Advice on placement of wires

[dude]

This conversion, pic below, every things a little tight.

I have a few question on placement of wires, I'd like to keep the amp as quit as possible.

The OT is on the opposite side of the power supply and 6V6s, where's the best place to run the OT primary to B+? along the side of the chassis..? and the OT plate wires are a ways from the 6V6's, twist them or not, run along the chassis below the tubes..?

The presence knob is next to the toggle S/B switch, not wired yet. I was going to run a 47K R off the leg of the 8 ohm tap on the speaker jack to the pot, can I run that wire under the bd., if so what should I avoid running it near?

The populated bd has nothing soldered yet. I know that 200 ohm sag R is just hanging off the stand by over the bridge R, (gets hot and not real secure as least yet) is that a problem for hum? I was going use a few tie downs to make sure nothing touches that sag resister.

This is a conversion from a Crate VC20, I know I've been asking a lot of questions and appreciate all the help.

The amp is a version of an 18 watt TMB with 6V6s, I used Mark Huss's schematic and the 18 watt el84 schematic too. I don't have a schematic draw up yet with all the changes. I lot of them came from Stuckley's amps, hope that's ok, I means some values.

Any help on the routing of any wires, please let me know. I'm going to use a bar grounding system and run everything to one ground point. Preamp on one end running up to the power section then that going a ground under the filters, to the standby I have a few solder tabs there. So one ground point near the power supply, it's under the filters.

thanks as always,
al       

[eleventeen]

Personally, this is a case where I'd run all the OT wires on the outside of the chassis. I would rotate the OT 180 degrees and have the wires come out of the OT on the other side of where they appear to come out now. (only affects lead length) Drill a new hole and have the OT wires come into the chassis a tad to the right (as viewed in your pix) of the output jack, betw said jack and the fusepost. I like to find a length of jacketed cable or go buy a nice thick piece of clear plastic tubing and run all those wires through a very protective jacket, couple of nylon cable clamps along the way to control the routing of that bundle of wires on the outside surface of the chassis.


Twisting the output tube wires is neither here nor there IMO...if you twist them all the way to the OT it will INCREASE the size of the bundle of wires whether you run them inside or on the outside. Be sure you ascertain which 6V6 gets which OT primary lead (blue, brown) in other words, the phasing of the OT, before you spend time making those wires pretty inside the chassis. Since there is no way to predict how this will turn out , leave the leads long, tack solder them to the plates, pin 3/pin 3, and get your phasing right. It looks like you'll be having to splice the OT wires, which is fine. Make those splices really sound, use decent, fat wire to extend those leads. I reco 18 ga or better. Remember, those wires carry 400-450 volts. Another good reason to enclose any kind of bundle in a plastic tube of some kind. I modded a Princeton Rev to take a 35 watt tranny and it is all the way at the far end of the chassis, with all the OT wires on the outside of the chassis, exactly as I am describing. Been working fine for 35 years.



Looks pretty good! Wire those filaments before you mount the parts board, I know you know that, make your work a lot easier.

[sluckey]

The OT is on the opposite side of the power supply and 6V6s, where's the best place to run the OT primary to B+? along the side of the chassis..? and the OT plate wires are a ways from the 6V6's, twist them or not, run along the chassis below the tubes..?

I highly recommend that you move the OT close to the output tubes, right next to the PT.

[eleventeen]

"I highly recommend that you move the OT close to the output tubes, right next to the PT."


Sometimes this can create an interference problem with the spider or magnet of your speaker. This was the reason I mounted the OT all the way at far end of the chassis....but, I was using an Altec 417-8H speaker which has a very deep spider and a big magnet relative to most speakers I see today. This can be very difficult to predict, you have to physically test whether or not it will fit. BUT if you have to change it after you've built the amp...it can be quite irritating.

[HotBluePlates]

And if that is your speaker jack right next to the preamp tube sockets, I'd move that as well. Meaning, move the (added?) fuseholder to a better spot, and put the speaker jack in the hole where the fuseholder now sits. That would allow OT wires to go in and out of the chassis through holes right by the output tubes.


I think you'll be flirting with the oscillation issues in this thread with the setup you are going towards now.

[dude]

The problem is the cab is small, one ten and the speaker magnet is about 1 1/2" from the center of the chassis, that's why you'll see in this picture that I drilled the tubes on the bottom side of the chassis (they would have hit the speaker). That sheet metal is covering the el84 holes.

I had to put the OT to the opposite side, (fits between the speaker magnet and PT on the other end. I can switch the fuse holder with the speaker jack and get it away from the preamp tubes, easy.

But I don't like running the OT center tap outside of the chassis, voltage with this PT is low, (brown tone plexi) about B+320. Can I run that center tap under and alongside the tubes sockets along the chassis, running right on the crease wit hthe plate wire too ,same spot. If I have to run the OT outside to prevent noise I will but I don't have any material to protect those high voltage wires at the moment.

