The official G9 help thread

[Deepdark]

some things come to mind.

Lead dressing: You should twist al your ac lead as tight as possible
I see you audio lead from the xor to the board passing near high voltage leads. Keep them as far from each other as possible.
Run your HT on the bottom of the chassis, on the corner formed by the rear plate and the bottom plate. I don't see really well your safety ground connection. Could you take a picture of your IEC and star grounding?

 

[Voodoobeat]

Do you mean the ACs Coming-out from the Transformer?

 

[Voodoobeat]

And here the xlrs

 

[johnheath]

It looks like you should clean up and sort your grounding.

There are a few things you could try:

Shorten the ac secondaries… twist them tightly. Shorten AFTER you have orientated your power transformer for best noise performance.

Tuck away HT leads from the "open air" into the corner of the back plate and the bottom plate (as mentioned before)

Make sure your grounding connections (XLR screws , cap sustainers and such) have a clean metal connection… it looks like you haven't scraped of the black paint… it could be poor grounding from this.


Best regards

/John

 

[tanstafl]

I have a newbie question related to the TL783 regulator IC circuit.  How does one determine the appropriate power rating of the R34 given a particular output voltage and the values of R35+R36?  I want to use the circuit for 200vdc out at 70ma in a tube headphone amp.  My understanding is that if I set the R35+R36 to 82ohms so that the IC sees the minimum unloaded current needed of 15ma, then R34 is going to see 200V* .015A = 3 Watts *4 = 12 watt resistor.  I dont want to use 12 watt resistors they are to big and expensive. : )  So why is this circuit able to use a 2W resistor here.

Thanks in advance

Bob

 

[APL]

Doesn’t look like anybody has any answers to last question (you could try asking in drawing board as it’s a design question), hope you don’t mind me jumping in.

After 2 years+, I recently finished my G9. It sounded excellent no noise, everything seemed to work as expected. Unfortunately, I had forgot to wire the lamp. The schematic recommends 12v/50mA, the closest I could find was a 12v/65mA filament lamp. When I retested everything sounded the same as before. Although the volume may have initially increased, when I switched off, instead of slowly decaying as previously.
Next time I used it I noticed that the silver coating on top of one of the tubes had flaked off, the tube was also cracked (possibly as I gently removed it). As tubes were new, I assumed the problem was related to the lamp or wiring it, so I disconnected lamp and fitted some cheaper JJ tubes. Everything was back to normal.

Is the lamp current 50mA critical? Would using 65mA bulb cause a surge on turning off sufficient to damage the tube?
Should I have put a 1k? resistor in series with lamp as with LEDs?

 

[Spencerleehorton]

I've just done the mod to the 4.7uf caps and put in 20uf in parallel, giving me 24.7uf as output caps, this s should hopefully solve the low end cut which I seemed to be getting. I'm using OEP transformers.
Will report back once tested.

 

[Alexandru marian]

Spencer, if you have oep on both in and out, it is likely the bass cut comes from the input, according to older discussions.  Get a nicer input tx.  The oep out has sufficient inductance, you don't need more than 4.7uf. 

 

[Spencerleehorton]

ah, ok, well i wind my own input transformer, but i will try this option to see if helps, as ive already done it!! easy enough to unsolder the extra caps.
what transformer specs are ment to be better?

 

[Alexandru marian]

I am afraid I do not know much yet about tx construction. Probably best when starting at it is to buy nice tx and measure and maybe even dissect them   What would work very well for G9 input should be something in the 1:4 to 1:7 range, look at Lundahl 1528/30/38/76, Sowter 4935 or 9045, Jensen 13K7 etc.    You can also consider a beefier 600ohm imp primary if you have high imp output mics like the G7. 

 

[Spencerleehorton]

thanks, i'll look at them transformers and try something out, pretty sure i have them Sowters to try.

 

[Spencerleehorton]

If what your saying is true the bass cut on the input txf would be due to the bias of the txf. If I have the oep 1:6.45 ratio in there on input and loosing bottom end, if I change to lower ratio this essentially is acting like a bias, so I will try a 1:4 ratio and see what the bottom end looks like.

 

[Alexandru marian]

My first guess would be a clear lack of inductance.  i have good bass from a lundahl 1530 with 1:7 ratio. It is probably "medium" inductance, definitely not a "monster"  transformer.

 

[Spencerleehorton]

slightly frustrating, when the lundahl 1530 doesnt seem to have any induction specs!!
i think i have some spare nickel lams but that might be overkill I'm sure M6 will be good enough?
anyone have any idea on induction specs?

 

[BeeHaniwro]

Hello everybody,

I'm very new to this forum even if I read the threads for a long time now. I just bough a G9 PCB from PCB Grinder and received the REV#1 2002.

And this is maybe stupid, but I can't find C24 place. I followed tacks going out of C19, to the light and to the tubes. Bu I don't saw any emplacement for C24... Am I missing something ? Every search on this forum or on google didn't help me....

Bee

Ps : sorry for the broken english. Legend say that it's it's more acceptable when pronounced with a french accent  ;D

 

[APL]

Bee,
Welcome.  C24 is as far from C19 as you can get, bottom left corner next to big C7.
Enjoy your project.
PS  Don't forget to do the DI trace cut modification before you start.

 

[BeeHaniwro]

C24 is as far from C19 as you can get, bottom left corner next to big C7.

Thank you ! I found it, I hadn't follow the track sor far...

PS  Don't forget to do the DI trace cut modification before you start.

I'm sorry but I don't understand what you are talking about  :-[ I try a search here but I don't really understand what I'm suppose to cut, where and most of all, why.

 

[APL]

The DI (instrument jack) does not connect to the connections TO INST and FROM INST  (connecter in bottom left hand corner ). The board needs modified, its mentioned many times in thread but look at this:

http://www.gyraf.dk/gy_pd/g9/G9-EDIT.GIF

I only mentioned it as its easier to do before you start soldering components on board.

 

[BeeHaniwro]

The DI (instrument jack) does not connect to the connections TO INST and FROM INST  (connecter in bottom left hand corner ).

I'm confused,

Following tracks on my PCB, it does strictly the same thing than the purpose modification. If I understand this modification, linking instrument jacks to PCB thru long asymetrical and non-shielded wiring was causing buzz and this modification is here to replace the non shielded wiring buy a shielded one. Am I right ?

So actualy, there is no need to cut trace, do we ? if i don't use the modified tracks on the 5 pins connector, there is no contact ? Am I Right ?

The board needs modified, its mentioned many times in thread but look at this:

Yeah, I didn't found it, my bad. It often comes to me that this project is done since years and years, and this thread  is here since 2006, and has 104 pages. No newcomer will take the time to read the 104 pages. And it's difficult to find these kind of information organically.

Don't you think that it would be a good idea to edit the first post and make it an abstract of all "required to know" informations ? It would help. Like "hey, before you start, here are modifications to do...."

Anyway, thank you very much for your help

 

[APL]

Hi Bee,
It is recommended to cut the traces so the  jack connects directly with input transformer and C2, instead of the route thro board to connector, which apparently can cause oscillation problems, I think most people do it.

There is a lot of information here, good and bad, but see  posts #418 and #1700 they are by Jacob, he should know he designed it.