Feb 26, 2016

MC1/60, E60M, TM100 SE amplifier - Part 2

Back on the air with amplifier circuit

Voltage requirements.

We need 600V for the final stage, 300V for driver, negative bias voltage, heater voltage.

High voltage is not very high, I can take advantage of vacuum tube rectifier (helps for soft start) and polypropylene capacitor for main supply. I prefer the sound of these caps over the usual electrolytics.

For driver stage I choose choke input filter with bleeder resistor. Choke input is less disturbing for the power transformer and ripple is very smooth.

Main power transformer windings.

1- 500_0_500 V will give me the proper 600V high voltage with GZ34 rectifier.
2- 350_0_350 V will feed the SRPP with 30H choke input filter and ultra fast soft recovery diodes.
3- 50V for bias.
4- 7.5V for MC1/60 to provide 4V choke input filtered too.
5- 6.3V for 6SN7.
6- 5V for GZ34.

On the bench

Sub chassis ease construction a lot.........

Amp finished

Tamura TN351 interstage transformer with it's 1:2 voltage ratio helps a lot to drive the final tube easily with minimum distortion from the driver.
The little black switch next to the 6SN7 socket is for a local NFB loop. I can choose between 0 / 3.5dB feedback. Personnaly I prefer no feedback.
Screw speaker terminal, grey paint and AEI silver plated socket give a retro fashion look to the amplifier.

The second black switch next to AC connector give me the choice to earth or not the amplifier, helps to get the lowest noise floor.

Screwdriver potentiometer and large panel meter for easy current setting.

The mighty E60M tube @ 600V / 75mA

Listening test

Amplifier is dead silent on my Klipsch, I have to put my ear against tweeter to hear a slight hisss.

First impressions .... punchy, very clear and detailed without being tiring. Beautiful and delicate mids and highs (as fine as the 10/VT25 amp !! I can make comparison on mono recordings VT25 amp on one side, MC1/60 on the other), voices are natural, very articulated and living like (Madeleine Peyroux_Careless Love).
Bass are impressive, this is the first time I can physically feel bass with my Klipsch (Bach_ Cello suites, Pierre Fournier). Excellent soundstage with lot of depth, very airy and detailed, I ear the very, very slight shift of the bottle neck on the guitar, the slight fingers taps on strings ( Pedro Soler_Sombras or Selmer 607 Gypsy guitar CD) never heard before! It's good, very good in fact even on very complex music ( Verdi_Messa da Requiem_Giulini).
I also listened to E60M and I have great difficulty in distinguishing the tubes. More body may be? It depends a lot upon input tube. Best with MC1 / 60 are the VT231 Ken Rad (sooooo punchy in the low end), Hytron VT231 or Brimar 6SN7 GTY with E60M or TM100.

Amazing to see after so many years that the 4 V tubes have always been killers compared to the other ones (2.5, 6.3, 7.5V …..). I have been playing with plenty of these classics (2A3, 45, 50,811,211, 845 and so on) and found each time they were inferior to the 4 V ones *. Is it a matter of cathode coating, is 4 V the best voltage for regular emission ? I have no answer, just listening facts that aficionados of the PX4, PX25 and AD1 perfectly know.

* Just one exception, the Visseaux A710, a 10 with BIG plate (as big as a 50) using a 7.5 V oxide coated filament. It's to my knowledge the only 10 of that kind and the only one that sounds like a PX4.

Have to wait for some friends to come and make a very serious listening.
At that time this amp is the very best I have ever built.

Some CD's for this test


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