Vacuum tube Amplifiers
6098/6AR6WA POWER AMPLIFIER
This is a small monophonic
power amplifier. It uses a pair of 6098/6AR6WA(Tung-Sol) beam
tetrode designed by Bell Labs as a power tube for sweep amplifierrs for air bone radar indicators.
It uses 586470(Northern Electric) as the input transformer. It uses a 5691(RCA) as the driver
stage and a 5R4GYB(RCA) as the rectifier. This little amplifier was quite an eye opened for me.
It has fantastic output transformers, 22S67(Thordarson). The output tubes drive a potted
transformer which is arguably the best ever built. It was potted by P&C in Tokyo.
These transformers look like iron, but sound like gold. This output transformer manufactured
for 6L6 push-pull amplifier. Impedance ratio 6.6K: 8/16 ohm. All of components in this amplifier
used high grade it: aluminum can electrolytic capacitors(MALLORY FP377.1), film & foil polypropylene
tubular coupling capacitors(HOVLAND MusiCap), carbon composition resistors(RIKEN RMA 1% type),
metal film resistors(WE GA type and IRC RN type), wirewound resistors(IRC NAS5 non-inductive 1% type).
This amplifier use a schematic diagram modified the Western Electric No. 118A type theater amplifier.
The amplifier uses a pair of 6098/6AR6WA tubes in the output stage that are connected in
a beam tetrode configuration with individual cathode bias. I am current using a 250 ohm, 25 watts
resistors(DALE RH25 1% type) bypassed by a 80uF /150V electrolytic(SPRAGUE ATOM TVA1418).
This amplifier not use a negative feedback in the same way a traditional Mullard or
Williamson type tube amplifier.
This amplifier is only rated power for 16 watts. It employs push-pull 6098/6AR6WA tube to
provide full 16 watts output per channel. This work well with old speakers, and in fact do sound
very good with my early model Electro-Voice Regency floor speakers.
The present upward trend in amplifier power is necessary to keep abreast of other recent
advancements in the audio art. In many cases 16 watts power is adequate to obtain
the full dynamic range of my favorite recordings.
Also, Susumu Sakuma; Japanese amplifier builder says "Many audiophiles use high power
amplifiers to get powerful midrange and bass sound. But excellent speakers refuse brute power.
The most important goal is not 'Power', but 'Energy' and 'Frame of tone'."
This amplifier give me a truly fine performance at any of the finer speaker systems.
3A107A/CV249(4019A) POWER AMPLIFIER
Western Electric developed
the #100 series vacuum tubes for the telephone use, and these
most abundantly even of the other. These vacuum tubes used for voice-and carrier-frequency amplifier
for telephone repeaters. These vacuum tubes had high reliability from that use purpose.
As for England, ST&C(Standard Telephone & Cables, Ltd.) was being manufactured the same vacuum
This is a small monophonic power amplifier. It uses a pair of 3A107A/CV249(STC/ITT) direct heating triode
per channel. STC 3A107A is similar to the type WE 101F tube. This amplifier uses L63/CV1067(GEC)
as the driver stage and a 80(RAYTHEON) as the rectifier. It uses 850N(HAMMOND) as the input transformer,
834(HAMMOND) as the inter stage transformer and ECL86(ANDIO NOTE UK) as the output transformer.
The input stage is comprised of a L63 octal medium-mu triode with a 1mA constant current cathode load.
Also, the driver stage is comprised of a same tube with a 4.7mA constant current cathode load.
Push-pull 3A107A's using cathode bias. I'm current using a 880 ohm, 25 watts resistors(CTG HSN25
non-induvtive 1% type) bypassed by a 25uf/250V electrolytic(WE KS19658 L10).
Output transformer were manufactured for EL84 push-pull amplifier by AUDIO NOTE UK.
Impedance ratio is 8K: 4/8 ohm. This amplifier uses a power transformer with a primary 115VAC,
secondary 300VCT 50mA, 6.3VCT 2.5A, 5V 2A(TRIAD HSM203) and filament transformer with a primary
115VAC, secondary 8.5VCT 1A(HAMMOND 166J8). All of components in this amplifier used high grade it:
metal can oil capacitors(AEROVOX P172J17), aluminum can electrolytic capacitors(WE GA50520),
oil-impregnated paper tubular coupling capacitors(WEST-CAP), carbon composition resistors
(RIKEN RMA 1%type), metal film resistors(WE GA, KS type and CORNING FP2 type), wirewound resistors
(IRC NAS5 non-inductive 1% type). And I usually use high performance resin flux cored solder:
almit KR-19RA made by NIHON ALMIT CO., LTD. TOKYO. JAPAN.
This amplifier use a schematic diagram modified the Western Electric No. 46E type theater amplifier.
Western Electric No. 46E type theater amplifier was the last power amplifier in theater amplifier
with all direct heating triode.
I handcrafted this amplifier by using British made tubes and output transformer with referring to
this original schematic diagram that Western Electric devising it in the 1930's.
This amplifier not use a negative feed back. This amplifier delivers a full hi-fi rated only 1.2 watts
per channel at 1KHz before clipping. Gain is relatively flat from 48Hz to 16KHz with a 1dB peak
at 200Hz. At the high end measured -3dB at about 25KHz. Estimated low frequency -3dB at about 20Hz.
But this work very well with old and high efficiency speakers.
The idea which tries to introduce the voice information with common to the vacuum tubes for
the professional use to the bottom of this vacuum tubes sound firmly appears.
This amplifier has the vivid sound with human sensitivity and kindly grandness.
2A3 POWER AMPLIFIER
This is a stereophonic
power amplifier. It uses a 2A3/VT95(RCA) direct heating triode
It uses a 6CS7(RCA) as the driver stage, a 5R4GY(STC) as the rectifier and Tango NC14
as the interstage transformer.
This amplifier use a simple schematic diagram original designed by Kouichi Tamura in 1987.
This single-end 2A3/VT95 power amplifier delivers a full hi-fi rated 3.5 watts per channel,
but frequency response is wide renge, from -3dB 13Hz to 54KHz at 1 watt output.
This amplifier not use a negative feedback.
Top quality parts are used throughout. All of the coupling capacitors in this amplifier used
oil-impregnated paper capacitors. This amplifier has the light sound that a soup bubble is splashing.
I have noticed the grandness of the sound of direct heating triode by this amplifier for
the first time.
Since, I came to make some amplifiers in search of the sound with human sensitivity.
And I will introduce these amplifiers at this web site, when they are completed in the future.
・Brief Self-An Introduction to The Audiophiles
・My Favorite Music Sources