The official G9 help thread

[sonolink]

Hello again everybody,
http://img526.imageshack.us/img526/8188/outputo.jpg
This is my p2p layout of the Phase Reverse switch section. I've been checking and rechecking but I still feel insecure.
Would someone kindly check if it is correct, please? I would appreciate it very much.
The 6 pads in the center are for a DPDT switch. They are numbered left to right and correspond to the DPDT pin numbers
Cheers
Sono

 

[sonolink]

Nobody? Ok, nevermind.

A question about the schem if you guys don't mind: the schem power supply reads: C16-18 3x25V 1000u. My question is: these caps are connected in series or parallel? I guess it's parallel but it never hurts to check

Thanks
Sono

EDIT: would a pair of these bridge rectifiers do for the G9? (I mean in a p2p build)
http://www.banzaimusic.com/DB107-Bridge-Rectifier.html?quantity=1

 

[gyraf]

The reservoir caps for the heater voltage are in parallel - you can use a 2200u or a 4700u instead.

That bridge rectifier is a bit tiny - will probably do for the HT, and probably not for the heater voltage (use at least a 1.5A type here)

Jakob E.

 

[sonolink]

Thanks for your reply Jakob. Do I need 1000V? I'm asking cos at that shop at 1.5A they have 560V max.
If it's not enough then I'll just go with 1N4007s on turrets then.
Please let me know what's best
Thanks again
Cheers
Sono

 

[gyraf]

If you follow the schematic function you see that HT is at max ca. 500V peak, heater is max. ca. 40V peak, and phantom is probably max around 100V peak...

Jakob E.

 

[sonolink]

Please excuse my ignorance but I don't understand what you mean by schematic function. Is it something you calculate? Is it indicated on the schematic? The only similar thing I could see was the ~60V indication on the PSU...tried also google but it gets more confusing...

Thanks for answering my question but please explain
Cheers
Sono

 

[My3gger]

Hi,

Jakob, isn't heater's 40V peak to peak value and not peak? I'm curious how you got that high numbers for peak values of transformer secondaries. Isn't Vpeak 1,41xVrms?
I like how this page explains conversion of AC voltages:
http://www.wisc-online.com/Objects/ViewObject.aspx?ID=ACE11505

 

[gyraf]

you're right - those figures are rule-of-thumb-worst-case-estimates...

 

[sonolink]

These might be more dumb questions but again in my p2p project I'd rather check:

1-on the schematic, wherever I read GND, ff, heater, 0V, Input Ground...all these are all connected to the same starground on the chassis and to earth, correct?

2-In the power supply, the 48V rail is connected to one of the SW1 Input Sel poles, the 12V rail is connected to the relays and the heaters and the 245V rail (that would be B+, right?) is connected to R31 and V2A anode, correct?

Thanks for your time and help
Sono

 

[MeToo2]

These might be more dumb questions but again in my p2p project I'd rather check:

1-on the schematic, wherever I read GND, ff, heater, 0V, Input Ground...all these are all connected to the same starground on the chassis and to earth, correct?

2-In the power supply, the 48V rail is connected to one of the SW1 Input Sel poles, the 12V rail is connected to the relays and the heaters and the 245V rail (that would be B+, right?) is connected to R31 and V2A anode, correct?

Thanks for your time and help
Sono

Grounding on a point to point build is a whole topic in itself. Do a search and you'll find many pointers both on this forum and elsewhere. You may need several goes to "get it right"

 

[gemini86]

This is a great article to read about p2p grounding, and tube circuit grounding schemes in general. I've used these techniques in high gain tube guitar amps with much success.

 

[sonolink]

Thanks a lot  for your replies and for the links.
I'd be grateful if you could also answer my 2nd question please.
Cheers
Sono

 

[gyraf]

yes, 245V goes to anodes, 48V goes to phantom, and 12V goes to heater and relays.

 

[sonolink]

Thanks Jakob

 

[Aleguitarpro]

I've built my G9 version few months ago and I've problem with hum and oscillations because I haven't done the mods that is described here:
http://www.gyraf.dk/gy_pd/g9/G9-EDIT.GIF

I have done a different front panel and I think to solve the problem radically putting a relay that switch between "mic" mode and "instrument" mode.



In this way I managed to keep the connections very short, solving all my problems.
I don't need a jack with the switch, eliminating while I use microphones any problem of noise/hum/oscillation!
I like to share this little idea here in the G9 help thread in case could serve as inspiration or help someone.

 

[gemini86]

Really great idea!

 

[chrispbass]

Ok, finally got around to finishing my G9 (apart from some cosmetics). All working ok, scopes out good and decided to build B supply off board from the start. Have 289V at the board with valves in, heater supply is about 11.9V, phantom working as it should.

The problem now - hum!

I've read and re-read this help thread, but I'm a little uncertain about how to implement correct grounding as there seems to be a difference of opinions!


I have IEC earth terminal bolted to the chassis.

ALL pin 1's of xlrs connected back to this.

I've done the trace cuts mods.

Transformers are well away from the main board, and are in their own compartment, so hopefully shielded from the audio.

Should pin1 of xlr 1 be connected to the board? I've tried either way - no difference.

Should the B supply have a separate ground?

Chris

 

[gyraf]

289V at the board

too much - should be some 235 to 245V. Your TL783 regulator is probably not regulating, passing ripple.

Jakob E.

 

[chrispbass]

289V at the board

too much - should be some 235 to 245V. Your TL783 regulator is probably not regulating, passing ripple.

Jakob E.

Thanks Jakob, will check it out.
Chris

 

[chrispbass]

Found the problem, I'd made a mistake when utilising the spare HV pcb for my off-board B+ supply. Because I'm not using those massive chassis mounting caps like some have, I thought I'd modify the un-used 12V section of this pcb to enable me to mount my 2 electrolytic caps (C14/15). This meant cutting a few traces and using some insulated links under the board. Great solution so I thought, anyway, it's amazing what a couple of minutes doing a continuity check can find!! 

I'd managed to get the caps mixed up, not polarity, but basically I was pretty much bypassing the TL783  ;D

Anyway, wired correctly, unfortunately I'm unable to test as R33 took a beating and I don't have a spare to hand.

Anyway, mistake admitted and will hopefully report back with a hum free G9 very soon.