glad the chip helped....ed!

i changed c-46 from a resistor to a 223j capacitor,c-54 from a 223cap to a 18k resistor,and r-40 from what looked like a blue resistor with a black band in the middle.it read 0.00 both ways on the ohm meter to a 3.9k resistor as shown on the print.i still have hum and also a hi pitched squeal.if i scope the ic chips in the preamp i get a sine wave on the first ic then the next ic looks simular with a little deformation with the middle parts missing on both sides.i noticed with the scope that if i probe the negative speaker lead i get a square wave pattern with the function generator set for a sine wave.when i probe the positve speaker lead i get a dc type pattern that jumps off the screen till i reposistion it.it looks irregular shaped tatterd.i smelled a small burnt smell after running it for awhile.might be r-40 as my guess since there was no resistance there earlier. i think i'm going to put the circuit back to what it originally was as it might of been a factory mod. i noticed the hum goes away when i turn down the guitar or unplug the guitar from the input.if i touch the treble pot on the amp or the  metal guitar tone control it squeals.i will read your last post and try to figure out what you mean and after putting the circuit back to where it was try to locate the hum area....

hi jm
just found somethings i overlooked.c-46 has a 5k resistor in it.r-54 has a green film cap in it and r40 reads 0.00 in all ranges of my multimeter. i checked it in both dirrections.guess i'll have to take it out of circuit and see what it reads.do you think i should change c-46 and r-54 to the proper components and values as listed on the print?maybe i'll get rid of the hum out of this beast yet. i'm not sure if these mods were done at the factory or by an individual.the amp works fine in all regards the way it is except for the humm.any ideas anyone!!!!......ed!

hartke gt60.zip amp schematic.

i have the schematic. how do i get it to this post?...thanks...ed

hi jm the amp is louder 0n 10 then on 0. with the gain down the hum is gone,,,,ed

the amp seems to have the gain control knob make the hum grow louder...any ideas...thanks...ed

the schematic shows a star washer and wire going from the input jack to ground,but there is no such thing here.should i try running a wire from it and drilling a hole in the chassis to make a ground....ed

the amp makes noise in any outlet.the noise goes away when the volume and gain knobs are turned to zero. when the volume and gain knobs get turned up the hum gets louder. the clean channel is the loudest. the dirty channel has hum,but is less predominant,but it is still herd.you could probably almost live with the dirty channel hum,the clean channel is pretty predominant.i herd a sound clip with 50 and 60 cycle hum and it probably is 60 cycle hum.i have 2 scopes.i just need to learn more about using them for tracing.i have a function generator also and a signal tracer.what do you think about checking for hum at the volume and gain potentiometers.all the diodes are good...ed!

getting a noise with the oscilloscope.the sine waves are not smooth @ c105 and c106.can i use a bigger value cap to help filter out more hum at these 2 positions.at present they are 2200uf @50v.can i use a 3300uf@50v in their place. if i do will it help filter out more hum?the wave pattern is a dc sine wave,but it is rough looking?....thanks....

i have a hartke gt-60 that hums on both the clean and dirty channels. it is predominately on the clean channel. awhile ago i remounted the reverb tank away from the power supply as it must of been made on a monday.the tank was mounted dirrectly over the transformer.the hum is alot less than before,but still not where it should be.any ideas?  i have an oscilloscope,but am new to using it. i tested the capacitors and all i get is a dc pattern that is the same on both the negative and positve terminals.i put brand new 2200uf caps in and they read the same.i thought i should get different patterns on opposite sides of the electrolytics.any ideas on learning to use my scope.how can i find the hum with the scope?....any help appreciated. i think this amp had design issues.i notice they have a red and black power wires running across the entire board hooking up on the opposite end. bad engineering...thanks.....ed

just learned from a tv repair friend of mine.to test for leaky and sorted capacitors.he put my ohm meter on the lowest scale and we read 2.2 ohm on a capacitor in a peavey classic 30, the amp melted 2 resistors due to the shorted cap allowing the power to go to ground.pretty cool. we took it out of circuit and sure enough it was bad...just thought i'd add this note to this subject....ed

thought i had the amp fixed. it still plays for a short time then the volume drops off for a few seconds then comes back to full power again.i changed u1 voltage regulator and it made no difference......any ideas.....ed

i got the light working.i was getting a bad  reading on the resistor in circuit. i removed them with my tennma desoldering station.and found an open resistor, the top one of the 3 resistor in a t shape. it was the closest one to the + side of the bridge rectifier.it works now.the light has a slight christmas tree light flashing if you look at it close.must be what you were talking about enzo....thanks for your help phil and enzo....you guys are awesome....ed!!

anymore help appreciated! any more ideas...thanks...ed