Are you using an insulated output jack? If so, reverse the feedback wire. Just a guess. The other one is to double check the size of your feedback resistor. Too small makes for too much NFB and "pumping" or "motor boating"
Dan
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
I have the same issue with my Liverpool, and I can tell you it is more than likely your NFB lead dress. I have run mine in various dress trying to get the NFB to not react with the powertube grid leads and have had issues in every configuration. I am now going to replace the NFB lead with shielded cable.
From my understanding, and it didn't work in mine quite right, is that the NFB lead needs to be run underneath the board tight against the chassis as far from the power tube grid leads. Run it to the back of the chassis then to the impedance switch. I've got mine behaving nicely as long as you don't dial the NFB back to far. My hopes are that proper dress and shielding will solve it.
i reverse the wire and it helped...but i still get a hiss when the presence is dimed ..Thanks for the tip!!!
Dartanion...
i think you are right about the neg feedback wire... I will have a go at your suggestion tomorrow...
I've been building this amp for the last 3 days...not going to mother-in-law Christmas souper
I had many issues on this build... managed to fix them except this one...The Express and Liverpool seem to be high strung amps, really sensitive...I like them a lot!
I will get a shave, shower and spend some family time and report back tomorrow for the record.
1. Put it in the headcab. My Express did this when not shielded.
2. Move it off the speaker cab.
3. Move the grid wire going to the volume pot around.
4. Step away from the amp!
dartanion wrote:I have the same issue with my Liverpool, and I can tell you it is more than likely your NFB lead dress. I have run mine in various dress trying to get the NFB to not react with the powertube grid leads and have had issues in every configuration. I am now going to replace the NFB lead with shielded cable.
From my understanding, and it didn't work in mine quite right, is that the NFB lead needs to be run underneath the board tight against the chassis as far from the power tube grid leads. Run it to the back of the chassis then to the impedance switch. I've got mine behaving nicely as long as you don't dial the NFB back to far. My hopes are that proper dress and shielding will solve it.
Problem solved!!!
Did shield the feedback wire and ran it under the board per Dartanion's recommendation...
I can now dime the presence knob.
Noise is goner...
Thanks to Dana, Dartanion, Skyboltone and Keithrick for back-up !!!:D
My wife and 12 year old just left for a 3 day ski trip down at Mother-in-Law.
I'm all alone in the house with my strats/tele/express/liverpool/18/5c3...
