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studio project VTB-1 tube circuit died

post #1 of 12
Thread Starter 

I request pleased help for your little advice or guidance with a Studio Projects VTB-1 purchased Used (online on foreing country).

 

I have spent my low budget in this. I am no specialist or electronic, just a poor fool who has been deceived. I decided to learn and change the damaged pieces, but I am not able to identify.  I don't have tools for that. everything I've learned has been last two weeks reading every night thousands of threads and component manufacturers informations on internet. Next days will buy a 15w soldier and I will buy the cheap parts on the repair shop.

 

I've received and the tube circuit does not work. I have a behringer mic2000 and I changed the tube and either the same (work in mic200).  without tube gain works perfect. when it comes to the 4 o'clock (right on tube blender) turns off complety the output signal. the insert path works perfect but the line/out loss the signal. I have completely removed the tube and does the same,  I think that any component of the tube circuit was damaged but other components are fine.

 

Theseller (now not give more information) said that he put a phillips 5751 tube, but came with with a Sovtek 12AX7. I think that this damage the tube circuit, because I found in a tubestore page info about phillips 5751, and warning about this tube soft the signal 30% but force the power circuit.

 

on: http://bounav.free.fr/wp/?s=vtb1 I found a img of the board but is not the same.

 

The board say "JRP PROD RUN REV-B DEC-01" and all of the opamp are BB OPA2134PA in U1, U6, U2, U5 (I have many nights reading) there are many capacitors and other parts. the board does not appear modded or tampered with, just seems to change the valve and said before send me.Highlights near the tube a three-legged piece indicating 7812ct. At the store, their  try to help me little free, but don't  know  this device and only guided me telling me to prove if this piece was put on a burn. after 12 hours on, all components are cold and not smell burned. is over all the help I can get.

 

I'veseen on your site that you are a specialist in these questions. if it does not involve any discomfort, you could tell me which part or parts group might try to replace myself?

 

What would be the most probable components to replace?

 

I thank you for listening only, and apologize for any inconvenience.

 

 

PS: I am very happy found this forum,. I read read read... superb. I think about to learn and begin my DIY's.

 

img001.jpg

 

ime002.jpg

post #2 of 12
Thread Starter 

nobody can help ? only a little little advice ?

post #3 of 12

I'm afraid I am not much help but the 7812ct is a 12 volt voltage regulator. If you have a multimeter you can check the voltage between the pin closest to the tube and the middle pin you should see approximately 12 volts. Have you tried replacing the tube with the original? Also, you could try contacting the manufacturer. I doubt they will honor any warranty since it is used and has modified parts, but if you can get hold of an engineer they might be willing to help you trouble shoot the circuit.

post #4 of 12
Thread Starter 

Is the first track I've had in two weeks !. THANKS ! I'll check tomorrow with a multimeter.

 

ps: contact with the manufacturer I thins is a good idea. I'll try.

 

Yes I put the original tube.  With this or even without any tube (I try) as the result is the same.

 

Works perfect except when I increase the blender to the tube. gradually muted to silence. no noise, no humm, silence.

 

If no volt detected or low volt., then should I change it?

 

Kind regards.

post #5 of 12

Yes, it is a very common part. Before you pull it out though check the voltage between the pin furthest from the tube and the middle pin. The middle pin is ground, pin closest to tube is Vout, and pin furthest from tube is Vin. So if there is no Vout either the regulator is dead or something earlier in the circuit is dead. So if you have voltage on the furthest pin you know the regulator is dead and replacing should fix it if that is the only problem. If there is not about 14+ volts on between the furthest pin and middle pin then your problem is somewhere else. There are a couple other devices in the middle of all those capacitors in the bottom right part of the photo. Looks like a couple of transistors and another 3 pin device - could be a transistor or another regulator. If the 7812 is ok you might want to check these next

post #6 of 12

Can you tell us whether or not the tube heats up?

You should be able to see an orange glowing filament in it... especially in the dark.

post #7 of 12
Thread Starter 

Yes ... cold cold, ice cold. No smell of burning in any site of the board.

 

I was put on and left on 24 hours.

 

The tube cold, every black piece cold, capacitors cold.  As cold as if it was turned off. I tried it with my fingers

 

Tomorrow I will to buy a cheap multimeter and try to test volts on components (Just I discover DIY world, I like everything related to DIY, I find it fascinating, no more ebay, next preamp I'm going to do it myself).

 

After 24 hours on, no smoke & cold.

 

Cheers.

post #8 of 12
Thread Starter 

#bcg27 #nullstring THANKS!

 

This afternoon with my new toy (a multimeter), learn first with a 1,5 battery to test volt.

 

Put dcv, 20m, go to 7812ct and put black on middle, red on left (Vin). 1.4v.  toggle maximun gain, minimun, ever 1.4.

Then with maximun gain & blend, put black on middle, red on right (Vout) 0.0 ...hoho !!! no Vout ?

 

Play with gain knob and blender know...ever Vout 0.0

 

7812ct dead ?

post #9 of 12
Thread Starter 

sorry explain:  on 7812, right is closest to the tube.

post #10 of 12
Thread Starter 

Tomorrow I'' buy a new 7812ct

post #11 of 12
Quote:
Originally Posted by mancini View Post

#bcg27 #nullstring THANKS!

 

This afternoon with my new toy (a multimeter), learn first with a 1,5 battery to test volt.

 

Put dcv, 20m, go to 7812ct and put black on middle, red on left (Vin). 1.4v.  toggle maximun gain, minimun, ever 1.4.

Then with maximun gain & blend, put black on middle, red on right (Vout) 0.0 ...hoho !!! no Vout ?

 

Play with gain knob and blender know...ever Vout 0.0

 

7812ct dead ?


Unfortunately this probably doesn't mean that the 7812 is dead. Regulators need a higher input voltage than their output to function. Since the 7812 outputs 12 volts, it requires a couple volts higher than 12 in order to function, probably about 14-15 volts. Since you are only seeing 1.4 volts, the problem is somewhere earlier in the circuit

 

post #12 of 12
I know this thread is fairly old but just in case someone comes across.... If I understood what was said is that you have OPA2134's in U1, U2, U5, and U6. Those are not original and the reason your preamp won't work is because they are not the correct opamps for U2 and U5. Originally U2 had a JRC2082 but it would be better to replace it with an LM353N. U5 originally had a JRC2114 but a better replacement would be an LM833N. Leave the 2134's in U1 and U6 but change out the others.
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