Mark IV - Tweed Power Loss - I am stumped, Please Help

[jman7272]

Hi folks,

I have been troubleshooting an issue all day and am stumped. I am hoping that someone can shed som light on what the hell is going on with my Mark IV. I started this thread as the other thread had gotten off the track and I can now pinpoint what is happening.

Here are the symptoms:

Turn on the amp and let it warm for a minute in Tweed power mode and then when you come out of standby, the sound is barely audible. Here is the catch - If you then go into FULL for power 15 seconds and back to TWEED, it sounds great again. Louder than it was in tweed before and not muffled.
I can reproduce this on command even if playing for 1/2 hour. Just turn it off, back on, out of standby and there it is.

Also, there seems to suddenly be a HUGE, WALL SHAKING difference in volume between Tweed and Full power. It was never there before. If I am playing on tweed and then switch to full, I have to turn down a great amount to have it not break glass. I used to have the same settings (before this started happening) and switch between the two and there was a slight volume increase, but nothing that would have to make me redial the amp completely.

I have replaced all 4 6L6 power tubes and all 5 12AX7 preamps.

I am completely at the end of my rope here.

 

[phyrexia]

bad tweed/off/full switch, maybe?

 

[MesaDCLP]

I don't qualify to guess this, so...
I think it may be the caps ??? :?

Someone here has the answer!!!

8)

 

[Alivefor5]

OK, let me give this a go ...

I had this same thing happen on my new head a few times but not as bad as you are describing. At the same time I noticed my Master pull switch for silent recording ceased to work. It did volume fine but did not turn off when pulled.

In messing with the pull switch the low volume on tweed went away. The switch still does not work correctly, when pulled you can press it in one direction and get the signal to shut off. However I've never had the low volume in tweed issue again. Since I've got 4 and a half years left on my warranty I'll get a new pot sometime.

Bottom line ... mess with the Master pull pot about 20 times and see if the switch allows better contact in tweed.

 

[jman7272]

OK, let me give this a go ...

I had this same thing happen on my new head a few times but not as bad as you are describing. At the same time I noticed my Master pull switch for silent recording ceased to work. It did volume fine but did not turn off when pulled.

In messing with the pull switch the low volume on tweed went away. The switch still does not work correctly, when pulled you can press it in one direction and get the signal to shut off. However I've never had the low volume in tweed issue again. Since I've got 4 and a half years left on my warranty I'll get a new pot sometime.

Bottom line ... mess with the Master pull pot about 20 times and see if the switch allows better contact in tweed.

That is interesting. I will give this a try. It's the strangest thing as this amp was picked up from the retail store on Oct 26th of this year. It just passed it's two month birthday. :x

Something is just a miss here and I cannot figure it out.

Any and all help is truly appreciated. Thanks!

 

[Pundix]

My MKIV did something similar once, and I found that I had a capacitor leaking. I had the amp recapped and it's been it's old monster self ever since. If I were you I would take it to a good repair shop and let them have a look.

 

[jman7272]

My MKIV did something similar once, and I found that I had a capacitor leaking. I had the amp recapped and it's been it's old monster self ever since. If I were you I would take it to a good repair shop and let them have a look.

Yea, I am just irritated because I don't believe it is necessary to have to do that for a 67 day old amp of this quality /cost. :x