7868 to 7591

[nonsuchpro]

Hey all.

I'm about to rewire the sockets of an amp I have that takes 7868s to use 7591s. I can buy the socket converters on ebay, but I have the sockets already and can solder. I drew a diagram of what I think is correct but if you guys can take a sec and double check my work, I'd greatly appreciate it before I start.

Thanks in advance!

 

[kevinkr]

I can't follow your drawing, please just create a pin list for both tubes and post that along with the basing diagrams.

Plate
Suppressor
Screen
Control Grid
Cathode
Filament
Filament

You can list any duplicated connections next to the electrode they duplicate

 

[mississippi]

I think it's ok. And when I look to the spec's of both tubes, you don't need to readjust the biasvoltage.

 

[DAK808]

the 7591 and 7868 are the exact same tubes except they have different tube sockets. I believe this was done so RCA, the designer of the 7868 could take some business away from Westinghouse the original makers of the 7591

 

[nonsuchpro]

I can't follow your drawing, please just create a pin list for both tubes and post that along with the basing diagrams.

Plate
Suppressor
Screen
Control Grid
Cathode
Filament
Filament

You can list any duplicated connections next to the electrode they duplicate

This is the only way it makes sense to me. You really can't follow the colors?

 

[nonsuchpro]

The only thing I'm really concerned about is pins 2 and 6 on the 7868 going to pin 6 on the 7591. (2 pins going to 1)

 

[mississippi]

No concern necessary. It's interaly done for better stability of the mecanical parts of the grits for e.g. less microphony.

 

[nonsuchpro]

I think it's ok. And when I look to the spec's of both tubes, you don't need to readjust the biasvoltage.

Yeah, that's why they can successfully sell a socket converter for it. It's $65 USD for 4 of them.

 

[nonsuchpro]

Clarify

No concern necessary. It's interaly done for better stability of the mecanical parts of the grits for e.g. less microphony.

So are you saying I shouldn't make the connection physically? Or should I connect 2 and 6(7868) to 6(7591)?

 

[mississippi]

Hi,
You can take one or two wires to number 6 (7591). It's your choise.
Does not mater, it's internaly connected 2 - 6 (7868).

 

[nonsuchpro]

Hi,
You can take one or two wires to number 6 (7591). It's your choise.
Does not mater, it's internaly connected 2 - 6 (7868).

Perfect. That was the answer I was looking for.
!

 

[nonsuchpro]

Possible hitch

OK,
It looks like there is an internal connection from pin 1 to pin 7 on the (4) 7868 sockets. What do you think I should do here?

 

[mississippi]

That's true, when you look at the datasheet of the 7868 you will see that pin 1 and pin 7 both are connected to G2 inside of the tube. So you can do this also at the outside of the tube for e.g an extra point for a component. As you see on your picture.

 

[nonsuchpro]

That's true, when you look at the datasheet of the 7868 you will see that pin 1 and pin 7 both are connected to G2 inside of the tube. So you can do this also at the outside of the tube for e.g an extra point for a component. As you see on your picture.

OK.
I still have a problem grasping the concept of why you would do an external connection when there is an internal connection. When it's beneficial and when it's not, etc.
I'll go ahead and connect pin 4 to 8 externally on the 7951.

Oh, just to let you guys know what amp(s) it is, it's a Conn 6026. They are wired a bit differently then the Rowe you helping me with earlier. I acquired 4 Conn 6026s. Sure they are organ amps but they make wonderful hi stereo amps. Plenty loud and clear. I recommend picking these up if you come across them.

Stock they take 4 x 7868, 2 x 12AX7, 1 x OA3, and 1 x 6DN7
I use 6EU7 with socket converters in place of the 12AX7s. Alternatively you can use any 12A*7 of your power choice of course.

 

[mississippi]

OK.
I still have a problem grasping the concept of why you would do an external connection when there is an internal connection. When it's beneficial and when it's not, etc.

When there is an internal connection and you use both pins without connecting a wire between them, you might have a problem when testing, measuring etc. when there is no tube inserted in the socket.

 

[nonsuchpro]

When there is an internal connection and you use both pins without connecting a wire between them, you might have a problem when testing, measuring etc. when there is no tube inserted in the socket.

Ah OK. Thanks again man!