Dr. Humboldt
Active Member
Hello everyone,
I just picked up The Fisher X-202 with a wood case, supposedly working with noise but I haven't tested it yet. It looks well-loved (aka sorta beat), I will post pics eventually. I have, though, been doing my favorite part of restoration, which is reading all the X-202 threads I can here on AK. I have been lucky enough to get advice on other projects from Dave Gillespie (Dynakit ST-35 with EFB) and Sony6060 (some used Mundorf silver/oil caps for a bargain for a Fisher 500C) and I see they have some very informative threads (links below). In addition to using the straightforward caps suggestions in the posts below and removing the archaic damping circuits, I would like to use EFB II AND also implement a 4HY choke -- my thinking is that if both are good separately, then both together will be great.
My first question, then, as I have not enough knowledge to attempt this alone: is this a good idea or even feasible? Second question: Aside from deep cleaning and replacing the power switch and removing the circuits mentioned in "Pitiful X-202" (see copied passage below), and the mods above, should I try anything else to get top performance?
Primary duty for me will be phono: running an Empire 598II in and out to Wharfedale W90D's with oil caps. Seems like many people find this to be a good combination. (However, when all of my many projects are completed to my satisfaction, I intend to test this out through a face-off between the X-202, a Stromberg-Carlson ASR-433, Tube Nirvana modded Dyna PAS2 + EFB Dyna ST-35, Harman-Kardon A300, and The Fisher 600T... winner stays and the rest will go).
FYI: I work very slowly and I have not purchased any replacement parts yet, so please forgive any slow responses to suggestions.
These are my reference threads:
"Pitiful X-202"
http://audiokarma.org/forums/index.php?threads/pitiful-x-202.551073/
"Improving the Fisher SA-100 with EFBII"
http://audiokarma.org/forums/index.php?threads/improving-the-fisher-sa-100-with-efb-ii.476431/page-2
"Fisher X-202 One Sweet Machine"
http://audiokarma.org/forums/index.php?threads/fisher-x-202-one-sweet-machine.590556/
Particularly following this passage, copied from dcgillespie's "Pitiful X-202" thread:
"1. The antiquated damping circuit was removed. Because of how it was implemented in this amplifier, the fact is that most folks owning one of these amps today likely wouldn't even know how to activate this circuit if they wanted to. Plus, in normal (full damping) operation, it contributes nothing to circuit operation, so removing this circuit means removing something you were never using in the first place.
"The previous owner had already largely removed this circuit, but true to the work done, it was done with a snip here and and an air connection there, leaving all kinds of pig tales that just scream modification. Then, they grounded out all the unused terminals on the rear connection strip (including those for the phase reverse connections since they had removed that feature as well) which also added to the poor image.
"Ultimately, the damping circuit (and the previous work to it) was all properly removed (leaving no presence or indication of the original installation), the Phase Reverse feature reinstalled as shown earlier, with the up shot being that now, the two unused damping terminals on the output strip in each channel ("C" and "X") are now free to become test points for use in properly setting the output stage DC bias and balance controls for each channel, allowing use of a meter for both functions without having to remove the bottom cover, or unsolder semi-permanent shorting straps.
"2. With the work in #1 done, this then allowed the original 10 ohm 2 watt resistor, connecting strap, and grounding strap to be removed from the cathode circuit of the output tubes in both channels. In their place, was installed matched sets of 10 ohm 1/4 watt resistors, one connecting between each cathode and ground, with a lead connecting each cathode terminal over to its new test point terminal on the output strip.
"3. To complete the work, 100 ohm 1/4 watt Screen Stability resistors were added. The original design of the X-202 was not particularly known (to my knowledge) to cause premature output tube failure (arcing). But with the replacement of the existing filter caps with modern electrolytic caps that have lower ESR values, and as a possible prelude to installing EFB, the Screen Stability resistors were added as a safety factor, and because it just makes so much sense to do so while I'm in there."
