Vox Berkeley ll Low output

[vintagekiki]

Gary tremolo unit is Q10/Q11.
Put signal from generator or guitar to jack P5. Reverb delay line is disconnected. If you have low audio output power amp Q6..Q9 or theirs components is defect. Direct (guitar) signal from preamp Q1-Q2 power amp receive from Q3 (ReQ3=R16), Reverb mix control R24 and via C18 go to power amp.
In maintenance any amps check units step by step from speaker to inputs
Are you connect guitar to amp via P5 connector? Do you have high or low audio output?

[Garydean]

Correction, it has trem and reverb. I don't have the pan. This unit came in with no pan.

Base on Q3 is -500mV at the moment.
emitter is -1v
collector is 650mV


I'm going to try what kiki suggest next.

Thanks guys

[Garydean]

OK. I plugged the the guitar signal into P5 and was able to control the volume via the reverb pot. The volume was higher than going direct to the input jacks but still low power.

Gary

[52 Bill]

Gary:
Earlier you noted that the voltage on the base of Q4 was 1.77 volts. Q3 is direct coupled to Q4 so there should be the same voltage at Q3 collector and Q4 base. Is there continuity there on the board?

Still, check the reverb return signal and let us know what happens.

[Garydean]

Yes Bill there is continuity between Q3 collector and Q4 base on the board. I did the reverb test..... I plugged the the guitar signal into P5 and was able to control the volume via the reverb pot. The volume was higher than going direct to the input jacks but still low power.


thanks,
Gary

[Garydean]

I've been looking for equivalent transistors for this amp. I guess I could spend $8 a pop thru the Thomas site. Would you guys know what alternate works?

86-5044-2 Q1,2,3,5
86-5050-2 Q6,10,11
86-5073-2 Q4
86-5075-2 Q7
86-5089-2 Q8,9

thanks.

[vintagekiki]

All preamp transistors in your amp is low power NPN silicon type transistors
For replacement maybe use BC414 (used in VoxBass100 model 1204) or BC107-109 or BC182-184 or BC550 (some of this used in Vox Foundation series). For idea look their schematics.
Q7 is general purpose NPN silicon transistor as 2N3053 or 2N3054 (look type case!).
Visual check PCB on cool solder.

[Garydean]

I've got a few 2N2923 NPN transistors in stock. Will they work? They have the same pinning and are general purpose small signal transistors.

thank you,
gary

[Garydean]

Another question. How can I test the output transistors to be sure they are ok?

Thanks,
Gary

[52 Bill]

Another question. How can I test the output transistors to be sure they are ok?

You can pull them out of their sockets and test with your meter, but I'd fix the pre-amp problem before moving on to other things.

As Vintage Kiki stated Q3 is a basic NPN transistor, and almost anything will work in that position. I use 2N3391A's, because I happen to have a lot of them, and they are based with the same pinout.

Q4 however, is the output transistor for the reverb drive circuit and will need to be a higher power transistor, maybe 500mW. If you want to reuse the same heatsink, use a TO-5 cased unit. If not, a TIP series transistor will probably work as a replacement.

[Garydean]

I'm still stumped. I replaced

Q3, Q4, Q5, Q6, and Q7.

R15 and R17

C3, C5, C9, C11, C13, C16, C19, C20, C22, C29, C30, C31

The collector of Q3 and the Base of Q4 STILL have only 2.07V. The rail is reading 15V.

Q1 all voltages are close to spec
Q2 all voltages are close to spec
Q3 emitter 67mV, C 2.07V, B 667mV
Q4 emitter 1.5V, C 25.6V, B 2.07V

I'm loosing hair!!!

[guitician]

Hello, I'm new here. And this thread caught my eye. That .22 C18 may be the trouble if it's leaky. Lift one end and see it the voltages on Q3 fall in spec. How do the rails look while playing the amp? I'd monitor them under load to see if the power supply could be at fault. I've worked on amps that have been real pains in the rear, and it has always helped if I set it aside and come back to it another day and approach it from a fresh view. Good Luck

[Garydean]

Thanks for the tip. That was not it. The voltages to the board all measure in spec.

[guitician]

I'd look at Q3 on a scope, there my be some occillations that are above the audio range happening.

[52 Bill]

Man, you've been busy!

I'd look at Q3 on a scope, there my be some occillations that are above the audio range happening.

Interesting point. Did you replace the missing reverb tank? Try loading the secondary of the reverb drive transformer with a resistor.

If you clip a cap to the volume control and send the signal out to another amp, and your pre-amp is working you will hear a good strong signal.

Have you checked R16, R19 and the reverb pot?