Odd Problems With Dual Rectifier Tubes (PLEASE HELP)

The Boogie Board

Help Support The Boogie Board:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

JamesOsyris

New member
Joined
Dec 1, 2011
Messages
1
Reaction score
0
I'll try and make this short.

I've had my Dual Rectifier for over a year now. I bought it used but I believe it is the newer model since it has 5 buttons on the foot-switch. The power tubes in question are 5U4GB. Also a sign that it's the newer model.

Recently, out of nowhere, the amp lost all volume, then sparked and went dark. I could smell that something had burned up. After learning about fuses, I knew that the fuse had gone out. I then replaced the fuse just to see if the same thing would occur a second time. This time, the fuse did not go out, but instead, the power tubes were dark and at 0 volume I heard a VERY loud humming sound.

I went on a forum much like this one and every person told me that I merely needed to replace to power tubes. I had a feeling that 2 tubes going out at the same time was fishy, but I went with it. I spent 75 dollars on a pair of tubes (rush delivery). After installing them, I put the head in standby to let them warm up, and they seemed to be working. Then, the second I flipped the switch from standby mode, the same thing happened again. It sparked and went dark. No power. Possibly 75 dollars down the drain and I have a show and studio session this weekend.

Bummer.

So my question is, what is the problem? I really want to know what is going wrong with it before I drive out to see an amp tech. That way I'll know what I can afford and plan accordingly.

Thanks!
 
When a power tube blows it can also burn up the screen grid resistors (the burning smell/light smoke) accompanying it and pop the fuse. This happened on my Mark III the second time it blew a power tube. It isn't an expensive or lengthy fix for a good tech (should take a day, and maybe $5-10 in parts and a couple hours in labor). Just a resistor fix, but a pain, as you can see since the power tubes don't have proper voltage regulation and will blow again if not fixed.
 
Okay,to start with your power tubes are not the 5U4GB's.If you replaced those,you didnt replace your power tubes.Those are rectifier tubes.At this point I can only guess exactly what you've done.Did you replace your power tubes with rectifiers?Did you merely replace good rectifiers and leave blown power tubes?Is it actually the 5U4's that blew?I strongly suggest you get the amp to a tech.
 
If the fuse blew when you switched from standby to full on, chances are it is a blown power tube. As stokes said the 5U4s are rectifier tubes. Usually a blown rectifier tube will blow the fuse on power-up, not when switching from standby to on, so it's unlikely you needed to replace the 5U4s. (Although it's not totally impossible.) However having spares is not a waste of money...

What you need to do now is get a set of 6L6s. These are the power tubes. Chances are that only one is bad - certainly no more than two, even if one failed and damaged its 'pair' on the same side - and if you want to use one more fuse you can tell which one, and for sure whether this is the problem. It's probably a good idea to do this first.

Remove both rectifier tubes and the four power tubes. (But *not* the small preamp tubes.) Power the amp up with the rectifier switch set to Silicon Diode. If the fuse now blows either on power-up or turning the standby off, take it to a tech - it's not a tube fault. If not: fit one rectifier tube (5U4 - make *sure* you do not mix up the types or the positions; you want one of the two closest to the power cable) and try again. If the fuse holds, remove it and fit the other. If the fuse still holds, remove them both and repeat for each power tube, one at a time (still with the amp set to Silicon Diode). When the fuse blows, the bad tube is in the amp.

You can either replace just this one (you have to buy Mesa tubes in pairs, just get the same colour rating) or all four and keep the three good ones as spares. Until you're more familiar with choosing tubes, buy Mesa brand ones only. These are selected and tested for your amp.

Owning a tube amp is a bit like owning a car, it isn't totally maintenance-free. Spare tubes and fuses are like spare tires, it's always a good idea to have them and know how to change them. If you're buying tubes and don't have a spare 12AX7 yet, but one of those as well - they're not expensive.

Hope that helps.
 
Good advice from 94Trem,but I am concerned you may have put a pair of 5U4's where the blown 6L6's were.I dont mean to offend anyone here,but when someone describes his power tubes as 5U4's I have to question what exactly has been done.
 
stokes said:
Good advice from 94Trem,but I am concerned you may have put a pair of 5U4's where the blown 6L6's were.I dont mean to offend anyone here,but when someone describes his power tubes as 5U4's I have to question what exactly has been done.

That is good advice 94Trem...and I totally didn't see the part where he said it was the 5U4's...I really hope he didn't stick 6L6's in there.
 

Latest posts

Back
Top