These three certainly are not the three swordsman, but are PCC 88 from
MULLARD, MINIWATT and VALVO. They are the relatives of ECC88 because
they share the same pinout and rating, but --- they eat more filament
voltage than ECC88 to 7.6V. Moreover three brothers all have a common
that they have the cross scar of knife "wound" on their heads...... off
the topic..... we are not discussing the tubes anthology here. I want
to introduce the new kit of the vacuum tube buffer.
This electric circuit is originate from Music Fidelity vacuum tube
buffer X10. Years ago I was surprised to see this schematic on Japanese
MJ magazine! Why vacuum tube works at this low voltage? To be honest at
that time I was newbie for vacuum tube electronics, therefore on a
doubtfully manner I used this schematic to build one with PCB. It was
really good when I attached the main to the buffer..... successful ! I
had never thought that vacuum tube also may play like this. I make the
integrity design, enable to let diyers very easily to assemble the
circuit board and put it in the chassis.
It is like the PCM1732 DA kit that anyone can easily assemble it with the aluminum chassis.
The structure of entire circuit is composed by two ECC88 vacuum tube,
each vacuum tube is responsible for a channel. The original electric
circuit using ECC88, which I alter to it that it can use PCC88. They
share the same pinout and characteristic except filament voltage. Why
is that? Because I found out that the price of PCC88 is much cheaper
than ECC88. So using PCC88 can save you a lot of cash......
The original filament power supply is sereis filament of two vacuum
tubes together supplying 12.6V, and moreover the filament voltage
supplies have not been regulated, sometimes filament voltages can vary
along with the difference of the main power drifting. So I change this
design, let each vacuum tube has one independent filament voltage
regulated by LM317, and filament voltage can be adjusted to 6.3V or
7.6V. Heat dissipate when LM317s work, therefore I mount the 317s on
the chassis to dissipate heat.
I added a relay on the output to separate the instantaneous DC voltage
output on power-up. Isn't the schematic has a cap on the output to
eliminate DC? Why should we need the relay? Actually, you can use a DMM
to measure, that you can see a temporary DC on the meter.
The drilling had been done in the factory so you don't have to worry to
drill anything in your dining room or studyroom. The printing was
finished, too.
The assemling instruction will be posted next time.
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