New 50 watt kit noise

bartak · Post by **bartak** » Tue Nov 20, 2007 1:49 pm

I just finished my 50 watt kit, everything is clean and tight and the voltages are good, I checked and rechecked to make sure everything was correct. There is almost no hum. And the tone is great, but when i back down the volume and play quiet there is a crackle, or static, it doesn't follow the notes It's more random, I don't hear it at high volume but It's most likely there, It sounds very similar to when my 68 bassman needed the filter caps and plate resistors replaced, or when a power tube is going bad. The amp has been powered up for about 4 or 5 hours and there has been no change. The only strange thing is when I biased the the power tubes they were 5mA apart, my B+ is 444 so I set one tube at 40mA and the other is at 35mA. Anyone else have this problem? Or any one else have any suggestions? I emailed this Question to George as well. I'm hoping it will be an easy fix. Thanks in advance

el34on11 · Post by **el34on11** » Tue Nov 20, 2007 1:55 pm

bartak......
Congrats on your finished 50watt!!!

To me it sounds to me like a bad tube.......(preamp)
Do you have any known good tubes you can swap in just to try and confirm?

Derrick

bartak · Post by **bartak** » Tue Nov 20, 2007 2:23 pm

Thanks for the sugestion, I just got an email from George with a list of things to try, the first is checking the preamp tubes. maybe I shouldn't have had taco help me with the build?

bluze81 · Post by **bluze81** » Tue Nov 20, 2007 7:46 pm

Hey bartak Taco looks like he knows whats up! I have built some great amps thanks to the help from my standard schnauzer Einstein, nice amp and freind you have there. bluze

fillmore nyc · Post by **fillmore nyc** » Tue Nov 20, 2007 11:09 pm

Taco has that "I dont like the looks of this, daddy" expression on his face!! (ahhh, what does he know about preamp tubes anyway? He looks like more of a filter cap kinda dog!!)

bartak · Post by **bartak** » Wed Nov 21, 2007 1:15 am

George told me to try these things,

rotate preamp tubes

replace if you have extras

power up without the first preamp tube

if crackle persists, remove 2nd preamp tube

same for third

rotate and/or replace output tubes if you spares

if you still have static/crackling:

triple check all solder connections

insert a plug into each input jack and wiggle to see
if you can cause the noise. if so, replace the jack

wiggle each pot, try to cause the noise

I did everything except change the power tubes and nothing changed, I had preamp tubes so I replaced them. after listening more, it sounds like an unpleasant distortion under the notes and there is a slight oscillation, when I play a note and let it ring the volume will drop then rise almost like a tremolo but very slowly, all of this only happens at low volume when I try to play clean. cranked it sounds ok.

Roe · Post by **Roe** » Wed Nov 21, 2007 5:38 am

also try to move around the wired to and from V1 (except cathode and 6.3V)

toner · Post by **toner** » Wed Nov 21, 2007 9:41 am

el34on11 · Post by **el34on11** » Wed Nov 21, 2007 9:58 am

Derrick

bartak · Post by **bartak** » Wed Nov 21, 2007 1:02 pm

I'm going to try new power tubes, any other suggestions would be greatly appreciated.

neikeel · Post by **neikeel** » Wed Nov 21, 2007 1:04 pm

bartak wrote:I'm going to try new power tubes, any other suggestions would be greatly appreciated.

You mean new preamp tubes first

el34on11 · Post by **el34on11** » Wed Nov 21, 2007 2:57 pm

bartak....

Sorry to hear your still having troubles, but if you could post some inside chassis shots of your build I'm sure the eagle eye experts can help piont out anthing which may be causing you problems....

Derrick

bartak · Post by **bartak** » Wed Nov 21, 2007 9:14 pm

I got some new power tubes and a new multimeter. re biased and the problem is fixed, perhaps it was the multimeter, I'll put the old tubes back in tomorrow and see what happens.

neikeel · Post by **neikeel** » Thu Nov 22, 2007 4:10 am

bartak wrote:

I did everything except change the power tubes and nothing changed, I had preamp tubes so I replaced them. after listening more, it sounds like an unpleasant distortion under the notes and there is a slight oscillation, when I play a note and let it ring the volume will drop then rise almost like a tremolo but very slowly, all of this only happens at low volume when I try to play clean. cranked it sounds ok.

Ignore my post (ok so you did anyway

) should read more carefully!

Glad you got it sorted.

novosibir · Post by **novosibir** » Thu Nov 22, 2007 7:53 am

bartak wrote:I got some new power tubes and a new multimeter. re biased and the problem is fixed, perhaps it was the multimeter, I'll put the old tubes back in tomorrow and see what happens.

Did you have the prob only with the meter connected to the amp

Larry