hartke gt-60 noisy only when reverb knob is turned up!

[EDWARDEFFECT1]

anyone have any ideas what is wrong with my hartke gt60.it plays perfectly and is dead quiet till you turn up the reverb knob.when the knob is turned up any amount at all the amp gets a loud hum in it which gets louder as you turn the reverb knob up louder.i tried putting a shorted 1/4" jack in the input and foot switchable reverb jack and it didn't help. i also reflowed any solder joints that looked like they might be bad.i also noticed now that the amp is not switching channels since i took it apart for the second time(bad switching transistor?)amp stays in dirty channel.does anyone have a schematic for this amp or know where to get one as it would probably help me alot....thanks...ed

[phatt]

The Reverb bit is likely a bad RCA type lead (i.e. broken wire inside lead)
Replace leads,, or the tank maight have an internal broken wire.

Side note;
A lot of reverb circuits are designed with this major,, major flaw:
""if the pickup side goes open circuit (not uncommon with cheap RACA leads)
the amp either squeals like mad or hums like crazy.""

The next part:
You have likely stuffed something while tryiny to fix reverb.
Sorry somene who owns,, or has worked on one may be of more help with that part.
Phil.

[EDWARDEFFECT1]

i replaced the tank with a good working tank and the amp still hums.i tested the rca leads with an ohm meter and all four leads test @ .2 ohms.do you have any other ideas...thanks for your help.if i ground the input tip to sleeve the hum goes away...if that helps.....thanks....ed!!

[EDWARDEFFECT1]

replaced u3 ic and got the channels working
replaced
u1 ic
u10 ic
c12
c33
c35
the amp still hums.the channel switching stopped again.possibly a zener diode?
the amp seems to hum less when i get ther reverb tank farther away fro the output transistors and the transformer.the only problem is it is mounted in the cabinet right above the transformer.i thought i had it fixed till i reassembled it.i might of blown ic 3 again for the channel switching when i turned off a flourescent light as it was plugged into the same power strip. the channel switching is dead again.


any ideas welcome.i have the schematic ,but don't know how to upload it to the post as it says it is too large.unless i have to compress the file...helppp!...ed!

[J M Fahey]

Post it to some service like Rapidshare or a similar one.
What size is it?
Is it a PDF?
Enzo is always contributing his ample knowledge and also many schematics , he often uploads them to AMPIX, where they stay available forever with no silly download quotas.
Try that.

[phatt]

i replaced the tank with a good working tank and the amp still hums.i tested the rca leads with an ohm meter and all four leads test @ .2 ohms.do you have any other ideas...thanks for your help.if i ground the input tip to sleeve the hum goes away...if that helps.....thanks....ed!!

Hi Ed-fect,
               Reverb tank next to transformer :loco
Don't ya just love the professionalism shown in there design and layout of commponents. :lmao:

Anyone Armed with only half a drunk brain cell knows how prone Reverb tanks are to picking up hum.
Sadly this is not uncommon in even big name equipment.
yes you See *Hartke* and you assume they know the basics,,, obviously not!!

Get that tank as far away from the transformer as possible, Rewire it all if need be.

Make darn sure the Metal Case is grounded correctly.
mostly they are grounded at one (And only ONE) Point.
More often than not the pickup End also Grounds the Reverb Case.
Never ground both input and output commons,, one common has to float.
Pull the tank out completely disconnect it then with a DMM establish which common is connected to the Case.
One of the 2 ground Lugs will be directly connected to the tank Case.
If none (or Both) then you just found part of the problem.

Also be aware that Most Rev Tanks have no bottom and often the PU end just picks up all and sundry noise floating around,,
(you need to point the open end AWAY from any RFI)
Don't think by bolting a big sheet of metal on the bottom will fix hum issues because you will create a resonant chamber which will probably start to feedback and squeal at the most critical moment.

The Tank is open for very good reason,, they need to be acoustically DEAD. An open bottom is the most obvious way to do such things.
I notice Accutronics now use a cheap piece of cardboard as a bottom plate.
It matters little in Fender type Amps because they are mostly mounted inside a big vinyl bag anyway which offers enough protection when screwed to bottom panel.

If the tank is one of those small cheapies like some amp builders who just screw them to the Cabinet board with rubber grommets being the only shock absorber.
This is just plain stupid and shows Zero understanding of how it should be done.

The other part of the issue is quite hard to get your head around but I'll give it a go.

I Quote you here;

"if I ground the input tip to sleeve the hum goes away...if that helps.....thanks....ed!!

I'll assume you refer to the Reverb PU return cable?
Likely culprit is to much gain on the PU circuit.

Most Amp circuits rely heavily on BIG Gains at the PU end to capture the reverb effect. This saves them a lot in parts count (Read As $Profit Margin$) as the Driver end is where it all should be done but harder to do.$$$

If the Driver end is strong (Most are not) then you only need a small amount of gain (hence less noise) at the PU end for a strong Convincing Reverb.

The result of Hi gain return path is as you have described here,, when you turn up the reverb you get a lot of noise/hiss/hummm introduced back into the Audio path.

Sadly (more often than not) there is no easy fix or work around.
All I can offer you is to Disconnect the Reverb unit (Perminantly) and go get a seperate Rev unit.

After many years of frustration I Built my own Reverb unit and except for the slightest rise in hiss (mainly transistor noise or boltzmans resistor noise)
It's Dead quite,,, even when Reverb is on TEN.
(I will quite glady put it up against the BEST Spring Reverb units Ever built, including the Bottle powered units, Not claiming it's BETTER but just as good.  )

Which proves that If a humble hobby nerd like me can build a stunning reverb circuit with only limited ability and electronic Skills,,,,
Then one can only assume that Big Brand names does not mean the best brains are working on your beloved Amp circuit.

As to the channel switching issues,, well I'll leave that to the chaps who are better qualified to pass comment.
Hope you get it sorted soon.
Cheers, Phil.

[EDWARDEFFECT1]

tried uploading the hartke gt60 schematic to ampix...sorry no luck....ed