Bugera 333 212 combo, very low output

[cyclone]

You can make a little probe with a ground and a hot on alligator clips that plugs into the headphone output of a small fm radio, ghetto fabulous sig gen. Then you are not trying to play guitar at the same time with your hand on the strings and in the power section

*hijack on*I find that my Hickok 533 is excellent at testing small tubes for function and transconductance, and for wear with the "life" test. It really helps eliminate the situation with one or more bad preamp tubes being swapped back and forth (regardless if they are nos or used or new production shiite ) in a guitar amp with 4+ 12a*7's. There's a high likelihood that those tube failures were caused by insertion and removal at some point while troubleshooting.

A functioning transconductance tester like my 533 is useful in testing NOS and and used and new production power tubes for transconductance and life. You can easily tell when its' time to replace power tubes. I run large tube power amplifiers 24x7 and test tubes only when necessary as the voltages they put on the elements can be hard on tubes. *hijack off*

Excellent thread so far! hope you get 'er straight.

Pete

[nosaj]

On what is x17 on the schematic, which comes from the front board to the power board I have just a very faint signal that is lower than what the signal coming into the front of the amp from my laptop signal generator. Very strong signal on the few 2 pin harness's around that one on the front board, but little to nothing coming out to the power board.

Do you by chance have a signal injector? You can start at the speaker then the grids of the power tubes and work backwards.
I believe this was also in Jack Darr's book.
Nosaj
https://books.google.com/books?id=JT...20test&f=false

[bwheat]

I don't have a way to actually put a signal into a specific part of the circuit, I am just running a line out from my laptop to the front input jack of the amp with a signal generator program. I built a signal probe using a set of computer speakers and a multimeteter lead with a capacitor to block Direct current into a 1/8 audio cable, into the speakers. It works very well to trace the signal thru the circuit. I feel like I was wasting my time without it before. I have verified that the power amp section actually works a while back, something between the preamp tubes and power amp. Going to go probe around a little more on that front board and find where it stops I guess.

[Enzo]

I just plug a CD player or tape deck into the front of the amp. Test tones are boring.

Isolate your problem. So you have a weak signal at the power amp input.

You want a simple signal injector? Use a screwdriver. Seriously. X17 feeds the phase inverter via C1 and R15. If I touch a small screwdriver to pin 7 of V5, I should hear some hum. Move back to R15, touch that. No screwdriver? Use your meter probe, but leave the black one not connected. Now the meter probes act like antennas for hum.

If those work, back to preamp board. MAx the master volume, and touch the hot end of the control, get hum? Pin 2 of V5 is the master driver, so touch pin 2, get hum? Want a different way to test that point? Turn up the master and the reverb, now bop the reverb pan to crash the springs. Does that noise come out loud or real weak? Reverb mixes in at pin 2 there. Or I forget, is this one a digital reverb?

Unplug the FS so the FX loop stays on. Does a signal into the FX return make sound or not?

With input signal present, does it matter which channel is on? Did we already find if the FX send is strong or weak?

At the output of the preamp is relay RL5C, where you select which channel. From there through the connector and R57, then a mute transistor. Is that stuck on? See D8, D9? If one shorts, you get 15v on R57/R62. Is there? Then with the amp running measure resistance to ground from the junction of R57, R62, and the diodes. If it is low, then the transistor is bad or it is not being turned off at its gate.

[bwheat]

I just plug a CD player or tape deck into the front of the amp. Test tones are boring.

Isolate your problem. So you have a weak signal at the power amp input.

You want a simple signal injector? Use a screwdriver. Seriously. X17 feeds the phase inverter via C1 and R15. If I touch a small screwdriver to pin 7 of V5, I should hear some hum. Move back to R15, touch that. No screwdriver? Use your meter probe, but leave the black one not connected. Now the meter probes act like antennas for hum.

