project shown here is based on the construction
found at: http://www.triodedick.com/. Click
"Projects" and then "Stanley en
Oliver". Only available in Dutch.
1986 I bought the book
"Rörförstärkare" (valve amps) by Jean Hiraga
and for the first time read about the queen of triodes,
the 300B. This book is a Swedish translation and was sold
by Danish "High Fidelity" magazine. In the
years to come I built quite a range of valve preamps, but
only one power amp, a push-pull EL84 that really wasn't
very good: Loyes, "Grand Amateur 1960". I
finally bought a secondhand PP EL34 from Luxman, MQ70,
which I had until the early Nineties. For some 8 years I
wasn't doing much hifi and had some unfortunate solid
state amps and a CD player while all my vinyl was in the
attic. Around 1998 I bought the CLIO measuring system,
which really was what matured the idea of launching a
website on DIY loudspeakers. There's a time for
everything and from the last two years of work on
high-efficiency speakers, I needed a wider range of
low-wattage valve amplifiers, thus also a reference 300B
SET amp - 22 years after Hiraga's book. Better late than
some serious coupling cap tests, this amp
delivers some of the most enjoyable sounds I've ever had.
Despite 8 watts maximum output it runs the DTQWTs very
well and I'm always looking forward to setting it up
again after having used my other amps for testing
The 300B triode. Some references
on the history of the 300B tube: http://www.antiqueradio.com/300B_01-98.html, http://www.stereophile.com/features/229/
Loesch has these comments on the JJ 300B:
Made in the Slovak Republic in the former
Tesla Valve factory this Valve has been around a while.
The Valve has a substantial ceramic base and in general
appears well made. Internal structures are a little
different from normal. However the connection between
Glass Bulb and base was worryingly loose and lacking in
rigidity. I felt distinctly unhappy handling these
Valves. While no valve with a separate base should be
pulled out by its glass bulb this lack of solidity is
worrying and possibly has an influence on the sound too.
Both valves where identical so I do not think this was an
isolated fault. The valves where pretty new but run in
for around 100 Hours. Sonically this valve failed to
convince, sounding bright, harsh and edgy. Soundstaging
was lacking too. One positive side, the bass was quite
strong and well defined but the overall tonal balance was
subjectively objectionable and faintly unpleasant. This
valve may have needed "burn in", however my
experience has so far been that few valves change their
sound dramatically after burn in. Moreover, the friend
who bought them still reports similar sonics many 100
hours later. Microphonics are about average.
harsh and edgy... I couldn't disagree more. My
JJs have a rock-solid base and are detailed/transparent
with a wide soundstage and excellent tonal balance. For
reference I had the AVVT and some cheap Chinese valves.
The AVVTs have a more forward/up-front sound, not a good
match with this amp - to my ears. Point is: Read any
review on valves with a big grain of salt - including
mine. There may be an awful lot of circumstances
determining the outcome of a given construction.
R. Rochlin has this on the JJ valves:
Although a bit microphonic, it seems to have the
best balance of smooth mids with upper and lower
frequency extension in my beloved Wavelength Audio
Cardinal amplifier. If fact i love it so much it
now pretty much permanently resides on it as part of my
main reference system, only giving way to the WE300B when
i desire a more, um, seductive sound. Ambience and
imaging are excellent as it inner resolution too!
This is the latest 300B to arrive here in my humble abode
and also the best so far for direct replacement on a
normally run 300B amplifier. Some of you might
worry about a bit of that blue glow on the top, but then
again so did the WE300B have that at the beginning
too. I feel there is just too much emphasis on that
top blue glow. Yes, it does mean a few things, yet
it's not necessarily gonna make your system sound like
junk, burn down a small village, and release a nuclear
warhead on your government. Sheeesh, relax and
enjoy the music! The JJ Electronic 300B seems to have all
the things i love about 300B tubes! What more can I
say then that? May I humbly suggest you try the JJ
Electronic 300B? You too might find yourself in
love while enjoying the music.
mean, take your pick on valves.
