Bugera 333XL Tube Head Issue

[misterc57]

Hey Folks.

Trying to repair a 333XL. It had a broken main fuse which I replaced. All tubes tested good. Now I am getting poor sound quality and sporadic volume output. To me it sounds like the voltages are off at the tubes.

I have the schematic (attached) but it is missing voltages at the tubes. Unless it is there and I cannot find it.

Anyone see it or have a better schematic? If not I can take readings at all the plates and post them.

Also could not find the PS in the schematic or what value replacement main fuse to use. I inserted a 3 amp for now.

Thank you, MC

edit. this is a "infinium" version.


bugera_333xl_sch.pdf

[misterc57]

Perhaps these voltage readings are not too bad.

EL34, V1-V4

V1 3. 444
V1 4. 438
V1 5. -38
V1 6. 0.3

V2 3. 444
V2 4. 438
V2 5. -37.4
V2 6. 62 mv


V3 3. 444
V3 4. 438
V3 5. -36
V3 6. 0.5

V4 3. 444
V4 4. 438
V4 5. -38
V4 6. 0.5


12AX7, V5 - V9

V5 is the phase inverter
V5 1. 312
V5 6. 308

V6 1. 214
V6 6. 214

V7 1. 202
V7 6. 174

V8 is the first preamp tube
V8 1. 165
V8 6. 143

[g1]

Schematic has PSU on pg.1. Shows 2A FB for mains (F1) (edit: wrong F1, not mains, see below)
What do you get when you use the FX loop to isolate, preamp or poweramp problem?.

[misterc57]

Good suggestion on the FX loop.

I feel like a dummy. I sprayed the heck out of the many pots, switches and jacks. Amp sounds fine now.

Thank you, MC

[g1]

The 333 212 infinium (non-xl) shows 3A FB mains fuse. As neither schematic matches your unit, the fuse could be either. Possibly the owners manual will specify.
(edit: error, not mains fuse)

[misterc57]

Manual states T 3.15 which is what I put in there. Crazy that the back panel does not list the fuse type.

[Helmholtz]

The 333 212 infinium (non-xl) shows 3A FB mains fuse. As neither schematic matches your unit, the fuse could be either. Possibly the owners manual will specify.

Are you sure it is the mains fuse?
F1 on page one is the HT fuse.
I'd be surprised to see a fast fuse on the mains side.

[misterc57]

Are you sure it is the mains fuse?
F1 on page one is the HT fuse.
I'd be surprised to see a fast fuse on the mains side.

There is an F1 on the main board which is not the mains fuse.

[misterc57]

I had to cut and scrape the white stuff off the small PS board to remove the broken fuse holder and install an inline mains fuse.

Some pics that may be helpful in the future...

[g1]

Are you sure it is the mains fuse?
F1 on page one is the HT fuse.

You are correct. Attached is the drawing showing the mains fuse which matches post #6 (T3.15A)