testing 7868s?

[Randall]

I have a NOS pair of RCA 7868s that I want to sell, but my Hickok TV3B/U doesn't have a magnovar B9D socket to accomodate them. The manual says, use SA-4 adapter code 1050-144. I have scoured the net and I cannot find one nor a photo of one, so I can see what socket they adapt to. Would it be the nine pin mini or the octal? I would try to fashion something if I knew which direction to go in.

Anyone else been down this road?

[Leo_Gnardo]

AFAIK 7868 are simply 7591 on a different base. So... if your tester has a setting for 7591, octal socket of course, you'll have to make up some sort of adapter kludge between the tube & tester. Considering what NOS 7868 go for from tube dealers you should be able to finance a week's groceries plus a bonus case of decent beer or bottle of medium quality hooch from selling your prizes.

[Justin Thomas]

No, a Novar socket is its own thing. There's also the Magnoval; they're both 9-pin but larger. The two are NOT interchangeable; one will fit in the other loosely and the other will stretch or break the other socket. You MAY be able to salvage some old sockets from old gear that used these tubes, but I've never seen them for sale from "the usual places."

I believe Magnoval was a Euro thing. My Eico 667 has both, and they make VERY clear to not mix the two sockets up... sorry, but making your own adapter may be the only option. I would make a little turret board one, myself; just lay out the spacing, drill & seat the turrets, then give em a squeeze so they grip the pins. Quick & dirty, kinda ugly, but, whatever works.

And yes they ARE a 7591 on a different base & bulb.

Justin

[nosaj]

I have a NOS pair of RCA 7868s that I want to sell, but my Hickok TV3B/U doesn't have a magnovar B9D socket to accomodate them. The manual says, use SA-4 adapter code 1050-144. I have scoured the net and I cannot find one nor a photo of one, so I can see what socket they adapt to. Would it be the nine pin mini or the octal? I would try to fashion something if I knew which direction to go in.

Anyone else been down this road?

I have with my Jackson 648. Matter of fact this may work in your case. You will need a female novar socket and male octal socket.

Here's is the link of what I did.
http://antiqueradios.com/forums/view...245&hilit=7868

nosaj

[nosaj]

I have a NOS pair of RCA 7868s that I want to sell, but my Hickok TV3B/U doesn't have a magnovar B9D socket to accomodate them. The manual says, use SA-4 adapter code 1050-144. I have scoured the net and I cannot find one nor a photo of one, so I can see what socket they adapt to. Would it be the nine pin mini or the octal? I would try to fashion something if I knew which direction to go in.

Anyone else been down this road?

Here's someone who has done what you want to do.

http://www.antiqueradios.com/forums/...c.php?t=121108
nosaj

PS. you can probably get the sockets you need from someone in the classifieds on that site.

CA4 PDF http://bama.edebris.com/manuals/hickok/ca4/

[Chuck H]

Isn't that just the uber el84? If your tester has parameters for an el84 you could start there. The tester won't press the tube into service like any actual amplifier anyhow and I'd bet that it tests el84's and 7591's at the same voltages.?. Tube testers are only a rough guide anyhow. Especially problematic with the skinny tubes is their physical condition due to microphonics. I would test them in the tester as el84's as a guide for no major failures and then plug them into an amp to see how they actually perform. There are plenty of high voltage el84 amps out there and you're bound to have one on your bench soon enough.

JM2C

[nosaj]

Isn't that just the uber el84? If your tester has parameters for an el84 you could start there. The tester won't press the tube into service like any actual amplifier anyhow and I'd bet that it tests el84's and 7591's at the same voltages.?. Tube testers are only a rough guide anyhow. Especially problematic with the skinny tubes is their physical condition due to microphonics. I would test them in the tester as el84's as a guide for no major failures and then plug them into an amp to see how they actually perform.

JM2C

no go on that pin sizes are smaller like a compactron.

nosaj

[Chuck H]

no go on that pin sizes are smaller like a compactron.

nosaj

Pin sizes are smaller.?. As in you can't plug them into a novar base? I have never heard that. In fact I've known the 7898 to be recommended for el84 amps that are too hard on the el84's They both use the same base according to the specs. I'm having a little trouble reconciling the skinny pins relative to the issue at hand.

[nosaj]

Pin sizes are smaller.?. As in you can't plug them into a novar base? I have never heard that. In fact I've known the 7898 to be recommended for el84 amps that are too hard on the el84's They both use the same base according to the specs. I'm having a little trouble reconciling the skinny pins relative to the issue at hand.

Noval and novar are different..one is similar in diameter to an octal but it is 9pin skinny pins.

nosaj

[Chuck H]

Noval and novar are different..one is similar in diameter to an octal but it is 9pin skinny pins.

nosaj

So when an amp with those outdated novars loses a socket I guess you just toss it in the land fill

[Justin Thomas]

Okay...
7898 = hi-mu dual triode.
7868 = 7591 in different bottle with 9-pin Novar base.
EL84 = none of the above. Chuck, I think you're either thinking 7189 or 6973, both of which are audio power pentodes. One actually looks closer to a 6V6 for heater & plate voltage.

Noval, Novar, & Magnoval are all different. Noval is miniature 9-pin. Novar is larger diameter 9-pin, and Magnoval is large diameter 9-pin but also looks like thicker pins than Novar. So I believe a Novar tube will loosely fit in a Magnoval socket, but a Magnoval tube will blow out a Novar socket.
My Eico 667 has all three... along with 11 other assorted sockets for various shtuffs.

Justin

[Justin Thomas]

So when an amp with those outdated novars loses a socket I guess you just toss it in the land fill

Or you engineer a solution...

Justin

[Chuck H]

Ah, yes, right. I was thinking of the 7189 tube. Certainly not the 7898. Thank you. But I have looked at the 7868 tube also WRT amps that eat their el84's. That's how I got confused. If the base is significantly incompatible with a E-9-1 socket that would be an issue. I think it may NOT be though. The 7868 is an E-9-75 socket. How many damn miniature 9 pin E-9 sockets are there!?! More important is that the pinout for the el84 and the 7868 is different! So my above suggestion does't work.

[nosaj]

Ah, yes, right. I was thinking of the 7189 tube. Certainly not the 7898. Thank you. But I have looked at the 7868 tube also WRT amps that eat their el84's. That's how I got confused. If the base is significantly incompatible with a E-9-1 socket that would be an issue. I think it may NOT be though. The 7868 is an E-9-75 socket. How many damn miniature 9 pin E-9 sockets are there!?! More important is that the pinout for the el84 and the 7868 is different! So my above suggestion does't work.

Notice the pin spacing on the bottom.

nosaj

[Chuck H]

Right. Well, for one thing the drawing aren't in proportion. Note that the height and diameter of the second and third tubes are indicated as the same, though this is clearly not represented accurately in this drawing that is intended to demonstrate proportion.?. So there's that. But more to the point.

I never suggested you could plug different tubes into different bases. I suggested that you could plug a 7868 tube into a typical noval E-9-1 socket. That may or may not be true, but I think it is.