Kmd output problem

[grazzze]

I have a KMD GV-100S AMP w/8x10 Celestions, (2 4X10 cabs matched to 4 ohms)This amps preamp is ss and the power section is tube.When I play a note on guitar its very clear but during and after each note there's sound like a compressed distorted shhh and it bleeds off (fades)in nanoseconds.Also,How do they get 100 watts out of 2 6l6 gc's, Is it the 100 watt torroidial transformer doing the work,I cant even play this in my garage on #1.Can I get a schematic somewhere.Thanks

[Jazz P Bass]

I have heard that same sound on bad speakers.
Try to narrow it down.

[grazzze]

I tried a fender bassman head in each cab seperatly and the problem is not with the speakers.The notes are clear in the KMD head but that distortion fizzle sound is still there.

[ThermionicScott]

Kind of a fuzzy sound and clipped-off notes at low levels? Could be cold bias...

- Scott

[Jazz P Bass]

Cold Bias

ie: Crossover Notch.

[ThermionicScott]

ie: Crossover Notch.

Yep! If the tubes are biased near cutoff, small signals will get "eaten up" because the output tubes don't have very much gain at low currents.

- Scott

[grazzze]

Iwas told that this amp has a fixed Bias

[ThermionicScott]

Iwas told that this amp has a fixed Bias

"Fixed bias" doesn't mean the bias is non-adjustible; it means that a negative voltage is used on the grids, rather than a resistor at the cathode(s).

- Scott

[grazzze]

OK,Thanks I'l take to the shop and have them take a look.Thanks for the input.Can you tell me how they get 100 watts RMS out of 2 6L6GC.I thought you could only get 45 on push pull.Does the 100 watt troidial transformer have something to do with it.

[Jazz P Bass]

When you take it in, have the tech measure the maximum clean output voltage.
From there: P= VxV /R.
Power = voltage (squared) divided by the load resistance.
I seriously doubt (2) 6L6 tubes are going to get you 100 watts out.

[ThermionicScott]

Per the RCA specs, you can get an easy 55 watts out of a pair of 6L6GC's in class AB1, and that's without exceeding any ratings. You can get a lot more by using some of that SS trickery to run in class AB2 or by using a dual-rail power supply, but 100 watts is probably a little exaggerated.

- Scott

[teemuk]

Maybe they just advertised the peak power rating. I haven't actualy seen any literature stating that the 100 watts would have meant the continuos power.

[grazzze]

Icant run this amp above #1 in my garage,When I plug my 50 watt bassman head in the same cabs matched impedence,I Have to set the volume too #7 to have the same,Weired.The tubes in the KMD are the original ones from the 80's.Anyways,Thanks again,I'l run it down this week.

[Jazz P Bass]

7 on the Fender Bassman volume control.
Input to which side? Bass or Normal.
And where do you have the tone controls set?
Might be something wrong with the Bassman

[grazzze]

In normal channel,treble,bass and presence set @ 12 oclock,Someone modded from a 67 to 66 and added a mercury xfmr.