A complete set of transformers (five) were bought at AE
Europe/Holland including these JJ/300B.
Other tubes are 12SL7GT and NOS Siemens D3a. Someone told
me the 7788 (E810F) were better than
the D3a, so I bought a pair. To my ears the D3a are the
best, but difference is small, if any.
Left: The massive walnut wooden frame for the 300B amp
was a generous gift from John Eekels/Holland.
Right: Only a test set-up to view final appearance. Top
panel is 3 mm alu.
Left: Binding posts and attenuator from Taiwan, phono
sockets from Hong Kong, all trafos from AE
resistors, caps and tube sockets from TAD/Germany + local shops,
tubes from everywhere; quiet a global project.
Right: 300B heaters from Tentlab/Holland, quiet
expensive, but no hum. Very important with 95 dB
Left: First all heater supplies and signal cables. All
cables used are silver plated copper in teflon.
Teflon is great compared to e.g. PVC as it doesn't curl
up during soldering and you need a lot of heat here and
Right: High voltage lines shaping up.
Left: This chunky mains trafo has a lot of secondary
windings! Tube amps need a lot of different power
supplies. Siemens D3a tubes in front.
5U4G rectifier tubes at rear. The lay-out is for a 12SL7
and obviously 6SL7 can be used, but order main trafo with
7V/2A tab rather than 14V/1A
and use 7806 regulator. I don't know why Triode Dick used
12SL7 as the 6SL7 - from my google search - is available
everywhere. I had my 12SL7
from the US.
Right: Preliminary amplifying stage with whatever
coupling caps I had a hand. Silver/gold caps have been
Left: Ready for turning on the power switch. Right: No
smoke or bad smell!!
Time to measure voltages and see if I could reproduce the
values given by Triode Dick and John Eekels.
Bold red is John Eekels measurements. In circles my
measurements, left and right channel. Measurements done
with shorted input.
Fluke true RMS meter used. My mains supply was 235 volts
this evening, rather high.
5 volts RMS into 8 ohms resistor @ 1000 Hz.
The CLIO can be useful for amps too. Here THD = 2% @ 5
volts RMS into 8 ohms, 1000 Hz.
THD at 1000 Hz:
1% THD @ 0.84 watt into 8 ohms
2% THD @ 5.1 watt into 8 ohms
3% THD @ 6.6 watt into 8 ohms
5.4% THD @ 8 watt into 8 ohms
At 8 watts into 8 ohms the amp starts clipping. All as
It is claimed that only the 0.47
uF coupling cap has a significant impact on performance,
where the 2.2uF and 0.1 uF caps are of minor
importance. Buying high-quality 2.2 uF is seriously
expensive, so until later I have used a 2 uF Sonicap
For the 0.1 uF a Jensen copper should do well.
Left: Auricap 0.47 uF/600V. Right: Mundorf
silver/gold/PP, 0.47 uF/1200V.
Left: Russian FT3 teflon caps, 0.22 uF/600V. Right:
Hovland 0.1 uF/600V.
Left: VCaps, tin/teflon. Right: 2.0 uF Sonicaps replaced
by 2.2 uF silver/gold caps (prototypes).
Left: Russian Silver Mica, here 40 nF for C1. 178 nF used
for C3, see tweak section below.
Middle: PIO K40Y-9, 220 nF/1000V.
Right: Russian PIO (green), K42Y-2, 220 nF/500V
wait some time for the silver-gold coupling caps. This
amp is enormously sensitive to the quality of 0.47 uF
capacitor. Put in a low cost Solen cap - and you have an
amp you can listen to for hours and hours; smooth as
velvet. Add a 100 $ silver/gold and all of a sudden you
have treble extension and detail. Jantzen Superior cab
did well too but I like these Z-caps better for speaker
entering some comments on sound, let's see what others
have found (always a good idea!):
Capacitor comparisons Mundorfs, VCap, Sonicap Platinum,
good-sounding capacitor is essential!
