Marshall DSL 100 Power Trans - Overheating (Anyone see this?)

[Ryteone]

After messing with this DSL 100 for the last week I finally got it to shut down (and saw that the heaters were .83 one side and 6.71 VAC on the other, not counting the first two tubes where are running DC heaters).  But measured at the transformer and it was the the same.  I shut it off and with in a few minutes checked again and it had cooled off enough to bring it back to the 3.31 VAC on each side (but didn't take long for it to heat up and drop back to the .83 and 6.71 VAC).

It was driving me crazy that I couldn't get it to shut off like the customer sad but the problem was I was running it open on the bench in an air conditioned house.  I put it back in the head cabinet yesterday and got it to shut off and quickly pulled it out and measured.

From what I've read (online) it sounds like the smaller Transformers Marshall was putting in these DSL's was problematic for overheating.

I even saw where someone had hooked up a muffin fan to blow on and cool the transformer (guess that is less expensive than replacing the transformer).

Just wanted to see who else may have experienced this and what transformers they replaced it with.  Hate to get another "Marshall" replacement for it to just be the same way.  Yet I don't see the customer wanting to spend the money to go with a Mercury Magnetics replacement they have (looks like one hell of a replacement at over twice the size). But at $325.00 I'm afraid he will have a stroke or heart attack!

Thanks Scott....

[navdave]

Power transformers get HOT that's what they do. Are you reading you multimeter correctly? Set it to AC measure the voltage on the power tubes between pins 2 and 7 if it's 6 to 7 VAC your good. I wouldn't by any iron from Mercury Magnetics when you can get it for half price from Heyboer. If you haven't blown any fuses and the amp is running fine don't sweat it.

[Ryteone]

Yeah I've been that route with this amp having the first two preamp tubes running DC heaters then the rest of the amp on the AC.  There is nothing worse than having the wrong setting and freaking out.  Thanks for the Heyboer tip!  When you keep the transformer cooler it runs just fine.  Thought it seemed strange that the 100W power transformer in this unit is about half the size to the transformer in my 72 50W head.

[navdave]

Marshall uses a full wave BRIDGED RECTIFIER on their 100 watt amps that's why the iron may be the same size or smaller than a 50 watt Marshall.
Instead of 600VAC in full wave mode like in the 50 watt amp they use 375VAC in a full wave BRIDGED RECTIFIED MODE.
The bridged rectifier method is WAY more efficient than the full wave method. For a 100 watts in full wave mode you would need
like 750VAC @ 400mA hence bigger iron. Just because the iron is small doesn't mean its cheap.

Thought it seemed strange that the 100W power transformer in this unit is about half the size to the transformer in my 72 50W head.

[Ryteone]

Thank you Navdave for making me pull my head out!!!  (I'm so much into bigger is better guess it's how you use it not how big it is!)

I want to thank LooseChange because I was sure it was the transformer, but he kept telling me to check the DC heater circuit.  I took it out tonight and so far its holding just great.  I didn't think about it going out and messing the whole circuit out.

Scott..