My Classic 30 DIED!!!

[greentexasbandit]

Hi Everyone!
Well, here's the deal...a couple weeks ago I was playing at church on my Classic 30. I left my amp sitting for a few minutes before the service started and when I got back to play, it didn't work anymore!!! I wasn't sure what was going on because the the power/pilot light was still on but nothing was coming out. I checked the tubes and none of them were lit up so I knew it wasn't a quick fix.

I was finally able to check it, I found that the P.T. and all the tubes were not heating up in the slightest. I found this odd because they're normally pretty hot!
I checked the fuses and they all still had continuity so I'm assuming they're fine. I checked power going into the P.T. and it read about 117 volts (normal), but when I checked the other side of the P.T. at the fuses, I was only able to get a 3-5ma reading on one of the wire sets. My thought is that the P.T. is blown, but I'm no expert which has led me here...to ask some experts.

Anyway, I would really appreciate any input you guys have...

Thanks for the help!

[tubeswell]

I'm just at a loss right now as to what comes next.

a trip to your tech. Those c30s are a dog to work on

[Enzo]

Did you actually REMOVE each fuse and measure it with an ohm meter while it was out of its clip? Your 10A heater fuse will seem to measure OK while it sits in its clip. Otherwise, we might check those couple 3w resistors in the heater string.

[ermynn]

hi

Look at the wire between the two cards (near the power capacitors) in your classic 30. they would be broken ...

Regards
Denis

[greentexasbandit]

Yes, I removed all fuses from their clips and measured them with an ohm meter...they all kept their continuity while they were out of the clips. I also took out all of the tubes and checked them as well.

[greentexasbandit]

I'll take a look at the wires between the cards...haven't checked those too closely yet. Thanks

[Gunny]

Isn't it possible that one (power) tube filament just failed open circuit? Since they are wired in series, it only takes one 'open' to the kill the set.

Try replacing the power output tubes (one at a time) with a known good one.

[greentexasbandit]

Hmmm...I tried changing them out in pairs because I still have the factory tubes, but didn't get anything out of it. I guess I should try one at a time though.

[Enzo]

Pretty darned unlikely that more than one heater is oopen, but it takes only seconds to check.
If the heaters do not light and the heater fuse is good, then you have a continuity problem. Either a broken jumper link, or an open series resistor. R71,72 are 3 ohm 5w, on the end of the center board near the fuses.

[whickman]

No output from power transformer

I just worked on a Classic 30 for a friend of mine.

Had very similar situation and I thought the power transformer was bad. Found out that there is a fuse inside the transformer itself.

I removed the power transformer and removed the metal copper foil wrapped around the outside of it and found the mini glass fuse and replaced it with a new one. I believe the value was on the outside of it. The fuse in the 30 i was working on was a 3A 250V fuse, (5mf 3A 250V).

I reinstalled the transformer and powered the amp up again and nfortunately
it hummed real loud and then blew one of the fuses in the fuse holders on the circuit board.

To make a long story short I found the output transformer seemed bad and CR6 diode had shorted.

I replaced the transformer and CR4 and CR6 and that fixed the amp.

After running the amp for a few minutes I noticed the volume dropped a little and one of the output tubes was glowing red so I replaced the tube that was glowing and the amp works fine now.

Willis

[oc disorder]

The power light will still come on even if the power transformer is open circuit.
Hi whickman welcome to the forum ..That fuse in the power transformer is
a thermal fuse (see attached for two examples although the peavey one is slightly different)and now most power transformers are required by law to have them.
You have to be very careful as it wasn't intended to be replaced and some of the insulation may be damaged from the excess heat and could be dangerous.
It should have had a temperature stamped on it too (156deg c?)

greentexasbandit check the orange wires with your meter on the ac setting.
There should be 25 volts approx.
The red ones a little more dangerous maybe 180- 230 volts ac.
Someone may know these figures more accurately.

If nothing on the orange ones its safe to say its unlikely there would be any
HT as well.

A new power transformer would be the correct replacement if there is no voltage from the existing one.

[whickman]

No output from power transformer

Yes that is correct. The power light was still coming on because it was across the input to the power transformer.

I don't know if the fuse at one time may have been a thermal fuse but
the fuse I found was not a thermal fuse and was inside heat shrink tubing
so it could not short to anything.

Willis