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In Reply to: RE: Scott 130 preamp question posted by gkargreen on March 14, 2017 at 15:47:29
I have a 1960 Scott 299, and I replaced the Pyramid Imp capacitors that couple to the output tubes to prevent major meltdowns. I didn't replace them in the preamp section because they weren't leaky and, IMO, sound pretty good. That said, I check them periodically.
Deoxit D5 works for RCA jacks, but if they are heavily oxidized, I may first use something a little more aggressive like Noxon 7 polish, which is then flushed off with Deoxit or CRC QD, a non-residue cleaner.
For the rotary selector wafer switches inside, these usually have silver alloy contacts, so I've used Deoxit D100 concentrate or some kind of silver polish. The black silver sulfide can be hard to get off, but it makes a sonic difference.
Thanks, Therm! I use IPA on the switch contacts via a q-tip followed by deoxit on a q-tip to control the application area, the IPA gets the AgS right off easily and leaves a nice clean surface for the deoxit. The pyramids are almost always bad in the output couplers, I was just wondering about their use in the preamp section where the voltages are around 100 vdc.
What is "IPA"? It's not a contact cleaner I'm familiar with.
I hadn't realized isopropyl alcohol would remove silver sulfides, but I'll give it a try!
The Noxon 7 I mentioned has oxalic acid in it that removes stubborn oxidation on brass and tin-plated connectors, but it's not for use on silver. It can work wonders on miniature 9 and 7 pin tube pins if used delicately.
With the Pyramid Imps, I realize I'm taking a risk, but I work on a lot of older gear. 400V caps like this run at 110-120V DC are less likely to fail that when run > 300V, but it varies a lot by brand and type. CDE had a line called "Tiny Chief," and they are pretty much always bad.
I did replace the black caps with K40s but Thermonic is right when he said that the black Pyramids are great sounding caps.They are paper impregnated in wax.Today I use a mix of caps and in the 130 you are able to fit the FT2s
in a couple places and I use k40s and Solen film and tin foil or Rel multicaps or even the 716p caps.If this was going to be a daily driver like my Fisher 400CX2, or Mac C20, or Heathkit AA-11,I will put a couple Sonic cap Teflons in the mix as well.
What really helps these preamps is using a pair of 30uf to 35uf film caps in the power supply.I use one off 6X4 and one after the first resistor.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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