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Old 18th February 2011, 04:18 AM   #1
rknize is offline rknize  United States
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Default Simple SE + 8417s?

Anyone ever try 8417s? They are rather high mu, but I don't a reason why they wouldn't work....
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Old 19th February 2011, 04:43 AM   #2
w5jag is offline w5jag  United States
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And marginally higher Rp and input capacitance, but it does look like it could be made to work.

I don't have any 8417 and can't recall if I have ever seen any.

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Old 19th February 2011, 05:15 AM   #3
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I have a quad of them. They were one of the last audio output tubes to come out. They are sort of like a 6550 but easier to drive...more like a 6L6. That made manufacturing tricky, I guess. They've never been reproduced as far as I know.
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Old 19th February 2011, 05:23 AM   #4
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Be very, very careful, as these tubes have a disconcerting habit of self destructing, even when supposedly operating within their ratings. Reportedly the combination of high transconductance and high power makes them touchy. Some manufacturers fare better than others. I have a colleague with a Quicksilver amp that uses these, and he swears by Sylvania and at GE. Normally I'd be very happy with tubes made by either manufacturer. Check the archives for more info about this tube before you lay your money down.
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Old 19th February 2011, 05:31 AM   #5
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I already have them. They came with an amp that I am restoring. The amp ran them pretty hard, but this set actually doesnt have that many hours on them. I don't plan on using them in that amp once its done. These are RCA, which I believe were made Sylvania. I too have read about the GEs being problematic.
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Old 19th February 2011, 05:48 AM   #6
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The warning was for other folks temped to try them. I certainly wouldn't design anything around the 8417, in part due to their spotty reputation and the fact that these were some of the last tubes to come out, so NOS is kinda thin on the ground. Sad to say, some of the Quicksilver amps that use these (and blew them up with distressing regularity) have been refitted to use tubes that are more rugged and easy to find, and they reportedly don't sound the same (read different/worse). Having said that, I wonder if the change in design included an appropriate change in the driver circuitry to handle a tube with substantially less transconductance than the 8417?
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Old 19th February 2011, 04:04 PM   #7
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I think that was a common problem with guitar amps that used them as well. The bias circuit can be modified to run 6550, but the amp doesn't have enough drive.
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Old 19th February 2011, 11:26 PM   #8
w5jag is offline w5jag  United States
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Well, if you already have them, and want to try them out in the Simple SE, a couple of paths might be:

1) Single Ended Triode - pull the 12AT7, and drop in a 12AU7. The CCS current probably won't be right, but the 12AU7 won't self destruct immediately, and you can dial in the bias on the 8417's and play around with the current on the 12AU7, or

2) Keep the 12AT7 front end (maybe), and give Single Ended Pentode a try. Let the extra mu of the 8417 be absorbed with negative feedback. Plate to grid (Schade) local negative feedback is easy to implement, and gives good results on the Simple SE. I've been very pleased with SEP in my 6146 Simple SE.

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Old 20th February 2011, 12:05 AM   #9
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Wrt Quicksilver and exploding tubes..... It was the later GE version of the Quicksilver 8417 that had so many problems... I use the earlier Quicksilver Philips and Sylvinia 8417 version... never had a tube melt down for more than 10 yrs in operation.. The Philips 8417 is a fine sounding tube, I too am keeping my match Quad pair.


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Originally Posted by wrenchone View Post
The warning was for other folks temped to try them. I certainly wouldn't design anything around the 8417, in part due to their spotty reputation and the fact that these were some of the last tubes to come out, so NOS is kinda thin on the ground. Sad to say, some of the Quicksilver amps that use these (and blew them up with distressing regularity) have been refitted to use tubes that are more rugged and easy to find, and they reportedly don't sound the same (read different/worse).
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