Peavey Ultra Plus - dead...

[Twangmaster]

My Ultra Plus 120 head is dead - first the channel switching started to act strange and then one day after playing some time a fuse blew. I have identified the output tubes to have overheated and died - but there seems to be other issues as well - does anyone have experiences with fault on this amp - and does someone have a schematic for the amp? Any help would be appreciated - Thanks

[Amp Kat]

Make sure all the fuses inside the amp are not blown also but be carefull in there and let the amp sit about 10 minutes before you go poking around as theres high voltage in there. You can get schematics from Peavey at Customer Service so they will email them to you in pdf format for no charge and yes there are several here who know that amp pretty well.

[Twangmaster]

Ultra Plus still very dead...

Hi,

Thanks for the support !

I got the schematic from Peavey just now, and my god, this a complicated amp with a lot of switching and hundreds of components.

Has anyone out there tried to repair one of these before - or does it need to go to the official Peavey repair shop?

I anyone has some support - it would really help.

Thanks.

[Amp Kat]

Hi,

Has anyone out there tried to repair one of these before - or does it need to go to the official Peavey repair shop?

I anyone has some support - it would really help.

Thanks.

Ok yes I've worked on several of these. Do you have a multimeter and feel up to doing some soldering possible ? If you don't feel up to it tell me now so you can send it to Peavey. They are probably tops in Customer Service and Repair so that's a good thing. Right off the bat and as stated before make sure there is not any voltage on pin's 3 & 4 of the power tube sockets. You can check across R-200 thru R203 and make sure you can read 100 ohms across each of those resistors. Do the lights on the front panel change colors with the footswitch ?

[Twangmaster]

Ok yes I've worked on several of these. Do you have a multimeter and feel up to doing some soldering possible ? If you don't feel up to it tell me now so you can send it to Peavey. They are probably tops in Customer Service and Repair so that's a good thing. Right off the bat and as stated before make sure there is not any voltage on pin's 3 & 4 of the power tube sockets. You can check across R-200 thru R203 and make sure you can read 100 ohms across each of those resistors. Do the lights on the front panel change colors with the footswitch ?

Thanks KB,

No, first the footswitch stopped working, and then one day the main fuse blew with the result that the amp has no current what so ever. I can see that the two outer 6L6 tubes are "burned", so that must have caused a short.

I will not be able to open the amp and solder and measure before next week, since I have to go on a businesstrip - can I get back to you then - with feedback on the suggested measurement?

Thank you,
GOWE

[Amp Kat]

Sure no problem and we'd be glad to help you get it back up and running then. Have a safe trip !

[Twangmaster]

Hi Amp Kat - I'm back...

So I got around to testing - and found R202 and R205 burned, while the two other resistors are ok, As far as I can see from the schematic, it fits well with two of the 6L6's being burned on the inside of the tube.The mains fuse (3F) is also gone - all the other fuses are ok.

The meter shows 0.5 Ohms on the output tranny, measured on the speaker connection. - does this give any verification that it's still ok?

I ordered 4 new TAD 6L6 STR tubes - would it be safe to put them in, after renewing R202 and R205, and the mains fuse? - or do you have other measurements, I should do before I put in the new ($130) power tubes?

Thanks,
GOWE

[Amp Kat]

The meter shows 0.5 Ohms on the output tranny, measured on the speaker connection. - does this give any verification that it's still ok?

I would also check the ohms across the primary of the OT as that will tell more but the .5 reading is a good sign. You should get about 70 ohms from the middle (centertap) wire on that connector to each other wire and about 140 ohms across the winding If it reads OL or OL blinking real fast that's not good

I ordered 4 new TAD 6L6 STR tubes - would it be safe to put them in, after renewing R202 and R205, and the mains fuse? - or do you have other measurements, I should do before I put in the new ($130) power tubes?

I usually leave the power tubes out at start up and make sure everything is ok. Ground your DMM on chassis reading VDC and go around the tube socket with the red lead. Check pins 1 and 8 and make sure there is no voltage there. Then check pin 5 and make sure you have ^negative -55 volts there then, check pins 3 & 4 for high voltage (careful there) of 450 VDC then put the DMM on AC and check pins 2 & 7 for your 6.3 heater voltage which will more likely be about 7.5 VAC then you can try your tubes.

Hopefully your switching will come back and the front panel will light back up.

[Twangmaster]

I would also check the ohms across the primary of the OT as that will tell more but the .5 reading is a good sign. You should get about 70 ohms from the middle (centertap) wire on that connector to each other wire and about 140 ohms across the winding If it reads OL or OL blinking real fast that's not good .

I measured the secondary again - showing .2 - .3 - .4 depending on the speaker ohms - ok I guess.
The Primary gives very different readings, compared to the ones you expected:
Brown cord is middle, red and blue are outer wires; between red and brown I read 28.4, between blue and brown I read 64.8, and between red and blue I read 36.6 ohms....OK?

I usually leave the power tubes out at start up and make sure everything is ok. Ground your DMM on chassis reading VDC and go around the tube socket with the red lead. Check pins 1 and 8 and make sure there is no voltage there. Then check pin 5 and make sure you have ^negative -55 volts there then, check pins 3 & 4 for high voltage (careful there) of 450 VDC then put the DMM on AC and check pins 2 & 7 for your 6.3 heater voltage which will more likely be about 7.5 VAC then you can try your tubes.

Hopefully your switching will come back and the front panel will light back up.

I'll get the resistors and fuse tomorrow - and check the above. Do you think the front panel light is linked to the main problem of blown fuse - or do you think there could be other faulty parts earlier in the signal chain, that caused the burn down - or could worn/faulty output tubes be the only reason?

