18Watt.com

Just started an 18W tremolo combo build.
Mojotone chassis and parts kit, GDS xformers.
Will be using a Sourmash cabinet.

Initial heater and AC power wiring in place. Not yet soldered - wanted to get some review on what I’ve done so far before soldering

Heater wiring:
red to p4,p5 preamp tubes, p4 EL84s, p5 EZ81
black to p9 preamp tubes, p5 EL84s, p5 EZ81

Mains wiring:
White: live (hot), black: neutral, green: chassis earth

Grounds: AC main, heater CT, dual cap all grounded to solder tabs at screws on corners of PT

Photos attached.

Comments/criticisms welcome!

my thread regarding soldering (in my signature).

I'm guessing/hoping maybe you didn't bend the leads on the solder lugs yet because you were looking for feedback first. That mechanical connection is important on all solder joints when possible. Solder lugs are always possible.

Your preamp heater wiring is sloppy, and you need to tighten up the twists, especially going to pin 9.

You don't have to do the same method as me for the preamp wiring, but it should try and be as clean: Thanks,
Josh

Use a cordless drill to tighten up the heater wires. Plenty of videos on YouTube.

Josh - appreciate the feedback

>maybe you didn't bend the leads on the solder lugs yet because you were looking for feedback first

That’s correct - I wanted to make sure I had things as clean as possible before securing mechanically and soldering.

I like your technique of routing the wires over (well, under, actually) the socket base. Makes it easier to keep the twists tight and minimize loop area. Will revise what I’ve done and see how clean I can get it.

Jim

@Rvaughan68,

I did use a drill and vise to twist the pairs (the only way to do it well, really).

The fact that I was trying to route around the socket, and the thickness of the insulation on the 600V wire (overkill++!) are what caused the relaxation of the twist and the sloppiness.

Redoing the preamp tube heater wiring to route over (under, really) the socket base, not around, as Josh showed in the above pic (and as recommended by Morgan Jones and others)

Thanks for the comments and advice, though.

jimoreilly wrote: ↑

Mon 05/20/24 10:14 am

@Rvaughan68,

I did use a drill and vise to twist the pairs (the only way to do it well, really).

The fact that I was trying to route around the socket, and the thickness of the insulation on the 600V wire (overkill++!) are what caused the relaxation of the twist and the sloppiness.

Redoing the preamp tube heater wiring to route over (under, really) the socket base, not around, as Josh showed in the above pic (and as recommended by Morgan Jones and others)

Thanks for the comments and advice, though.

I use PTFE coated 20AWG wire. The insulation is thinner, and the wire is stiffer, so it's easier to work with. I also love employing heat shrink wrap whenever helpful.

My heater wiring method is as recommend by Merlin: https://www.valvewizard.co.uk/heater.html

I'm obviously not the only one to copy it.

Thanks,
Josh

Heater wiring is one of my favourite challenges too. I learned from Josh, though I developed my own thing. The current build was a challenge too. It’s a chassis with the tubes pointing down at the side panel.
Oh yeah, if you noticed the octal socket at V2 … it’s a Vibro King with a 36 watt power amp. It has a reverb tank built in, in front of the actual amp.

And this

Bieworm wrote: ↑

Mon 05/20/24 3:37 pm

And this

Look great, but some of the tubes would be happier with 1 or 2 twists going to the socket, or shrink wrap, etc. to keep it stable. Consistency.

JMPGuitars wrote: ↑

Mon 05/20/24 3:44 pm

Bieworm wrote: ↑

Mon 05/20/24 3:37 pm

And this

Look great, but some of the tubes would be happier with 1 or 2 twists going to the socket, or shrink wrap, etc. to keep it stable. Consistency.

I ran out of small zip ties. It will be fine after that

Latest iteration of heater wiring, following advice of Josh (above), ValveWizard, and others. Tightened up the preamp tube heater wiring - comments welcome!

Also would like comments/critiques of grounding. The heater CT is grounded at the upper left corner of the PT; the AC receptacle ground is grounded at the lower left corner of the PT; the HV secondary CT is grounded at the ground of the 32uF/32uF can cap. Should I run the heater and HV secondary CTs to that same point?

First photo is preamp tube heaters
Second photo is power tube heaters
Third photo is rectifier heaters and grounding (AC power receptacle, heater center tap, and HV secondary center tap)

Keep in mind I have not trimmed the wire ends nor soldered yet - I wanted to get this as clean as possible before doing so.

Next time, though, I’ll use wire with thinner insulation, to make the twisting easier - no need for 600V-rated insulation on heaters! I believe Josh mentioned PTFE - I used PVC-insulated 20AWG.

Definitely improving, but still needs some work. Take a closer look at Bieworm's wiring close ups. You can see how the color coded wires are independent of each other and twisted tighter together going to the sockets.

Heater wiring: definitely improved as Josh said. Only nitpicking would be the side of the transformer you pass. I would have taken the other side. That way these wires never come close to any DC and signal wires.
About the grounding. I don’t understand why people are still using the transformer bolts to attach ground wires. Believe it or not, a transformer is considered to be a moving part (vibration = movement). Never ever attach grounds on moving parts. That includes jack inputs for speakers too. Those neutrik metal inputs are often used as ground connections for the speakers. On most Fender amps this is the case. This puts your OT at risk.
All grounds you mentioned are preferably attached to the negative side of the 1st filter cap. I usually elevate my heater wiring by connecting the centre tap wire to positive side of the cathode cap of the EL84 tubes.

Watch out copying my heater wiring. I use 6N2P preamp tubes instead of 12AX7 types. The pinouts differ.

See also my ground scheme thread in my signature.

> still using the transformer bolts to attach ground wires.
Thanks to Bieworm for reminding us (me!) of things we know but allow ourselves to forget.

Have redone the grounding using solder tags NOT attached to transformer bolts; power outlet ground has its own connection; first power filter ground and center taps of heater and HV secondary all grounded at 32uF/32uF ground.

And per Josh’s comment, have rerouted the heater wiring around far side of PT. See first photo

Have also done the best I could with twisting the heater wires together at the preamp sockets. See 2nd photo.

As before, nothing soldered or trimmed yet - that comes next.


As always, comments/critiques appreciated and welcome.

While probably just fine as it is now, I would run the heater wires from the left side of the PT straight down to the lower chassis wall. Then straight angle to the right towards the tube sockets, keeping it in the corner. That’s the only way to avoid DC coupling.

I don't remember commenting on the heater wiring from the PT. If I did, I would have mentioned that I install the PT the opposite direction as you did to shorten the heater wiring. I also generally prefer SS rectifiers, and I can go PTP to the standby switch easier that way.

The heater wiring does look better, but you could still improve the power tubes if you choose to.

Also, one word of advice… since the hole for the cap can doesn’t perfectly align with the capacitor itself, I would rotate the cap can so that the negative lug is nearest to the edge of the hole. Thus gives the hot lugs the most clearance and you avoid possible arcing. Just a precaution.