The official G9 help thread

[APL]

Thanks for the reply Jacob.

More expense! I had a OEP transformer left over from Pultec build.  But Ill get Lundahl  for output

 

[gyraf]

If you have a OEP anyway, you should definitely try that first - you can always change in the Lundahl at some later time - this gives a good impression of transformer character. Who knows, you may very well like what the OEP does (quite a few G9-builders really like it, despite less-than-perfect measured specs!).

Jakob E.

 

[Deepdark]

For those who want, here is a mouser card with all resistor/caps/and stuff needed from mouser. The only things that are not on the card are the case, transformers, tube and sockets and the lorlin switch. Hope this will help someone

You will see I put 2 bridge rectifier instead of the diodes. It's for the installation on the spare psu board

I mostly go with Vishay / Cornell Dubilier stuffs. Everyone is free to change whatever they want.

The power caps are rated 220u instead of the original 100u.

http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=0bb030cf12

 

[APL]

Ive noticed differences between the  the schematic, the BOM (Gyraf site) and the actual pcb board.

Ive just changed C14 & C15 for 220u having originally bought 100u.

Now Ive noticed the PCB has c16,C17 & C18 as 35v. While the schematic and BOM show 25v (which I've bought)

Can somebody confirm If I should follow values on schematic only - is that 100%  correct?

 

[Deepdark]

Concerning the 220u, there is some folks who experienced hum and they fixed it by increasing the value from 100u to 220u. You could go with 100u, it's fine.

35v instead of 25v is ok, too. the schematic and original BOM recall some 25v, so this value include all safety margins. 35v is just a little higher, no trouble with both. It's probably there because they were easiest to get than the 25v, I don't know.

 

[APL]

Reading through the thread it seems the position and orientation of the toroids is very important. As I understand the toroids should be mounted on top of each other, but how should they be mounted in case:
a) verticaly - ie fixed into base

b) horizontaly -ie fixed to sides. If so should they be fixed
Back of case point towards front
or on side  pointing across case.

Ive seen all variations of above in photos

 

[gyraf]

mounted to base is the standard solution

 

[bruce0]

I did my power supply external... So you an take this with a grain of salt:

My experience has been that toroids are usually somewhat asymmetrical in their flux radiation pattern and thus the ability to turn them allows you to adjust the pattern to miss input trafo's and sensitive part of the circuit. 

Also from other projects I have found that if you "lift" the PCB or the TRAFO somewhat off the bottom plate of the case, you can reduce noise the bottom plate of the case acts as a system for transmission of the PSU interference (because of the square of the distance rule... in this respect 3/8" standoffs may be more than twice as quiet as 1/4" standoffs ). 

My experience was that while steel was good for shielding, it also carried the interference, and by using standoffs on PCB and the PSU to get the transformers away from the case structure.

That said, when pictures are posted they show that most of the people in this thread that describe "hum" have missed some of the basics... Twisting all AC wiring and signal wiring tightly, running power wiring at right angles to input signal wiring, creating as much distance as possible between PSU/AC wiring.  I would call these the "low hanging fruit" of noise reduction.

And APL, take a look and google for radiation patterns for toroids... quite a bit of flux density is radiated along the core axis.http://upload.wikimedia.org/wikipedia/commons/4/45/Magnetic_Vector_Potential_Circular_Toroid.png

 

[APL]

Bruce ,
Thanks for the detailed reply. I think most of the 85 pages here seem to contain some comment about hum problems, thats why I trying to consider best solution before I start.

Thanks

 

[collinTHEbrewer]

That moment when you realize you soldered in the transformers without putting the shielding cans on... 

 

[Deepdark]

Damn good luck

 

[Alexandru marian]

Hello everyone, my first post here  :

I'm about to start building a G9.  I was wondering if there would be any potential problems in building it in dual mono, point to point connections, with the PSU in a separate enclosure. 

Thanks! 

 

[collinTHEbrewer]

Hello everyone, my first post here  :

I'm about to start building a G9.  I was wondering if there would be any potential problems in building it in dual mono, point to point connections, with the PSU in a separate enclosure. 

Thanks! 

I can't see why it would be an issue. I think the PCB approach it pretty straightforward, but if you want to go p2p, why not?

 

[collinTHEbrewer]

So the Lorlin switches I ordered are the D shaped shaft type. They do not really correctly align with the default Gyraf front panel. Any way to change this? On some of the switches, I can just tighten the knob's set screw to the rounded section of the shaft to properly align, but on others it's too close to work.

Any ideas?

 

[gyraf]

Use a piece of cut-off shaft to fill the D-shape-space,  glue in?

D-shape shafts come in all different angles - you'll need to get the right types if you want to use D-type knobs (I wouldn't).

Jakob E.

 

[Alexandru marian]

we are on, Lundahls on the way!

Since I have no use for them, i thought about removing some small features:

-remove Line input:  I removed attenuation input resistors, relay, diode, 12V line.  Use a single pole switch instead of dual, right?

-remove  instrument jack:  input trafo goes straight to C2

-remove low filter: remove the switch and 2 caps

-remove phase invert:  remove switch and resistor from output trafo. 

Could someone more experienced check my revised schematic and see if everything is OK? 

Thanks!!

 

[gyraf]

Looks right...

 

[JayDubrek]

Finally got round to building my G9 after having the PCBs lurking in a draw for years. Used plastic cased toroidal transformers mounted off the rear of the case. No hum and sounds silky smooth. Thanks for another great project Jakob!

 

[APL]

I'm Just finishing the HT supply and  thinking about bleeder resistors.

1. I read that people have perminent  resistors directly across terminal s of capacitors (C14  and C15). Recomended values range 220k to 1 M.  Would 100k 2 W be OK?

2. Instead of having bleed resistor across terminals. Could I change mains switch to 4 pole and wire  2 bleed resistor/LED circuits  via the switch so C14 & c15 discharge in the "off" position.  Hope that makes sense.

 

[Alexandru marian]

Thank you very much a lot Jakob!

Some more (noobish) questions:

-toroidals: is 30VA required for each secondary or in total. I found units that might fit or not depending on how one reads this.  They are rated 50W, 230-2x12 V, 2 A each.  So we have 24 VA each, and if summed, 48 VA (close to the 50W rating (formula is smth like 0.8 times... right?) 

-preamp capacitors:  initially I wanted to use Mundorf Supreme everywhere but it costs a fortune so I went for WIMA MK4s.  I don't really buy all the snake oil cap thing anyway.  Still, just to make sure, are there any "more important" caps where I could  put something expensive if I have the money, or at least bypass?  Perhaps the ones that are in line with the + line (for example DC block, inputs, output etc) rather than across + and -

-  +245V  electrolytic filter, can this be replaced with a fancy film cap, or at least bypassed? 

-same question for C11  electrolytic cathode shunt

Thanks!