[Amp Kat]

I measured the secondary again - showing .2 - .3 - .4 depending on the speaker ohms - ok I guess.
The Primary gives very different readings, compared to the ones you expected:
Brown cord is middle, red and blue are outer wires; between red and brown I read 28.4, between blue and brown I read 64.8, and between red and blue I read 36.6 ohms....OK?

That sounds good to me ! Little lower than I expected but was going by the 5150 so your good.

I'll get the resistors and fuse tomorrow - and check the above. Do you think the front panel light is linked to the main problem of blown fuse - or do you think there could be other faulty parts earlier in the signal chain, that caused the burn down - or could worn/faulty output tubes be the only reason?

Hard to say but my guess is you had a tube short and it took out the fuse for the low side then fried your screen resistors and then quit obviously. Yeh I'd say the tubes caused the whole thing.

[Twangmaster]

Ups...wrong voltage readings...

I usually leave the power tubes out at start up and make sure everything is ok. Ground your DMM on chassis reading VDC and go around the tube socket with the red lead. Check pins 1 and 8 and make sure there is no voltage there. Then check pin 5 and make sure you have ^negative -55 volts there then, check pins 3 & 4 for high voltage (careful there) of 450 VDC then put the DMM on AC and check pins 2 & 7 for your 6.3 heater voltage which will more likely be about 7.5 VAC then you can try your tubes.

Hopefully your switching will come back and the front panel will light back up.

I put in the two 100 ohm resistors, and a new fuse - and got the following reding:
1 - no voltage
2&7 3.2 volt
3: rising from 490 to 540 volt - before I shut off.
4: dropping voltage from 450...to 0
5: 53 volt
8: 53 volt for tubes V5 and V6 (0 for V7 and V8)
The 100 ohm resistors that burned were connected to V5 and V7.

Not so good - seems to be a bit more tricky - what now?

[Twangmaster]

I put in the two 100 ohm resistors, and a new fuse - and got the following reding:
1 - no voltage
2&7 3.2 volt
3: rising from 490 to 540 volt - before I shut off.
4: dropping voltage from 450...to 0
5: 53 volt
8: 53 volt for tubes V5 and V6 (0 for V7 and V8)
The 100 ohm resistors that burned were connected to V5 and V7.

Not so good - seems to be a bit more tricky - what now?

Had it put on ½ power and 220v dc - so new readings:

1: 7.2 vAC for tubes V8 and V7, and -48v for V5 and V6
2&7 3.0 volt - but also 25 DC?
3+4: 495 volt
5: - 48 volt
8:0 volt

Does this give you a clearer picture?

[Amp Kat]

Had it put on ½ power and 220v dc - so new readings:

1: 7.2 vAC for tubes V8 and V7, and -48v for V5 and V6
2&7 3.0 volt - but also 25 DC?
3+4: 495 volt
5: - 48 volt
8:0 volt

Does this give you a clearer picture?

I'm kinda confused on V5 & 6 why 3.0 volts on 2 & 7 ? Something wrong there as it should be the same as V7 & 8. @ 7.2vac. The power tubes are elevated to +24 volts to quiet the hum down and the preamp tubes are elevated for +/- 24 volts for 50 volts. There are two (2) 100 ohm resistors R-93 & R94 from each leg of the power tubes to ground so if you ohm out each leg pin 2 to ground you should get 100 ohms. There should also be a status led when the screens are good the light is on driven by Q1. Is the status led on ? Are the power tubes lit ?

[Twangmaster]

I'm kinda confused on V5 & 6 why 3.0 volts on 2 & 7 ? Something wrong there as it should be the same as V7 & 8. @ 7.2vac. The power tubes are elevated to +24 volts to quiet the hum down and the preamp tubes are elevated for +/- 24 volts for 50 volts. There are two (2) 100 ohm resistors R-93 & R94 from each leg of the power tubes to ground so if you ohm out each leg pin 2 to ground you should get 100 ohms. There should also be a status led when the screens are good the light is on driven by Q1. Is the status led on ? Are the power tubes lit ?

Well - good to hear from you - I really need some help here !

First of all, my explenation was not good enough :

Pin 1 - V8 and V7 : 7.2 vAC
Pin 1 - V5 and V6 : -48v vDCfor
Pins 2 & 7 - V5, V6, V6 & V7: 3.0 volt (also 25 DC)
Pins 3+4 - V5, V6, V6 & V7: 495 volt
Pin 5: - V5, V6, V6 & V7: 48 volt
Pin 8 - V5, V6, V6 & V7::0 volt

So it looks like I have problems at pin 1 - where there is different voltage - and there should'nt be any. Pins 2 & 7 only give 3 volts !
I measured the secondaries on the power tranny - and it fits with spec.

I'll have to demount the board to measure R-93 & R94 - will do so.

The status leds are ok, but the is no light in the preamp tubes, and I haven't mounted the 6L6's yet - since the voltages are so much off - but I guess that 3v is too low for the heater.

Any other hint on what I should measure, having demounted the output board?

Thanks,
Gowe

[Enzo]

No, there is no problem. Pin 1 on a 6L6 is not used, so the cicuit board designer can feel free to put anything he wants on pin 1. All pin 1 is anymore is a spot on the road from one pace to another.

The heaters run on about 6VAC. That means there is about 6 volts AC from pin 2 to pin 7 on a 6L6. But you are measuring from chassis, and that 6v AC power transformer winding has a grounded center, one way or another. So you get 3volts on one side and 3 volts on the other. But that adds up to 6 volts across. If the tubes light up inside, then the heater volts are OK.