I just picked up The Fisher X-202 with a wood case, supposedly working with noise but I haven't tested it yet. It looks well-loved (aka sorta beat), I will post pics eventually. I have, though, been doing my favorite part of restoration, which is reading all the X-202 threads I can here on AK. I have been lucky enough to get advice on other projects from Dave Gillespie (Dynakit ST-35 with EFB) and Sony6060 (some used Mundorf silver/oil caps for a bargain for a Fisher 500C) and I see they have some very informative threads (links below). In addition to using the straightforward caps suggestions in the posts below and removing the archaic damping circuits, I would like to use EFB II AND also implement a 4HY choke -- my thinking is that if both are good separately, then both together will be great.
My first question, then, as I have not enough knowledge to attempt this alone: is this a good idea or even feasible? Second question: Aside from deep cleaning and replacing the power switch and removing the circuits mentioned in "Pitiful X-202" (see copied passage below), and the mods above, should I try anything else to get top performance?
Primary duty for me will be phono: running an Empire 598II in and out to Wharfedale W90D's with oil caps. Seems like many people find this to be a good combination. (However, when all of my many projects are completed to my satisfaction, I intend to test this out through a face-off between the X-202, a Stromberg-Carlson ASR-433, Tube Nirvana modded Dyna PAS2 + EFB Dyna ST-35, Harman-Kardon A300, and The Fisher 600T... winner stays and the rest will go).
FYI: I work very slowly and I have not purchased any replacement parts yet, so please forgive any slow responses to suggestions.
These are my reference threads:
"Pitiful X-202"
http://audiokarma.org/forums/index.php?threads/pitiful-x-202.551073/
"Improving the Fisher SA-100 with EFBII"
http://audiokarma.org/forums/index.php?threads/improving-the-fisher-sa-100-with-efb-ii.476431/page-2
"Fisher X-202 One Sweet Machine"
http://audiokarma.org/forums/index.php?threads/fisher-x-202-one-sweet-machine.590556/
Particularly following this passage, copied from dcgillespie's "Pitiful X-202" thread:
"1. The antiquated damping circuit was removed. Because of how it was implemented in this amplifier, the fact is that most folks owning one of these amps today likely wouldn't even know how to activate this circuit if they wanted to. Plus, in normal (full damping) operation, it contributes nothing to circuit operation, so removing this circuit means removing something you were never using in the first place.
"The previous owner had already largely removed this circuit, but true to the work done, it was done with a snip here and and an air connection there, leaving all kinds of pig tales that just scream modification. Then, they grounded out all the unused terminals on the rear connection strip (including those for the phase reverse connections since they had removed that feature as well) which also added to the poor image.
"Ultimately, the damping circuit (and the previous work to it) was all properly removed (leaving no presence or indication of the original installation), the Phase Reverse feature reinstalled as shown earlier, with the up shot being that now, the two unused damping terminals on the output strip in each channel ("C" and "X") are now free to become test points for use in properly setting the output stage DC bias and balance controls for each channel, allowing use of a meter for both functions without having to remove the bottom cover, or unsolder semi-permanent shorting straps.
"2. With the work in #1 done, this then allowed the original 10 ohm 2 watt resistor, connecting strap, and grounding strap to be removed from the cathode circuit of the output tubes in both channels. In their place, was installed matched sets of 10 ohm 1/4 watt resistors, one connecting between each cathode and ground, with a lead connecting each cathode terminal over to its new test point terminal on the output strip.
"3. To complete the work, 100 ohm 1/4 watt Screen Stability resistors were added. The original design of the X-202 was not particularly known (to my knowledge) to cause premature output tube failure (arcing). But with the replacement of the existing filter caps with modern electrolytic caps that have lower ESR values, and as a possible prelude to installing EFB, the Screen Stability resistors were added as a safety factor, and because it just makes so much sense to do so while I'm in there."
