Octal Tube wire twisting

Hi,

I'm thinking of building an Akido ACF Octal tube buffer

Akido ACF Octal - http://www.tubecad.com/2011/07/blog0206.htm

This would be built with a wood box with a steel plate top. I’d buy the ACF-2 Octal PCB. I was thinking of buying two surface mount octal tube sockets to mount on the top of the steel plate. I like exposed tubes. I’d be running wire from the PCB up to the tube sockets… I’m trying to sort out what wires I’d want to twist…

The ACF Octal would run 6SN7 or similar

So I’m trying to sort out what wires to twist from PCB to Octal… Like "Twist #8 with #6" , "Twist #1 with #3" etc.

This would be the pinout of a 6sn7


PS - I love my passive preamp.. I'm toying with the idea of running a passive Attenuator to this ACF unity gain buffer to two outputs.

Twist 7&8, you could additionally shield them once twisted. Run everything else as straight as possible.

How about mounting all the tall parts on the opposite side of the PCB, and mounting the board 1/4" below the panel? Sockets would be about flush, tubes would be exposed. The transistor on the heatsink is the only component that would require some thought... it may have to be offset with the part flipped.

Both posts are good advice. I have to think about both.

How do you do a simple sheilding on wire? I've got some 20ga wire... Can I do something to shield it?

For running the wire grounded... I'm thinking I can just use insulated 3 wires and twist them real well and tight. I'd use 2 wires for the heater wires to 7 and 8 and then ground the third wire to provide the shield.

The third wire to ground. I was going to build this ACF with a 3 prong IEC connect. The IEC would have a ground to my home. Could I connect to the 3rd wire ground/shield to the IEC power ground?

Can anyone help with the shielding question?

I'd connect the grid stopper resistors directly to the tube socket, not run wire jumpers from the board with the grid stoppers on the board. Grid stoppers must be physically close to the tube to be effective. As for shielding, line the wood box inside with aluminium foil, which in turn gets grounded via your tube socket chassis and to ground.

Squidward said:

Twist 7&8, you could additionally shield them once twisted. Run everything else as straight as possible.

Click to expand...

+1 ALWAYS twist the heater wires together and keep them away from all the other wires as best you can. Tuck them in the corner of the chassis.


Cheers,
Bob

bonsai said:

For running the wire grounded... I'm thinking I can just use insulated 3 wires and twist them real well and tight. I'd use 2 wires for the heater wires to 7 and 8 and then ground the third wire to provide the shield.

The third wire to ground. I was going to build this ACF with a 3 prong IEC connect. The IEC would have a ground to my home. Could I connect to the 3rd wire ground/shield to the IEC power ground?

Click to expand...

You need to use single strand 20 gage wire for the heaters. Your going to see a decent amount of current to the heaters so be sure your cable is capable of say 600V to be safe. No need for ground shielded wire here, just use best practice with 600V solid core wire (tight twist). There's HIGH VOLTAGE on that wire....shielded wire is best used for SIGNAL wiring from the input RCAs back to volume/selector pots where the voltage is very low. 350V on a signal wire and you will catch fire/meltdown and it will be fast.

Cheers,
Bob

Great advice on the wire. I'll use that bobrown14. I remember getting the heater wire into the corners on the Bob Latino ST120 amp I built to keep away from signal path.

wa2ise,
I appreciate the grid stopper resistors advice! I remember these again on the ST120 build I did. Key to have by the socket

The grid stopper resistor needs to be connected to pins #1 and Pin #4 if I'm not mistaken. correct?

I am thinking of buying an 11 ga brushed steel plate to have as a surface where I mount the octal sockets... Wood side box with a steel plate top and bottom. I could use that steel plate as a ground? Get some stand offs on the plate bottom to ground to? I'd connect the grid stop resistor to the tube socket and the other end to the ground stand off and then run a wire from the stand off to the PCB location where the resistor should be but is omitted?

Am I off?

Should I run a wire from the top plate to bottom plate to have more ground?

Sorry for the questions... I was thinking with the PCB this would be more simple...

bonsai said:

The grid stopper resistor needs to be connected to pins #1 and Pin #4 if I'm not mistaken. correct?

Click to expand...

that's correct.