I know from experience that OT sec. can cause problems running under the bd. I don't mind running the 8 ohm tap out side the chassis. but as far as the plate wires, I'd like to keep them inside if posssible.

You can see from this picture that the OT wires are over a bit and they were just push over to the side of the bd.

Maybe this picture without the bd. will help some.

What about the presence knob, can I run the neg feedback wire under the bd. to the presence (next to S/B) from the speaker jack?

Thanks,
al

[HotBluePlates]

I hate to be pessimistic, but I think this may be foolish economy shoe-horning things in where they don't really fit. Bottom line, if you have to put the fuse holder where it doesn't belong, and the speaker jack and OT wiring near the preamp, then I believe you risk oscillation problems. You may get the whole thing done to find it just won't work within the space limitations.

You may save more money by assembling the amp the way you know it will work, rather than having to pitch everything after it's completed and you find you can't make it work.

I don't mean this to be a knock on you; I've learned the hard way by making this mistake myself.

[sluckey]

What about the presence knob, can I run the neg feedback wire under the bd. to the presence (next to S/B) from the speaker jack?

yes

[TeslaRect5150]

Hey al,
The OT placement could put a hitch in your giddy-up. The first amp I built had the OT and PT on separate sides of the chassis. The amp was a noisy screeching bowl of spaghetti, and it didn't matter how much chopstick wire bending I did. The amp was rebuilt using the OT next to PT method sluckey suggested. Those OT wires running across the inside of the chassis is bad news in my experience. Like previously mention, could have oscillation issues. I think Eleventeen had a good suggestion running the wires outside of the chassis (and wiring those heaters up). I have never done this personally, but I think it would be a good way to finish this particular amp. You may even have to move the bundle of wires around on/off the chassis to get it to work out right. Maybe mounting the OT off the chassis, bolted to the inside side of the cabinet (not the speaker baffle, but the side) under the PT would work. This moves the OT away from the preamp, but doesn't make the wires any shorter. At least they would be away from the preamp tubes all together.

NFB wire is usually one of the last wires I put in. So that I can decide where the best place in relation to all the other wires. I usually keep it tight to the chassis and the furthest way from anything it comes close to. If I have to cross a wire, I'll cross it at a 90 degree angle. Each amp is it's own animal. I've thought for hours (believe it or not) about where to place wires, placed them thinking they were in the right spot, just to move them to the BEST spot when the amp was done. Of course use something non-conductive to push wires around and be super careful.
As far as the sag resistor goes. If you are second guessing the reliability/safety aspect, change it. Would you feel comfortable leaving it on for a couple days while your out of town? Risk of burning any other components or your house down? These are things to consider. A little extreme...I know.
 Making good mechanical connections before soldering is always good. That way you know if it gets hot enough to soften solder or burn other components, the component itself won't move at all. Maybe you could fit another terminal strip down in there to mount it on. You could also move the AC fuse to the front panel next to the power switch and if you have enough room on the front panel, put a B+ fuse next to the SB . That will give you some tie points in that area to wire to, and a fuse on the B+ never hurt anyone. Or a normal/SAG switch.
Grounding still throws me for a loop..hehe. This website helped me though, http://www.valvewizard2.webs.com/Grounding.pdf

Good info about lead dress in tube amps. Other good stuff on that site also.
http://www.geofex.com/Article_Folders/lead_dress/lead_dress_in_tube_amps.htm
http://www.geofex.com/Article_Folders/pt-to-pt/pt-to-pt.htm

Just my .01 cent.
Hope it turns out well Al.

-Aaron

[dude]

And if that is your speaker jack right next to the preamp tube sockets, I'd move that as well. Meaning, move the (added?) fuseholder to a better spot, and put the speaker jack in the hole where the fuseholder now sits. That would allow OT wires to go in and out of the chassis through holes right by the output tubes.


I think you'll be flirting with the oscillation issues in this thread with the setup you are going towards now.

I can't believe it, I lost my post by not looking looking at the attachment size before I posted, 

Anyway, I said I thanked everyone for the info and will follow your advice.

How about this:

I can't move the OT, the Crate VC 2010 cab is so small this is the only place it will fit without hitting the back of the speaker.

Switch the fuse holder and speaker jack, Run the OT wires outside the chassis along the bottom, primaries and sec separately. encase them in a plastic chase like used for stereo speaker system, use tie downs to secure the wires to the bottom of the chassis. Drill holes near the 6V6s for the plates and B+ which is close to 6V6s. Sec. OT wires to speaker jack and use the grounding system below? Can I twist the plates and OT primary together to there home, keeping the sec separate?

Is this a plan?

al   

[HotBluePlates]

I think that will work a lot better.