with some surprising results:
Electric The Great Capacitor Shoot-Out
Interesting review from Chinese magazine
Frontline Magazine, November, 2006
from the very expensive V-Cap
Teflons, consensus is not the first thing that
comes to mind after reading these reviews. As always:
Read a lot and do your own tests.
be quite amusing reading what people come up with in
terms of describing sound. I've collected a range of
"- infinite shades of resolution riding on
the oh-so-smooth sonic flow": How about
1. Auricap 0.47 uF/600V
2. Mundorf silver/gold/PP, 0.47 uF/1200V
3. Russian FT3 teflon caps, 0.22 uF/600V
4. Hovland 0.1 uF/600V
5. Solen MKP-FC, 1 uF/650V
6. Jantzen Audio Superior Z-cap, 1 uF/800V
7. VCap, tin foil/teflon, 0.1 uF/600V.
8. Russian Silver Mica, here 40 nF for C1.
9. Russian Silver Mica, 178 nF for C3.
10. PIO K40Y-9, 220 nF/1000V.
11. Russian PIO (green), K42Y-2, 220 nF/500V
tests here were done with the 300B amp driving the DTQWT
speakers and front-end was vinyl/DV20X-high/Transcendent
RIAA w. Mundorf silver/gold/PP coupling caps. Digital was
Shanling T80 with silver/gold coupling caps and WE396A
tubes in buffer stage.
To cut a
long story short:
have already been commented. Smooth and easy on the ear,
but (seriously) lacking in treble balance and resolution.
FT3: Smooth, smooth as described by Jon, I
couldn't agree more on his characterisation of this cab.
Transparency is quite good and if you have trouble with
sibilance, try this cap. Not my cup of tea.
An overall smooth sounding capacitor with fairly good
resolution - if it wasn't for the Hovlands just being
This is a cap I could live with. Transparency is fine and
overall tonal balance excellent if it wasn't for the
Mundorfs being better.
Z-cap: I need to try this again, because I
couldn't decide how I felt about this cap. I love them
for speakers, but as coupling cap.... not sure.
Silver/Gold: There's no free ride when we're
entering the very high-end range of capacitors. These
silver/gold/pp have all the transparency I could ask for;
they have the right tonal balance and listening to female
vocals I found out I had to further fine-tune the VTA on
my LINN tonearm! If vertical tracking angle was less than
perfect the Mundorfs will clearly tell you from
emphasized sibilance generated by poor cartridge
alignment. Solen/FT3/Auricap would to some extent smooth
things out here being more forgiving in upper mid/lower
treble but we don't want caps to "repair"
shortcomings in other places.
The king of caps - or is it? Fortunately we can get away
with 2 x 0.1 uF for this 300B amp, some 100 US $. These
caps are heavy despite their average size, but tin foil
is significantly heavier than alu foil. When I play the
VCaps, I miss the up-front aggressiveness of the Mundorf
silver/golds and when I play the Mundorfs I miss the
calm, authoritative presentation of the VCaps. Having to
compromise, these VCaps probably are the best of them
all. I don't find much difference in terms of
transparency between the two; they are both extraordinary
good. What I will try is having a blend of both from
phono cartridge to power amp. In all I have 3 coupling
caps here, two in the phono stage and one in the 300B
amp. So, the set-up could be Mundorf + VCap (RIAA) and
Mundorf - or - VCap in the 300B amp.
Silver Mica, here 40 nF for C1. 178 nF used for C3.
PIO K40Y-9, 220 nF/1000V.
