Any one know how to troubleshoot a transformer?

[firmani99]

About a year ago I purchased a dual rectifier. It always sounded great with my peavey ms412 cab and my marshall 1960av cab but sounded absolutely terrible with my mesa rectifier cab. I just figured I didn't like the rec cab. But I recently purchased a used mark V. (Deal I couldn't pass up) The mark sounds good with all of the cabs including the mesa. (I still prefer the marshall over the mesa but that's a different story)

Anyway today I tried messing around with the rec and plugged it into the rec cab and it sounded terrible. Just like the amp was running out of steam. No low end and the low end that was there was choppy and terrible sounding so I messed around some more. The amp sounds great with the peavey cab and marshall cab still. But then I tried running the marshall 4 ohm input (using the 4 ohm spot on the rectifier head) and it started to sound bad. So my conclusion after all of my experimenting is that its the head. It sounds great with a 16 ohm load but terrible with an 8 or 4 ohm load. (In there respective outputs) What could cause this? Could it be power tubes? Could it be the output transformer?

 

[ryjan]

I'd suspect the jacks themselves or the leads soldered to them.

 

[firmani99]

I might take the amp apart and take a look. But it seems to happen on all 8 or 4 ohm jacks.

 

[firmani99]

Another thing I just noticed. It even happens on the 4 and 8 ohm jacks with a 16 ohm load. (safe mismatch)

 

[firmani99]

jacks seem fine. The only two things I could think of would be tubes or output transformer. I ordered new tubes so we'll see. Anyone know how to test the transformer? Anyone have anything similar happen? Seems like it wouldn't be tubes since it sounds perfect with the 16 ohm output but who knows,

 

[ryjan]

I've never heard of this problem but I think you're diagnostics are on the right track. Please post when you find out what the problem is.

 

[firmani99]

I definitely will!

 

[firmani99]

Doesn't seem to be the tubes. I had some 6l6's laying around that someone gave me. I don't know what kind they are but he said they are good. I wouldn't normally trust a test with random unknown tubes but it sounds exactly the same with both sets. I'm going to see what happens when the new ones come in.

 

[firmani99]

Called Mesa tech support and they just said I had to take it to a service center. I wish they offered more detailed help. I'm handy with a soldering iron I'm sure I can fix it if I knew what it was. Anyone know how to test the output trans?

 

[afu]

A transformer can have a short in part of the secondary and the taps will have issues. Tubes can also have issues, but this doesn't seem like the case. Since the taps are connected directly to their jacks in the amp, you could check to make sure the connections are good. A 2 Channel has the 16/8 as one set and the 4 ohm is wired to the slave out. The 3 Channel has the 8 ohm and 4 ohms split to run 2 16 ohm or 2 8 ohm cabs, or two run one of each of it's stated ohms when only one plug is used. The 4 ohm is still wired to the slave out. If you have another head and enough 2 speaker cables to keep a load on the transformers of two heads, run the DR into the effects return of another amp and see if it craps out. The 8 ohm is the tap for presence. Put it in Vintage turn the treble all the way up and see if the presence is working correctly.

For sheets and giggles, you could pull the outer tubes and plug your 16 ohm cab into the 8 or 4 and see what happens. When the tubes are pulled, don't use the 16 ohm jack. (Kaboom)

Failing all that, I found you a good page on testing the transformer. http://www.geofex.com/ampdbug/outtrans.htm

Please don't do the testing if you have any reservations about it. High voltage is no fun to feel. Trust me.

 

[MesaTim]

Take the caps off of your pre amp tubes. Turn the amp on without a guitar plugged into it and tap the pre amp tubes with something to the nature of a pencil. I use a drumstick. If you hear a ding noise coming out of the speakers it means your have a bad pre amp. Based off of the description is what it sounds like. Simply replace the tube that dings.

 

[firmani99]

Thanks guys! I'm going to try a few things.

 

[firmani99]

afu, I don;t understand what you mean that 8 ohm is the tap for presence.

 

[domct203]

afu, I don;t understand what you mean that 8 ohm is the tap for presence.

He means that the presence circuit gets it's feedback from the OT's 8 ohm secondary
Tap.

Dom

 

[firmani99]

Oh ok gotcha. Well I tried brand new tubes and same thing. I'm going to take a look inside the amp tomorrow if I get a chance.