[dude]

I edited my post above, can I twist the OT primary CT and plate wires together under the chassis keepin gthe sec away from them?

HBP, thank you - eleventeen and Sluckey thank you guys too, Ive learn so much from you guys. I'm just a player who loves tone.

al

[eleventeen]

My opinion is: I don't think *anything* you choose to do with OT leads (only considering the OT leads themselves) will have any perceivable effect. Yes, if you run them next to preamp stages, effects loop jacks, certainly you can get into feedback issues. We've established that. Run them next to low-level stages whose output signals gets amplified, it stands to reason that radiation from those leads can leak into the preamp and cause problems later on in the amp.


In ancient times, remember that on a field-coil speaker where the field coil acted as the power supply choke, it was common practice to run only-one-cap-filtered B+ right out of the rectifier to the "choke", generally unshielded, the choke output back into the [radio]......while the B+ lead(s) feeding the output tube plates ran to the OT, mounted on the speaker frame. All in one bundle, no shielded cable or anything like that! For sure, lowest-possible hum and noise was probably not the prime directive for a mass-produced radio set, but if these tended to cause unacceptable problems, that scheme of things wouldn't have been used. The same scheme was used in expensive floor-standing upright radio sets too. Plus, in a push-pull config, noise et al tends to be cancelled. So my conclusion is that twisting or not twisting OT wires is a nothingburger.

[dude]

Thanks, eleventeen.

Hope I'm not driving you guys crazy just that I have had oscillation and squeal before but I was lucky that chop sticking solved the problem but I've tried to help friends and no chop sticking could fix their layout, things had to be moved.

Anyway, I'm at the last of the questions before the solder comes out.

In the pic's below, I'm using a MM OT from a tweed deluxe the ground is soldered to the case. If you look at the other picture of the layout for the grounding scheme I'm using, there is only one star grounding point for all. Preamp on up to power supply to that ground. I don't want a ground loop. Will that soldered ground (the only ground on this OT, bare coil copper wire) cause a ground loop? The yellow wire is the 8 ohm tap. The OT is bolted to the chassis at the opposite end from the one ground point, that makes two grounds points, a loop, hum...?

Should I isolate the OT from the chassis with shoulder washers and run that ground to the one main point near the B+?

thanks, al

[eleventeen]

Should I isolate the OT from the chassis with shoulder washers << No.

and run that ground to the one main point near the B+? Maybe. Probably better to just take it to the speaker output jack*and* from there, to your central gnd. 

[dude]

Should I isolate the OT from the chassis with shoulder washers << No.

and run that ground to the one main point near the B+? Maybe. Probably better to just take it to the speaker output jack*and* from there, to your central gnd. 

That's the way it is in the layout I posted, thanks. On with the solder.

al

[PRR]

If anybody does run the OT primary wires outside the chassis:

I did that, once. It was Tweed-like build where the chassis "top" faces the speaker board so it is very unlikely someone will reach in and up and get near the wires. (However I was running 560V.)

In any case, I'd also extra-insulate. Find that heavy-duty outdoor extension cord you ran over with the mower. Cut off a foot or so. Pull the wires out of the jacket. Thread your OT leads in there. Use several wire-clips (Doug stocks them under "Fuses/Cords/AC", called "Power cord clamp") to keep the cable snug and un-snagged.

[eleventeen]

That's almost exactly what I did. At Home Depot or any hdwe store, you can buy clear (or black) plastic tubing with up to 3/4" internal diameter. It's nice because the wall thickness (once the ID is up to 1/2"+) is pretty thick. It's not that it is electrically rated at anything in particular but it is an excellent physical guard for that exposed bundle of wires carrying your B+. And don't forget---you are going to have splices in those wires 3-4-5" away from the OT. In the case of big volts, I like to both heat shrink some tubing over the splices AND find some shielded cable where you can slip the outer jacket over those splices. Enclose the whole thing in your thick plastic tubing and you are good to go. 


Incidentally---that clear 1/2" ID tubing cut into about 2-1/2" lengths friction-fits over a fusepost magnificently and insulates the side and rear (if you leave it long enough) terminal on a fusepost beautifully. Yes, you can use heatshrink but heatshrink doesn't impress me that much in terms of its abrasion-resistance and of course you can only take it off and replace -without unsoldering then resoldering the wires it in rare cases.

[dude]

Threw out the extension cord my wife mowed over, .

But I came up with this idea from Eleventeen and PRR.

It was easy to get the inside wires out but hell to get the paper out, I'd probably never use 12 gauge plastic electrical wire again cause of that paper. I had to run hot water inside to soften the paper and took about an hour to get it all out. I used compressed air to dry the insides.     "But now it's UL rated..... "

I'll post pic's when done and hopefully a mp3 and schematic of the changes I got from here.

Thanks as always,
al
 

[eleventeen]

There ya go. Looks fine.