   #8
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Hi Everyone,

I have the parts necessary for that amp (30W PP by Claus Byrith) from my friend's abandoned audio project. (I bought them for a few bucks) My only problem is that I have only one mains transformer for both channels. So I will solder the things together as a stereo amp. As I have read in the pdf it's possible coz the transformer is capable of supplying both channels. Only there is nothing about what I should change in the schematic in order to supply both channels from the single power supply. (There is something about changing the 10k and 100k resistors but no more) So my question would be: Have someone of you built the amp as a single stereo unit? What changes should I apply to get the thing working?
Sorry for the noobish questions, but I'm only a beginner with a schematic, the parts and basic electronic knowledge, so any help would be great for me!

Andrzei

EDIT: There's the link to the pdf: http://www.lundahl.se/pdfs/claus_byr...fier_30wpp.pdf

Last edited by Andrzei; 7th November 2009 at 05:48 PM.
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