Fisher X-202 Rebuild
- Thread starter 2dbit
- Start date
Before I hear too much about it, I am aware that in several pictures there is debris, leads that require trimming, or lack of solder. The pictures were taken on the fly and typically after a picture was taken, I continued general maintenance in the area.
My overall goal in component placement was to be as close to original as possible with one exception... I put caps on top. It seems that Fisher wasn't overly concerned about their stereos ever requiring capacitor replacement and placed a lot of them below all the resistors...
My overall goal in component placement was to be as close to original as possible with one exception... I put caps on top. It seems that Fisher wasn't overly concerned about their stereos ever requiring capacitor replacement and placed a lot of them below all the resistors...
bhamham
Super Member
Incredible workmanship, very meticulous :thmbsp:
I don't mean this as a criticism for I do it too but I often wonder if measuring cap values at static conditions - w/o applied actual voltages - is all that accurate? And, doesn't test for leakage.
I've gotten where I just let film caps be unless their reputation is such that they're known failures, like Hunt and those melted waxy paper ones. But, I'm not working on an heirloom piece like your X-202.
I don't mean this as a criticism for I do it too but I often wonder if measuring cap values at static conditions - w/o applied actual voltages - is all that accurate? And, doesn't test for leakage.
I've gotten where I just let film caps be unless their reputation is such that they're known failures, like Hunt and those melted waxy paper ones. But, I'm not working on an heirloom piece like your X-202.
I absolutely agree that a static test of a capacitor used in an audio circuit is almost a waste of time. But, at the same time, it's a rough indicator of health. I had been curious how the Mylar caps held up over time. I was actually surprised by the electrolytics... But, they're all getting replaced, so fresh start all around...
Supposedly, all the electros in mine were tested and I replaced them anyway. Cheap insurance. Your work is very nice, but, having done one of these myself, the replacements BETTER last 50 years or at least outlast what's left of my time on Earth! I'm not going to do another recap when I'm in my 80s!
Yeah, I am doing my best to facilitate future maintenance. I didn't wrap the leads and I put the caps on top, so removal will be as simple as heating and lifting the leads. Of course, without wrapping, I make double sure that I have excellent flow between lead and terminal. Now, restuffing the can caps... That's something I won't want to do again....
bhamham
Super Member
I hear you about wrapping. I just do a good hook so it makes a solid mechanical connection.
Ever worked on a Sansui tube amp/receiver? Those factory guys made a few wraps for each lead - takes a lot of patience to clean off those old terminals.
tube-a-lou
Addicted Member
Wow! I like the way you mark all the components very detailed job, that amp going
to sound great when your done.
Tube
to sound great when your done.
Tube
Been a while! Have had a few projects that got in the way of progress, but I'm picking back up where I left off!
I'm over to the output tubes right now and ended up doing a slight reconfiguration to allow for cathode resistor/fuses.
Here's some before pics and after pics.
Here's everything removed except the old jumper wires, shorting wires, and resistor for adjustment...
Finally, a completely nude picture...
Here's what I've done drawn into the schematic...
I removed the jumper wires, the old R134 resistor, and moved R124 and R125 so they connect to pin 3 of each output tube. Then, installed a single 10ohm 1/4watt resistor from pin 3 of each tube over to ground. I also put shrink tube over the cathode resistor leads so that if they should ever go POP, it's less likely that a lead could short to someplace not good.
I'm over to the output tubes right now and ended up doing a slight reconfiguration to allow for cathode resistor/fuses.
Here's some before pics and after pics.
Here's everything removed except the old jumper wires, shorting wires, and resistor for adjustment...
Finally, a completely nude picture...
Here's what I've done drawn into the schematic...
I removed the jumper wires, the old R134 resistor, and moved R124 and R125 so they connect to pin 3 of each output tube. Then, installed a single 10ohm 1/4watt resistor from pin 3 of each tube over to ground. I also put shrink tube over the cathode resistor leads so that if they should ever go POP, it's less likely that a lead could short to someplace not good.
2d -- Your continued work is again superb!
If I may however, the schematic did you a disservice in its depiction of R124 and R125. While the schematic shows these resistors connected to the cathode terminals of the output tubes, in theory, and in the original build, they were in fact (and should be) connected directly to ground -- as they were (and still are) in my unit as well.
Now ultimately, if you install jumpers to ground out each cathode after completing the adjustment process, then it does not matter if you connect the resistors this way. But if you allow your cathode terminals to float on the new 10 ohm resistors installed during normal operation (which I do), then having R124 and R125 connected directly to the cathode terminals in this way negates the benefits of letting the cathodes float in the first place.
It's not an earth shaking concern, but from a technical point of view, the original build was correct, and the schematic is wrong, which is why the build of the unit did not match it.
I just wanted to let you know now, so you could reverse the work as you might deem necessary.
You will clearly have a super X-202 when you're finished. Good luck with it!
Dave
If I may however, the schematic did you a disservice in its depiction of R124 and R125. While the schematic shows these resistors connected to the cathode terminals of the output tubes, in theory, and in the original build, they were in fact (and should be) connected directly to ground -- as they were (and still are) in my unit as well.
Now ultimately, if you install jumpers to ground out each cathode after completing the adjustment process, then it does not matter if you connect the resistors this way. But if you allow your cathode terminals to float on the new 10 ohm resistors installed during normal operation (which I do), then having R124 and R125 connected directly to the cathode terminals in this way negates the benefits of letting the cathodes float in the first place.
It's not an earth shaking concern, but from a technical point of view, the original build was correct, and the schematic is wrong, which is why the build of the unit did not match it.
I just wanted to let you know now, so you could reverse the work as you might deem necessary.
You will clearly have a super X-202 when you're finished. Good luck with it!
Dave
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THANK YOU!!!
I have no knowledge to go by, other than what I have in my schematic. I do my best to reproduce what I see on the amp, but sometimes with the creative wiring that Fisher did, my perception is a bit skewed.
It was my belief that R124 and R125 should be removed from ground and tied to pin 3 since when the jumper is removed for adjustment purposes, that is essentially how the system would then be wired.
With this new information, I will remove R124 and R125 from the cathodes and put them to ground.
The plan for R134a and R134b was to be a permanent installation, to serve for both spontaneous bias readings, and also as a fuse.
Thanks again!!
I have no knowledge to go by, other than what I have in my schematic. I do my best to reproduce what I see on the amp, but sometimes with the creative wiring that Fisher did, my perception is a bit skewed.
It was my belief that R124 and R125 should be removed from ground and tied to pin 3 since when the jumper is removed for adjustment purposes, that is essentially how the system would then be wired.
With this new information, I will remove R124 and R125 from the cathodes and put them to ground.
The plan for R134a and R134b was to be a permanent installation, to serve for both spontaneous bias readings, and also as a fuse.
Thanks again!!
