mattsd
Super Member
Man, it has been awhile since I posted one of these threads! Everything has taken off so fast in the past couple of years, I've been crazy busy keeping up with everything. Some background on this unit, I got this from a guy who I restored a SPEC-1 and SPEC-2 for about a year and half ago. Long story short, he had a second one in the basement and gave it to me for free! He reads AK and I believe he's a member here, so if you read this Rick, thank you very much!
It is not without problems though, it would not come out of protection. Upon inspection of the boards I found the caps and transistors had been replaced on both power amp boards with a weird mix of good and bad replacements. Let us start with the left power amp board, as it has some interesting things done. Side note: I got a new camera and it is much better than my previous one. The first three images are the old camera, the rest of them are the new one.
The left channel STV diodes had homemade replacements made from three 1N4007 diodes in series for the STV-3H and four 1N4007 diodes in series for the STV-4H in a weird plastic case screwed to the heatsink.
Some close ups with the plastic cases removed:
An interesting way to replace the STV diodes, however not ideal for good thermal tracking. I managed to find (with the help of AK
) an original STV-3H diode from a seller in Germany. The STV-4H came from a parts receiver that I had here. The 4H diodes are not easy to find, so I was thankful I had a parts unit with one in it.
Board before (note I have already replaced the STV diodes):
Molex pins (note I cleaned the right 2 to show the differences):
A cool thing I noted when I was looking for a polypropylene replacement for the input cap, the board actually provides pads and lead holes for bigger capacitors than the little tantalum being used currently. It allows for, in addition to the 5mm lead spacing of the tantalum, 10mm, 15mm and 22.5mm lead spaces via the trace here:
And after! In total 8 caps, 14 transistors, 6 diodes, 3 variable resistors and the bias relay were replaced.
Molex pins:
Bias relay, the bottom molex pins were also cleaned:
STV-3H and STV-4H diodes back in place:
Close up of the new input cap and transistors, I matched the differential pair to 1% and then heatshrinked them face to face for better thermal stability. Maybe a little overkill, but hey, I'm going a little crazy on this unit anyway.
The outputs were also replaced by the previous tech, however they do not look good, some look like somebody hit them with a punch and they are dented pretty good in the middle of the case. Not going to trust them.
Have to wait on new micas for the outputs, forgot to add them to the order so I'm currently waiting on them to arrive. A big thank you to @EchoWars for the bias relay mod and @markthefixer for part recommendations. More to follow soon!
It is not without problems though, it would not come out of protection. Upon inspection of the boards I found the caps and transistors had been replaced on both power amp boards with a weird mix of good and bad replacements. Let us start with the left power amp board, as it has some interesting things done. Side note: I got a new camera and it is much better than my previous one. The first three images are the old camera, the rest of them are the new one.
The left channel STV diodes had homemade replacements made from three 1N4007 diodes in series for the STV-3H and four 1N4007 diodes in series for the STV-4H in a weird plastic case screwed to the heatsink.
Some close ups with the plastic cases removed:
An interesting way to replace the STV diodes, however not ideal for good thermal tracking. I managed to find (with the help of AK
) an original STV-3H diode from a seller in Germany. The STV-4H came from a parts receiver that I had here. The 4H diodes are not easy to find, so I was thankful I had a parts unit with one in it.Board before (note I have already replaced the STV diodes):
Molex pins (note I cleaned the right 2 to show the differences):
A cool thing I noted when I was looking for a polypropylene replacement for the input cap, the board actually provides pads and lead holes for bigger capacitors than the little tantalum being used currently. It allows for, in addition to the 5mm lead spacing of the tantalum, 10mm, 15mm and 22.5mm lead spaces via the trace here:
And after! In total 8 caps, 14 transistors, 6 diodes, 3 variable resistors and the bias relay were replaced.
Molex pins:
Bias relay, the bottom molex pins were also cleaned:
STV-3H and STV-4H diodes back in place:
Close up of the new input cap and transistors, I matched the differential pair to 1% and then heatshrinked them face to face for better thermal stability. Maybe a little overkill, but hey, I'm going a little crazy on this unit anyway.
The outputs were also replaced by the previous tech, however they do not look good, some look like somebody hit them with a punch and they are dented pretty good in the middle of the case. Not going to trust them.
Have to wait on new micas for the outputs, forgot to add them to the order so I'm currently waiting on them to arrive. A big thank you to @EchoWars for the bias relay mod and @markthefixer for part recommendations. More to follow soon!
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