Russian PIO (green), K42Y-2, 220 nF/500V
The three caps here were all tested against the
Mundorf Silver/Gold cabs and these PIO caps really aren't
bad at all. Surprisingly good, actually. The Mundorfs may
excell by a fraction in overall resolution, but I might
as well pick one of these two PIOs for smooth and
The Silver Micas are some chunky beasts (178 nF) and to
cut a long story short, I might as well leave these caps
in the 300B amp for good. These cabs can be stripped from
the metal case (magnetic) and put into some wooden
containers filled with wax. I got two of the 178 nF for
17 US $. Two 220 nF Mundorfs are ~82 US $.
cap (C2) is claimed to only have minor
significance to the overall presentation and I have been
running the 300B for a long time with some 2.0 uF Sonicap
leftovers from the Audio Mirror amp. Now this C2 is
directly connected to the most important cap in the whole
construction, C3. C3 needs to be the very best we can
afford, but being under constant AC, like the C2, I have
my doubts that C2 will not have an impact on the
performance of C3. I'm not an expert in valve circuitry,
so I have to try out stuff - and listen. The Sonicaps
were replaced by silver/gold caps - and I think it pays
caps is a never ending exercise. We easily end
up wanting one cap for a particular recording and another
cap for another recording. No cap will be the best for
all circuits and whatever is in front of your amp and
behind. Tuning a complete system takes a lot of
compromises in making the best match of components from
our phono cartridge/CD-player to the final speakers.
really happy I made this 300B amp. It's the best
I've ever had although the Audio
Mirrors are getting close with the latest mods.
The 300B differs significantly from all other amps I have
had. It has this expansive, holographic midrange I never
heard from any other amp and from good recordings it can
bring you close to the music like few other amps can do -
that is - if connected to high-efficiency speakers. Don't
count on 90 dB or less speakers to experience what 8
watts from 300B SETs can do. They need more, a lot more
to reveal the dynamics it is capable of! The Audio Mirror
amps have better low-end punch, but I can live with the
more soft presentation of the 300B.
My 300B amp can run the TQWT and DTQWT to ear-splitting
levels without serious distortion - something the MAE1 amp couldn't
(only TQWT tried). I guess the oversized trafos of the
300B amp plays a role here. 1½ watts difference can't be
the whole story, but I'd like to hear the MAE1 again with
some good OTs driving the DTQWT speakers.
Mail from an experienced 300B builder (and
my comments in red)
#1) The most important (sonically)
capacitor is the 300B Cathode capacitor and the
Powersupply capacitor for the 300B Stage, because they
are such large values and electrolytics, even Black gates
are quite bad.
Connect the best quality 22uF/450V (value quite
critical, 23.8uF is theoretical ideal) capacitor
you can locate between the 300B Cathode and the top of
the Output transformer and connect a resistor equivalent
to 1/4 of the DCR of the Output Transformer but at least
47R between the +B capacitor and top of the output
transformer. This 22uF capacitor now closes our output
current loop at most frequencies (above around 300Hz),
instead of the series connection of the two electrolytic
capacitors, which help out at the very bottom end. See
the Lynn Olson slides on currentloops at www.nutshellhifi.com to understand
the goings on.
Tweak #1 was tried and left on for about two
Trying modifications like these, the best thing to do is
to stay with the modification for quite some time and the
remove it and listen again. That is, if the modification
is not immediately apparent in terms of improved sound.
And this tweak wasn't. No improvement could be heard,
neither immediately nor after 6-8 days of burn-in. After
two weeks I removed the capacitor and restored the
original set-up and again no change to the sound could be
After a few hours of listening I came in doubt whether
there was a slight midrange warmth associated with the 22
uF in place, thus I inserted the cap again and left it in
for experiments #2-4.
#2) The second most important
capacitor is the coupling cap, as you know. I use
nonmagnetic silver/mica ones.
Silver Mica caps, 178 nF, were bought and replaced 0.47
uF Mundorf Silver/Gold caps. The micas were stripped from
their metal case.
#3) The THIRD most important one
is the bootstrap capacitor in the Mu-Follower, C1. This
is another coupling capacitor. If I use mu-Followers I
use 10nF Silver/Mica with a 4.7M Gridleak resistor
instead of 470K/100n.
Silver Mica caps, 40nF, were bought and replaced 0.1 uF
V-Caps. The micas were stripped from their metal case.
Gridleak resistor was changed accordingly.
