6505 Plus Power Tubes Not Powering / No LED lights

[Dfahb44]

Hello ya'll,

This is my first post, and I'm enjoying this process of learning to operate on tube gear. I'm a semi-noob and attempting to repair a 2015 Made In China Peavey 6505+ that I purchased as broken a long time ago. Originally the issue was that everything turned on except for the preamp tubes but there was no sound. I discharged and took the whole thing apart. Looks like a few turrets weren't completely attached. I soldered those, and the preamp tubes are firing up now which is great. Now there's a new issue where the Power Tubes and LED standby/power aren't lighting up. I'm relatively new to amps conceptually, but I've tried to narrow it down to a few things:

-Checking the fuses again
-Testing connections on the board/jumpers/cables for continuity from the transformer following it out to the power amp jumper
-Checking resistors/diodes in the rectifier
-Checking the power transformer


I tested the FX loops guitar direct in/tried cleaning those inputs as you see often online, and there's still nothing.

There is no visible damage to any of the board indicating burning damage or anything like that so I feel like it's probably some sort of connection.


Has anyone dealt with this before? I did some heavy digging into understanding how amps work in the sense of the flow of power to everything. If I need to try to test the amp with it running, I'm trying to find information related to accomplishing that. I'm an adult who is completely aware of the potential risks, but I am interested in the trade and am looking to expand my skills.

Anything advice, thank you ya'll.


https://www.thetubestore.com/lib/the...-Schematic.pdf

[Helmholtz]

Schematic?

Did you check power tube heater voltage between the socket pins?

[Jon Snell]

Please confirm make; Peavey?
Schematic?

[Dfahb44]

I updated the original post with the schematic and it is indeed peavey!

https://www.thetubestore.com/lib/the...-Schematic.pdf

Schematic?

Did you check power tube heater voltage between the socket pins?

I have not. Does this require the amp to be running? What is the best way to approach that?

[Jon Snell]

I always find the best method of fault finding, is to split the amp down to the possible faulty portion.
The power LED gets its power from the filament power supply. If there is an issue, poor soldering/failed diode, at the point I circled in orange, there will be no valve heaters or LED. The power valves get their heater supply from the diodes circled in red.
Ensure the 6.3volts for power valves and smaller valves that use DC heaters are fed between +FIL & -FIL

[Dfahb44]

I always find the best method of fault finding, is to split the amp down to the possible faulty portion.
The power LED gets its power from the filament power supply. If there is an issue, poor soldering/failed diode, at the point I circled in orange, there will be no valve heaters or LED. The power valves get their heater supply from the diodes circled in red.
Ensure the 6.3volts for power valves and smaller valves that use DC heaters are fed between +FIL & -FIL

Thank you for the thoughtful reply. I was eyeing that area as well as it seems like those diodes being replaced are a common repair. This is going to sound extremely new, because well that's what I am lol.

What is the process in measuring power to valve?

[Jon Snell]

Output valves; heaters 6.3volts AC between pins 2 & 7. Pin 4 is the screen grid 400volts ish. Pin 3 anode 450 ish. Pin 1 & 8 cathode (internal suppressor grid) ground. Pin 5 control grid -bias voltage -45 ish. See manual for correct values. Measure with great care!!!

ECC8* (12AX*) 1 Anode a 2 grid a 3 cathode a, 4 & 5 heaters, 6 anode b, 7 grid b, 8 cathode b. 9 heater centre tap. Values vary, see manual.

[Dfahb44]

When you're measuring the valves, are you attaching the multimeter to the valve pin or do you have the PCB board removed to access underneath? Also, would the negative of the Filament be ACFIL2?

[g1]

Just want to verify this is a head, as the combo version uses a different schematic.

[Dfahb44]

Just want to verify this is a head, as the combo version uses a different schematic.

Yup it's the head

[Jon Snell]

When you're measuring the valves, are you attaching the multimeter to the valve pin or do you have the PCB board removed to access underneath? Also, would the negative of the Filament be ACFIL2?

The ACFIL is AC, not DC so the 6.3volts AC is between pins 2 & 7 of the output valves. R69 lets the AC heaters hovver around +24volts DC.

[Mick Bailey]

Remove the output tubes and measure from that side - it means your probes can't slip and short out something. The amp can be in standby for this check.

[Dfahb44]

I did it, felt pretty insane. My gf helped me take down the numbers as I held my hand in my pocket in fear, lol. Huge thanks to everyone for the advice. I got the LED's working, there was a short. I also changed out the diodes just in case, it was $2 at the store so whatever. There were a few turrets that weren't soldered securely so I also redid those.

I did 3 tube sockets from the pcb because those were the easiest to access with the giant amp being upside down. Multimeter set to AC volts, Ground of multimeter attached to amp chasis, and then touching pins of the 3 visible ones.

Here are the numbers:

1 .473
2 .24
3 .038
4 .458
5 .202
6 .453
7 .459
8 .035

1.48
2 .239
3 .29
4 .467
5 .190
6 .47
7 .474
8 .482

1 .485
2 .24
3 .471
4 .354
5 .208
6 .472
7 .477
8 .486


I think hypothetically it’s working, just sending the wrong voltages? It didn’t say in the manual so I’m not sure. I swapped the tubes out with a spare set but every tube could possibly be bad because they still aren’t lighting up in my most recent test.

[Mick Bailey]

Measure the heaters between pins 2 and 7, not to chassis (See Jon's posts). AC readings to other pins are meaningless as they are either DC, or only AC under signal conditions.

I don;t advise changing parts unless they're proven to be faulty - this can lead to further complications.

[Dfahb44]

My apologies for the ignorance. Still my first time. The readings I got were pretty much all .020 with both pins on 2 and 7.