Mains transformer overheating with higher attenuation

[sickman82]

Ok.. correcting myself here.. I think the leads on my MM needed reinserting and I was a bit groggy earlier.

So readings taken tonight are as follows..

Load - 14 ohms
-16db - 15 ohms
-14db - 6 ohms
-12db - 7 ohms
-10db - 7 ohms
-8db - 8 ohms
-6db - 9 ohms
-4db - 10 ohms
-2db - 11 ohms
Full - 13 ohms

That's taking in to account the 4 ohms across the leads themselves. The Full setting matches the reading from the cab, so all good there. I don't understand why the resistance is lower between -14 and -2db. Due to it being a reactive load or because it's faulty? I'll send the measurements to TAD and see what they say.

[sickman82]

Spoke with Majestic this morning. They reckon that 60° above ambient temperature is pretty normal, and since it's pretty new then the varnish hasn't crystallised yet and it will still produce vapour. One more piece to the puzzle I guess.

[Littlewyan]

Hmm those readings are a bit weird. I have to admit I can't see how the attenuator could make the mains transformer run hotter, without making the valves red plate. It could just be pure coincidence. Like I said my mains transformer has become really hot before and has also smelt slightly, but I was informed that this was perfectly normal.

See what TAD say about the attenuator as I don't like those low resistance readings on the inbetween settings.

[sickman82]

So the guy at TAD asked if the 'punch' switch was engaged when I took the readings. Sure enough, I had it on. I redid the measurements with it off, and I get between 14-15 ohms on every attenuation setting. I wonder if this could be the root of my problem? I'm going to try running it without the switch engaged today, and see if it gets as hot. I don't always use that switch and so maybe the times I haven't had it on have been the times that it has run cooler.. that could be what lead me to think that it doesnt overheat with less attenuation - the louder the amp is, the less I feel the need to use the 'punch' and 'bite' switches.

Definitely no redplating going on though, that's for sure - everything seems to be normal other than the heat. Perhaps there is a combination of things at play here and my own paranoia that something must be wrong is fuelling it all. But I'm definitely wondering about that punch switch.

[Littlewyan]

Hmm odd. Maybe it is a resistive attenuator but with reactive elements. See how it goes. It would be odd if the attenuator was working the amp much harder but your valves weren't red plating.

Just keep a close eye on it

[sickman82]

Well, a couple of weeks have passed and I've put the master back in and returned the attenuator for a refund. I can't explain why, but the Silencer was certainly the cause of the overheating. I've been pushing the amp hard with the MV, way harder than I would normally and the mains transformer kept cool. No more varnish smell. No more frying eggs on my amp.. I guess I'll have to go get a frying pan now.

It could have been a defective unit (I've had two of these attenuators by the way, the first blew quite dramatically at a rehearsal with smoke rising from its top grill), or it could just be poorly designed/put together. Your guess is as good as mine. But if their customer service is any indication, I know what I would put a wager on.

Either way, problem solved and moving on to fitting the ZL Loop next (just ordered it this morning). Cheers for your help along the way Littlewyan.

[Littlewyan]

Thats alright, glad you got it sorted. If you want an attenuator again then let me know. I use a redesigned Airbrake that works really well.

[sickman82]

Thanks for the offer.. do you build them yourself? I tried looking for schematics before I bought the Silencer because I'm pretty handy with an iron but I didn't find anything.

What do you reckon to using a 5751 in the PI slot after installing the loop? I have a nice GE 5751 that hasn't had much use, and my thinking is to tame the PI a little to help with delay/reverb in the loop.

[Littlewyan]

I built this one myself. Its the only one I've made! I saw Kendrick did a redesigned Airbrake so I tweaked that. I also included a solo boost option that will go to a lower attenuation level when you push the footswitch. How much attenuation do you need?

I don't know what difference that would make to your effects loop to be honest. I've never used effects loops, I don't use any pedals except for a wah .