#4) The 2.2uF is also important,
but most important here is a sufficient value, 2.2uF is
definitely marginal, at best. I would personally prefer
to clamp the screen grid with at least ten times as
22 uF is a lot! But having the 22 uF at hand from
#1 tweak. I inserted this one. All other things
"as-is" (Mundorf, V-Cap, etc.). No change to
the sound could be heard from increasing the value 10x.
With tweak #1 in place, tweak
#2-3-4 were all added at once and some 10 hours of
burn-in was allowed before sonic evaluation began.
First of all, had I known these silver micas, I'd
probably not bought the Mundorfs. That's how good I think
they are. The Mundorfs may offer a fraction better
transparency, where the micas seem to produce a more
"naked" presentation, i.e. colouration seems
very low. The micas do not in any way smooth things out,
make things sound "nice", rather adds a
fraction of presence compared to the Mundorfs. These two
caps appear so close, it's really hard to tell the
difference, and I don't think I'd be able to pick one
from the other in a blind test.
After having had tweak #1-4 on for several days I
restored the 300B back to the starting point and plugged
it in. For some strange reason my brain wants to state some
difference, but I cannot pinpoint any significant change
to the sound from going back. Again I don't think I would
be able to pick one from the other in a blind test. And
blind tests can be very tricky and the few times I have
tried, I often find myself confused after a few minutes
because you tend to swap back and forth too quickly, too
many times, and after a while we can't hear a damned
thing, in particular when trying to evaluate minute
differences between coupling caps. I have to listen to a
particular cap for a considerable length of time before
making a change, and while a range of recordings are
still in my aural memory. Choosing the best cap - from a
range of really good caps - is a matter of taste and may
depend on how the overall system in put together.
While doing the tests described here, I had the
opportunity to borrow a TRAM w.o.t. line stage. After
building the Grounded Grid line stage, I though there'd
be peace on the line stage front for a while. This turned
out not to be the case and despite a modest priced
coupling cap (Obbligato) in the TRAM, this amp has a
midrange transparency I didn't think possible. The TRAM
amplifying stage is extremely simple, while the power
supply is not, being valve rectified and valve regulated.
Point in bringing this up here is that another circuitry
may require a completely new cap test - with completely
new results. The better the basic circuitry, the less
critical our choice of coupling caps may be. We'll see
once I've cloned the TRAM line stage.
From left: 40 nF silver mica, 178 nF silver mica, Mundorf
Supreme silber/gold, V-Cap. Micas still in metal housing.
#5) Another thing to try is to add a
gridchoke on the 300B to the Mix...
Tweak #5 and #6 will have to wait
for another 300B project.
#6) Finally, I am not the greatest fan of
the 12(6)SL7 Mu Follower. It is okay, but tends to sound
a little mechanical and artificial. Given you already
have a D3a (about the best driver tube for a 300B Amp I
can think of) in your amp, why not use it? Wire it as
triode with 100R from both screen grid and suppressor
grid to the Anode. Use a 22K/12W anode load resistor
(Mills), 240R cathode resistor and a suitable bypass
capacitor (at least 140uF). I use 80uF/35V Film
Capacitors, two in parallel, but these are virtually
impossible to get, as are the Rubycon SWR series which
includes 100uF/35V. Given the capacitor issue, if you
like, find a 2V large size button cell (Lithium Type)
plus socket and connect it to the grid of the D3a,
negative to grid, parallel it with a 0.01uF capacitor of
the highest grade (I use Silver Mica) and a 4.7MOhm
resistor. Then connect the cathode to ground. Change
Battery every two years or so, together with the tube.
This simple triode stage to my ears is much better
sounding than the Mu Follower with 6SL7 or 12SL7. If you
don't like it, you can easily convert back.
Anyway, have fun. NN
Tweak #1 again, this time with 22 uF/630 V Obbligato caps
and 47R Kiwame resistors.
Maybe - and only maybe - it adds a slighly lush
tone to the midrange, where the un-modded situation
clean and - well, right. I'm sure I wouldn't be able to
pick one from the other in a blind test. This tweak just
simply doesn't pay off.
Left: Bogart at the counter and lady on the floor playing
with flying saucers!? Right: I guess we don't...