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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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In Reply to: FISHER 80C preamps posted by Richard CWY on March 21, 2004 at 19:14:10:
Hi Richard,I also run a Fisher 80C in a mono set up driving a Western Electric 94C (Mine actually has the Mohagany cabinet). I liked your post but wanted to make a few comments. This pre uses a low impedence cathode follower output, and this is the reason for the large value output cap (1 uF). In the earlyn 1950's cathode followers were not often built into preamp circuits, but would be added on in a seperate box by those who wanted to run long cable lengths. A few preamps had them built in, including the 80C. I often woderred about the parts selection for this pre. Howver, I recently aquired a box of NOS wax capacitors of the kind found in the 80C. The 1 uF value is huge, larger than the oils you installed. In keeping with a 1940's design philosophy, everything is pretty bolted down to the chasis on the 80C. This is in stark contrast to the late 400C that used point to point wiring. Basically, no other cap would have fit in this position in a way consitent with the rest of the parts placement. Unfortanately, the sonics associated with the 1 uF electrolytic are not great to begin with and decline with age. (By the way most electrolytics are rathed +/- 20% or so)
I recently installed a 1.0uF oil cap in this position (NOS), and after break in, found the sonics to be much better, smoother, more detailed, a little sweeter. One of the cool things about this pre is that one can hook up the adjustable tape out and compare it to the pre out. They should should almost exactly the same. One trouble spot on this pre is that the two 0.0047 uf caps that form part of the bass network are mounted on a peg board on the chasis near the tubes and power supply. Wax caps hate to get hot, even warm, and much of their bad press probably comes from using them in amplifiers where they get too hot. Anyway, if you are hearing some major differences between the tape and pre outs, and everything else is spec, take a look at these caps. The ones in my 80C showed a little deformation, the smooth finish had become slightly pitted and rough. In any event, the sonics had degraded a bit. I would replace these with oils to maintain close to the original sonics, but that obviously is a personal decision.
On another note, are those EF36's in the amp behind the two 80C's? It looks home brew, what are you driving with them?
\Take care, good luck,
Rodney
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Follow Ups
- A few comments... - rodney 03/22/0409:25:35 03/22/04 (0)
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