Stupid wiring on my G9?

Hello,

Due to some strange placement of the IEC inlet on my G9 chassis, I had to turn the PCB 90 degrees which led to some strange wiring. Because I had to run the cables a bit longer I decided to shield them, but since I had microphone cable around I used that.

The thing that might have been stupid is that I used one microphone cable to and from the instrument as well as to and from the phase switch. Can these interfere in some way?

I have an extremely low and distorted output on my G9, I have checked all the components over and over again but this is the only thing I can think of.
Otherwise it might be the tubes?

Please help!

Robert

NO there should not be any interferance from the wiring unless you connected it up incorrectly which it doesn't sound like you have. I suggest checking for cold solder joints espeically in the power supply. Lastly I have run into tube mics that have had a similar situation and a new tube rectified(no pun intended) the situation.

[/quote]The thing that might have been stupid is that I used one microphone cable to and from the instrument as well as to and from the phase switch. Can these interfere in some way?

can you clarify this a little? it seems confusing. are you using a switching jack like the schematic specifies. screwy and longer wiring may result in oscillation and or more noise. distortion doesn't make sense here.


check B+ voltage through the circuit and visually examine for cold solder joints. are you building both channels? is the problem common to both channels? Are the tubes known good tubes?

just some thoughts.

joe

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what the crap? how do you quote people here?

There is a quote button in the upper right of each comment. __________________________ ^^^^

:wink:

what the crap? how do you quote people here?

Click to expand...

2 ways at the upper right hand corner of ewach post press quote and you will quote that whole post. Or if you just need a section when typing a reply, Hit the quote button then type the message and at the end hit quote again. the idea is the quote should be inetween the quote buttons.

[quote author="rpd"]There is a quote button in the upper right of each comment. __________________________ ^^^^

:wink:[/quote]


oh, i think i get it. like this?

[quote author="funkydiplomat"][/quote]The thing that might have been stupid is that I used one microphone cable to and from the instrument as well as to and from the phase switch. Can these interfere in some way?

can you clarify this a little? it seems confusing. are you using a switching jack like the schematic specifies. screwy and longer wiring may result in oscillation and or more noise. distortion doesn't make sense here.


check B+ voltage through the circuit and visually examine for cold solder joints. are you building both channels? is the problem common to both channels? Are the tubes known good tubes?

just some thoughts.

joe

Click to expand...

[/quote]

This became a very strange quote :wink:

ANyway, what I mean is that I use one of the wires in the microphone cable for the "send" to the front panel / switching jack, the other one is used for the return. Both are shielded by the same shield (well, it is the same cable...).

So if it isn't the cables, could it be the tubes? They are cheap tubes, but I don't wan't to invest a lot more into this project until I know that it will work. But even if it is cheap tubes, shouldn't it at least sound ok? THis is just distorted and very very low gain.

And by the way, all power outputs seems to be ok...

Thanks, I think I have to tryto go thru it again and come back to you. If you think of anything, don't even dare to hesitate to tell me :wink:

Robert

lets try this quoting thing again....

And by the way, all power outputs seems to be ok...

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so you can probe the b+ and see it's voltage on a meter correct? i assume it's somewhere in the 200 to 250-ish range. if you probe the plates of the tube ie pins 1 or pin 6 you should see something in the 90v to 150v range or so. it you probe the cathodes (pins 3 and 8 you should see something smaller...anything from a couple of volts up to maybe 10 or so.... i'm not sure how the gain stages in the g9 are biased, but a 12au7 gives you a lot of room if you look at the charts and compare negative grid voltages. If you have a cheap meter as i do, make sure you have good batteries in it.

If everything seems ok here, take a non-conductive object, like a sharpie marker or something, and physically tap and push things around a bit inside the unit while listening through headphones. hook up a cd player with a DI box or something so you can listen to some tunes while you do it. keep one hand in your pocket and your wits about you when doing this. you may be able to track down a bad solder joint this way. the audio may snap crackle and pop as it makes and brakes the bad joint.

So if it isn't the cables, could it be the tubes? They are cheap tubes,

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eh... cheap is ok as long as they work. did you buy them new from a halfway reputable dealer?

like asked before are you building one or two channels? if two, are the problems common to both channels? if it is common check the power supply again.

how are your filaments heated?

Thanks funkydiplomat...!!! I will go thru the power supply again and see what I can do. And yes by the way, I am building two channels and have the same problem on both channels. I am using the same PCB design as on gyraf's site.

So thankls again everybody, I will check these thigns first and come back to you.

Robert

yeah. you're on to it. if the problem is with two channels the only things they share are the B+ supply and filament supply. Perhaps you could argue that they share 'ground' here also. but most of the time when we are addressing 'ground' problems it's hum problems we're after, not distortion.

if it's on both channels, then would have to be a power supply issue usually a tube that has low output and distortion means it is starved I.E. not getting enough V.