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7868 substitute tube?!?!?!
- Thread starter tubeboob
- Start date
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Careful shopping can net you a matched quad for $160 on ebay. vacuumtubes.net has NOS for $45 each. EH can be found for $99 per quad. Some change out the 330K grid resistors to 200K using the EH. I suspect the EH has slightly higher grid leakage due to less vacuum inside. I think NOS were pulled to 10-7 Torr vacuum. Perhaps EH is at 10-5 Torr.
I plan to keep my Fisher 400, thus bought 4 NOS quad sets. Some were as inexpensive as $35 a pair in NOS. I guess up to 8000 hours operating time when biased conservatively.
I plan to keep my Fisher 400, thus bought 4 NOS quad sets. Some were as inexpensive as $35 a pair in NOS. I guess up to 8000 hours operating time when biased conservatively.
battradio
Electron trainer
6GT5 are cheep and a pin for pin drop in , BUT you have to lower the screen voltage to 200volts DC
http://www.nj7p.org/Common/Tube/SQL/Tube_query.php?Type=6GT5A
http://www.nj7p.org/Common/Tube/SQL/Tube_query.php?Type=7868
http://www.nj7p.org/Common/Tube/SQL/Tube_query.php?Type=6GT5A
http://www.nj7p.org/Common/Tube/SQL/Tube_query.php?Type=7868
the EH ones work. Honestly by this point those sockets may not be in optimal shape to deal with old stock ones anyway. The fatter pins may actually be to your advantage. Or you could swap the sockets out for ones that properly fit the EH tubes. The ones you want are Magnoval, the originals are Novar. I fitted a set of Magnovals into my Sherwood when I converted it from 7591 tubes.
bhamham
Super Member
I like the EH 7868s a lot for my Fisher 400 and X-100-B.
However, I bought a matched quad of NOS Brimar EL506s to try one day - cheap as chips - and from all I can find should be an equivalent for the 7868. You would need to rewire the sockets and it's a magnoval so will stretch the old novar base.
Still trying to find the original Brimar tube data so if anyone knows where it is please let me know.
Here's a couple of links for the EL506:
https://tdsl.duncanamps.com/~duncanam/tdsl/show.php?des=EL506
http://www.r-type.org/exhib/aaa0711.htm
However, I bought a matched quad of NOS Brimar EL506s to try one day - cheap as chips - and from all I can find should be an equivalent for the 7868. You would need to rewire the sockets and it's a magnoval so will stretch the old novar base.
Still trying to find the original Brimar tube data so if anyone knows where it is please let me know.
Here's a couple of links for the EL506:
https://tdsl.duncanamps.com/~duncanam/tdsl/show.php?des=EL506
http://www.r-type.org/exhib/aaa0711.htm
Attachments
NOSValves
Super Member
Actually once you go through the nerve racking experience of working those EH tubes into the NOS sockets they fit real well... But you have to be very careful or you will crack the glass on the EH tubes and most dealers will not replace broken glass envelop. It take downward easy and steady force with a very mild circular motion to work the EH's in those tight sockets. The EH tube pin diameter is how the NOS 7868 should have been all along. In reality any tube with that bulb size shoudl have a bakelite full base like the original 7591 had. The 7868 was a copy of the 7591 that was developed strictly to get around paying royality fees.....
Numerous instances of that over the years. Make the same tube with different basing and call it something else.
vroom_vroom
Member
I gotta tell you the eh tubes still sound superb I am running them in a bogen 100 and they sound better than the ge tubes I had before
Destructor
Super Member
How are the EH tubes to remove? I have the EH tubes in my 400 but I've never removed them.
drknstrmyknight
Addicted Member
I'd say do more research in finding some original, tested, 7868's. Hit the auction sites, the AK vendors and post in Barter Town. Be patient and you'll be rewarded.
Are there NOS 7868's? Maybe, but the tester is more important than the cosmetics.
Are there NOS 7868's? Maybe, but the tester is more important than the cosmetics.
NOSValves
Super Member
Removing them is a much easier task then installing them for the first time! But you do have to be careful. Once they have been in and out the task becomes much easier. The real killer is the first time getting them in.
As far as the EH sounding better then GE......I bet the GE 7868 were warn out so the comparison is not valid. A fresh set of output tubes is always going to sound better then a warn out set regardless of brand. I will say buying used output tubes is asking for trouble especially on eBay the land of sellers quoting percentage of life..... I've never seen a vintage tube tester give that type of score. Then factor in most all vintage tube testers do not test them at true electrical operating conditions.... talk about a scam!
NOSValves
Super Member
I like the EH 7868s a lot for my Fisher 400 and X-100-B.
