12xxx kit completed, almost no gain

Vegard · Post by **Vegard** » Thu Jan 22, 2009 3:26 pm

When i first finnish an amp i dont hook up effects in the chain! Its just guitar-cable-amp.
Even if you set the amp to 16ohm and run it with a 4 ohm cab it just dont loose its gain turns in to a cleanamp. Off course i dont do that.

I got a 1960 cab, and i also have a 16ohm 1x12 speaker... and again, the amp will not break up and overdrive...

neikeel · Post by **neikeel** » Thu Jan 22, 2009 5:03 pm

I have to agree something is not quite right I would not test an amp with anything but a guitar and good quality lead.

Did you check the NFB resistor and that all your pots are the correct values (I had an amp which had a 50k presence pot installed which sounded very clean/dull etc - turned into a monster with the 5k restored)?

Tried different preamp valves?

This is probably bugging me nearly as much as it is bugging you

Vegard · Post by **Vegard** » Thu Jan 22, 2009 5:17 pm

yes, my NFB resistor was 48ohm i think, and the presence pot is 5K.

I am very thankfull for the answers and very glad you guys wanna help me.
Hope we can find out what the problem is.

Is it possible that the problem is somewhere else than arounds V1 and V2?
Is the PI filter wired correctly?
Is the biasadjust section correct? Ive seen many ways to do this...

Something holds it back to break up properly....

Omn · Post by **Omn** » Thu Jan 22, 2009 5:43 pm

Which of the lug is grounded on the phase inverter? It is difficult to see from the picture, but it seems as if the "clear" one is grounded. From the 100w-manual the black-colored is for ground. I have a red one which I thought was ground.

Vegard · Post by **Vegard** » Thu Jan 22, 2009 5:44 pm

The blank is ground, and the red is hot...

Flames1950 · Post by **Flames1950** » Thu Jan 22, 2009 5:45 pm

Vegard wrote:yes, my NFB resistor was 48ohm i think

Is this a mistype, or was it really 48 ohms? It needs to be a 47Kohm resistor.........48 ohms would be way too much feedback.

Omn · Post by **Omn** » Thu Jan 22, 2009 5:53 pm

Thanks Vegard!
I am trying to help, and I am the one in need of all the help I can get.
That is irony...

Vegard · Post by **Vegard** » Thu Jan 22, 2009 5:56 pm

Oh yes, 47Kohm... yellow purple orange! It was alittle bit more, because the AB resistors are not very accurate...

Ricky Lee · Post by **Ricky Lee** » Thu Jan 22, 2009 6:00 pm

At this point nothing seems to be visibly suspect, therefore I would go over all my lead dressing, solder joints, both under and on top of the board and I would check values on all my electronics especially those CC resistors. A little trick I use when troubleshooting an amp that has issues that are not so obvious to find, I play the amp in the dark and see if there is something going on inside the chassis like arcing or that the tubes are all evenly glowing. By doing this I have found loose connections Bad tubes etc. Just don't go feeling around inside the chassis in the dark!

Vegard · Post by **Vegard** » Thu Jan 22, 2009 7:07 pm

Is it correct that the 4, 8, and 16ohm taps has connection with ground?

Doug H · Post by **Doug H** » Thu Jan 22, 2009 7:39 pm

recheck the wiring on the tone stack? You can't really see where the wires go under the board from the pictures.

Omn · Post by **Omn** » Thu Jan 22, 2009 7:42 pm

I am a novice in reading diagrams but the SL2330X suggest that it has no dedicated grounding but are grounded through the speaker outputs.

Ricky Lee · Post by **Ricky Lee** » Thu Jan 22, 2009 10:33 pm

Vegard wrote:Is it correct that the 4, 8, and 16ohm taps has connection with ground?

Grounded by way of the output jacks, there should be a ground wire coming off the output jack to a ground lug attached the v4 tube socket screw.

Vegard · Post by **Vegard** » Fri Jan 23, 2009 11:47 am

I tried the amp again today. cranked it, and the powertubes starts to redplate...!

Ricky Lee · Post by **Ricky Lee** » Fri Jan 23, 2009 12:13 pm

Vegard wrote:I tried the amp again today. cranked it, and the powertubes starts to redplate...!

check your bias setting. with 500V your bias should be around 35ma that's 70% dispisation.

Heres the formula: 17.5 divided by 500=35. Considering the reliability of modern tubes I set my bias around 33ma.

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12xxx kit completed, almost no gain

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