The official G9 help thread

[Godders]

There's a thread in the G9 meta. I believe 470n is the correct value although either will work.

Cheers

Nick

 

[ubxf]

Try with a electrostatic shield (a grounded metal plate or foil of some kind) between the transformers and the pcb/frontpanel-pcb..

Thanks Jakob everything works as it should. thank you for sharing and supporting this design
francois

 

[gyraf]

:thumb:

 

[nashkato]

hello,
i´ve just finished the work on a g9.
how to get some pictures in here??
my questions before i get the missin output potis and turn the lights on.:
---???----i used 230volt trafos ,couldn´t get other,how will this affect the currents on anode?(245V)
----????----- the heatercurrent can´t be adjusted.wouldn´t it be more lifelasting to the tubes to set it to 12,6V?

 

[gyraf]

..the 12V for the heater is well within the specified +/-10% range for heater voltage, and will not influence tube life for the worse...

Jakob E.

 

[veermaster]

Dear members,
I just finished a G9 but I´m having serious trouble with the output trannies. You might wanna follow this link here since I posted this problem also in the Lab, but I don´t have a solution yet:

http://www.groupdiy.com/index.php?topic=22602

Thank you in advance, Emre

 

[laiben]

Hi,

I am having problem with the channal 2 of my G9, the output volume of channel 2 is very low. Channel 1 is fine.
On my crappy scope, I can see that on the grid of V2A is signal is very week,
but on the grid of V2B is signal is still strong on both channel. I suspect it is
the bad tube but I swap both tube the problem still exists. I suspect it is the bad tube socket so I move the tube while my mp3 player is plugged in the preamp it still does not help.

I measure the DC voltage of the V2 on both channel and the reading is similar.. so I really have no idea what else I can do, could someone give me an insight?

The DC readings of the V2 is shown in the pic.

Thanks
laiben

 

[gyraf]

DC points arenot that bad off - Maybe a short at the transformer solderings?

 

[laiben]

[quote author="gyraf"]DC points arenot that bad off - Maybe a short at the transformer solderings?[/quote]

It is very hard to desolder the transformer from the PCB to check.. hope not the solder goes into the shield when I put the mu-metal sheild on the OEP... will report the result.

 

[maxime]

you can check for shorts with a ohm meter instead of desoldering...

 

[nashkato]

hi,
got just ready ,and got no signal on the scope.wether mic nor instr.-input
heat is exactly 245V,ff is 11,9V
tubes are new, all connections to the scope checked.
maybe i got something wrong with those lorlins?(haven´t used them till now)
anyone got an idea?

 

[gyraf]

There is no way to guess what your problem might be.

Any of the usual suspects..

Try tracing signal through the unit, following the schematic and looking at the pcb layout. And read the function description at the gyraf page.

Use an continuity/ohmmeter to check if the switches do as you would want them to.

Jakob E.

 

[laiben]

[quote author="nashkato"]hi,
got just ready ,and got no signal on the scope.wether mic nor instr.-input
heat is exactly 245V,ff is 11,9V
tubes are new, all connections to the scope checked.
maybe i got something wrong with those lorlins?(haven´t used them till now)
anyone got an idea?[/quote]

just my guess: if a lorlin is bad you will only have problem in one channel..
do u see any signal going into the transformers?

 

[nashkato]

ok, now,
you can´t imagine how stupid one can be, not seeing the wood cause all of the trees.
( i didn´t solder the 10pin connections ,they fit that good)

now it´s so far that i got a really good sinus on the scope until i turn up the gain to setting 6,7, or 8,i guess.

then it gets weird: this must be some kind of very high frequency and the sinus is gone. on both channels the same.
didn´t hear it right now,thats what i saw on the scope.

 

[maxime]

hello happy G9 users,
it's been a while I'm using the preamp with great pleasure. I just have one little annoying bit with it. mine have some crosstalk from channel 1 to 2 (but not the other way around).
I checked many details upon its wiring, and every step seems to have been executed in the nice manner.
so I followed the crosstalk on channel 2 from a 10khz sine signal on ch.1.
and:
1. bleed source on channel 1 lies after the output pot (as output pot gives no bleed when down)
2. ch. 2 attenuation (gain pos1-4) affects crosstalk, but not gain (gainpos5-11)

I really suspect some bleed from output circuit of channel 1 to the input circuit of channel 2.
so I grounded temporally some parts of the circuit to locate the bleed source. the source of bleed lies in the output section between the first grid (after r45)
and before the output capacitor (c13). (disconnecting the tube gives no crosstalk, disconnecting one end of c13 gives bleed)

do you think of one factor connecting to my problem? experiences of this type?

capacitor size (some of mine are rated 400V, instead of 250); capacitor type and orientation tube shields? pcb traces?

to get the idea:
-40dB /fullgain on channel 1 at 10kHz gives -17dB on channel 2

thanks
Maxime

 

[maxime]

do you think capacitor geometry/ shape can affect the crosstalk in this circuit?
would other caps (scr or or solen) give me different results?

best
Maxime

 

[josh]

I am nearly finished with this bad boy and I have just a few questions.

-The BOM I used calls for 10mf 500V caps at C25 & C125, the pcb asks for 250V caps. Can I use the ones I have? I ordered the 250's and they'll be here in a few days anyway.

-The BOM I have also crosses out C7 & C107, but another one does not. What's going on with that? I also have these arriving soon anyway.

-The instrument jacks I bought have 4 pins on the bottom, 2 fore and 2 aft. The pcb has 3 positions, from to and ground. Which goes where?

-Underneath the psu section I see a "to light 12V/50mA" with F+ and F-. Is this for the power on/off LED?

 

[maxime]

the 12V is for the LED. make sure you are using a properly rated lamp or LED with series resistor. 500V ratings for the caps are ok.
the jacks meant to be used are of the mono type but with a "normalizing pin". it should be wired so that when nothing is plugged in, the signal comes from the pcb ("to") and gets back to it ("from") . the tip is connected to "from" on the face pcb.
best
maxime

 

[gyraf]

..and 250V is also fine for the caps - remember to take a look at the description at the gyraf/diy page..

 

[josh]

One more question while I'm waiting for D06 to arrive.

I know where the power grounding comes in, but where is this point?

"Connect 0V/Gnd to chassis at one ..."