Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Dave on October 19, 2010, 01:25:56 pm

Title: Mesa Nomad 45 Output Transformer.
Post by: Dave on October 19, 2010, 01:25:56 pm

Hi there fellas,

Hey, I have a Mesa Nomad 45 here I am working on. It is cutting in and out, so I have to do some trouble shooting.

I noticed something I thought I would share and get comments on.

The output transformer is tiny. It is the same size as an old Deluxe Reverb transformer but it is in a 45 watt amp that runs a quad of EL84 power tubes. What gives?

Dave

Title: Re: Mesa Nomad 45 Output Transformer.
Post by: phsyconoodler on October 19, 2010, 03:12:47 pm

Ok,first off,a quad of EL84's might put out 35 watts run on the ragged edge,so it's likely about that. 45 watts is very optimistic.Some of those messy booger amps had rather small looking OT's that's for sure.
  I bet the amp would sound better with a bigger OT anyway,so go for it!

Edit: looking at the schematic it has 425v on the plates and 342v on the screens with a -15v bias.Hot as a firecracker,so maybe it might put out a good wattage after all.

Title: Re: Mesa Nomad 45 Output Transformer.
Post by: PRR on October 19, 2010, 06:30:34 pm

It sounds like it is working EL84 as-if they were 7189. Pair 7189 can do 24 Watts, so a quad may legitimately be 45W rating.

EL84 used to be rated 300V-330V, but many guitar amps abused the rating, and most recent production guitar-market "EL84" must be made with 400+V plate-stuff.

The teeny OT colors and distorts large bass. It should play loud and clean on higher frets. If it isn't perfect in the lowest octave of guitar, that's the way it's supposed to be. (Whether artistic or economic, I dunno.) And some newer electrical iron can stand a lot more power than the old stuff used in 1950s designs.

The cutting-out is probably not in the OT.

Title: Re: Mesa Nomad 45 Output Transformer.
Post by: Dave on October 19, 2010, 07:25:05 pm

Quote from: phsyconoodler on October 19, 2010, 03:12:47 pm

  I bet the amp would sound better with a bigger OT anyway,so go for it!

I might do exactly that if there were ANY more room on the chassis. Unfortunately, I have never seen an amp that made so much use of geography.

Quote from: PRR on October 19, 2010, 06:30:34 pm

The cutting-out is probably not in the OT.

Yeah, I know, but the OT is so teensy tinsy that I thought it was worth mentioning.
I'm glad to know that the modern stuff has more umph than the old stuff, otherwise I would probably have tried to squeeze in a little bigger OT.

Dave

Title: Re: Mesa Nomad 45 Output Transformer.
Post by: Jack1962 on October 20, 2010, 02:44:43 pm

Yes the OT does appear to be small in the Nomad 45 but by the specs it is rated for 50 watts. have you checked the tubes , because I seriously doubt that , the problem it the OT.

                                                               Rock On

Title: Re: Mesa Nomad 45 Output Transformer.
Post by: Dave on October 20, 2010, 06:30:29 pm

OK, for the record.......


I NEVER thought that the OT was causing the cutting out problem. I just thought that you guys might be interested in knowing that these amps have a microscopic OT.

Dave