Changed power tube layout 180 degrees. Need help.

[Mike_J]

I changed the power tube layout for the power tubes for my 5f6a build from the Hoffman method to the Fender method. Reason is the chassis has a hole for the blue and brown OT wires that is between the sockets. It will allow the grid wire to be at the bottom of the socket which will shorten the grid wire by at least an inch and probably more. I can then go to the pin four slick as can be to connect my and then pin 3 three with my blue or brown OT wire. I have my heater wires neatly tucked in the top corner of the amp, held in place by those white things that have a hole in them (will include a picture of those as well because I fear I have not explained them well), ready to do a nice loop on a two to seven axis straight to the center of the tubes and the black wire going nicely to the other side of the tube to pins one and eight.


I bet you are asking, why is this guy posting? He has it licked. Not so much I fear. My grid wires for V5 will be what I fear to be perilously close to the 50K trimmer pot. I have included a picture to show you my possible dilemma. The trimmer pot is about 3/16" away from pin six of V5. Don't know if that is a problem but someone on this forum once told me, I believe it was PRR, you don't mix dirty power with clean and I fear this may be part of what he was talking about.


Now lets talk about solutions to this possible dilemma. One, could go back to the Hoffman layout even though my chassis is designed for the Fender layout. Not my first choice, especially when the trimmer pot would be perilously close to pins two and three and the screwdriver I would use to adjust the pot is all metal. Two, I could move the trimmer pot back on the board which would have an added benefit of reducing my chances of getting electrocuted when I adjust the bias of my power tubes. I guess my question is how far do I need to move my trimmer pot away from the grid sockets, pins five and six on V5, to keep the dirty power away from the clean? Hopefully, your answer is not more than 7/16" because I have some turrets that far away holding some bias supply circuitry.


Have decided I will move the pot in any case for safety reasons. Would design a tool out of a bamboo skew to adjust the pot myself. However, once my marketing plan is in place which would of course have a mention of the bias adjustment pot and the one ohm resistors for ease of biasing in it. Then of course some poor guy that never ever looked inside a chassis would get his all metal screw driver out and meet his maker. Of course then his family would hire a lawyer and all the wealth I created with my marketing plan would go to that blood sucking attorney. Have to plan for such things and try to avoid them. Would form a corporation but the corporate vail may be pierced if the blood sucking attorney can prove gross negligence. Not something I want to risk with the wealth I am going to create from my amp sales on this single amp I have been working on for 22 years.

[Mike_J]

Oh the trials and tribulations of an amp builder. Had to remove the pot from my first attempt of creating a board for this build, at least in the last score of history. I had installed the 50K pot and nothing else on the board. Not having the sense that God gave a goat I ordered one not ten of the 50K pots like I should have because you know of all things I needed to install on the second board I created for this amp in the last score of history is the replacement pot. Now I am going to move the pot and it is soldered in.


I was concerned about damaging the trimmer pot removed from the first attempt of creating a board for this build, at least in the last score of history. I removed that pot from the first board and can now report the first pot is measuring 45.6K from tip to tip and otherwise looks like new. Maybe a win at least for now.

[Mike_J]

Does anyone else see what I see on the left side of the board below. Pure luck. Made a big space in the board for the screen resistors when before I decided to turn the tube sockets 180 degrees. Have a space to remove a turret to the left side of the pot to make room to move the pot towards the middle of the board.


Still haven't heard whether 7/16" is too close of a distance between the dirty bias circuit and the clean grid wire. I know sluckey is probably working on my marketing plan for the fancy IEC thing so I can understand why he hasn't responded. I am fairly certain I will be okay and I can probably move the pot another 1/16" away without a problem but would like the input of someone more knowledgeable than myself. I have done considerable pondering where this amp is concerned to make it a good build but this one scares me. Don't want to get everything installed and find out this is a problem. Think I might have most everything else licked.


As promised, the picture shows two of the white things with a hole in them in use. Before I turned the tube sockets I needed both of them to run the grid wires to the sockets in an orderly fashion. Now with the sockets turned I plan to use the right white thing to direct the screen supply wire.

[HotBluePlates]

... My grid wires for V5 will be what I fear to be perilously close to the 50K trimmer pot. ...

I personally wouldn't worry about getting a grid wire close to the bias trimpot carrying a d.c. voltage that will soon connect to that same grid.

... once my marketing plan is in place which would of course have a mention of the bias adjustment pot and the one ohm resistors for ease of biasing in it. Then of course some poor guy that never ever looked inside a chassis ...

If you want to sell the amp to Guitarists, better give them a screwdriver adjustment they can get at without removing the chassis or unscrewing a cover.

Probably be wise to let them go buy a Bias Probe as well, since they're gonna need to know plate voltage to calculate dissipation.  And some of them won't know which end of the soldering iron you hold, so poking a tube plate is maybe a bad idea.

[Mike_J]

... My grid wires for V5 will be what I fear to be perilously close to the 50K trimmer pot. ...

I personally wouldn't worry about getting a grid wire close to the bias trimpot carrying a d.c. voltage that will soon connect to that same grid.

You come at this from a different viewpoint than I had. I believe I would call yours coherent. Still think I may move it back a little to make it a little more accessible. I thank you for putting me at ease regarding this matter.


Sincerely
Mike

[Mike_J]

Having studied Doug's layout I see the blue dotted underboard wire going from the junction of the 220K resistors in the PI to the pot. That diode converts the AC to DC I presume and those ecaps must filter it before it reaches the power tube grid. Thereby I have clean next to clean disregarding the fact it is going there anyway I presume through the grounded end of the cathode through the one ohm resistor that we could probably call a wire for purposes of this explanation I would think or is it through the junction of the 220K resistors, through the resistors and on to the grid connection on the socket of the power tube. Probably the latter. I learned something new today I am pretty sure. Please correct me if I am not understanding this.


Thanks
Mike

[HotBluePlates]

... underboard wire going from the junction of the 220K resistors in the PI to the pot. That diode converts the AC to DC I presume and those ecaps must filter it before it reaches the power tube grid. Thereby I have clean next to clean ...

Right, that's how I see it.

The bias trimpot is carrying filtered d.c., so it's not a problem area.