Category Archives: 50EH5

A new Obsession- The simplest possible amp

This story is the first of a series:
The simplest amplifier obsession Part 0 – this one
Breadboard amplifier Part 1
Chassis building Part two
Assembling the 6S45P amplifier Part three
Finalizing the 6S45P Part four

6S45P
It´s the little tube that could! Rumor has it we are talking about 2mm titanium plates, platinum wire etc. It´s most famous use is in a radar pulse scan preamp in MIG 25.

No larger than a an ordinary 12AT7 it is all you need for a very reductionist single ended triode amp.  A potentiometer, grid stopper, the 6S45P and a output transformer are all that is between you and the signal.
Torbens HIFI in Denmark has the specifications.
I have found a push pull version by poinxie” who has cleaned up the curves, and posted a nice set of curves. Klausmobile has tested the tubes and built an amp. Here is a nice design by Paeng
Here is an extremely interesting story of pushing the tube to its limits

Take a look at Carstens amp the single ended 6s45p.
And Greenvalve pushing the tube to its limits
And here the Thai Audio people are at is as well.

Over at VT52.com they have tested an amp built on the 6s45p
They also have a nice description of the circuit.
A very comprehensive site of 6s45P circuits by Stefano Perugini. 
Stefano Perugini has a Pspice model and suggested PCB layout as well.
Sergeev21 has this schematic
Diy Audio Guide has a schematic with a few embelishments.

7mari has a really well speced version on an experiments chassis, that he is running at 250v

But is this the simplest?
The absolute simplest?
One tube, with one triode to do it all is pretty cool, but we still need a transformer with a secondary winding for heaters. wouldn’t it be cool to get rid of that heater winding?

50EH5
The 50EH5 is the absolute champion of simple. If you have a simpler solution – send it to me. You can series-heat two of them with the same voltage as B+
The only down side is that this tube is not a triode, it is a pentode. You might be able to triode strap it but you still need a few extra solder points.

 

Here is a description of a circuit and a build by Giovanni Militano on DIY Audio projects.com
For now I will focus on building the 6S45P, but in the future I´d love to try this one as well.

Here are links to the rest of my 6S45P project:
The simplest amplifier obsession Part 0 – this one
Breadboard amplifier Part 1
Chassis building Part two
Assembling the 6S45P amplifier Part three
Finalizing the 6S45P Part four