If those work, back to preamp board. MAx the master volume, and touch the hot end of the control, get hum? Pin 2 of V5 is the master driver, so touch pin 2, get hum? Want a different way to test that point? Turn up the master and the reverb, now bop the reverb pan to crash the springs. Does that noise come out loud or real weak? Reverb mixes in at pin 2 there. Or I forget, is this one a digital reverb?

Unplug the FS so the FX loop stays on. Does a signal into the FX return make sound or not?

With input signal present, does it matter which channel is on? Did we already find if the FX send is strong or weak?

At the output of the preamp is relay RL5C, where you select which channel. From there through the connector and R57, then a mute transistor. Is that stuck on? See D8, D9? If one shorts, you get 15v on R57/R62. Is there? Then with the amp running measure resistance to ground from the junction of R57, R62, and the diodes. If it is low, then the transistor is bad or it is not being turned off at its gate.

Running a signal into the effects return gives me full volume, I used another amp and did a line out from that and into the return. The power amp amplified it and it was as loud as the amp should be. I also ran the effects send to the input jack on the other amp and got a very weak signal out of that amp. Incredibly low volume. So yes, signal into the effects return makes the amp work, and the signal from the send is very weak. Power amp seems to work good. Wouldnt this also mean the phase inverter is working properly since it is before the power tubes? Also this one has digital reverb. I will have to locate the transistor and diodes, i can't really go off numbers listed in the schematic, they are mostly not right for this model. I will check that out though.

[Enzo]

I have 333 and 333XL. The circuits are real similar if not identical, but the numbers on things are different.

For example, your X17 as input is on 333XL. On 333 that same connector is X15. My R57/62 are on the 333XL, the same parts on 333 are R62/63. The mute transistor is T3 on 333, and T4 on 333XL.


The phase inverter is part of the power amp, which is working. We are exploring the preamp.

Please tell me whether you have 333 or 333XL.

[bwheat]

I have 333 and 333XL. The circuits are real similar if not identical, but the numbers on things are different.

For example, your X17 as input is on 333XL. On 333 that same connector is X15. My R57/62 are on the 333XL, the same parts on 333 are R62/63. The mute transistor is T3 on 333, and T4 on 333XL.


The phase inverter is part of the power amp, which is working. We are exploring the preamp.

Please tell me whether you have 333 or 333XL.

Mine is the 333.

[Enzo]

But you are using the 333XL schematic.

The 333XL drawing is #P0623.

The 333 drawing is #P0406

Just looking them over, I think the circuits are identical, but the numbers differ. SO one could look at both and translate, , but that is a ton of work. See if you can find the plain 333 drawing.


I am guessing, but I suspect the reason for this is they made up a new board set with the layout changed and the parts are sitting in different order, so the numbers changed.

[bwheat]

But you are using the 333XL schematic.

The 333XL drawing is #P0623.

The 333 drawing is #P0406

Just looking them over, I think the circuits are identical, but the numbers differ. SO one could look at both and translate, , but that is a ton of work. See if you can find the plain 333 drawing.


I am guessing, but I suspect the reason for this is they made up a new board set with the layout changed and the parts are sitting in different order, so the numbers changed.

It is a pain in the butt for sure trying to find things with different numbers than the schematic. For the most part I can do some continuity tests to find where things are, and what is connected to what. This black pcb is very hard to see the traces also. Getting ready to drag it out of the closet and check the function of that transistor.

[bwheat]

R62 and r63 are both right at .07 volts.

[Enzo]

There is a thread around here for a BX1200 Behringer amp..\ Look it up. Jazz P Bass posted your schematic over there, I assume by mistake. Go get it.

[Enzo]

OK< if there is no DC on those resistors, check the JFET for problems by resistance to ground while running.

[bwheat]

I did check resistance to ground at the point where the diodes are connected to the resistors and got .437k . Thanks for the link to that schematic that is very helpful. I have been looking for that for a long time.

[Enzo]

.437k is 437 ohms, which seems really low.

Look at the gate pin of that JFET, is ther voltage present? Or simply remove the transistor and see if your sound comes back.

[bwheat]

that is the pin on the right looking at the flat side of the transistor correct? It has .477 volts there.