Peavey 5150 no sound, tubes not glowing

[zork]

a kid here at school asked me to help him with his 5150. There is no output at all.
In peeking in the head, the tubes are not glowing at all. None of them, neither output nor pre-amp.
I checked the PT windings to ground, between each etc and everything seemed okeedokee, no shorts to ground or shorts between windings.
I have not checked output yet tho. I wanted to post first for some guidance from the experts.

He said that the thing was working fine, he loaned it to a friend, and now, poof. dead. friend won't say if anything happened or if he did anything to it.. just that he went to use it and it didn't work.

I did a cursory look at the board, nothing obvious jumped out like crispy components, also no burned smell either. fuses are all OK too.

power lights, channel lights etc on the front panel all work just fine, just that none of the tubes glow at all.

normally I would just say "hey, take it to a tech" but as a poor student it's tough to come up with the cash to do so. one local shop wants almost $100 just as their initial bench fee to get started. I"m hoping to at least figure out which components so he can get prices to decide if it's worth it to get fixed and how long he'll have to save up to afford the repair

thanks!

[52 Bill]

Have you checked all of the fuses on the pc board?

If you search the forum you will probably find the schematic here. When you look at it you will see that there are a number of internal fuses. Check them all with an ohmmeter and see what you find.

[zork]

52 Bill:

yea, there were 5 on the board (I think).. checked them all, all good.
thanks

[Prairie Dawg]

52 Bill:

yea, there were 5 on the board (I think).. checked them all, all good.
thanks

Well, you're not getting 6.3v to the filaments and that's probably what the source of your discomfort is. Check that fuse with a voltmeter and go from there.

[zork]

that you know, are there others besides the 4 or 5 in a row on the PCB? They are right where the connectors from the Primary xfrmr connect to the board. Those have been checked and are good, but I'll pull them again tonight and check them just to be sure.
thanks

oh.. after checking those fuses, are there test points on the board where I can check the 6.3v for the heater? a point on the bus, or test points, or would it be best to just test output of the transformer?

I do have a variac I can use to lower input if necessary.. I'll have to take my tesla coil apart to do it, but that's no big deal

thanks again

[defaced]

5150 heaters are not wired like most amps, they are DC, but I'm having a hard time making out what voltage is delivered to the tubes and exactly how they're wired. At a minimum, start at the PT and measure AC voltages. Start with the highest setting on your AC volt meter because the HT winding on that is going to be pretty high.

Have you re-seated every quick disconnect in the amp?

[CharlieP]

I forget which pins for heaters but, you need a schematic anyway and you can get that info from it. The power tubes need to be checked. Usually a power tube is the main cause.

[zork]

thanks for the help guys.. I appreciate it.

I have a fluke meter, goes up to 750VAC.. otherwise I have a scope I can use if necessary.

would one bad tube cause all to not function? what about then pulling tubes one at a time to then see if they start to function, or would that bad tube have killed the others?

I do have a schematic on the computer somewhere.. just gotta find it. and I know off the xfrmr there were 4 or 5 connectors to go along with the 4 or 5 fuses.. red/red, yellow/yellow, orange/orange.. and I forget what else.

I'll check it tonight when I get home

thanks again

[bluesfreak]

on the 5150 the Preamp Tubes are wired in series and heated by DC while the Power Tubes are heated AC. F2 (should be 2A FB) is for the Power Tube Heaters, F3/F4 for the DC Heating. Is the Power LED illuminated when you switch it on? If yes the DC circuit is wirking as Poer and Status LED are tapped off this DC supply. If everything is dark the problem is most likely before the secondary side => PT blown.

[defaced]

I have a fluke meter, goes up to 750VAC.. otherwise I have a scope I can use if necessary.

yea, that'll be fine. I wouldn't expect to see more than 360vAC or so on the HT.

[zork]

vielen Dank fuer die Hilfe ;-)

at power on, the lights come on, power, standby, channel etc. just that the tubes do not and of course, no output.
ich guck mal heut' abend wenn ich zu hause bin.
danke

[zork]

hmm.. been a long time since I've spent much time pouring over schematics.. but it looks like F3 and F4 feed into a rectifier, with +-24V.
I can see on the drawing where the pre-amp tubes are on that (what's appropriate for an amp? bus? rail?)
anyway.. the power and status LEDs work.. therefore fuses F3,F4 have to be good (as indicated by my meter too)
but if I have the +-24 and the LEDs work, what would prevent the heaters in those tubes from working? I don't see another fuse.
If it's possible to pull a single tube out and have the amp continue to work, they can't be in series, have to be parallel.
but now I also know some other things to check.

thanks again for the guidance (and a place to think 'aloud' to see if I have any errors)

Paul

[CharlieP]

vielen Dank fuer die Hilfe ;-)

at power on, the lights come on, power, standby, channel etc. just that the tubes do not and of course, no output.
ich guck mal heut' abend wenn ich zu hause bin.
danke

Put in new power tubes. If all the lights are on, it should fix it.

[zork]

Put in new power tubes. If all the lights are on, it should fix it.

ooof.. that's what we were kind of afraid of.. the cost of the new tubes with a chance (is there one?) that whatever the issue is might kill off a new set of tubes.. saving up for tubes from minimum wage will take a while for the guy.

I really appreciate everyone's help

thanks!

Paul

[defaced]

ooof.. that's what we were kind of afraid of.. the cost of the new tubes with a chance (is there one?) that whatever the issue is might kill off a new set of tubes.. saving up for tubes from minimum wage will take a while for the guy.

I really appreciate everyone's help

thanks!

Paul

There's lots of things that could cause those symptoms and not be fixed by replacing the power tubes. For instance, if the heaters aren't glowing like you're describing, replacing the power tubes won't fix it.

You've got a symptom, the heaters don't glow, now find the problem. Start at the PT and check everything in the heater circuits. Just because the lights on the panel come on doesn't mean anything about the heaters aside from that secondary winding is working.

Have you checked the quick disconnects?
Have you checked heater voltage at the tube sockets? Seems silly considering what you're visually seeing, but I've seen stranger stuff.
What happens when you plug a guitar into the FX return jack?