5150 212 Combo Fuse

AT · 02.02.07, 03:03 AM

Hi Folks:

I'm the proud owner of each version of the 5150 series amps. I scored the 212 combo off eBay a few weeks ago for a great deal ($330 local pickup). Wednesday night at band practice, however, I blew the fuse. Upon removal I was surprised to find it was glass, not ceramic like the 5150 heads. Is this right? Should the 3A fuse for the combo also be ceramic, and if so was this likely the reason it blew?

When searching some forums just now, I found a post about how disconnecting speakers can cause fuses to blow. I was running into a 5150 cab at the time, and at the request of my singer I switched from my top cab to the lower one; I put the amp on standby before doing so. Could this have caused the fuse to blow?

Ideas?

Here's hoping it's not a bigger problem!

**HipCat5** · 02.02.07, 05:01 AM

The type of fuse shouldn't matter (ceramic or not). I think its accepted as common practice to use a SLow-Blo type fuse of the approved current rating. Not 100% sure on the need for ceramic but I've not seen evidence in print or from personal experience to think otherwise.

As for the reason for blowing a fuse, the most common would be a power tube failure or capacitor failure. In either case, the failure could cause a dead short between B+ voltage and ground, thus drawing excessive current and blowing the fuse.

Running a tube amp without speakers is a very bad idea because if the power tubes run without a load for even a short amount of time, they are prone to failure [in a nutshell]. In regards to running the amp with an odd impedance, the combo amp wants to see either 16 ohms from the main speaker out (found under the chassis behind the back grill) or two 16 ohms if you use both the main and back-panel speaker outs (16 ohms, respectively, I should say). I wouldn't run 8 ohms in either of these speaker outs because that will do harm to the output section eventually. Running 16-24 ohms shouldn't be a problem (more never seems to be an issue ... within reason of course).

I've run clusters of speakers wired in odd ways to the tune of 24 ohms impedance total and my 5150 combo sounded fine and worked properly.

If there's a capacitor failure, you'll either blow fuses immediately upon B+ application OR you'll hear an immense amount of 60Hz/120Hz hum. either way, probably time for a cap job.

Good luck

AT · 02.02.07, 05:11 AM

Hey HipCat:

Thanks for the info. I recall getting some 60Hz hum when I first powered up Wednesday night, so I wonder if you might be on to something about capacitor failure. (I hope not.)

It was my understanding the 5150s used ceramic fuses to help withstand the heat. I vaguely recall using a glass fuse in my original head a few years back when attemting to just get through a recording session, and it blew within a couple of hours.

**HipCat5** · 02.02.07, 06:28 AM

re: testing for hum: if you're hearing more than the usual amount of hum with your guitar NOT plugged into the amp (remove the cord from the amp itself) and listen with the preamp and master knobs in various positions. Obviously you'll get some hiss/hum with everything cranked up, but it shouldn't be terrible at "1" on the pre and master, for example.

re: ceramic fuse: ah, I get it. I can't imagine it getting *that* hot inside the chassis but anything is possible.

Good luck. I haven't played inside my 5150 combo yet with the exception of rolling tubes around but if I can help, let me know.

Cheers!

**fifty150** · 02.05.07, 09:09 PM

I blew the same fuse a few years ago and if I remember right it was glass. My combo didn't sound quite right after replacing the fuse and it kept blowing them out. I had to finally send it back to Peavey and they fixed it, but it has never sounded the same to me??? It really lost that THUMP it used to have??? Hopefull its not something serious but if it is, bring it to someone else other than Peavey if at all possible.

**HipCat5** · 02.06.07, 05:00 AM

I had a Marshall clone which I did a capacitor job on and it too lost that bass response "thump". An EE friend of mine (and tube amp mentor) gave me a clue that the power supply capacitance could be beefed up to bring back that thump. After doubling up on the power supply caps (instead of using a pair of 50uf, he suggested using a pair of 100uf [if I recall] due to the inherent +/- 20% tolerance on the caps I bought), the thump was back. The reason is that those power supply caps not only filter, but they store the charge necessary for those hard hitting bass notes. I can't say what would be a tolerable upgrade in the 5150 combo but I'd be willing to wager that the caps Peavey used in the repair might have been in the -20% tolerance range. (better to have more capacitance than less).

Note: you don't want too much capacitance in the first capacitor immediately after a tube recitifer though. That will overdraw that tube rectifier and ruin it. (Peavey 5150 uses solid state rectifier ... my Marshall clone had a tube recitifer).

Good Luck