Hello everyone! First I would like to say I know nothing about tube amplifiers & it is all very new to me, but I am familiar with electronics and I enjoy repairing car audio amplifiers, but again, tubes are very new to me. I am interested in learning about tubes and how they operate, as I have been curious about that for a while.
Anyway, on to the amp in question: My dad has played guitar for many, many years & has used his Fender "Twin Reverb Amp" since before I was born! Well it has worked all this time perfectly other than of course he changes tubes when needed & maybe cleaning the potentiometers. This amp has been all over the place when he used it a lot, so it has seen a lot of traveling. The amp was made I think in 1971. The amp uses (4) 6L6 output tubes.
Well, the last time he used it a couple months ago it worked fine, he was using external speakers from another amp with this amp at the time & again, worked with no problems, he then hooked the internal speakers back up before he was done and it worked fine still, so when he was finally finished using it, he said it worked & showed no signs of problems other than some scratchy knobs. The knobs have now been cleaned. Now when the amp is powered up everything seems fine other than absolutely no sound output, nothing at all, not even a hiss or an air type sound, dead quite! He looked at it a little bit, basically just cleaned it out to see if that would help & it did nothing, since I enjoy repairing electronics he asked me to take a look at it, so here I am now.
Here is what I have done so far:
I tested the speakers and they work fine.
I tested the output wires from the amp with my multi-meter set to ohms and it showed a direct short, from what I have read that is common in these types of tube amps so there is always a load on the Output Transformer when the speakers are unhooked. I never heard of shorting the outputs on an amp before, but again, tubes are new to me.
I unhooked the Output transformer to test its secondary Out Of Circuit & it still shows a direct short, or about 0.3 Ohms, which I would still consider a short as my meter reads close to that sometimes when I touch the leads together.
So my question at this point is: Is it normal for the Output Transformer to show a short or 0 Ohms on its secondary where the speaker connects?
And if this were not normal, why would the Output Transformer be faulty after all this time of working fine?
And, can I temporarily somehow bypass the Output Transformer to see if that is the problem?
Ok, thank you to all who reads this, & I hope to maybe get some help so my dad can use this again! Take Care & Happy Holidays. Kyle
Anyway, on to the amp in question: My dad has played guitar for many, many years & has used his Fender "Twin Reverb Amp" since before I was born! Well it has worked all this time perfectly other than of course he changes tubes when needed & maybe cleaning the potentiometers. This amp has been all over the place when he used it a lot, so it has seen a lot of traveling. The amp was made I think in 1971. The amp uses (4) 6L6 output tubes.
Well, the last time he used it a couple months ago it worked fine, he was using external speakers from another amp with this amp at the time & again, worked with no problems, he then hooked the internal speakers back up before he was done and it worked fine still, so when he was finally finished using it, he said it worked & showed no signs of problems other than some scratchy knobs. The knobs have now been cleaned. Now when the amp is powered up everything seems fine other than absolutely no sound output, nothing at all, not even a hiss or an air type sound, dead quite! He looked at it a little bit, basically just cleaned it out to see if that would help & it did nothing, since I enjoy repairing electronics he asked me to take a look at it, so here I am now.
Here is what I have done so far:
I tested the speakers and they work fine.
I tested the output wires from the amp with my multi-meter set to ohms and it showed a direct short, from what I have read that is common in these types of tube amps so there is always a load on the Output Transformer when the speakers are unhooked. I never heard of shorting the outputs on an amp before, but again, tubes are new to me.
I unhooked the Output transformer to test its secondary Out Of Circuit & it still shows a direct short, or about 0.3 Ohms, which I would still consider a short as my meter reads close to that sometimes when I touch the leads together.
So my question at this point is: Is it normal for the Output Transformer to show a short or 0 Ohms on its secondary where the speaker connects?
And if this were not normal, why would the Output Transformer be faulty after all this time of working fine?
And, can I temporarily somehow bypass the Output Transformer to see if that is the problem?
Ok, thank you to all who reads this, & I hope to maybe get some help so my dad can use this again! Take Care & Happy Holidays. Kyle