Mesa Boogie Nomad 55 OT

[Wombaticus]

Hi All,

I’ve got a Mesa Nomad 55 on the bench with a dead OT. I’ll be dammed if I’ll pay MM $170 for their drop in replacement. Presumably this is a fairly standard 50W class PP OT. It’s a standup style. The amp can take either 6L6s or EL34s. Mesa part # is 562051 - I think they use it on several other amps. Anyway, does anyone have a line on a replacement that has the right mounting screw dimensions (apologies, I forgot to measure these before heading home)? And does anyone know what the primary impedance might be?

Thanks,

Paul

[Enzo]

What does Mesa want for one?

[drewl]

You could probably find a generic Fender OT that will do the job.
Check the specs of the expensive replacement and find one similiar at a reasonable price.

I have an old hybrid Peavey Classic with a bad OT.

Found a few that will do the job without costing too much.

[The Dude]

^^^^^^ Yep. You can buy a lot of drill bits for $170.

[Leo_Gnardo]

What Enzo said. ^^^ Call Mesa for a price. They've always come through for me, and kept prices very reasonable. Shipping - I can't help you with. FDX & UPS have the world by the short hairs on that one. OW!

Just don't call on a Friday. They're all out surfing.

707 789 3324 Richard Duvall - Service Department - I hope he's still there, I haven't had to call for a couple years.

If you can't score the OT from Mesa, this ClassicTone oughta do very nicely:

https://shop.amppartsdirect.com/Proj...1-40-18091.htm

[Wombaticus]

Leo,

Spoke with Richard -- good advice, and thanks for the number! Unfortunately they want $130 + shipping for the (fairly dinky) mesa OT.

So... trying again here to get answers to the very specific questions I care about.. does:

1) anyone happen to know the actual primary impedance of the Mesa transformer?
2) Does anyone know the mounting hole dimensions? (Yes, I'm trying to save myself a drive down to the workshop).

Cheers,

Paul

[Leo_Gnardo]

Leo,

Spoke with Richard -- good advice, and thanks for the number! Unfortunately they want $130 + shipping for the (fairly dinky) mesa OT.

So... trying again here to get answers to the very specific questions I care about.. does:

1) anyone happen to know the actual primary impedance of the Mesa transformer?
2) Does anyone know the mounting hole dimensions? (Yes, I'm trying to save myself a drive down to the workshop).

Cheers,

Paul

Primary impedance - you should have asked when you called Mesa. Know? I don't, but if it's compatible with both 6L6 and EL34, you could look at other OT's that are recommended for use with those tubes and take an educated guess from them. FWIW I have on occasion installed EL34 in Fender amps, no change of OT, they ran fine and in most cases gave a boost in power around 20%. Maybe someone has an exact answer for you. But I'd say, don't sweat it, find an OT that fits and go with it.

Mounting dimensions - again, Mesa would have the answer. Unless someone here happens to have a Nomad ready to hand.

If Nomad's OT is "dinky" as you mention, it's possible the OT I recommended won't fit. Oh well, the search goes on.

Not many cheap deals available when it comes to transformers, that's the way it is.

[Helmholtz]

4k primary impedance would be a good compromise between typical/optimal values for EL34 and 6L6 at 400V to 500V plate voltage.

But I would like to check with the circuit: Please post schematic.

[Jazz P Bass]

4k primary impedance would be a compromise between typical/optimal values for EL34 and 6L6 at 400V to 500V plate voltage.

But I would like to check with the circuit: Please post schemattic.

boogie_nomad55.pdf

[Helmholtz]

Unfortunately the link doesn't work.

I would like to mention that in very rare cases a differently constructed OT having different primary self-capacitance and leakage inductance can cause HF instability at certain amp settings. So I would be willing to pay a little more for the original.

[Enzo]

Just thinking about it from the other direction, how much do you think a new OT ought to cost?

[Helmholtz]

Just thinking about it from the other direction, how much do you think a new OT ought to cost?

You're not asking me?

(I'd probably order the drop-in Mesa OT and explain to the customer that a cheaper generic OT bears some risk. I've measured Mesa OTs and found them to be good quality. Don't understand what "dinky" means in this context.)

[Leo_Gnardo]

You're not asking me?

(I'd probably order the drop-in Mesa OT and explain to the customer that a cheaper generic OT bears some risk. I've measured Mesa OTs and found them to be good quality. Don't understand what "dinky" means in this context.)

Enzo's is a very good question and I'm sure directed at Wombaticus. "Dinky," apparently Mesa's OT looks compact compared to other OT's claiming similar power handling. My view, if there's not enough space on the chassis to fit a larger replacement OT then your only choice is to buy from Mesa.

[Dave H]

But I would like to check with the circuit: Please post schematic.

Boogie_nomad55-1.zip

[Pedro Vecino]

It has a somewhat complicated location and is fixed only at two points, but I would measure it to find a substitute.

Like this for example:

https://www.hammfg.com/files/parts/pdf/1750M.pdf