Transformer Orientation… yet again!

[Kier]

Well I finally have the transformers for my build!
I guess this question gets asked a lot, but I wanted to make sure…

I have a 125ESE OT, which stands on top, and a 291CEX PT which lays down through the chassis, which I guess makes them off axis from each other, so does it matter which way either of them face?

Which way should the copper bands of the PT face?

Also, does it matter how close the OT is to the preamp tube?

(BTW, I never realised just how much a PT could weigh!!)

[M Fowler]

I quick answer is no since the PT is horizontal mount laydown type and the OT is Verticle mount standup the magnetic field of the coil is less; however, you should space the OT over some to make darn sure.

Some people go through the trouble of the headphone trick then mark the best orientation. I just make ample spacing. Most punched chassis already have your mounting holes. If you look on Weber website they have chassis drawing showing the spacing of the holes.

Mark

[Kier]

Ah, that’s great news then! – I’ve mounted them now at far ends of the chassis so it should be alright.

I’ve started to wire it all up now and came across something; the PT I have has an orange lead on the primary called “Shield”… do I do anything with this? There’s no mention of it in the book..

There was also a 50v tap, but I’ve already covered the end and tied it up out of the way.

Kier.

[M Fowler]

You identified the orange wire as the shield that should go to a ground tab along with any of the PT center taps.

In some PT’s that orange wire can be a bias tap, I went through that with a guy asking for help, so one never knows. LOL You covered your unused bias tap so your good to go.

Mark

[M Fowler]

You said you put the PT on one end and the OT on the opposite end of the chassis. You didn’t need to back the OT up that far! LOL But it should work just fine. Just make sure that you keep the input away from the output wires!!!

Mark

[Kier]

Oops! lol… I’ll make extra care with the in/out wires then!!

The wiring seems to be going good so far though! I have one question that I hope you don’t mind me asking…

The cab I’ve bought is 16ohms (single 12″), and I was wondering which OT wires I should use for the switch for the best options based around this output?

Kier.

[Robin]

If I understand your question, I believe the best you can do with the 125ESE is to use the white secondary tap (which would give you primary of 2500 at 8 ohms and 5000 at 16 ohms. With the single 16 ohm speaker it will be 100% mismatch, if you could add another 16 ohm speaker you could get it to 8 ohms. Fender has used 100% mismatch forever with the aux. speaker and it’s works (although not as efficiently as if it was properly matched). A better solution if you are only using one speaker would be to use an 8 ohm model.

[M Fowler]

Not sure what tubes your using but we know your going to be using the 16 ohm speaker so can we all agree that the poster should wire both the 2k5 and 5k secondary to a switch so he can hear the sonic difference between them?

EL84 forum says 2k5 for EL34’s and 5K for 6L6 but they are using an 8 ohm speaker load.

Looks like a mismatach regardless which isn’t all that bad since a lot of amps run this way and no problems.

[Kier]

Hmm, got me worried now lol! I’m not so savvy on the whole impedance thing!

I have a 6K6GT lying around, but I was planning on using either a single 6V6 or one larger one (leaning towards either 5881 or KT66 for some reason? maybe 2 x 6V6 seeing as i’ve built the 2 tube version!)
Probably just a single 6V6GT for a while until I get another job…

The reason I have a 16 ohm cab is that i’ve lost my job (shop shutting down), and as money is an issue I just bought the cheapest I could get – an Orange PPC112 with the Vintage 30 (got it for quite a good price off that auction site!)

Sometime in the future I may swap the speaker out for an 8-ohm if i find I don’t like the V30 (I was thinking of a G12M? We’ll have to see)

So should I just wire up the White and Yellow for now?
Also, can anybody explain wiring the 3 terminals of the Carling switch with 2 on one side and 1 on the other, with one being a slimmer and smaller shape? I read about it somewhere but can’t find it now!

And sorry for the long post and lots of silly questions, but I’m having trouble soldering the ground wires to the copper grounding sheet? I’m trying with a 40w iron and have sanded and scratched where I plan to solder but it just isn’t happening… the slightest movement and it snaps off!

[M Fowler]

I like to use the three position impedence switch, isn’t cheap but are very well made and versitile. System would not allow me to upload a pciture http://www.mojotone.com/amp-parts/Switches/Mojotone-Impedance-Selector-Switch

Use what tubes and speaker you have for now and wire the amp for the highest impedence.

Soldering is going to require some heat for the copper grounding shield so it takes a rather large iron for this. Mine is quite old and large unit infact I’m not even sure where it went to.

[Kier]

A 3-way sounds good.. I’ll have a look around…

So I should wire it up to use the White wire (for now at least) and run whichever valve through that then?

I would have thought a 40w iron would be hot enough? I’ll have to keep trying I guess… I only just bought this one, can’t afford another

If all else fails, could I drill a small hole in the chassis and use a screwed solder tab like that for the inputs’ shields?

[Kier]

Well, I finished wiring it up yesterday, and the valves came in the post today and I couldn’t resist trying it out

I’m very pleased to say that it works perfect first time, and it sounds awesome! (Going through the white tap into 16ohm V30)

The valves I’m using are :

Tung-sol 12AX7
Tung-sol 5881 (new re-issue)
NOS JAN 5Y3WGTA

Never had a valve amp before, but it seems a little toasty out the back? The glow is oh-so good though

I’ll tell you how I solved the soldering to the grounding sheet problem : I put the sheet on a hot radiator for a while, then while it was still on there I did the soldering! The extra heat worked a treat!

I’ve added some photos to the gallery – Don’t know how to embed them onto here though?

I can’t thank you all enough for all the help!

[M Fowler]

Glad you got it going.

[Robin]

Looking good Kier, congrats

[Kier]

Bah – something seems odd lately

The volume pot has started acting odd; hard to explain really!

The amp seems noisy, particularly the bass/lower notes sounding wrong/fuzzy?, and it’s louder than usual – even with the volume on 0 the guitar still plays out loudly…

If I put a little pressure on the volume knob, ie push it “up” a little, then the sound and volume goes back to normal and everything is fine again? but obviously something is wrong and I can’t hold the volume knob while playing!

Any ideas on this would be a great help! Also, how would I go about making a cap discharge tool to help me work on it when I need to?

[Author]

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