Single Ended power amplifier with type '45 triode (1)
Periphery..
lots of ideas... at least I have. Most of the time they pass, not in this case..
What idea? Well, the latest modifications regarding Super E-cap indelible impressed
me, both mentally and fiscally (referring to the price...!). When using BlackGate
N/NH/NX in super E-cap, the sound is unbelievable clean and colorful, almost
like there's no capacitor... What if a complete amplifier is built using solely
super E-cap, instead of "only" as cathode-bypass? My current preamp
"Mystique" is already equipped with super E-cap, both cathode-bypass
as power supply, with VERY good results. In my power amplifier is this not feasible
due to a power supply voltage of 425 Volts. The BlackGate NH can coop with 350
Volts max, so putting them in series can be an option, expensive though and
not guaranteed (never tried it, too expensive...).
The idea.
A
power amplifier with the '45 or 2A3 as power tube will not exceed 350 Volts
B+, and because of the '45 being one of my all-time favorite tubes, this would
be the choice. The '45 can deliver a full 2000 milliWatts of output power, not
much... Low-end response is not impressive but mids and highs are almost undefeatable.
When used with super E-cap this maybe could be solved as "energy"
and "power" are some of the benefits of super E-cap. When also power
chokes with 0,05mm silicium steel-core are used, low-end response might be very
good. So the idea is basically a SE-amplifier with super E-cap and 0,05mm sil.steel
power chokes...
The design.
A power tube is driven by a driver (?). I prefer "iron" as plate load,
so an interstage seemed a good option here: no coupling capacitor is used and
a grid resistor for the power tube can be omitted. The power tube needs an amplification
of about 6 for full power when using Mystique as preamp. Also the plate resistance
should not exceed 5 KiloOhms regarding the design of the interstage. At the
internet I ran across the Philips 4606,
an "Post" tube used in telephone repeater amplifiers back in the '60's.
With a Rp of 5K5 and a amplification of 5.5 and a powerful 4.5Volts/1Ampere
cathode, the choice was not difficult. The filament of the '45/2A3 will be AC-heated
and the 4606 DC-heated. Cees Pel, a fellow tube-enthusiastic, advised me in
also using super E-cap at the filament power supply. The filament power supply
is carrying signal since the filament is also the cathode in DHT designs...
Cees has tried it and never took the super E-cap from the filament supply since...
what more to add? The power tube will have a hum-pot as will the DC-heated 4606!
Why? well, when using Schottky diodes and 2 x 2x2200mF/16V and not willing to
dissipate an awful lot of power on a resistor in a pi-filter, a residual hum
is obvious...AC-heated power tubes at 2,5 Volts are remarkably quiet, even at
high efficiency speaker systems (101dB, in my case). The chassis will be made
of wood, no metal used(!), this because of the benefits as experienced with
Mystique. Click here
to see the schematic.
"Iron".
As
in every tube amplifier, a reasonable amount of transformers are part of the
design. Silicium steel cores with 0,05mm laminations are very good sounding,
so all transformers should be made using these cores. AE-Europe
from Schagen also uses these cores and when spoken to, they agreed in making
the transformers for these mono blocks. Each mono block will carry 8 transformers:
3 power supply chokes, an OPT and an interstage on 0.05mm sil.steel and 3 power
transformers, 1 power supply and 2 filament, on EI-core. All "on top"
mounted transformers are potted and have a powder-coated finish.
The chassis.
Also available from AE-Europe were 2 chassis frames: nice round curved 18mm,
at front and rear even 36mm thick white oak. These are the chassis TriodeDick
uses for his "Little Ceasar". Top side is intended for inserting a
copper/aluminum plate, this will be replaced by oak as well...
_______________