Output Transformer Question

[Salty Dog]

I'm building a Mission Amps 5E3. It is going in a cab featuring two 8 ohm speakers. The output transformer does have a 4 ohm tap, but I heard it said somewhere that you get better tone if you use all of the output winding (8 ohm lead).

How much difference in tone would there be between the two?

If there is a noticeable difference, would a viable alternative be to wire an 8 ohm speaker motor (less cone) in series with each speaker, then wiring the speakers in parallel, so that the OT sees an 8 ohm load?

Thanks in advance.

[rudutch]

I did notice any 'tone' difference, I do think the mis-match may shorten tube life. The OT is would for 8 or 4 ohms, I'm sure Bruce had a reason for this when he spec'd it

http://www.missionamps.com/PRINTS/MA59.pdf

[ziess]

I've *heard* that. Once.

Personally I'd get it buckled up and then see how it sounds. Is it a 2x10" cab or a 2x12"?
You could always change the OT to an appropriate type that would present the power tubes with 4Ω at a later date if you want.

Tommy.

[Salty Dog]

Tommy, the cab has a one 12" and one 10" cutout. I already have the 12" speaker, a Weber Blue Dog, 8 ohms. And I assume the 10" speaker I buy should also be an 8 ohmer.

[steve25]

Yes, for a 4 ohm total load wire 2 8 ohmers in parallel.

[cdw2000]

You could always change the OT to an appropriate type that would present the power tubes with 4Ω at a later date if you want.

Tommy.

His OT does have the proper 4 ohm tap... There should be no problem with tube longevity at all provided he uses the 4 ohm tap with a 4 ohm load. I agree that using the 8 ohm tap with a 4 ohm load *could* shorten tube life, unless you modify the bias appropriately. This involves drawing load lines and such and determining the appropriate plate current from that, etc...

Regarding tone - yes the tone will be different. It's impossible to say if it will be better or worse, that's up to your ears. The speaker itself will probably be the biggest cause of any tone change. Even if a certain speaker is available in both a 4 ohm and 8 ohm version, they will sound slightly different.

Regarding connecting a coneless speaker motor assembly in series with each speaker to maintain 8 ohms - I think you may find this too lossy (unless you want to reduce the output of your amp). This also has secondary impedance effects that will differ from presenting a normal 8 ohm speaker load to the amp (the interaction of the motor circuit to the cone also affects the dynamic speaker impedance).

I say, just hook up your two 8 ohm speakers in parallel to get the 4 ohms, use the 4 ohm tap and if it sounds good to you, it IS good.

The other option is to buy 16 ohm speakers and connect these in parallel... again it's impossible to say if this will improve things to your ears.

You can drive yourself buggy with all the options.

[ziess]

His OT does have the proper 4 ohm tap...

Yeah man, I meant that if he felt his tone could be improved by using all the OT secondary winding rather than the 4Ω tap then he could swap the OT for one that will show 4Ω only.

I say, just hook up your two 8 ohm speakers in parallel to get the 4 ohms, use the 4 ohm tap and if it sounds good to you, it IS good.

That's the best advice you're gonna get.

Tommy.

[Kap'n]

IMHO, impedence matching has a greater sonic impact in a 5E3 or other open loop amp than it does on one that has negative feedback.

[Salty Dog]

Thanks to all of you for your advice to this greenhorn.

Tone is the quest. And impedence matching is a necessity.
I want this to be the best amp I've ever built. Then again, it will be my first.
So I will be using all of the output coil (8 ohm lead), and hooking up two 16 ohm speakers in parallel. And buying two speakers will require selling a 2002 Gibson SG Special (with crescent moon inlays and ebony board) ... should anyone be interested.

[rudutch]

mission amps are great, you should achive fine results