Hughes And Kettner Trilogy noise

[redneckgeek]

This Trilogy sounds great in Clean channel. In Lead or Ultralead there is a loud hum that varies with master or lead volume changes. I've checked tubes and most all electroklytics. I'm aboutn to signal trace it but since I've already got the boards dc'd is there any one who might have an idea of what else I should check?

[redneckgeek]

Unique problem ... at least to me

I had really hoped for a magic bullet on this. But, no such luck. So, I thought I'd ad the latest troubleshooting attempt to the mix. It may be interesting to you if nothing else. I connected a 1000 Hz sine wave signal to the amp input and guess what? The thing worked fine. All four channels worked well. So here's where I'm at: With nothing or a guitar applied to the input, Clean is fine. Crunch is fine. Lead is noisy (low frequency loud hum and Ultra Lead is also noisy but the pitch goes up a few hundred Hz when you push ther Ultra Lead button). On the scope: When the signal generator signal is applied, the signal on all applicable grids is a clean sine wave. When the guitar is used or nothing at all is applied applicable grids have a square wave (or I should say the noise shows up as a square wave). One other thing, The lowest signal I can generate is at 2.4V pp. The output of my guitar may make 0.5V pp. Also, the output of my signal generator has an impedance of 50 Ohms. The Amp Z input is 1 Meg ohm. Some component is oscillating in the Lead section of the pre-amp???? Any suggestions? I am close to a river, but I've got too much money in the thing to give up now.

[Enzo]

2.4volts???

Wire up a pot - oh I don;t care 250k 100k, whatever reasonably high value you have - as a simple volume control. Connect the pot element across the output of the generator, and the wiper is now the output. Dial it down to whatever you want.


You "checked" the preamp tubes? or you actually substituted other ones in there?

Have you tried a different guitar and different cord?

Don't plug anything into the inut jack. Bring your finger right next to the jack. Does this increase the hum - does it pick up the presence of your finger? If it does, your input jack is not grounding the tip contact when empty.

With nothing plugged into the amp you have square waves at the tube grids? How about the plates? How large is this square wave signal? What freq?

[redneckgeek]

OK Back to the Trilogy

Had to do other stuff. Now, I wired the pot . It works great. Even put it in a little box with BNC's at both ends. I have tested as well as replaced the pre amp tubes. Yes I tried a different cord. This noise happens without any input at all. The input jack has a good ground without a plug in it. The noise starts at T3. It is present at either plate (12ax7). I have looked at all power supply voltages. They are without any ripple. The noise is at 220 Hz at as much as 1Vpp at the preamp plates (T2 and T3). It is a very consistent wave form that varies in freq with the movement of the gain controls in the infected stages. I have tested every part near these two stages. Even removed the pots and tested them. Checked all electrolytics with ESR meter and removed them and tested them at high voltage (Insulation tester) for leakage. I replaced a couple of them just for the heck of it. I have pictures of the waveforms with the signal generator input. I can't capture the noise waveforms though as I'm using a camera to take pictures of the scope screen and the frequency of the noise in too low. I also have a PDF file of the repair manual including schematics if anyone is interested.

[redneckgeek]

C33

Found C33 a dielectric filter cap in the B+ line in the preamp section was breaking down under full power. I tested this cap with an ESR meter, analog ohmeter, capacitor meter and an insulation tester (450V cap and the insulation tester had 250V and 500 volts potentials to test with). Finally I just replaced it and the amp works fine on all channels.

[bnwitt]

I also have a PDF file of the repair manual including schematics if anyone is interested.

I'd love a copy

[pontiacpete]

I'd like a copy too, if you don't mind.
thanks

[redneckgeek]

H & K Trilogy manual

Sorry but the forum has a limit as to what size file can be attached and the Trilogy PDF excedes that limit. If you want to you can email me at redneckgeek@charter.net and I'll send it from there. Jim

[Jonni101]

Hi, did anyone manage to get a copy of the Trilogy schematic?