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DISCLAIMER: Vacuum tube circuits work with dangerously high voltages. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

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Saturday, November 17, 2012

Making of 211 / VT4C Mono Amplifiers

Hi!

In this post I will show the construction process of a pair of 211 mono blocks which I assembled during summer.



The circuit of these amps is the same as shown in a series of articles last year, with just some minor improvements. The circuit is shown here.


 
 
The assembly followed the same approach as shown in part 2 of last years posts. It starts with a pair of metal plates shown in the next photo rigged up in assembly jigs:
 
 
 
 
 
In the first step all sockets, connectors and switches are mounted:
 
 
 
 
 
 
 
Then the paper in oil capacitors:


 
 
The caps are clamped to the metal plate with two aluminum profiles:
 
 


In the next step the high voltage power transformer and output transformer are mounted:




Some initial wiring of the capacitor bank:


The filament transformers are mounted on the bottom side:




Then the chokes are added, 5 in total. 3 for smoothing of the high voltage and separate decoupling of the driver stage. 2 filament chokes for the 211:




Next the interstage transformer, completion of the filament supply, cathode and bleeder resistors and completion of all wiring. All wires carrying high voltage have double insulation. All signal wiring is done with solid core silver wire:



Now everything is ready for an initial test and listening. Afte rthe first tests were ok, the assembly got inserted into the wooden frame:


 

Another test and final adjustment of voltages then the transformer covers can be mounted. The large ouput transformer had to be attached sideways so that the cover (150 * 150mm) fits:




And the bottom lid attached.




The finished amps in all their glory:









Best regards

Thomas

10 comments:

  1. So excited! Can't wait to fire these babies up!

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  2. Great looking amplifiers !

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  3. Please forgive my ignorance but is it possible to build a stereo amp with a single 211 tube? As some rare tubes can sometimes be found as singles.

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    Replies
    1. Hi!,

      No, with one tube you can only build mono....

      Thomas

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  4. Oh well, I'm only just starting in this hobby (audio) and I'm putting together my first system. First thing I'm building some speakers and I'm looking for quality kit to add to these when I'm done. Your passion and skill are evident and I can only hope I'll be able to get one of your designs. Is everything you sell build to order?

    Paul

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    Replies
    1. Hi Paul,

      these amps are built to order and can also be purchased as kit or partial kit.

      Best regards

      Thomas

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  5. Hello Thomas,

    Thanks for your excellent site! Can you tell a little more about your experiences with the 211 OPT? The high primary impedance makes me wonder what high frequency extension you achieve and with exactly which 211 version (between the near endless variety of 211 designs, internal impedances also vary quite a bit).


    Kind regards,

    Aaron

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  6. Hi Aaron,

    beyond 20kHz the OPT start to roll off. Which is ok for me. I used General Electric and Elrog tubes

    Best regards

    Thomas

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    Replies
    1. Thanks Thomas! Given that you have now also had them made in silver, I can only conclude you are satisfied with their basic design.

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