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300B 5V DC filament supply from 5V AC windings

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cowneko

Member
Joined 2013
Hello,

Here is my problem; I have a 300B SE amp and, until now, they where driving a pair of 91db sensible 3 ways speakers (Davis Matisse HD), the Hum was then manageable with the help of the Humbucket pot.

I recently switch to a pair of Klipsch HeresyIII speakers witch have a 99db/1w efficiency....... the hum is quite there now, witch was predictable.

I think it's time to think about switching to DC filament supply for the 300B, and I need recommendations in this regards.

My 300W PT as the following secondaries:
- 390-320-0-100-320-390 0.3A (B+)
- 5V 4A for the rectifier
- 6.3V 4A for the two 6sj7
- two 5V-2.5V-0V 5A secondaries for each 300B/2A3 power tubes filaments

Can I regulate a 5VDC from those 5V-2.5V-0V 5A secondaries or must I add another transformer (for witch i don't have much space, since I'll have to find available clearance for the regulation boards too)
Witch should be the most tiny/efficient circuit for the regulators?
 
E

Eli Duttman

Member
Joined 2004
Each 300B filament draws 1.2 A. So, you will be OK, if you phase up the 2X 5 A./5 VAC windings, in series, and FWCT rectify the composite with 2X Schottky diodes. The low forward drop (approx. 0.5 V.) of a Schottky is important in this situation, as is dealing with only a single forward drop. Use appropriate, low drop out, adjustable, IC regulation, after substantial cap. I/P filtration.
 
Ketje

Ketje

Member
Joined 2012
Probable he needs two independent 5volt sources.You could try rectifying the 5volts from the transformer with a bridge followed by a capacitor of at least 10mF (10V).Gives allmost 5voltsDC with a little ripple, but much better then full AC.
Mona
 
kmaier

kmaier

Member
Joined 2007
I'm guessing this is a stereo amplifier, yes? As the power transformer has a 100-volt tap, are you using fixed bias or cathode bias?

Two options:

1- If Cathode bias is used, you're using one of the 5V winding per tube. With a 5 amp capacity, you could make a full-wave voltage doubler and have sufficient current and voltage to provide a clean regulated supply per tube.

2- If using fixed bias, you could do as above, or take both 5V windings in series, and use a pair of diodes for a full-wave center-tapped supply with heavier filtering (CLC) and likely get ripple low enough without regulators.

Regards, KM
 
M

MelB

Member
Joined 2005
You can use the 6.3v supply for one of the 300B's and both 6SJ7's. Rectify the 6.3V and you will get ~6.6v => large cap => small dropping resistor => 6SJ7s and also to a low drop 5v regulator then one of the 300B's.
If you need separate windings for the 300B's
 
E

Eli Duttman

Member
Joined 2004
The doubler idea is good. Approx. 1/4 of a winding's RMS rated current is available as DC. 5 A. rated windings yield 1.25 A. of DC, which is adequate.

The "hen scratch" schematic I've uploaded shows the topology needed. Higher current diodes, larger stack caps., and a low drop out regulator are in order.
 

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nautibuoy

nautibuoy

Member
Joined 2010
The thing to remember is that with DHTs like the 300B the filaments are actually part of the audio path so its not as simple as just getting 5VDC if you want to optimise the SQ. I would do it properly with something like the Coleman or TentLab DHT filament supplies, though you'll need an additional transformer (with a separate winding for each 300B).

For my 300Bs I use DHT filament supplies that were developed on a UK audio forum;

DHT Heater using VCCS - PCB or Kit (Possible Group buy) - audio-talk
 
Rod Coleman

Rod Coleman

Member
Joined 2004
The latest versions of my Filament Regulator (V5 and V7) can accept input voltages down to 8.5V for 300Bs (at low mains); Aim for about 9.4V for nominal value, with these. The voltage headroom allows a high-isolation buffer against noise, and a higher impedance, looking out of the filament.

A Voltage doubler is certainly a useful way to build the raw dc for them.
 
C

cowneko

Member
Joined 2013
Thanks for all your suggestions ;)

Rod, If I understand correctly, I may use a voltage doubler for both my 5V 5A secondaries, like this
voldoub.gif


Shall I use some 10000uf 16V here? low impedance caps (panasonic FC) ?

Then directly at the input of your boards?
Enregistrer
Enregistrer
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Last edited:
C

cowneko

Member
Joined 2013
B

bbp

Member
Joined 2005
orthoaudio.blogspot.com/
cowneko said:
Hello,

Here is my problem; I have a 300B SE amp and, until now, they where driving a pair of 91db sensible 3 ways speakers (Davis Matisse HD), the Hum was then manageable with the help of the Humbucket pot.

I recently switch to a pair of Klipsch HeresyIII speakers witch have a 99db/1w efficiency....... the hum is quite there now, witch was predictable.

I think it's time to think about switching to DC filament supply for the 300B, and I need recommendations in this regards.

My 300W PT as the following secondaries:
- 390-320-0-100-320-390 0.3A (B+)
- 5V 4A for the rectifier
- 6.3V 4A for the two 6sj7
- two 5V-2.5V-0V 5A secondaries for each 300B/2A3 power tubes filaments

Can I regulate a 5VDC from those 5V-2.5V-0V 5A secondaries or must I add another transformer (for witch i don't have much space, since I'll have to find available clearance for the regulation boards too)
Witch should be the most tiny/efficient circuit for the regulators?
Click to expand...


Hi Cowneko,

Try active rectifier. Something like ideal diodes. You can get 5.0V x 1.4=7V, and then select an ultra-low drop out LDO for further lower voltage ripple.
I think it is possible, but require a lot of SCH design and PCB work.

BR
Paul Lu
 
Rod Coleman

Rod Coleman

Member
Joined 2004
cowneko said:
Perfect! thanks a lot Rod :)

Witch type of diode should I choose, Schottky I suppose, will those be good?
C3D06060F CREE - Diode: Schottky switching | TME - Electronic components

As for the caps, I may use Nichicon UPW 10000uf (x3 per secondaries) like this:
UPW1C103MHD NICHICON - Capacitor: electrolytic | TME - Electronic components

The res:
KNP05SJ033KA10 ROYAL OHM - Resistor: wire-wound | TME - Electronic components
Click to expand...

The rms current in the diode is higher when the doubler is used, so a good choice is MBR1045 (manufacturer ON, Fairchild etc):

MBR1045G ON SEMICONDUCTOR - Diode: Schottky rectifying | TME - Electronic components


The capacitor from TME, probably the best is:

HE1E109M22040HA SAMWHA - Capacitor: electrolytic | TME - Electronic components

The PW does does have a ripple rating at 100/120Hz, and is a bit low for the doubler duty.

Resistor is OK, please but some extras - say, 0.1 and 0.22Ω, so you can adjust the raw dc, if necessary.
 
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