I am thinking of buying an 11 ga brushed steel plate to have as a surface where I mount the octal sockets... Wood side box with a steel plate top and bottom. I could use that steel plate as a ground?

Click to expand...

Make it aluminum and you can use it as a heat sink for the transistor. Aluminum works better than steel for heat sinking. That way the heat has an easy way to escape, not be trapped inside the wood enclosure. Use heatsink insulating mica or silpads to electrically isolate the transistor collector from the heat sink, so you can ground the aluminum plate. And yes, ground the bottom plate too.

I could use that steel plate as a ground? Get some stand offs on the plate bottom to ground to? I'd connect the grid stop resistor to the tube socket and the other end to the ground stand off and then run a wire from the stand off to the PCB location where the resistor should be but is omitted?

Click to expand...

I'd run the grid stopper resistor's other end directly to the circuit board trace hole where the on board stopper resistor's "other end" would have gone. I'd use insulating tubing on the resistor lead to avoid it shorting to something. An easy way to get such tubing is to use stripped off wire insulation off some wire whose copper part is a bit thicker than the resistor lead.

Not sure which circuit you're going to use, but if it's http://tubecad.com/Product_PDFs/ACF%209-Pin.pdf you may find it easier to place R3 at the tube socket (goes between the two triode sections). And connect C2 directly to the tube socket, and the other end directly to the output RCA jack. Idea is that this makes for a few less wire jumpers from tube socket to board, thus making for a neater wiring job.

Another possibility would be to mount the tube sockets to the board using standoffs. These standoffs would be metal barrels with "female" threaded holes at both ends, about 1 inch long. Carefully drill a hole (be sure you don't cut into, or go near any circuit traces, so the mounting hardware doesn't short anything to ground, have at least 1/8 inch clearance) maybe near C7 and C8, the spacing being one octal tube socket's pair of mounting holes' apart, where the other hole is the existing corner board mounting hole. That way you can assemble the tube sockets to the board, then test it. this gives you a module you then in turn mount to the metal plate. Then cut tube socket holes with the holes for the screws that hold the tube sockets' ears to the standoffs, in the metal plate (you must measure accurately to get the holes where they should be). Then you remove the screws that hold the tube sockets to the standoffs, position the tube sockets in the tube socket holes, and then reinstall the screws back thru the metal plate, the tube socket ears, and then to the standoffs. This would allow you to remove the module as a unit if you want to work on it, without flexing any wiring between the sockets and board. Thus avoiding broken wiring. And the associated cussing. :dammit: And get to do this

Looks like there may be holes in the PCB already that would line up with the socket mounting screws. Standoffs may have to be plastic though - the holes are pretty close to some components.

A bit of a bummer.. The ACF Octal and 9PIN are out of stock - http://glass-ware.stores.yahoo.net/acpcbocandus.html. I e-mailed them yesterday to see if more are on the way. No word as of yet.

Plan on!

http://tubecad.com/Product_PDFs/ACF 9-Pin.pdf

Click to expand...

I did not see that .PDFbut it is excellent. This PDF you mention is for the older 9pin version AIKIDO ACF. I don’t see the same type of pdf for the Octal. I hope if you buy the Octal ACF PCB you get this type of document specific for the Octal ACF. The resistor values outlined for each tube type etc. Nice.

place R3 at the tube socket (goes between the two triode sections). And connect C2 directly to the tube socket, and the other end directly to the output RCA jack. Idea is that this makes for a few less wire jumpers from tube socket to board, thus making for a neater wiring job.

Click to expand...

This would be a good idea and I’ll run with that for sure… Assuming this would apply to the Octal tube type as well.

I'd run the grid stopper resistor's other end directly to the circuit board trace hole where the on board stopper resistor's "other end" would have gone. I'd use insulating tubing on the resistor lead to avoid it shorting to something. An easy way to get such tubing is to use stripped off wire insulation off some wire whose copper part is a bit thicker than the resistor lead.

Click to expand...

This makes sense and would be easier… The PCB has a star grounding and this would allow me to just run with that. I think I may try to get some sort of insulated stand off to have next to the tube.. Just so one end of the grid stopper resistor is connected to the Octal socket pin and then the other the lead wire . I’d like to insulate the lead wire end as you say and then just secure it to something.