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Wednesday, March 5, 2014

The 10Y / 45 drives 45 / 2A3 amplifier


After the posts about the rather high power 211 amplifiers, here some pictures of a recently finished pair of flea power mono amps.

These mono amplifiers are similar in construction, chassis layout and parts choice  as the 10Y/45 drives 45 amps shown last year. Except that this time also the output tube can be selected between two types: 45 or 2A3.

The amplifier set consists of 4 chassis. Two amps with separate power supply for each.

Same chassis design as the remote controlled 10Y line stage in the previous post with which these amps will be used. Both the driver tubes and output tubes have DC supplied filaments for zero hum operation. Elaborate filament supplies with separate filament transformer and LCL filter chain for each tube ensure best sound quality without impact through the filament supply. In my opinion a properly DC heated 45 even sounds better than an AC heated one.

With both driver and output tube selectable, these are actually 4 different amplifiers in one. Some might find the configuration 10Y drives 45 a bit ridiculous since the driver tube is physically larger than the output tube:

But anybody who heard this configuration with it's very detailed and beautiful sound accepted it as a viable combination.

The 2A3 driven by 10Y looks a bit less strange:

The 10Y is a good candidate to drive the 2A3 with a 1:4 input transformer this gives reasonable input sensitivity. Sensitivity is the lowest with the combination 45 drives 2A3. Similarly low for the 45 drives 45 set up. This configuration needs about 2.8V RMS to reach full output power of 2W. While low this is still reasonable in most systems.

The sound of this combination is well worth it. A 45 lovers dream! Pure 45 bliss, especially with the globe UX245:

This is not just double the 45 fun, it is 45 squared!

Some more views of the amp:

The amp section from the top:

The entire set of 4 chassis:

I am enjoying these amps during their one week test run, before they are picked up by their new owner.

So is this as far as you can get in terms of 45 amplification? Stay tuned for more 45 bliss in upcoming posts.

Best regards



  1. Great stuff, Thomas!

    I think you can imagine wich "next step" i'm impatiently waiting for:
    a single stage 45 push-pull amp :) Would probably look exactly the same like this one.


  2. Hi Peter,

    no need to be impatient: order one and one will be built ;-)


  3. Thomas, this is awsome!
    I am big fan of your 45 and a proud owner :) Me I am one chasis guy. What is your opinion on how much less performance one would get from 45 /45 design in two chasiss? Btw. What is the type of wood you are using here?

    1. Hi!

      It would sound just as goof in two chassis but would be unbearably heavy


  4. Hi Thomas!

    Great looking amp as always!

    may i know what DC heating filament you're using there?
    is it voltage / current regulated?

  5. Hi!

    It is mentioned in the post: Pure passively filtered with separate LCL chains for each tube.


  6. Hi Thomas, how would you describe the difference between this all DHT 45 and your version with the 6N7 as driver? Are they comparable? As a comparison is the difference as great as switching from Lundahl to Tango iron? Thank You!

    1. Hi! The all DHT version is quite a lot better. It is a bigger step as compared to the change from an indirectly heated output tube to a DHT. There is another one in the works which will be shown soon.

      Best regards