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Thursday, January 28, 2016

The 27 Line Preamplifier


When I introduced the 27 as tube of the month in June last year, I mentioned that it could make a nice line preamp tube. In the meantime the 27 line stage is finished.

I already experimented with the 27 many years ago and used it in a preamp and as driver for a 45. In both cases it worked very well. So it was time to put it to good use again.

This is the latest addition to my offering of line stages.

Being indirectly heated the 27 requires no fancy filament supply. AC heating is good for hum free operation at line levels.

Many people have space constraints and have difficulties to place the two chassis of a 10Y line stage.

So I squeezed everything into a single chassis, including the power supply.

Of course the proper rectifier to use with it is the 84.

Top view:

The two 27 tubes on vibration damped socket mounts at the front and the rectifier in a corner at the back. The 3 white covers are housings for chokes. All the rest went inside:

Quite tightly packed. Two separate power transformers, one for the high voltage and a heater transformer for the 27s. Another choke, 4 more capacitors, the line out transformers and two autoformer volume controls.

A neat little package. In fact with all the iron it is quite heavy. The backside:

The on/off switch had to move to the back. I didn't want to disturb the look of the front with the two knobs. Of course it would be possible to have it on the front as well.

Side views

This time I picked white for the covers and capacitors.

Here the preamp equipped with globe UY-227 tubes:

With ST tubes:

A nice preamp. It has all the advantages of transformer coupling and transformer volume control. A bit less refined as the 10Y line stage, or any of the other DHT line stages. But therefor it needs half the space and comes at about half the cost.

A few more detail photos:

Those globe tubes are really nice

Best regards



  1. Amazing you got it all in one chassis. How much does it weigh?

    1. Hi!
      I didn't with it yet. I think it is around 25kg


  2. Hello, what is the gain of the amplifier?

    1. Hi, It is rather low gain around 3dB. Similar to the 10Y preamp

  3. A very beautiful preamp. Great industrial design.

  4. Curious when you say that this 27 tube being non dht is not as refined as a dht? What exactly is the deciding. Factor?


    1. Hi! I don't quite understand your question. What do you mean by deciding factor?