5150 combo keeps blowing fuses

[Funeral]

I powered up (or attempted to) my peavey 51510 combo last night for the first time in about a month. Normal for a few moments, then it started making a weird electrical noise. I shut it off, and checked all the power connections. Seemed fine. Powered it up again, and the standby light just wouldn't come on. So, I left it alone for the night. Today, I took the chasis out and checked the fuses, as that seems to generally be the problem with this thing. Yup. The 2 amp fuse was blown. I replaced that, put the amp back together, and powered it back on. Standby light worked again and whatnot, but seconds later the weird electrical noise even though I had turned it back and standby, then the fuse blew again.

I'm not entirely sure what commonly causes fuses to blow, but any advice would be excellent. it seems to be only the fuse in charge of the standby switch, and not any of the others, if that is any help.

[micri5446]

hi....try to pull all output tubes and replace fuse....if it does not blow replace tubes and you should be good to go.. however,it should be checked out by a tech as you might want to have bias also checked to make shure of no other shorts

peace.........................mike

[52 Bill]

First thing to check is the output tubes. They are the most common reason for blown fuses.

You can try removing them before you power up the amp again, to see if the fuse still blows. If the fuse holds without the power tubes, then there is a bad tube or a problem with the circuitry at the output tubes.

If it blows without the power tubes, then the power supply needs to be checked.

[John G]

Hi Funeral,
You couldn't do me a favour and look at the Accutronics number on the REVEB tank.
I had a combo in for repair a while ago with very weak reverb.tank measured ok and the number was 4EB2C1B, just thought it may be an incorrect tank fitted.
THanks and sorry to hijack your thread.
John G

[Funeral]

Hi Funeral,
You couldn't do me a favour and look at the Accutronics number on the REVEB tank.
I had a combo in for repair a while ago with very weak reverb.tank measured ok and the number was 4EB2C1B, just thought it may be an incorrect tank fitted.
THanks and sorry to hijack your thread.
John G

I'm not any kind of expert on this or stuff, but it you tell me where to look for that number, I will definitely check for it. The reverb does seem pretty weak, now that I think about it. I can barely tell it's in use unless I'm using it for "clean" tones. As for the output tubes, I will definitely check that out tomorrow when I can get more fuses.

[John G]

Hi,
The type number is printed in a blue/Purple coloured ink stamp on the top surface of the reverb tank with a number -letter sequence the same or similar to the one I posted .....4EB2C1B.
Thanks
John G

[Billy R aka DynaFreak]

If you determine that you have a problem with output tubes and replace them, I strongly suggest that you check to make sure you have screen voltage to all the pwr tube sockets. The big 100-120 watt Peaveys are prone to blown screen resistors. It is rare to get one in the shop that doesnt have at least one bad one. I worked on one recently that the customer said "just did not have the tone and power it used to". Three blown screen resistors. It was operating on one power tube. Pwr tubes were OK, by the way.

[Enzo]

Those resistors were probably blown by previous bad tubes. Ir would take like 250ma of screen current to stress those 100 ohm 5w resistors.

[R.G.]

I'm not entirely sure what commonly causes fuses to blow, but any advice would be excellent. it seems to be only the fuse in charge of the standby switch, and not any of the others, if that is any help.

I apologize if this sounds like sarcasm or patronizing you. It's not intended that way. It's intended to get your amp back to working as quickly and reliably as possible.

I may be wrong about your level of electronics skill and understanding just inferring it from your posts. If so, I apologize.

There is really very little that one can do inside an amp by themselves until they understand schematics, can use a soldering iron and voltmeter (and have one of each), and appreciate the voltage dangers. Until one has that skill base, they're limited to replacing what can be plugged and unplugged without tools - tubes, fuses, and cords, and making sure the screws are firmly tightened, and not even that last until they understand how not to get electrocuted doing it.

Fuses do not in general just blow. There is a cause. If new tubes and new fuses do not fix it, take it to a competent tech. It is possible to further damage the amp, and even one emergency room visit costs more than a new amp.

[Billy R aka DynaFreak]

Those resistors were probably blown by previous bad tubes. Ir would take like 250ma of screen current to stress those 100 ohm 5w resistors.

Correct. That's my point. people keep blowing tubes, then replacing them without checking for blown screen resistors. Then they turn up because the amp is not as loud as it was, then they blow more tubes and resistors....

[JerryP]

The 5150 combo has no screeen grid resistors.

Your amp probably needs a new fuse and a set of power tubes.
Jerry

[Enzo]

You're right, of course, Jerry, the 5150 Combo has no screen resistors, Billy's example of other amps did. And I fell into his trap.