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McGyver 2nd June 2009 09:33 PM

Renovation of fifty years old tube amplifier
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By accident I bought fifty years old german tube amplifier Braun CSV-13. It is 12W EL84 push-pull. All the goodies are closed into metal case, the frontpanel is made of alluminium, the cover is heavy, made of perforated steel. At the rear panel we have archaic terminals in german DIN standard. Even mains terminal is strange and it's impossible to buy suitable plug.
I replaced it first, and connected the amplifier by DIN terminals....and the sound was horrible. Slow, fat bass, no shape, no space, no details, and many distortions at higher sound levels. So I replaced all the tubes. And nothing was better. I started to search schematic, and I found it. After short inspection I decided to bypass preamp and tone control, and... bingo! It plays quite well. But after few days of playing electrolytics started to leak. No way out, there's need to solder. I made new power supply, I replaced old selenium rectifier, and I rebuilt driver section to omit electrolytics in the signal path. In the end I replaced old flimsy plastic rear panel with DIN terminals by new panel made of solid aluminium and equipped with modern Monacor speaker terminals and RCA signal terminals. Unfortunately OPT's haven't ultralinear taps, but the sound is very good anyway.

McGyver 2nd June 2009 09:35 PM

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Old terminals:

McGyver 2nd June 2009 09:39 PM

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Power and driver tubes:

McGyver 2nd June 2009 09:42 PM

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New power supply:

McGyver 2nd June 2009 09:44 PM

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New rear panel with modern terminals:

McGyver 2nd June 2009 09:45 PM

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lowering feedback:

McGyver 2nd June 2009 09:46 PM

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Rebuilded driver stage:

McGyver 2nd June 2009 09:48 PM

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Rear view:

Wavebourn 2nd June 2009 10:04 PM

Everything is fine, except what for did you lower feedback?

McGyver 2nd June 2009 10:12 PM

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It was after Dynaco ST35 schematic, something like that:

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