Fisher 500C restoration - Printable Version
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+--- Thread: Fisher 500C restoration (/showthread.php?tid=19614)
RE: Fisher 500C restoration - morzh - 03-24-2019
Russ
Try to explain that to hardcore purists on Audiokarma
(no, not all of them...but most).
RE: Fisher 500C restoration - EdHolland - 03-24-2019
Found the PECs, which was about all I could do today, as family demands occupied my time. Also noted their places in the schematic.
It is interesting that the majority of the circuit is laid out with discrete components, yet these small building blocks were used in filter and tone circuits. I wonder what the motivation was? Cost? Better tolerance? Convenience?
I have no plans to change these parts in the near term.
As to audio purists, I find a lot of that world to be particularly obtuse, if not nonsensical. So many "philosophies" and clique-ish behaviour. Not to mention a significant layer of pseudo-science. I'll have no truck with that side of things. Over the years, I've built many a piece of audio gear - solid state and tube amplifiers, designed and built a CD player DAC, and a phono preamp. Not to mention things restored and repaired. Basic principles, no nonsense, good sound. I don't care about the whimsical affirmation of hifi purists.
When it comes to radios, however, I do pay close attention - especially to folk here. It is obvious to me there is a great deal of experience, skill and knowledge displayed among the forum members, and comments on my projects are taken very seriously, and in good faith.
RE: Fisher 500C restoration - morzh - 03-25-2019
You are absolutely right about pseudoscience.
This here 500C is a tube gear, and the vintage tube is a disappearing lore, so it does pay to heed the experience of the older folk who dealt with it in its heyday. I know that me being an EE, I don't know about the tubes and their application nearly as much as some guys here who are not even necessarily formally trained in electronics.
RE: Fisher 500C restoration - EdHolland - 03-27-2019
Had a moment today to get that last axial capacitor. Sometimes these little tykes are hard to remove, as the assembly line ops were very thorough in wrapping the leads before soldering. With that done, notes were made on the selenium bridge rectifier for the bias supply and wiring to the smoothing cap, in preparation for their replacement. It makes sense to work on these together, as they are quite intertwined.
After that, the above deck cans, HT rectifier diodes and addition of the inrush current limiter. It seems a good place for this is to put it in place of a wire to the fuse holder.
RE: Fisher 500C restoration - EdHolland - 03-30-2019
Today I got about an hour or so into the 500C. The 1000 uF +1000 uF multi-cap hidden under the chassis was replaced with the part from the Hayseed Kit. While it was out, I removed the selenium bridge rectifier and replaced it with a modern substitute. I also added the inrush limiter to the mains line. Three twist-locks to go, perhaps tomorrow.
Cheers
Ed
RE: Fisher 500C restoration - morzh - 03-31-2019
It actually had 1000uF caps by design or someone just put them in?
RE: Fisher 500C restoration - EdHolland - 03-31-2019
They are by design, Mike.
A 2 section 1000 uF + 1000 uF is clip mounted under the chassis. They are part of a section providing DC filament power for 4 12AX7 tubes. Grid bias for the output stage is also derived from this line.
RE: Fisher 500C restoration - EdHolland - 03-31-2019
Today I got one of the twist-lock cans replaced, 200 uF + 50 uF + 50 uF + 50 uF. Quite a fiddly corner of the chassis, and fun teasing the component leads from the capacitor's lugs. Even more tricky to get the tip of my bigger iron onto the two twist lugs that had been soldered to the chassis.
With that done, I documented the next difficult multi section 40 uF + 40 uF + 40 uF + 20 uF, and set about desoldering and detaching the connections.
On the 200/50/50/50 I tested with the capacitance meter. The 200 section read 300 uF, two of the 50's read about 68 uF and one only a few hundred nF. The other test I did was to charge the sections up with a 9V battery and look at the discharge rate (10 Megohm meter). Most looked very poor, especially the 200 uF which would discharge to zero in a couple of seconds. The 2x 1000 uF can was also tested, each section reading around 1300 uF. These seemed to hold better, and may even have been useable, but the Hayseed Kit included a nice replacement.
Funny, I thought the work would go faster, and I would have the cans all done by now, but after playing a full game of soccer (football) this morning, I soon found myself tired standing at the electronics bench.
RE: Fisher 500C restoration - morzh - 03-31-2019
Ed
You could reform the caps and they would hold charge longer. But with a prized hifi like yours, why bother.
RE: Fisher 500C restoration - EdHolland - 03-31-2019
I might play with re-forming, just for the learning as I've never tried it. As for the amp, the new caps are paid for and very nice quality, no doubt they will see good service.
RE: Fisher 500C restoration - morzh - 04-01-2019
There are different ways of reforming; I take the safer approach and reform through resistors (50K or so) while measuring the drop across the resistor. When it drops to microamps level I consider the cap reformed.
With cheaper sets or non-hi-fi equipment that is not sensitive to minor things I do it if possible; else I put new caps in or restuff the old ones.
I restuffed the 1" twistlocks on my EICO monoblocks: look original and probably has better caps inside than the originals did.
1000 uf caps - I would totally replace them as today much better quality is available.
RE: Fisher 500C restoration - TV MAN - 04-02-2019
Still lurking. I have a 500c that I shelved out of pure frustration over the do this and do that. I am eager to see how yours turns out and get mine back on the bench moving forward. I went Hayseed on mine too, and did burn an output tube, so there is probably some merit to the resistors to protect. The bias setter is what I really want to see something on. Anyway, carry on
RE: Fisher 500C restoration - Ron Ramirez - 04-02-2019
(04-02-2019, 11:38 AM)TV MAN Wrote: The bias setter is what I really want to see something on.
https://audiokarma.org/forums/index.php?threads/ta-600-service-bulletin-early-version.676168/
https://philcoradio.com/phorum/showthread.php?tid=16481&page=6&highlight=fisher+TA-600
RE: Fisher 500C restoration - EdHolland - 04-07-2019
Slow going today... mostly in reaching the bench! I did persuade the 40 uF + 40 uF + 40 uF + 20 uF can to leave the chassis, and set the surrounding components in a systematic place. It is a very cramped area of the chassis to work - hard not to leave those amateurish iron burns on the surrounding stuff, but so far I managed well. Perhaps tomorrow I can fit it's replacement.
RE: Fisher 500C restoration - EdHolland - 04-14-2019
Busy busy busy - I did at last install the replacement 4 section cap. Just one can to go, at which point we'll be ready for a first test.
/Ed