Jump to content
Gibson Brands Forums

Octal socket -- NO diagram! Help!


Recommended Posts

I'm not ENTIRELY sure how to wire up the octal socket on the TurretBoard I got! The diagram is for NINE PIN!

 

Is there a translation table i.e.

 

9|Octal

---------

1|n/a

2|5

3|...

 

etc? I could try looking at the layout for the EL84's pins versus the EL34 and match plate-to-plate, filament-to-filament, etc; or I could look at the SEWatt octal mods; but ... rather not screw this up

Link to comment
Share on other sites

Here's what I have.

9 | O
------
2 | 5 (control grid)
3 | 8 (Cathode)
3 | 1 (Suppressor grid)
4 | 2 (filament)
5 | 7 (filament)
7 | 3 (plate)
9 | 4 (screen grid)
-
1,6,8 | 6 (Not connected)

 

Cathode and suppressor grid can be on the same lead in octal?

 

... looking at the SEWatt octal mod, I'm guessing this is right EXCEPT pin 1 (suppressor grid) on octal should go STRAIGHT to ground? i.e.:

 

9 | O
------
2 | 5 (control grid)
3 | 8 (Cathode)
4 | 2 (filament)
5 | 7 (filament)
7 | 3 (plate)
9 | 4 (screen grid)
X | 1 (Suppressor grid) (GROUND)
-
1,6,8 | 6 (Not connected)

Link to comment
Share on other sites

Try this. http://www.turretboards.com/vjr/Vjr_board_layout_fenderish_octal.pdf

 

You can connect the octal's pin 1 to ground if you plan to try an EL34. If not, then it doesn't matter cuz the EL34 is the only octal not connected internally.

 

Another old trick from the RCA manual is to tie pin 1 to pin 8, AND attach R16 and R17 there, instead of attaching them to ground. Tying the heater (by way of the 100R's to the cathode lifts the heater a little more above ground level, plus it's ready for an EL34 with the cross tie between pins 1 and 8. This really isn't necessary unless you have hum problem that you can't seem to resolve, but if you do, it'll pretty much kill any remaining heater hum and doesn't seem to change the tone one bit.

 

Gil...

Link to comment
Share on other sites

Thanks Gil, that's basically exactly what I wired up; however, shouldn't you ground 1 (suppressor grid)? Also should I ground it to the power transformer or to the alternate ground path? I think it goes to the PT because it's output stage (yay 2 point star)....

 

http://www.sewatt.com/files/sewatt/Octal.pdf See pin 1 (suppressor grid)

 

Edit: Oh I see your notes now. Not sure about the diagram you linked but nice notes. Do I still need to ground Pin 1 if I tie it to Pin 8, or can I leave that ungrounded and let it run through the Cathode to ground?

Link to comment
Share on other sites

Either way is fine. There are a zillion ways to skin the cat.

 

I opted for method 2, where you tie pins 1 and 8 together and run the center-tap heater resistors there, because:

A) the suppressor grid is normally tied to the cathode in all those other tubes anyway, and

](*,) it killed a hum that was bugging me, so now I just do it that way from the start.

 

Gil...

Link to comment
Share on other sites

In the case of the input jack ground' date=' it is the farthest point

upstream from the power supply, so it should be connected directly

to the ground point of the first cathode resistor. If you give it an

alternate path to ground through the chassis, it will be influenced

by ground currents in the chassis.

[/quote']

 

Should I connect to C5(-) (where R14 connects to the wire that runs down to ground) and take advantage of the capacitors filtering the ground path; or connect right at the ground point by the diodes? Do you have an opinion? The input jack is grounded to the chassis on the diagram they sent me.

Link to comment
Share on other sites

Ah I see, I want to connect it to where R8 reaches ground. First cathode resistor is the first gain stage cathode resistor, which is R8 (coming off Pin 3 of the 12AX7, first gain stage cathode). So I want to connect it to the same ground point R1 is connected to, which is an additional solder lug on the chassis now.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...