Tentlabs Tube AMp Upgrades
TentLabs Directly Heated Tubes Supply
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Despite their massive linearity, Directly Heated Tubes (DHTs) have one major
disadvantage. Their filament is part of the signal flow, i.e. is included in
the audio path, hence the heater supply is affecting the sound. TentLabs now
introduces a novel module, based on traditional techniques, but with some
major advantages over existing solutions. Read further!
Reviews
• Read what Dick van Merwe (Dutch triode expert) writes about these filament
supplies. English translation can be found here:
" What I hear, compared with my earlier applied DC heating, is increased
articulation, an improved focus and clearance between instruments and
soloists. The soundstage increased in depth. The original supply has a
softer tone, you could call it dull - do I want that back? No way, not at
all. And I was surprised by the result, especially compared with the small
amount of work to be done... "
• Clive Meakins tests the DIYhifisupply ladyday kit, including Tentlabs
filament supply, and concludes:
" Part of this smoothness is attributable to the Tent Labs heater supply,
comparing the standard supply to the Tent Labs one shows a higher degree of
smoothness "
" Hum levels are vanishingly low, with my 100db loudspeakers I can just hear
a trace hum up to around 8cm from the main driver "
• Read what Rob Hubertse experienced with these modules
• " I installed the Tentlabs filament supply on my DIY lady day 300B monos
and I must tell you it is a very worth while and cost effective modification.
The tonal quality of my amps has improved as well as lowering the noise
floor to almost undetectable amounts "
• " A few weeks ago I asked about using the Tentlabs filament power supply
for my field coil speakers. Well, I tried them and I have to say that they
are best power supply I've used with these speakers "
Purpose
TentLabs filament supply is designed to heat DHT's the cleanest way possible,
without affecting the music currents generated inside the tubes' heater, see
this presentation that explains the advantages of current source filament
supplies. The supplies generate a very low noise output, while maintaining
its' high output impedance. Result areas are:
• Bigger soundstage
• Better focus0
• Cleaner tone
• Better resolution
Existing current supplies lack true high output impedance and need
adjustment during use. This new module is truly different in many areas -
read on !
Technology
TentLabs has investigated the effect of the heater supply in Directly Heated
Tubes. For detailed information and a rationale for the use of current
heating, see the presentation on filament supplies for DHTs. An overview of
the TentLabs supply is shown below:
The current source maintains the high output impedance (typically > 10kOhm),
whereas the voltage control takes away the need to trim the output voltage
after installation, or during use. The accurate reference guarantees long
term stability, and contributes to a clean output current. The module
exactly supplies that amount of heater current, until the required DC
voltage is achieved, e.g. 5V for a 300b.
The rectifying bridge consists of low noise Schottky Barier diodes and
Electrolytic capacitors (a total of about 20.000uF for the 2.5A version and
34.000uF for the 5A) with a well chosen amount of ESR, to dampen and reduce
the current peaks - all contributes to low noise output !
Application
A typical example is shown below:
Each tube needs its own filament supply, in turn fed by a separate winding
from the power transformer. The whole supply then is floating, and only has
one connection to ground, as shown above. This example above shows the DHT
in fixed bias mode. When using cathode bias, the grounded leg has to be
connected to the top of the cathode resistor instead.
These are the only connections to the filament, so no caps, no hum-bucking
pot, no nada!
The total output current is limited, depending on the version, but they all
start-up slowly. Especially when the tube is cold, this is a nice feature.
Cold tubes, when heated with traditional supplies, draw currents up to ten
times their nominal current. Using TentLabs heater supply will gently switch
on your tubes.
The units are factory adjusted at your order. After installation, the supply
needs minor DC adjustment, to compensate for possible voltage losses in the
wiring (some 100 mV are easily lost at high currents). During use, no
adjustments are needed anymore, not even after changing the tubes !
The new generation filament supplies has an over temperature indicator and
shutdown, in case the heatsink-temperatue exceeds 90C. The LED and wiring is
supplied separately with the modules.
Specifications
Electrical
All versions voltag adjustable between 1.5V and 12.6V, specify when
ordering.
• Output current: automatically adapts to required level to reach voltage
specified above.
• Input voltage should not exceed 1 V above specification (see application
info).
• Output noise < 20 uVrms (1 Hz - 20 kHz).
• Output hum < 200 uVpeak at 100Hz / 120Hz.
• Output impedance 10 mOhm at 0Hz.
• Output impedance 10kOhm > 5Hz.
• The heatsink is electrically isolated from the circuit and can be attached
to a chassis
• Over-temperature shutdown with LED indication
Notes
1. The unit will not work without output load, a minimum of 200mA is
required
2. The output is not short circuit proof
Available versions
Currently 3 hardware versions are available:
• Low noise version, output currents up to 1A. These typically serve small
size triodes to be used as line stages. Output noise is 26dB lower compared
to the standard version. Often used in conjunction with type 26 tube,
integrated heatsink.
• Standard version, output currents up to 2.5A. These typically serve small
and medium size triodes up to output tubes like 300b and 2A3, and have an
integrated heatsink.
• Output currents up to 5A. These will suit the beefy types like 211, 813,
845 and SV572 and have a bigger heatsink.
Mechanical specifications
1A and 2.5A unit:
• Total size 50*90*40mm (W*L*H, heatsink included, standoffs excluded).
• Weight each 90 gram (each, excluding packaging)
• Hole pitch 41* 81mm.
• Needs 10mm stand-offs to mount on chassis, supplied with modules.
5A unit:
• Total size 50*100*90mm (W*L*H, heatsink included).
• Weight 375 gram (each, excluding packaging).
• Needs M4 bolts to mount on chassis, not supplied with modules.
Specials
If you don't find a suitable supply in terms of currents / voltages, please
apply. For example for the GM70 we can supply a derived version from the 5A
supply, generating 20V.
Pricing & warrantee
1A low noise and 2.5A unit, € 116.81 / pair (ex VAT, ex shipping) (€139
including VAT)
5A unit, € 158.82 / pair (ex VAT, ex shipping) (€189 including VAT)
Single units cannot be ordered. 5 years of warrantee is valid for the
filament supplies, assumed they are build in according application
information.