The official G9 help thread

[radiance]

Bump.. :roll:

 

[clintrubber]

[quote author="radiance"]Bump.. :roll:[/quote]
We gaan hier om half drie 's nachts toch niet zitten bumpen, right ?
Ook net uit de kroeg gevallen ? :wink:

 

[radiance]

[quote author="clintrubber"][quote author="radiance"]Bump.. :roll:[/quote]
We gaan hier om half drie 's nachts toch niet zitten bumpen, right ?
Ook net uit de kroeg gevallen ? :wink:[/quote]

Nee, moest er nog heen..... :sam: :guinness: :sam:

 

[clintrubber]

[quote author="radiance"][quote author="clintrubber"][quote author="radiance"]Bump.. :roll:[/quote]
We gaan hier om half drie 's nachts toch niet zitten bumpen, right ?
Ook net uit de kroeg gevallen ? :wink:[/quote]

Nee, moest er nog heen..... :sam: :guinness: :sam:[/quote]
JIJ BEEST ! :green: :green: :green:

 

[gyraf]

I'm noticing a low end roll off starting at 60Hz

Depends on your source impedance, and the primary inductance of the input transformer used. As standard, Lundahl, and 200 Ohms source impedance, we go below 30Hz

Jakob E.

 

[radiance]

[quote author="gyraf"]

I'm noticing a low end roll off starting at 60Hz

Depends on your source impedance, and the primary inductance of the input transformer used. As standard, Lundahl, and 200 Ohms source impedance, we go below 30Hz

Jakob E.[/quote]

Ok thanks. I was testing this by inserting the G9 between the in and outputs of my RME ADi8 pro soundcard. Input impedance from the ADI is 10K and output impedance is 47R. Forgive me but I'm a total noob when it comes to understanding impedance. Could this be an impedance mismatch?

EDIT: Oh, and BTW I 've used OEP in and output trannies...

 

[INDI03]

hi there - Im nearly done but I got some strange voltage problem - I get 370 volt output after the TL 783 - shouldn`t there be just 245 ? couldn`t find anything at the forums about that - well first when I turned on the amp I havent put the tubes inside to do some measuring without them - after 10 to 20 seconds I heart 5 little explosions ? maybe some condensers said goodbye ? lol - well I put the tubes in and tested it again - still 370 volt after 5 seconds I turned it off not to ruin the tubes - I did a test by building a save switch with 2 resistors and suddenly it went down to 235 volt. when I turn it off it goes back to 370 - hm - any help would be nice - sorry for my bad english I hope you understand what I mean ...

well here a photo of the preamp - thx to everybody for making this possible

[/img]

 

[gyraf]

If your regulated HT voltage is more than 250V (with tubes in!), you have a problem in the regulation section.

 

[INDI03]

just figured out that the TL 783 needs 15m-amber to start working - hm but Im not sure why it doesent get it. any experience on that ?

 

[maxime]

a blown 12volts regulator can lead your preamp to that behaviour (no mA drawn from B+). it happens readily as the 78s12 is not sufficiently cooled...
best
maxime

 

[INDI03]

will check that thx

 

[MrShhh]

Hi there,

Having cut my teeth on Jakob's awesome 1176 and Pultec clones I decided to make the G9 and have just finished putting it together.

Just one tiny problem, there is way too little gain on both channels and no bottom end. I have to crank it up to 11 with full output to get any meaningful signal (having cut traces etc. to cure the oscillation problem). This is the same for line or mic inputs.

I thought it might be the HT supply as the 783 is regulating from 270V down to 238V with all 4 valves in place (<245V)

However, I see people are running with as little as 208V HT with no problems and that there should be barely any audible difference until the HT voltage drops as low 150.

I've read almost every thread on the meta and sweated over the schematic for hours but my knowledge of what to do next just isn't there. I tried changing the 783 but it made no difference at all to voltage readings or the lack of gain.

Can anyone suggest what I should check next?

Thanks in advance :grin:

Mark

PS. 12v and P48 are both ok
I'm using 30VA 2 x 15V transformers

 

[radiance]

Did you mount the transformers correct? For example when using OEP's the in and output trannies look almost the same except for the text on top. When canned it's hard to tell the difference...

 

[INDI03]

I think I got mine running now - thx for help - btw when turning the G9 on the voltage jumps over 300v until the tubes get warm - therefor I made a small automatic saveswitch so the voltage never goes over 245v and automatically turns itself off when the tubes got warm ( its called "schmitt - trigger" ) - also I have made a "star" ground system so there can be no groundloops at all - works like a charm - next thing is I think we figured out some "errors" on the original thats why we designed the whole new schematics in AutoCAD - if anybody needs it I can send it

cheerz , INDI

 

[idylldon]

Just finished mine and it sounds fantastic! In my never-ending quest to find old enclosures and breathe new life into them, I put a new front panel on this one and haven't had the time to get it to the laser engravers yet.

Cheers,
--
Don

 

[MrShhh]

[quote author="radiance"]Did you mount the transformers correct? For example when using OEP's the in and output trannies look almost the same except for the text on top. When canned it's hard to tell the difference...[/quote]

I'm using OEP A262A3E input and Llundahl LL5402 output transformers. I read somewhere it was ok to do this. No real reason, I just had the LL5402's spare and the OEP's were cheaper.

 

[radiance]

[quote author="MrShhh"][quote author="radiance"]Did you mount the transformers correct? For example when using OEP's the in and output trannies look almost the same except for the text on top. When canned it's hard to tell the difference...[/quote]

I'm using OEP A262A3E input and Llundahl LL5402 output transformers. I read somewhere it was ok to do this. No real reason, I just had the LL5402's spare and the OEP's were cheaper.[/quote]

Nah, you will not mix those up....

 

[INDI03]

@Mrshhh

maybe this could help you - check the R34 , R35 , R36

Vo ("245") = Vref ( 1+ 100Kohm/470ohm+47ohm ) means the same like Vo ("245") = Vref ( 1+ R34/R35+R36 )

Texas instruments TL783 says that Vref = typical 1,27v ( min. 1,2v , max. 1,3v )

I think you know that the TL783 needs a minimum load of 15milliamber to start regulating ?!

cheerz , INDI

 

[laiben]

I am buying the heat sink. A quick question:

Among the TL783 and 7812, which one is hotter?

Thanks
laiben

 

[gyraf]

78S12 is by far running the hottest of the two

Jakob E.