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Sunday, February 27, 2022

Tube of the Month : The 394A


For all the mercury vapour friends out there, this months tube is a thyratron, the 394A.

Thyratrons are basically rectifiers with a control grid through which the output voltage can be regulated. The 394A is mercury filled.

In September 2020 I already showed a thyratron, the 323B. The 394A is a smaller thyratron with the advantage of much lower filament current. While the 323B eats a whopping 7A, the 394A lights up with 3.25A. It still can deliver a lot of current. The data sheet specifies an average current of 640mA for one tube and it can handle short peaks of 25A for periods of 100ms. More than enough for most audio applications. As with the 323B you can simply skip the control capability and just use the control grid (which actually is a cage around the filament) as plate and leave the actual plate, which is at the top cap, unused. I have never used thyratrons in audio projects but there are some reputable audio designers out there who love them. Of course the blue glow they give off is always a show.

Here we have a bunch of 394A made by Electronic Enterprises Inc:

These came in military packaging.

Some close ups:

Western Electric 394A:

And now some blue glow.

The pictures above are with the high voltage applied to the actual plate. Below with the control grid used as plate:

I hope you enjoyed the presentation of this beautiful tube.

Best regards


Thursday, February 17, 2022

Silver TM300B Mono Blocks: How Do They Sound?


Some people asked about the sound of the recently shown all silver mono amplifiers using the TM300B tubes. Since I am of course highly biased with regard to the sound of my amps, I prefer to let others speak about their sound

These amps had been commissioned by a customer after auditioning a pair of silver 46 monos against a pair of copper TM300B monos.

He is using these amps with this silver differential linestage:

Here is his feedback:

I had the opportunity to hear the 46 mono silver power amps with my Aries Cerat horn speakers and it was immediately obvious why the 46 power tube is so highly regarded by Thomas. The level of subtlety that the 46 presented in these mono power amps was deeply impressive. Unfortunately, the 1.25 watts of output power wasn‘t enough for my horns though they claim to be quite efficient. The reason for this is probably the impedance curve that isn‘t that linear.
With the TM300b silver monos, especially in combination with the differential silver preamplifier, I got a wonderful alternative, which in my view is in no way inferior to the qualities of the 46s. For my taste, there are even advantages here in terms of somewhat more liveliness that is not exaggerated and effect hash, but supports a realistic presentation. In any case, I am highly satisfied with these power amplifiers and can recommend them to anybody with adequate speakers.

Later this year a silver phono preamplifier will be added to his system.

Best regards


Monday, February 7, 2022

Two 10Y Line Preamplifiers


Here some photos of two 10Y linestages which just got finished.

The 10Y preamp along the D3a phono stage are my most demanded pieces of gear.

The set on the left is in walnut chassis, graphite grey transformer covers and white capacitors while the set on the right has both caps and covers varnished in metallic maroon red and comes in smoked eucalyptus chassis.

Each 10Y preamp is customised with the required set of inputs and outputs.

If you want to configure your very own 10Y line preamplifier, email me to discuss details.

Bets regards