Hi, a "Tony Bruno Design" Amplifier made by Vox and called the TB35C1 is giving me serious headaches.
What's the problem then?
First there whas a harsh sound at moderate level. After changing the power tubes that 's solved. The amp is now clean until the gain is set beyond "3 hours". That seems normal to me.
Oeps, One problem though!
Clean, yes, only when the reverb out, the cable towards the "Reverb Can In" is removed. If that cable is inserted, with other words, if the reverb can is connected to the amp, the following happens.
The gain knob of the amp is set at 12:00 hours and when the guitar is plucked hard, the lower frequencies are distorted and they die out in a stutter to stop very abrupt. The position of the main level is of no importance to the sound as the next problem is in the preamp section.
After changing the original reverb tranny it all went wel for about a day or two. Then it came back.
Off course, tubes have been changed, reverb can have been changed, voltages looks ok...
I have no schematic of this amp.
I have to rely on the expertise of other fellow contributors to find a sollution for this very curious problem.
Thanks for any suggestion and if possible a schematic.
What's the problem then?
First there whas a harsh sound at moderate level. After changing the power tubes that 's solved. The amp is now clean until the gain is set beyond "3 hours". That seems normal to me.
Oeps, One problem though!
Clean, yes, only when the reverb out, the cable towards the "Reverb Can In" is removed. If that cable is inserted, with other words, if the reverb can is connected to the amp, the following happens.
The gain knob of the amp is set at 12:00 hours and when the guitar is plucked hard, the lower frequencies are distorted and they die out in a stutter to stop very abrupt. The position of the main level is of no importance to the sound as the next problem is in the preamp section.
After changing the original reverb tranny it all went wel for about a day or two. Then it came back.
Off course, tubes have been changed, reverb can have been changed, voltages looks ok...
I have no schematic of this amp.
I have to rely on the expertise of other fellow contributors to find a sollution for this very curious problem.
Thanks for any suggestion and if possible a schematic.
Hi,
I can trace the circuit but time is not my best friend right now. Other repairs are waiting.
The reverb tranny is not bad I assume but after eliminating everything else it seemed bizarre that with a new tranny I had laying around the problem dissapeared.
Maybe, Maybe, when a hard (loud) signal is applied to the transformer it distorts.
The questoin remains then,
Why did the new tranny worked for a couple of days and then shows the same symptoms.
You mention an ECC81; Here an ECC82 is used.
Why should I replace the anode resistors?
The transformer is the anode load of the ECC82.
I can trace the circuit but time is not my best friend right now. Other repairs are waiting.
The reverb tranny is not bad I assume but after eliminating everything else it seemed bizarre that with a new tranny I had laying around the problem dissapeared.
Maybe, Maybe, when a hard (loud) signal is applied to the transformer it distorts.
The questoin remains then,
Why did the new tranny worked for a couple of days and then shows the same symptoms.
You mention an ECC81; Here an ECC82 is used.
Why should I replace the anode resistors?
The transformer is the anode load of the ECC82.
I said to check the anode resistors. They can fail under stress as all engineers know, causing low anode load and distortion. There is no anode resistor on the reverb driver.
If you consult the owners manual, this amplifier uses 4 x ECC83/12AX7, 1 x 12AT7, 4 x 6V6
An ECC82 in the wrong place may cause your problem.
If you consult the owners manual, this amplifier uses 4 x ECC83/12AX7, 1 x 12AT7, 4 x 6V6
An ECC82 in the wrong place may cause your problem.
Time went by and finally I had the chance to continue on this amp.
Tubes are as should.
Checking the Anode resistors is of no use here as the problem is with the reverb and the transformer is the "load".
Solder joints? No way.
As written before the problem is only there when the reverb can input is connected to the transformer output.
When the connection is removed, the problem is gone.
I tried other different reverb cans I had in stock, but all with similar symptoms.
Until yesterday, I had to repair a Fender Blues De luxe and after finisching it I used that reverb can. I have no such can in stock.
This time the sound is crystal clear, no distortion or stuttering sound.
So what to conclude?
The stock can is of a wrong impedance?
Or a short in the reverb coil driving the springs?
Unfortunately both cans have a Belton code on it instead of the common 2AB... or the like.
The reverb from the original can sounds heavier, as if it's overloaded (and probably is).
The one from the Blues de luxe is softer but clean.
Now I have to contact Beltone to find out what these codes stands for unless someone has these codes. (they are in the workshop and not here right now)
Still it troubles me that with the new transformer it worked for several days and failed afterwards. Weird...
Tubes are as should.
Checking the Anode resistors is of no use here as the problem is with the reverb and the transformer is the "load".
Solder joints? No way.
As written before the problem is only there when the reverb can input is connected to the transformer output.
When the connection is removed, the problem is gone.
I tried other different reverb cans I had in stock, but all with similar symptoms.
Until yesterday, I had to repair a Fender Blues De luxe and after finisching it I used that reverb can. I have no such can in stock.
This time the sound is crystal clear, no distortion or stuttering sound.
So what to conclude?
The stock can is of a wrong impedance?
Or a short in the reverb coil driving the springs?
Unfortunately both cans have a Belton code on it instead of the common 2AB... or the like.
The reverb from the original can sounds heavier, as if it's overloaded (and probably is).
The one from the Blues de luxe is softer but clean.
Now I have to contact Beltone to find out what these codes stands for unless someone has these codes. (they are in the workshop and not here right now)
Still it troubles me that with the new transformer it worked for several days and failed afterwards. Weird...
If you take DC resistance readings, this article will cross reference those with the actual AC impedance and corresponding letter. Spring Reverb Tanks Explained and Compared | Antique Electronic Supply See "Input and Output impedance" section close to the top. This should get you to the original Accuronics system, 4AB...
Are you sure the tank originally in the amp was the correct one? If the improper impedance is used, is it possible to have the circuit start to misbehave after a while due to stress caused by mismatched impedances? Just something to consider.
Further down in that article, the 1-4 numbers regarding whether the inputs are grounded/insulated is explained as well. This mismatched spec could also lead to it not working properly. Each input/output is required to be grounded/ insulated accordingly.
Anyway, there's lots of good info there to help with circuit examples of common amps for both tube and solid state.
Are you sure the tank originally in the amp was the correct one? If the improper impedance is used, is it possible to have the circuit start to misbehave after a while due to stress caused by mismatched impedances? Just something to consider.
Further down in that article, the 1-4 numbers regarding whether the inputs are grounded/insulated is explained as well. This mismatched spec could also lead to it not working properly. Each input/output is required to be grounded/ insulated accordingly.
Anyway, there's lots of good info there to help with circuit examples of common amps for both tube and solid state.
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