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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: The Mighty 6GH8....... posted by MrTanner on September 8, 2003 at 04:40:02:
I was hoping to find somebody who had tested a large enough number of these tubes to make some overall observations. Thanks for replying. So far, I've only tested these RCA versions from 1973 - which as I indicated have quite a sloppy tolerance in the pentode section. I'm not sure how close this date is to "the end" you mention, but your observations of later tubes having greater variations in the pentode sections seems to be correct at this point.With the 6GH8A being relatively cheap, I think I'm going to buy small quantities of the same lot (15-25 tubes) and see what kind of results I get. I've got some Zenith and GE's coming in the mail, but I haven't been able to find a small bulk quantity of the Sylvania's. I've also heard that there are some National branded "Made in China" tubes that are of good construction and work well in audio.
I'm neighbors with a Seasoned Citizen who used to make his living in the TV rapair business. He seems fairly certain that when he would order 6GH8A's from his distributor he was given a choice between audio or TV applications. Unfortunately he only ordered the ones for TV, and doesn't know what the differences were. He is in his eighties, but is sharp as a tack so I'm thinking this is probably credible. If true, then some manufacturers either had to make specific batches of 6GH8A's for audio, or they were screened and selected out of their regular production tubes. Selecting the best tubes for audio out of a batch of tubes that have already been screened once would surely result in a large number of rejects!
I'm not ready to use a substitution as of yet. Four higher gain 6GH8A's matched to around 5% work great. Even with the 67% rejection rate of this first batch, my cost of the 8 good ones is around $10.00 each. This was with an initial cost of $3.25/tube. The two batches I have on the way work out to just under $2.00/tube. With the same 67% rejection rate the cost will only be about $6.00/tube. I just don't know what to do with the rejects. I don't think they're good enough to sell, but who can bring themselves to throw away NIB NOS tubes - even if they are cheap?!?!?!
Who is ESRC in Forida??? Do they have a web-site????
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