ATS sixty distorted channel low volume

I have ATS sixty two channel amp with ecc83s valve. Clean channel isbok but distorted channel has very low volume. What can be problem? How to test valve? P.S. after i switch channels to distortion 1 or 2 sec is distortion loud but then became to lower down

It did originally sound to me as though you have a valve problem which is what you suspect I think.  The usual problem would be that a triode which is only brought into circuit when the Overdrive channel is selected is going soft.  You have that setup in your ATS60.  The Clean channel is totally solid state.  The Overdrive channel then switches to a completely different gain setup which is based around the valves.  Swapping out your valve is the best way to check and rule out a valve problem.  Read on...

For the record, while swapping an ECC83/12AX7 for an ECC82/12AU7 may work temporarily without causing damage is not a "good thing" to do as a matter of "valve rollin'" tonal cork sniffing.  An ECC83/12AX7 and an ECC82/12AU7 are NOT, I repeat NOT, equivalent valves no matter what anyone tells you, I don't care who they are!  They are not a part of a "valve family" just because they share the 12A*7 number.  They are totally different valves which are designed for totally different jobs and putting one in a stage designed for the other will screw everything about the stage design, even to the point of damage in some cases.  Could you fit a part from a VW Polo for its equivalent part on an Electra Solo because they share *OLO in their names and expect it to function as it should?  These valves, and the 12AY7 as well, are totally incompatible.  Everyone has been warned here about this myth ad nauseam, the choice is up to you.

Looking briefly at the ATS60 schematic the channel switching is done using a solid state switch IC.  This has on it 3 separate solid state switches.  These are all controlled from the footswitch or the Channel Select switch on the amp.  One switch selects between the solid state Clean channel circuitry and the valve Overdrive circuitry just as we would expect.  One changes the gain of the input stage which is based around an opamp so it increases when Overdrive is selected.  This may be just to prevent noise or oscillation.  The third switch controls the Reverb level from high to low to drop the level when Overdrive is selected.  This may not be an exact description but it is pretty close.

While it is possible that the problem is in other areas I would start by testing the valve to rule it out.  You can swap your valve out for your ECC82 to test it.  It should be clear whether your ECC83 is faulty from that.  If you do find it is faulty then I strongly recommend that you get a proper ECC83 replacement for it.  I would not use the ECC82/12AU7 as a long term replacement.

Let us know how you get on and what you find with the swap.

So swapped it for ecc82 but the same resul,maybe little bit different volume. It go ok few seconds and then i goes down. Do you have schematics for footswitch to ars 60? I tried before this just a switch from other combo whe is just solid state switch and led diode. Cant it it be part of problem? Tomorow will i buy the right valve. I hope it helps

From what you have said I don't think it will be the valve in this case, though getting your hands on a new spare might be a good thing. I'm not sure it is likely to be the footswitch either though it is just possible. How does the amp behave if you don't plug the footswitch in and just use the Channel Select switch? You could also try just putting a jack cable into the footswitch socket and shorting the tip to the sleeve of the plug. This acts exactly like the footswitch will without using its switch and LED.

Its the same with or without switch

Ok, does the Channel LED perform as it should? You say that the Overdrive level is fine for a couple of seconds and then it drops. Does the LED stay illuminated strongly or does it change at all as the gain drops?

Stays the same

Ok. We must assume the issue is not in the footswitch/amp switch circuitry. The only other area I can see which would affect the level is in the first stage of the overdrive channel. This is not shared with the Clean channel so would not affect it. This stage has a FET transistor which is used to set the gain of that stage at either a low level for when the channel is not in use or a high level when it is selected. The FET switches along with the channel selection when the footswitch is pressed. If there is a fault around that area then this could happen.

That could be due to the FET, the chip which controls its switching action or the components which set the gain around the opamp stage. This really does not sound like it has anything to do with the valve stages themselves. If that is the case then I would guess you will not be able to fix that yourself. It will require test equipment to check out that area of the circuit and you would need to replace components on the PCB as they were found to be faulty. Unless you have the setup and the skills to do that yourself I would say take it to a tech for investigation.

Is that type of work within your experience and skills?

Yes i repair lcd tv's.

Aha!!!

Ok. I would not normally do this for a current H&K model but, as this is such a legacy amp try looking here: ATS60 Service Info You should be able to get the service documents which include the schematics. The text is in German but there is nothing you need there anyway, the schematics are fairly clear.

Our problem seems to be that the correct switching action occurs but the Overdrive state cannot be maintained. It would seem to me to be a problem related to the charging or discharging action of a capacitor.

Look at IC4 4053. This is the switch chip. You can follow pin 15 out to T6 the FET which does the switching. First check the voltages on the connected pins 9/10/11 with the footswitch in both positions. It should vary between 0V and 6V and stay steady in both cases. Check that the voltage on pin 1 is +7.5V and on pin 2 is -7.5V or pretty close to that. You should then see pin 15 swap between +7.5V and -7.5V as you click the footswitch and stay steady. The junction of R41 and T6 should do the same.

If that is all ok then you seem to have a problem with the FET or in the components just behind it, somewhere around R42/C20/R48. Are you ok with that?