Wow congrats on finishing the Bijou! This takes me back. My kit (also with photoflash caps) still remains on the backburner as the cans I listen to nowadays are low impedance... but maybe one day I'll finish it.
Neat work Tony. What PCB did you use? Also what was the noise like? Noticed the heater wiring wasn't twisted all the way to the EL34's. I've always struggled slightly wiring htrs on octal sockets on power valves which are pins 2 & 7 unlike a small signal triode like the 6SN7 which have htrs on pins 7&8. Wonder why they wired power valves differently?
Andy.
Andy,
i am sure i will raise quite a lot of eyebrow's, the psu is nothing you probably have seen...
noise os quite good, excellent even....twisted wires for ac heaters need not go all the way....
we made a pcb to incorporate all psu parts and then some...so that wiring is kept to minimum....
will post as built and revisions, the 6f12 has far too much gain than the 7199...
i am sure i will raise quite a lot of eyebrow's, the psu is nothing you probably have seen...
noise os quite good, excellent even....twisted wires for ac heaters need not go all the way....
we made a pcb to incorporate all psu parts and then some...so that wiring is kept to minimum....
will post as built and revisions, the 6f12 has far too much gain than the 7199...
Attachments
There are lots of reasons to use a vacuum tube rectifier . . .
Marketing and Sales: Looks pretty; is said my many to "sound good"; can make it an all tube amplifier.
Negative Performance: A direct heated tube rectifier has a quick turn on; makes the B+ voltage less stiff than solid state rectifiers; has a B+ voltage drop.
Positive Performance: Indirect heated tube rectifiers have a soft start; TV damper diodes have an even longer time soft start.
Marketing and Sales: Looks pretty; is said my many to "sound good"; can make it an all tube amplifier.
Negative Performance: A direct heated tube rectifier has a quick turn on; makes the B+ voltage less stiff than solid state rectifiers; has a B+ voltage drop.
Positive Performance: Indirect heated tube rectifiers have a soft start; TV damper diodes have an even longer time soft start.
How much longer, please ?
I did look fast at some datasheets ( PY81-88-500 ) but could not find nothing explicitly, except maybe some indirect info in one ( PY81 maybe, not sure off-hand ).
yes indeed, i saw this idea in a Japanese blog, maybe ten years ago, it made sense to me so i adopted it, and i will do it over and over again, there are still millions of tv damper tubes out there waiting to see action...
the rectifier tube then served as a big power resistor....
I hope nobody is using a directly heated rectifier tube to delay the B+ turn on time.
Unless, you are using a special application, like this one for example:
A separate 6.3VAC filament winding (dedicated to the rectifier tube Only, No other filaments on this winding),
and a 5Y3 5V 2.0Amp filament, in series with a 0.65 Ohm 10 Watt resistor.
At power on, the 5Y3 cold filament is Much less than 1 Ohm, so lots of the 6.3VAC is across the 0.65Ohm resistor, eventually the 5Y3 filament warms up to 2.5 Ohm, then the filament is at 5V, and the 0.65 Ohm resistor drops 1.3V from the 6.3V filament winding.
Unless, you are using a special application, like this one for example:
A separate 6.3VAC filament winding (dedicated to the rectifier tube Only, No other filaments on this winding),
and a 5Y3 5V 2.0Amp filament, in series with a 0.65 Ohm 10 Watt resistor.
At power on, the 5Y3 cold filament is Much less than 1 Ohm, so lots of the 6.3VAC is across the 0.65Ohm resistor, eventually the 5Y3 filament warms up to 2.5 Ohm, then the filament is at 5V, and the 0.65 Ohm resistor drops 1.3V from the 6.3V filament winding.
i have a quad of 3b28's to try...if i get crazy enough...
anyway, in my power transformer i have a dedicated filament with suitable insulation to go...
Last edited:
The delay time will vary depending on the rectifier tube type.
If the cold amplifier does not provide a full load on the 1/2 cold 1/2 warm rectifier, than there will be little or no delay of B+.
When the amplifier is turned on cold, it is not just cold rectifiers, it is cold output tubes.
I expect 2A3 or 300B AC filaments will warm up very quickly.
But I know that a KT88 filament warms up very slowly.
That means the time varying load on the rectifier at cold power up varies according to the rest of the amplifier tubes.
YMMV
By the way, why do you need delayed B+ ?
If the cold amplifier does not provide a full load on the 1/2 cold 1/2 warm rectifier, than there will be little or no delay of B+.
When the amplifier is turned on cold, it is not just cold rectifiers, it is cold output tubes.
I expect 2A3 or 300B AC filaments will warm up very quickly.
But I know that a KT88 filament warms up very slowly.
That means the time varying load on the rectifier at cold power up varies according to the rest of the amplifier tubes.
YMMV
By the way, why do you need delayed B+ ?
it is not the delay per se, but the avoidance of surges, hence the soft starting wherein inrush of currents to the transformer and psu caps are mitigated, the impedances along with the rectifier dynamic impedance all collaborate to achieve this soft starting...yes, with a delay of course...
in my 6C33 SET, i used a 10k power resistor from psu rectifier cap to the tube circuits to achieve a ramping up of voltage whilst waiting for the filaments to warm up to operating temperature, and at which time the series resistor is them shorted out by relay contacts to bypass that current limiting resistor...it has been almost 12 years since ad the amp still lives on....https://www.diyaudio.com/community/threads/my-russian-set.216206/
in my 6C33 SET, i used a 10k power resistor from psu rectifier cap to the tube circuits to achieve a ramping up of voltage whilst waiting for the filaments to warm up to operating temperature, and at which time the series resistor is them shorted out by relay contacts to bypass that current limiting resistor...it has been almost 12 years since ad the amp still lives on....https://www.diyaudio.com/community/threads/my-russian-set.216206/
Attachments
Some photos of the Acrosound TO-300 ultralinear amplifiers which I just built. I'm at the stage of checking for errors and performance testing. There's 4 mono channels of amplification.
Octal plug setup for McIntosh c8 and c8s preamps.
6sl7 6sn7 and 2 matched 6l6 per amplifier, solid state rectified.
~20 watts per channel and they are very nice to listen to with 12 db of global feedback.
Power supply is 3x overkill, ultra beefcake! And there's 4 of them.
Octal plug setup for McIntosh c8 and c8s preamps.
6sl7 6sn7 and 2 matched 6l6 per amplifier, solid state rectified.
~20 watts per channel and they are very nice to listen to with 12 db of global feedback.
Power supply is 3x overkill, ultra beefcake! And there's 4 of them.