Recommendation for 7868 tubes

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gkargreen

Well-Known Member
Got 3 amps with these tubes in them and while I may be lucking enough to get a good. somewhat matched quad out of them, I will need at least one if not two quads of 7868 to finish these amps off. JM is no longer selling 7868 tubes according to his webpage, are there any current tubes worth buying, or am I doomed to finding something on ebay? Thanks!
 
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Unfort EH is the only new production 7868 being made and the pins are fatter so they will likely stretch the tube sockets and won't be able to use nos tubes after. But considering the price for nos it might be your only option.
 
Why eBay? Doesn't antique electronic supply sell them?

I would not buy tubes on eBay unless no reputable vendor had them.. too much risk. Keep in mind that the reissues may have compatibility issues with the original sockets due to pin diameter, as is well documented on forums. Originals are now $77 each though at AES, so looks like you need to pay one way or another.

I think becoming an AK subscriber and putting up a bartertown ad for strong used originals may bear some fruit.. that's probably what I'd do.
 
Thanks guys, prices are so steep for that tube, wondering if I should not just re-socket and use 7591 tubes, would that be an issue? Or maybe going with 6GT5 and adjusting the screen voltage?
 
EH or NOS is really it, and NOS can be pretty much a gamble unless it comes from a reliable source. I bought a set of NOS 7868 on Ebay a few years ago. They were indeed 4, brand new, in matching boxes, etc. Electrically they're so different I don't even have 2 pairs. I can just barely get the channels to idle at the same current after adding bias and balance adjustments. Got them cheap, and I got what I paid for. I have another set that actually matches up reasonably but those cost a bit more $.
 
gkargreen said:
Thanks guys, prices are so steep for that tube, wondering if I should not just re-socket and use 7591 tubes, would that be an issue? Or maybe going with 6GT5 and adjusting the screen voltage?
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If it was mine I would try the eh 7868 EH first to see if I liked them if you going to get rid of the sockets anyways.

I believe @gadget73 did the reverse going from 7591 to 7868 in a sherwood? I forget now.
 
Yea, about the same price for 7591 vs. 7868. Problem is now McShane is no longer selling or recommending the use of the EH-brand tubes, so no 7868 from him.
 
gkargreen said:
Yea, about the same price for 7591 vs. 7868. Problem is now McShane is no longer selling or recommending the use of the EH-brand tubes, so no 7868 from him.
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There are other places I can't comment on how matched they are but I bought my 7591 from vivatubes and they said they were "matched" they have been working fine for almost a year now but I have no way to test them to be sure.

https://www.vivatubes.com/new-matched-quad-4-electro-harmonix-7868-vacuum-tubes/
 
So gadget, you are pleased with using the EH 7868 tubes? Is there recommendations on installing them in an amp, I have heard the pins are a bit big for the sockets and amps that use 330K resistors should have them down sized to 220K with a change in the coupling cap. Thanks!
 
I'm fine with them. Pins are fatter, but when I converted the Sherwood I sought out magnoval sockets that already have the larger pin size, so I didn't have to stretch anything. If you're fitting them into old sockets it can be a challenge. They do want more negative grid voltage in order to bias correctly, so making that adjustable and monitorable (is that a word?) is a good idea. On the Sherwood S-7000 I did the 10 ohm resistors from cathode to ground and just put in a single trim pot to do all 4 at once. With a matched quad it works out OK.

Some amps need the resistors changed, some don't. Depends on the particulars. The Sherwood did not.
 
Thanks gadget, I will order a matched quad for my Fisher X-100-C and Fisher 400 and make the changes you mentioned.
 
My impression was that Jim McShane quit supplying the EH 7868's because he was getting too many customers breaking them around a pin trying to force them into the standard sized pin sockets. The last quad I bought from him of EH 7868's he quizzed me pretty closely to be sure I understood the risk and was taking steps to mitigate it. I enlarged the pins in the existing sockets before I inserted the tubes and lubricated them with a bit of D5 when inserting. Truly, installing magnoval sockets is probably the best idea. The tubes are fine, by the way.
 
@gkargreen: Four years ago, when Dave Gillespie resto-modded my Fisher KX-100, I bought a matched quad of EH 7868 from Jim McShane. They have been fantastic and it’s a shame that McShane no longer sells them but... if this quad ever tanks (no sign of that happening any time soon) I will not hesitate to replace them with another quad of EH 7868.

Oh, and my amp is running with the original sockets.
 
ESRC lists 7868's for $35 ea. That isn't too much more than the new Russian made versions. They say all tubes are tested before shipping but I don't what that means.
 
I am using them in my Fisher 400 with the original sockets. They sound great. But now my only choice is to re-tube with EHs when the time comes.
 
That's a good thing to have. I have a dud Brimar EL506 that I keep on hand for just that purpose!
 
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