I found a nice little guitar amp in one of my favourite second hand electronic dealer which is a Crate TD 35 watts, a 35watts amp based on two transistors and a tube pre-amp which is why I was unable to resist !
The amp came with a huge buzz when powered on and looked like it passed the last two years in a wet basement so I thought it would be my first project to post on this site !
enjoy
The amp came with a huge buzz when powered on and looked like it passed the last two years in a wet basement so I thought it would be my first project to post on this site !
enjoy
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Signing UpStep 1: Dissambly of the board
The first step was to track back the HUM in the speaker. After the dissambly of the main PCB board, the problem was easy to find :
- First some rust around the tube connector due to too much time spent in the garage !
- Secondly, a capacitor clearly rusted and dead in the PSU to change, they are easily distinguishable they are near the diode bridge which were also dead and had to be replaced
When the diodes and the capacitor had been replaced with some test capacitor, the HUM was still present when I plug the power back and 5 seconds after the transistor (3rd photo) began to smoke really hard.
So third step : a pair of transistor was replaced, they came by pair and the one in question was a TIP120, very common in amplifier, coupled with a TIP125. So I replaced both of them with a pair of TIP121/TIP126 along with a really burned resistor and ...... tada ! Clear sound when plug back !
To improve the sound a little and prevent another explosion of the capacitor, the two 3300uf 35v capacitors were replaced with 2 Nichicon Golf plated 6600uf 35v and their way now !
- First some rust around the tube connector due to too much time spent in the garage !
- Secondly, a capacitor clearly rusted and dead in the PSU to change, they are easily distinguishable they are near the diode bridge which were also dead and had to be replaced
When the diodes and the capacitor had been replaced with some test capacitor, the HUM was still present when I plug the power back and 5 seconds after the transistor (3rd photo) began to smoke really hard.
So third step : a pair of transistor was replaced, they came by pair and the one in question was a TIP120, very common in amplifier, coupled with a TIP125. So I replaced both of them with a pair of TIP121/TIP126 along with a really burned resistor and ...... tada ! Clear sound when plug back !
To improve the sound a little and prevent another explosion of the capacitor, the two 3300uf 35v capacitors were replaced with 2 Nichicon Golf plated 6600uf 35v and their way now !
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HotSauce1080 (author) says:
Feb 2, 2013. 10:25 AMReply
Thank you ! I am waiting on the last parts to see if all the problems are solved ! It is really great to restore this kind of amp and give it a second life ! I post the results as soon as it is finished !
rudolphdiesel says:
Jan 19, 2013. 8:44 PMReply
Awesome find! Great repair job. If you need tubes....You probably are aware that some of the best tubes are still produced in Russian and Czech factories. Much of their equipment still uses it. Audiophile sound of analog is superior to digital since it does not 'clip' the sound. Digital will never attain this level of "True to life" audio.
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pfred2 says:
Jan 17, 2013. 3:03 PMReplyGreat job that you got it working again. I'm not a big enough fan of tube gear to try to fix any of it myself. I prefer solid state.
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