Hey guys, any opinions on this tube supply?

wildswan · 3rd February 2007, 09:28 PM

I am designing a supply for a tube preamp (A few old skool passive EQ stages

). It will be fairly high gain (To make up for the EQ losses) so I'll need low ripple above all else. I'll be putting it in a 1u 19" rack, so space is an issue.

The heater supply has to run off a 6.3v winding, hence the shottkey diode and half wave setup. As you can see ripple is taken care of by a pair of capacitance multipliers. (Which also supply a slow turn effect)

The plan is to put the rectifiers in a shielded compartment, and the 'regulators' in the main compartment to minimise hum.

Just wanted to get some opinions before I build anything....

Also, anyone got any suggestions for a better HV mosfet than the IRF820?

316a · 3rd February 2007, 09:43 PM

Hi ,
The 0.47uF bypass cap should really go at the gyrator input . I used to use darlington pairs of TIP50 rather than mosfets in gyrators , used to get the odd f.u.c.t (failed under constant test) mosfet every now and again . Is that a half-wave rectified PSU on the heaters ? If so I'd get rid of that and use a bridge

cheers

316a

wildswan · 3rd February 2007, 10:15 PM

Hi 316,
Yep the darlington is a much better idea. I was going to use the mosfet because I thought they were more rugged in this setup.

But if BJT's are ok here I'd definately prefer to use them.

I only have 6.3v ac at the heater winding of the transformer so I need a very low drop across the rectifier. I'm using indirectly heated tubes, so I figured a small amount of lower order ripple won't hurt. The gyrator is supposed to take care of all the higher order stuff. Am I being unrealistic?

Thanks,
WS

316a · 3rd February 2007, 10:25 PM

Hi ,
You should really use another transformer

Either that or connect a pair of diodes as a voltage doubler . I don't like the idea of half wave rectified anything , unless it's only got an LED on the end of it

cheers

wildswan · 3rd February 2007, 10:50 PM

I know. But I like this Tx

(It's a cute little toroid that fits in my case!) With a voltage doubler I'll waste more power. Oh btw the heater winding is only rated at 2.5A, and I'll probably use 2A of heater current eventually if I can. (I wanna see how many 6sn7s I can fit in

) Surely the doubler will also give me lots of ripple anyway?

A tube heater is a bit like a vintage LED

Is it worth a try?

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3rd February 2007, 09:43 PM	#2
316a diyAudio Member Join Date: Dec 2002 Location: West London	Hi , The 0.47uF bypass cap should really go at the gyrator input . I used to use darlington pairs of TIP50 rather than mosfets in gyrators , used to get the odd f.u.c.t (failed under constant test) mosfet every now and again . Is that a half-wave rectified PSU on the heaters ? If so I'd get rid of that and use a bridge cheers 316a

3rd February 2007, 10:15 PM	#3
wildswan diyAudio Member Join Date: May 2006	Hi 316, Yep the darlington is a much better idea. I was going to use the mosfet because I thought they were more rugged in this setup. But if BJT's are ok here I'd definately prefer to use them. I only have 6.3v ac at the heater winding of the transformer so I need a very low drop across the rectifier. I'm using indirectly heated tubes, so I figured a small amount of lower order ripple won't hurt. The gyrator is supposed to take care of all the higher order stuff. Am I being unrealistic? Thanks, WS

3rd February 2007, 10:25 PM	#4
316a diyAudio Member Join Date: Dec 2002 Location: West London	Hi , You should really use another transformer Either that or connect a pair of diodes as a voltage doubler . I don't like the idea of half wave rectified anything , unless it's only got an LED on the end of it cheers

3rd February 2007, 10:50 PM	#5
wildswan diyAudio Member Join Date: May 2006	I know. But I like this Tx (It's a cute little toroid that fits in my case!) With a voltage doubler I'll waste more power. Oh btw the heater winding is only rated at 2.5A, and I'll probably use 2A of heater current eventually if I can. (I wanna see how many 6sn7s I can fit in ) Surely the doubler will also give me lots of ripple anyway? A tube heater is a bit like a vintage LED Is it worth a try?

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