MKI Hd100 loss of distortion/cutting in and out

[mcevan110]

Hi all, I've tried searching for someone that's had the same issue and maybe I'm just blind, dumb, or the combination of both.

 

I'm the original owner of the amp and it's been well taken care of.  My amp, after years of faithful service, started cutting in and out with loss of distortion literally 2 hours before my new band went to play our first show.  So, I'm looking it all over for loose connections or anything that may indicate what the problem is and find the input jack is loose. The nut fell out as I was actually going to tighten it and the jack board fell inside.  So, I take the amp out and put a tiny bit of blue loctite on the threads and screw it back in place. Didn't get a chance to test it because we had to load up for the show.  So, I packed it up thinking I fixed the issue but when we went to soundcheck, it's doing the same thing.  Luckily we grabbed a spare amp with us just in case something like this happened.  So, I thought maybe the tubes were bad.  They hadn't been replaced in about a year and we've been practicing heavily so it was totally possible.  I put new preamp and power tubes in and biased them. I plugged the guitar in and went to go play (after the normal powering on method).   It seemed ok for the few minutes I played it.  Let the amp cool down like normal and shut it off. The next night was band practice.  I power it on like normal, let it warm up, and find out it's doing the same exact thing it did before.  Did a factory reset - no luck.  I tried several different guitars, several different cabinets, and tried running different effect pedals and a power conditioner. I sprayed some electric connection cleaner in the input jack and put the plug in a few times with no luck.   Then I plugged into the power amp in and there's no issues at all.  She sings like she always did.  I'm under the impression that the preamp and power are all together and the power amp in would just be bypassing the effects, correct?  I feel like I'm missing something and I'm just lost here on where to go now. 

 

Anyone able to offer a solution or opinion?

 

Thanks!

[napynap]

...I'm under the impression that the preamp and power are all together and the power amp in would just be bypassing the effects, correct?  I feel like I'm missing something and I'm just lost here on where to go now. 

 

Anyone able to offer a solution or opinion?

 

Thanks!

The preamp section includes all of the amp and the effect models. The signal is then fed to the power amp section which includes the 12AX7 as well as the 6L6 tubes. If there is no drop outs when connecting to the power amp section, something is happening within the preamp section. It could be some electrical component failure in the circuit board, or something as simple as one of the knobs moving from sound vibration.

[mcevan110]

Thanks for the reply napynap.

 

I'll take it back apart and see if anything looks suspicious.  I don't think it's a knob vibrating issue since I have tweaked them all while playing with no luck in getting rid of or having any affect on the issue.

[BillBee]

The pre-amp and power amp are on separate boards. When changing tubes I always spray some contact cleaner on the pins and a wee squirt in the socket as a just in case.

 

Like Napynap sez: Try running a fan pointed at the rear of the chassis to see if it may be a heat related issue causing it. Those puppies can run really hot and there is not much ventilation and if any solder joints are iffy they can show.