Multichannel G9 PSU hints

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producer4000

Well-known member
Joined
Jun 4, 2004
Messages
56
Location
Memphis, Tennessee USA
Hello, all. As summer quickly approaches, I'm getting ready to begin my first big project for this year. I want to do an eight channel G9. However, I'll need some help with the power supply. I think Bjorn may still be having a little trouble with his PSU, so maybe we can both benefit from some discussion with everyone.

Electronics school has been 14 years ago, so I don't really remember that much of it anymore (wish I'd paid better attention) and some of the 'rules' escape me at the moment. Hopefully some of the members who have working multi-channel G9's can help me sort this out.

What I'd kind of like to do is get a Xformer for each of the required supply voltages. First, can I do this? If not, I'll just get two 15V 120VA Xformers (there is room in the PSU compartment). If so, should I rectify and regulate right there and then buss the supply voltages out to each 'card' (a card being two channels, just like the PCB except a little bigger)?

What then would I have to do to the capacitor values to handle the increase in current (I know the voltage values remain the same and I have to spec the rectifiers and regs). IIRC, Jakob has said that the 245v draws <10mA per tube and the 12v draws <250mA per tube. 48v phantom should not really be an issue but I'll make sure it can supply at least 500mA.

Would it be easier to just get the supply voltages and rectify/regulate on each 'card'? I don't think you're supposed to use more than one rectifier per voltage but I'm not sure about that. :?

Anyhow, any help from the multi-channel guys (or anyone for that matter) is greatly appreciated and respected.

:guinness: Chris
 
..You could distribute "raw" DC to the four boards, that is, from after the rectifiers and the first supply cap. And then use the on-board regulation as local sub-regulators..?

Jakob E.
 
If I was doing an 8ch G9, I'd get one big trannie customwound, with one HV, one heater & one phantompower winding. I would then use HV regulators for each channel and individual heater Vregs as well. I would probably only use one TL783C for the phantompower.

Getting a customwound trannie is not very expensive. Certainly not compared to the price of the whole project.

I'd put the big trannie in a seperate box with rectification and smoothing caps as well, so only DC enters the 8ch G9 box. Makes sense? :?

Using 16 15V trannie is crazy :shock:
 
[quote author="gyraf"]..You could distribute "raw" DC to the four boards, that is, from after the rectifiers and the first supply cap. And then use the on-board regulation as local sub-regulators.[/quote]

This is one of the possibilities I was considering. Can I use separate Xformers in parallel to get the supply voltages, like a 1:2 step up for the HT circuit in // with a 10:1 step down for the 12v in // with a 48v for the phantom? I can't remember if this is 'legal'? :?

I'd get one big trannie customwound

Getting three 'off the shelf' Xfo's will be cheaper, if that's 'legal'.

in a seperate box with rectification and smoothing caps as well, so only DC enters the 8ch G9 box. Makes sense?

Another possibility to be considered and makes a lot of sense. What must be done to the cap values, then, as asked previously?

Using 16 15V trannie is crazy

Not sure where that came from. If I cannot use three separate Xfo's, I'll just use two 15v, 120vA Xfo's back-to-back, just like the schematic.
:guinness: Chris Memphis, TN USA
 
I can get a single customwound job done cheaper than three off the shelf trannies, so I wouldn't use indivduals. It's also messy and heavier.

If you use a single trannie for the lot, I'd beef up the resovoir caps 8-10 times.

A single trannie would really make things a lot easier, imo. If not then use the stepup & down trick. Just remember 16 tubes do draw some heater current, 2,4A, so you need thick wires!

I misunderstodd you with that 16x trannie thing, sorry :oops:
 
[quote author="gyraf"]..You could distribute "raw" DC to the four boards, that is, from after the rectifiers and the first supply cap[/quote]

What changes, if any, to that first cap?
Thanks. Chris
 
make them large enough that you don't have too much ripple voltage at the drawn current. You may need to experiment. Look at Kev's GroupDIY psu pages for rules-of-thumbs

Jakob E.
 
For example, should I use four (or more) 1000uF caps in // after the rectifier for the 12v heater? Or would you reccomend higher value of uF instead? Thanks, Jakob

:guinness: Chris Memphis, TN USA
 
I would check out guitar tube amp transformers. none of the power in my G9 is regulated, except for phantom. it is super quiet. I just have butt loads of capacitance.

I would however regulate the heaters.

a Vox AC30 power transformer supplys about 290V to the pre amp section under load. so with some fat power resistors you could get the voltage right.

so one big TX for the B+ one for phantom and one for 12v heaters.

look at a hammond TX's they might have some in the 250v range. you CAN find a large power TX off the shelf if you look. not to mention a local electronics surplus store that might be in your area. my tube eq (passive)has 6 12au7's and I used the TX from an ols tube signal generator I picked up for $20.

just my 2 cents.
 
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