Peavey ValveKing 100 Head

[m1989jmp]

Hi all,

I'm having some problems with the amp in title.

Came in with a blown mains 3.15A fuse. Tested it with a lightbulb limiter, it indicated a short. Narrowed it down to one of the main filter caps, after removing it LBL doesn't glow bright anymore.
Next thing I did was insert tubes in it, but limiter still glowed a bit more than normal. As you may know, this amp has around 32VDC heater supply, distributed on 4 power amp tubes in series with PI tube, from which 6VDC supply goes to V1 and V2 in parallel.
The amp does not blow fuses anymore with all tubes in, but I'm getting 5VDC across 4x 6L6 tubes, which leaves 12VDC for PI, V1 and V2, which causes preamp tubes to glow really bright. I didn't leave it on for more than 5-10 seconds at a time while taking measurements.
Anyone seen something like this on these amps?
It's a PITA to remove this board as V1 and V2 sockets are soldered to the board, so I'd like to address as many issues as I can when I do remove it again.

When I do remove one power tube for example, LBL stays dim, so I suppose +14VDC relay supply is fine and not causing short?



peavey_valveking_100_212.pdf

[Enzo]

You can turn the amp on without tubes for various tests, but you cannot operate the amp with any tubes removed. The three small tubes are wired parallel heaters, and that is in the series wiring with the power tubes. Remove any power tube and ALL heaters will go dark. If you remove one or more of the small tubes it will upset the voltage balance.

THE most common reason for fuses to blow in a tube amp is the power tubes. You likely have a bad one. In fact that might explain your odd heater voltages. There may have been a bad filter cap, but we still have problems.

You shouldn't have to remove the tube sockets to take the board up.

[m1989jmp]

You can turn the amp on without tubes for various tests, but you cannot operate the amp with any tubes removed. The three small tubes are wired parallel heaters, and that is in the series wiring with the power tubes. Remove any power tube and ALL heaters will go dark. If you remove one or more of the small tubes it will upset the voltage balance.

THE most common reason for fuses to blow in a tube amp is the power tubes. You likely have a bad one. In fact that might explain your odd heater voltages. There may have been a bad filter cap, but we still have problems.

You shouldn't have to remove the tube sockets to take the board up.

I think that preamp sockets go a little bit over the chassis hole from the top side of the amp, I may be able to slant them a bit and get them out.

You think one bad power tube can cause 5VDC drop over all power tubes? I understand this heater setup in the following way: 32VDC and 900mA should flow; 900mA through each 6L6 and 900mA/3 through each preamp tube in parallel, right?

I'll be sure to check out all heater connections to V1 and V2 and try whole new set of tubes. Is there a possibility of ruining the tubes when running them on 12VDC for a short period of time, I understand it would ramp up emission.

I have -45VDC bias on ribbon cable connector. Customer complained that the clean channel stopped working first, lead still worked. After he continued to play it, both disappeared, so I think the fault started with V1.

I'll probably use high dissipation resistors instead of tubes until I sort the heater voltage problem.

[g1]

You are on the bulb limiter? Do not use math based on 32V total for heaters, measure it. What is the DCV across C211?
Measure each power tube from pin 2 to pin 7, not to ground. Measure pin 4 to pin 9 of V1,2, or 3.

[m1989jmp]

You are on the bulb limiter? Do not use math based on 32V total for heaters, measure it. What is the DCV across C211?
Measure each power tube from pin 2 to pin 7, not to ground. Measure pin 4 to pin 9 of V1,2, or 3.

All measurements I've mentioned were made without bulb limiter.

Voltage across C211 is around 34-35VDC without tubes (unloaded) and 32VDC with tubes. Also, all heater measurements were made pin2-pin7 and pin4-pin9, like you suggested.

C145, C7 and C8 test good, I'll check C119 later.

[g1]

You must have all tubes in circuit to check voltage. If any of V4 - V7 are removed, no tube should light up.
If all of V1,V2, and V3 are not installed, you could get a result like you are measuring.
Right now it sounds like the V1 - V3 parallel combination is double the resistance that it should be.

[m1989jmp]

You must have all tubes in circuit to check voltage. If any of V4 - V7 are removed, no tube should light up.
If all of V1,V2, and V3 are not installed, you could get a result like you are measuring.
Right now it sounds like the V1 - V3 parallel combination is double the resistance that it should be.

Thanks so much for your help fellas; turns out all 3 preamp tubes that came with the amp are shot (heater filament reads way above few ohms while tubes are cold) AND 2 out of my 5 spare tubes I usually test with, so I was constantly testing with at least one bad preamp tube.

Power tubes are fine when tested in another amplifier, good heater voltage and they bias well.

I've resoldered all dodgy connections and tried with good tubes this time around and everything seems well.

Customer wanted really bad to get rid of it, so I'll purchase it and make a decent turret board amp out of it, got a regular power transformer with 6.3VAC heater tap laying around.