Hartke Attack 7000

[alkyhauler1953]

At very low volume, like checking harmonics after tuning and gently brushing the e-string, as the sound fades it sounds like a speaker buzz. At playing volume it is undetectable.
I had the bass checked, built a new cord, and am using a brand new Seismic Audio 3-10 cab rated at 750W.
The preamps are usually set at 12 to 2 o'clock; and the master about 5 (the small clubs I play don't need much volume.
I turned the tube amp off and it was still there, I turn the SS amp off and it is there. I am going to replace the 12AX7 anyway.
Any ideas?
I bought the amp used in 97 and it has seen many road miles in a 2 horse trailer.
Any help would be great.
Thanks

[oc disorder]

Hi Alkyhauler1953 and welcome to the forum.
The early Hartkes suffered from dry joints particularly on the pre-amp board.
The taller components were the main culprits as usual ie the regulators(look like 3 terminal transistors mounted vertically on heatsinks)and the capacitors.Its possible the power amps may have them too but that is a more delicate operation to get to the back of the board.
When removing the front panel/pre amp screws note that some are self tappers and others are threaded.
As I recall the led's are glued on for power and compression so you can either bend the leads straight to slide off the connector (note which way round the leds are connected)or lever the whole lot away and reglue later.
I also have replaced a few NJM 2068 IC's with subtle distortion problems (have spent ages on this) and also replaced ones that didn't work at all !
Oh just remembered.. the pre-amp has a few grounding points with the screws holding down the PCB going into welded "standoffs" on the chassis.
Take the lid off and tighten these first.You can see them with a little piece of metal under the screw head.
There were so many revisions of the schematic with part numbers and location numbers changing its hard to get an exact schematic.
If the grounding and dry joint fixes fail to fix the problem I would get some turned IC sockets (low profile plated ones) and replacement NJM 2086 IC's - think there are only 3 and there is one that is common to both channels but this will be very hard to determine so I would change all three.
If this is all a bit daunting take it to a tech who is experienced as it is possible that none of the above will fix the problem.
Oh yeah check the patch point jacks at the back by putting a guitar lead from send to return.These can get dirty contacts which have to stay closed when there is nothing plugged in.
The pots (volume tone controls) may need cleaning too as the fan is pushing the dust around.
Caig Fader Lube is what I usually use but there are probably other products not as expensive.
Good Luck and Happy New Year !

EDIT: Read Enzos post... re check speakers first !

(p.s. Edit stays open for hours after a post..! )

[Enzo]

SO aside from assuming the speakers are OK, did you play the amp through different speakers? DId you play a different amp through these speakers? If it sounds like a speaker buzz, then we would first want to se if it is in fact a speaker buzz or not. Just because speakers are new doesn;t mean they can;'t have a buzz.

[alkyhauler1953]

OC and Enzos

Thank you for the input...I will check everything I can before I take it to a shop.
You guys are great. Will let you know what it was.
Bud

[alkyhauler1953]

Happy ending

Enzo and OCD, thanks. I did everything you both said, and replaced the 12AX7.
Douched all the sliders, knobs, etc.
Vacuumed the case and reset all screws. Works great. Thank you for all your help.
You would be amazed at how this 3-10 sounds; it is awesome. At 5 the windows rattle and the neighbors call, LOL.
Seismic Audio is putting out some really affordable stuff. Check them out.
Thanks,
Bud

[alkyhauler1953]

Tube preamp in Hartke

Just for info/question; the old tube burned real bright yellow/orange; and the new one is very low light.
Thanks guys.
Bud