Line6/Bogner spyder valve hum.

[catstrat]

I have this Line6/Bogner Tube amp, 100 watt, here with a bad hum that's affected by the master volume. As you turn up the master,the hum gets louder. If i unplug the power to the effects board, the hum stops. I did notice a low voltage problem. The power to the effects board is supposed to be +/- 12 volts. I only get 8.2 volts +/-. The O/P tube plates are only 340 volts. I find no a c ripple at all. Could the low voltage issue be an open rectifier diode? I've never ran into an open rect. diode before. Plenty of shorted but never an open one. I'm not familiar with these amps at all. I've had no luck finding a schematic. Any help will be welcomed. Thanks.

[g1]

If it were a rectifier problem I would not expect both the + and - sides to be equally low.
This plus the low plate voltage seems like a possible low AC problem.
What do you measure for heater voltage at the power tubes?
Has the amp previously worked correctly with 120V line voltage?

[catstrat]

Hi G-one. The amp did work before and it developed a hum out of the blue. The cust. replaced the tubes and that didn't cure it. I tried test tubes and that's not the problem. I said before the hum would stop if the effects board was un plugged but i mis spoke. The hum is still there. I know most tube amps the master control is either before the PI tube or after. I assume this is no different. The tone controls have no affect on the hum. The hum appears to be 120 cps, according to the read out on my scope. I was sure it was a filter cap even if i didn't read much ripple. I did a recap and the have the hum still there. Each O/P tube has it's own bias pot and i set the bias at 35 mv per tube according to what's on the board. I did measure the heater voltage and it was 3.2 volts on pins 4/5 and 3.1 volts on pin 9. With the amp dead quiet when the master is turned down, it may be in the prreamp. The other thing is my bulb limiter is lit dimly. I'm confused with the 340 volts at the o/p tube plates. That seems awfully low to me for a 100 watt amp. The screens are about the same voltage. I just pulled the Rect. diodes for grins and they all check good. I've looked for cracked solder joints when i had the board and found none. A schematic would sure help. Seems like i saw a schematic on here the other day. Let me see if i can find it. Thanks.

[catstrat]

spyder valve.

It looks like the effects board and the o/p tube plate voltage are almost proportionately low. I'm beginning to suspect maybe a power supply problem? But again, i'm not having much luck running up a schematic. Is this a Line 6 first or a Bogner first. Either way i couldn't find a schematic from either. I'll keep looking.

[catstrat]

line 6

More troubleshooting results. If i remove all the o/p tubes the pin 3 voltage goes up to 490 volts and the effects board voltage goes up to 12 volts and the pre amp tube plate voltage goes up to 170 from 110. The bias voltage is about -45 volts at pin 5. I installed another set of new 5881 tubes and the voltage goes down again. At the o/p tube plates i'm losing about 120 volts when the tubes are plugged in. I believe that is dragging down the overall voltage causing the hum. But what's causing the voltage drop in the first place. Let's see, the tube elements pulling the most amps are the heaters i believe. Is that causing an issue some how? The plot thickens. I don't think i've ever encountered this problem before.

[Jazz P Bass]

Try disconnecting the output transformer.
If the voltages pop back up then the OT is suspect.

[catstrat]

Hi Jazz P. I've done that already and the voltage went back up to the 490 volts. So the out put transformer may be the problem. I measured the resistance across the primary and got,as i remember, 54 ohms one end to center and 33 ohms the other end to center. Is there more of a definite way to check the o/p tranny without substitution ? Thanks

[g1]

You can build a very simple tester with a neon bulb, resistor, and battery, like this:
http://www.geofex.com/FX_images/xform_test.gif
and more test info here:
Output Transformers

[Jazz P Bass]

Also, you could hook up an ammeter between the Red B+ wire & the OT & measure the dc current that the OT is pulling.

[catstrat]

Thanks everybody. Since i have a homebuilt 100 watt Marshall clone i'm thinking of repackaging down to a 50 watt, i'll go ahead and harvest the transformers from that one and use that o/p trans. as a test piece. But i do need to build the open winding tester.

[catstrat]

I just subbed a good 100 watt o/p transformer in this line 6/Bogner. The voltage came up 470 volts but the hum is still there. It won't even pass signal. I told the customer he may have to send it to Line 6. If i can't get a schematic, and that appears to be the case, there isn't much else i know to do. Thanks.

[catstrat]

No Takers on this one i guess. I did find out it's a hybrid amp which shows i've never worked on one before. I'm just going to have to trace out the circuit best i can and shoot in the dark. Thanks

[g1]

Did it pass signal with the old transformer?
It may help to know the model number.

[Jazz P Bass]

The power amp is still a power amp.
To see if It works, plug a signal into the IN jack on the poweramp board.
The Master Volume should still be operational.

Is this amp the Spider Valve HD100?

[catstrat]

spider valve

It did pass signal but it was drown out by the hum. You could hear the signal but faintly. The only model number i have is a Line 6 spider valve HD 100. You're right, a power amp is a power amp. I'm thinking more and more it may be a bias issue instead. With the tubes in it, if i adjust the bias pots the plate voltage starts to go up. After studying the board last night it looks like it has 2 P I tubes and each half of each tube drives one o/p tube. That's why each o/p tube has it's own bias pot. In review, when the o/p tubes are out then the plate voltage goes up to 480 volts. As you install each o/p tube the voltage drops by probably 15 to 20 volts. I did notice the tubes were extremely hot just after 1 to 2 minutes being on. I have the bias set according to what is silkscreened on the board but i really need to determine what the plates are actually drawing current wise. Let me do that but i still could use a schematic if some one has one. Thanks.