However, I bought a matched quad of NOS Brimar EL506s to try one day - cheap as chips - and from all I can find should be an equivalent for the 7868. You would need to rewire the sockets and it's a magnoval so will stretch the old novar base.
Still trying to find the original Brimar tube data so if anyone knows where it is please let me know.
Here's a couple of links for the EL506:
https://tdsl.duncanamps.com/~duncanam/tdsl/show.php?des=EL506
http://www.r-type.org/exhib/aaa0711.htm
I just looked over an eBay auction for these NOS/NIB for $37 a matched/tested pair. If I was going to stretch my sockets out these are what I would use as long as they can be purchased NOS/NIB tested for that price or I'm sure less if one shops around. From the information I've found other then the larger tube pins (same as EH) these are direct plug in replacements. I bet sonically and long term reliability wise they floor the EH...
Gary Kaufman
Well-Known Member
The original 7868 is a Novar base, with 0.038" (1.02mm) pins. In common slang it is often referred to incorrectly as a 9 pin compactron. (The smaller, more common 9 pin socket like a 12AX7 is a Noval base).
The EH tube made use of available tooling and is a Magnoval which have larger 0.046" (1.27mm) pins. Magnoval tubes were more commonly European or WE.
It's not actually that hard to force a Magnoval tube into a Novar socket, although I'd find a cheaper tube like a 6GB5 to initially work the sockets a bit looser rather than risk a EH7868.
Once you stretch the sockets out for a Magnoval the old stock Novar type won't hold nicely. You can re-tension the sockets, but in most cases the're would be no reason to go back in the future as NOS will only continue to rise in cost.
I'm just thankful that the 7591 and 7868 have been re-introduced, as both types were tough to locate 10 years ago. While the re-introduced types may not be perfect, they are actually quite good. They've helped put lots of older Scott, Eico and Fisher gear back into service.
- Gary
The EH tube made use of available tooling and is a Magnoval which have larger 0.046" (1.27mm) pins. Magnoval tubes were more commonly European or WE.
It's not actually that hard to force a Magnoval tube into a Novar socket, although I'd find a cheaper tube like a 6GB5 to initially work the sockets a bit looser rather than risk a EH7868.
Once you stretch the sockets out for a Magnoval the old stock Novar type won't hold nicely. You can re-tension the sockets, but in most cases the're would be no reason to go back in the future as NOS will only continue to rise in cost.
I'm just thankful that the 7591 and 7868 have been re-introduced, as both types were tough to locate 10 years ago. While the re-introduced types may not be perfect, they are actually quite good. They've helped put lots of older Scott, Eico and Fisher gear back into service.
- Gary
I converted my Sherwood 7000 from 7591 tubes to 7868. The modern production 7591's are on the fat side, and would not fit under the chimney. New 7868's however are the right size. Since I had to replace the sockets to do this, I just bought new Magnoval sockets and mated them to the EH tubes. Fits quite nicely. I didn't see any point in buying new Novar sockets and then stretching them out. I actually had a harder time finding a quality Magnoval socket than anything else.
I'm really curious about those EL506 tubes though. If I can score a couple pairs of those cheap, I may do so, even if I only use them for spares.
I'm really curious about those EL506 tubes though. If I can score a couple pairs of those cheap, I may do so, even if I only use them for spares.
thefragger
Certified Crazy.
Even cheaper in group buys... :scratch2:
I like the EH 7868s a lot for my Fisher 400 and X-100-B.
However, I bought a matched quad of NOS Brimar EL506s to try one day - cheap as chips - and from all I can find should be an equivalent for the 7868. You would need to rewire the sockets and it's a magnoval so will stretch the old novar base.
Still trying to find the original Brimar tube data so if anyone knows where it is please let me know.
Here's a couple of links for the EL506:
https://tdsl.duncanamps.com/~duncanam/tdsl/show.php?des=EL506
http://www.r-type.org/exhib/aaa0711.htm
The above is the only truth about old tubes. NOS is often just an illusion. I can clean used tubes to make them look like new. I can pay a small fortune for empty old tube boxes. I can claim that every tube I have is NOS. Or buy tubes that are 40 or 50 or 60 years old that are claimed to be NOS.
What I am trying to say is that its not that there aren't any unused old tubes, its just that I usually can't personally confirm their heritage.
I can instead test the tube. If it is strong, stable, and isn't microphonic, I want it. I don't care if it sat forever on a shelf or did intermittent light duty for a decade or two. If a tube isn't strong, stable, and quiet, I don't care how pretty it looks, what box it comes in, or if its never been used.
Indeed. I've got a number that I know have hours on them, but they work just dandy. Most of my tubes have been purchased or otherwise obtained in assumed to be used condition. Once in a while I get one in a box that even matches the tube, but I still have no real confidence they are unused.
