Pot position in the layout - on tube side or in the opposite side of chassis ?

[kagliostro]

Which is your opinion, is better to have the pot on the same side of the tubes (like in Doug's Stout)

or is better to have it in the opposite side of the chassis reversing front and back ??

I refer to this layout



Thanks

K

[HotBluePlates]

... is better to ...

It depends. Whichever position gives the easiest, shortest, most-direct wiring is probably best.

But you still have to consider the size of the chassis and position of transformers. A small chassis may force the transformers to take up the rear of the outside of the chassis, pushing the tubes forward towards the pots.

A lot of layouts you might call "sub-optimal" have been used in different commercial products for reasons just like this.

[MakerDP]

Too many signal-carrying wires crossing the heater wires IMO.

[HotBluePlates]

Too many signal-carrying wires crossing the heater wires IMO.

In practice, that's not a problem, especially with a well thought out wiring scheme. I could show a pic of the preamp of the last amp I built where everything is fairly close to the heaters, but the orientation of all wires is such there is no hum pickup.

[kagliostro]

Thanks HotBluePlates & MakerDP

actually the version without bells and whistles of the circuit was simpler and gave me no doubt



this version with additional features, probably needs to review the position of the potentiometers

moving them on the other side of board

Franco

[EL34]

The chassis determines that
Either way is fine if you lay out your wires correctly


Both ways can be a problem for sloppy layouts

[kagliostro]

Thanks Doug

Franco

[kagliostro]

The amp has some lights and bells added from my friend and so the number of pot and wires increased

I tried to perform a better layout moving the pots on the opposite side of the tubes, doing that I obviously moved the IEC on the back panel







here the schematic



Do you think that this arrangement may be fine or the position of PT and OT can be a problem ?

Any council ?

Thanks

Franco

EDIT: here you can download the Visio .vsd file

http://www.mediafire.com/view/6657fu25wizxdi9/8-9_Cylinder_Layout_05_LarMar.vsd

[TIMBO]

Hi K, I think you have to consider VENTILATION/ SEVABILITY (is that a word  ) in your layout.
Some of the old amps I have, the tubes have been put in convenient position in the circuit but the layout have them wedge in an inaccessible position behind transformers.
I think it depends on how many tubes you have and the heat they generate.

[kagliostro]

Ciao TIMBO, Thanks

the tube that is more near the PT is the rectifier and it is at ~20mm distance

the tubes are on the back side of the chassis where the cabinet will have a window for aeration purpose

I'm wondering if the transformers, that are up a portion of the board, can be a problem or not

Franco

p.s.: I edited the previous post and attached a link to the Visio .vsd file

[sluckey]

I'm wondering if the transformers, that are up a portion of the board, can be a problem or not

I think they will be OK.

[Jim Coash]

I am dealing with a similar problem wright now in my current Plexi w/hot switch build.  The Masco MA-25 chassis I am using is tight for the board I made from Doug's plan.  The tube cutouts on the chassis are directly behind the front panel in a row parallel to it except for one of the EL34 tubes which is directly behind the other.  The two transformers are close to the back panel on either end.  I have kept the wiring as isolated as I can but space is limited and the board is sitting on two standoffs, close to the front panel making the leads from the pots short but the three 12AX7 tubes are actually under the board.  In order to make the board "hinge" up and over the front to access the tube sockets I must make some of the wiring long enough to permit that.  The two shielded wires are very short, the heaters between the bottom of the board and the tube sockets, the five filter caps along the sides and front of the chassis and I have tried to keep all signal wires as far from A/C as I can.  I am a little worried about the likelihood that I will have some hum issues.  Jim

[sluckey]

Franco, concerning your pot position, we don't often get the chance to post such a comparison, but here goes. As you know, Doug and I both recently built a Plexi 6V6 amp, same schematic, same size chassis. He put pots on the same side with tubes, I put pots on opposite side. Here are pics of both. This should help you decide which layout you prefer...

[kagliostro]

Thanks Steve

do you thinkI must use a shielded cable to connect the volume pot to pin #2 of the PI ?

---

@ Jim Coash

The initial version of the amp was simpler and there were less wires, so the version with the pot on the same side of the tube was near a must

but my friend decided to add some features and the number of wires was increased, giving me some doubt about the feasibility of the thing

without encounter noise problems, so I decided to move the pots on the opposite side of the chassis

---

I didn't use a chassis with fixed measures, I decided to build my own chassis, only I would like to have it the strictly indispensable long

so I asked about the PT and OT position; to me it will not be a problem to increase the chassis in lenght (if I do before I build the amp)

Thanks

Franco


EDIT: Steve we posted at the same time

[kagliostro]

Steve, all is around the board lenght, my layout has a long board and PT and OT are up a side of the board

OK there is the chassis in the middle that acts as a shield and, more, PT is up to the PS section of the board

and OT is up to the Power section of the board

I can build a longer chassis if necessary, but I didn't want to do it if I can go with a shorter one

What do you think ?

Thanks

Franco



p.s.: Oh, my transformers aren't laydown version

[sluckey]

do you thinkI must use a shielded cable to connect the volume pot to pin #2 of the PI ?

I would.

What do you think ?

I think it's... Hmm, now what did I say earlier?      

[Jim Coash]

My project amp looks much more like the top version.  The big difference is that the board is actually right over the three 9 pin tubes, with about an inch of clearance.  The amp will be used with tubes up and I have placed a small boxer fan over the now empty multi-cap can hole for some forced air ventilation.  It is a 9 volt unit and is now using the un-needed tube rectifier 5 volt tap with a diode to make it DC.  It runs at about half speed and is dead quiet.  My board will lift up and over the pots on the front panel without disconnecting any wires but that means that some of the wires, mainly from the tube sockets, are a little longer than I would like.  I could shorten them a lot by having them tie into the board from the back side instead of the front.  That would make access to the tube sockets very difficult.  With all wiring running under the board to the front panel and then over the board to the back where the connections are is the problem.  The shielded wires are very short and so are all the filter cap wires.  The tube socket wiring is where the extra length is.  I'm hoping it works when I'm finished and that it is quiet enough.  This will be my most ambitious project by far to this point.  I even plan to attempt starting the amp up without help from my tech friend.  I do now have a Variac and an isolation transformer.  The Eico 1078 should allow me to watch current draw carefully while applying A/C for the first time.  I will be crossing my fingers!  Jim

[kagliostro]

I think it's... Hmm, now what did I say earlier?

Yes, you are right Steve, you told it previously

I'm wondering if the transformers, that are up a portion of the board, can be a problem or not

I think they will be OK.

Previously I forgot to say that is possible to have a longer chassis

Thanks

Franco