M15Mk1 mod for 30W?

OscarVein

Hi there.

For starters I'd like to apologize for getting a little too "anxious" about the BP1, so sorry about that, won't happen again

Well, I had a real question too, could I mod my M15mk1 for four EL84 output tubes?

What else do I need to change than the transformer(s) and cathode bias? Would I need to modify the power supply or could I just add two tubes in series/parallel?

I'd like some more headroom with this, otherwise, this thing is serving me fabulously!
During summer you can find this amp on our bands recording, we're going to use one guitar driving two amps at the same time, with different sounds of course.
The M15Mk1 will be the "moderate gain" one , "crunch" channel boosted with stombox eq and DIY TS-clone to 4X10" cab...sounds very good ;D if you're into this kinda sound...
The other amp is now Peavey classic 30 with Big muff and eq driving 2X12" greenbacks but we're thinking about trying the A15mk1 for this one...we'll see...
And lastly, if you get the BP1 available before our recordings start, I'd surely would like to use that thing on bass too, I already have an old 4x EL34 all tube Pa-amp from 70's to drive my bass rig...thought the BP1 could sound nice with this=) (am I hearing a good pr here or what :P)

This could sound like "trying to please someone" but I can assure that it's just about the sound/cost ratio that has get me so excited...and the fact that I can do these on my own...wrap it all up in red tolex, or pink fur if I please

d95err

Re: M15Mk1 mod for 30W?

About the bass, have you tried using the M15Mk1? I've used my M15Mk1 for bass a bit in my home studio, and it sounds great. I use the normal channel and "fat" on.

If you want more deep bass frequencies, you can record both the direct and M15 sound and mix them together.

MAD

Re: M15Mk1 mod for 30W?

Hi,
when you use a PT with the same voltage as the original PT you only have to change the PT , OT and add 2 EL84 to the amp. When you are using a PT with higher voltages you need to change the filter caps (these are fine for upto 350V).
Regards,
Martin

OscarVein

Re: M15Mk1 mod for 30W?

Zitat von d95err

About the bass, have you tried using the M15Mk1? I've used my M15Mk1 for bass a bit in my home studio, and it sounds great. I use the normal channel and "fat" on.
If you want more deep bass frequencies, you can record both the direct and M15 sound and mix them together.

hmm, have to give it a try...in this band my guitars and basses are tuned down 2 whole steps (E=C), and I have to back off the bass pot already, but sure I'll try that!

Ok, think I'll add those two more EL84 to this thing, maybe with a switch (15w/30w)...I'll tell you how it went...

OscarVein

Re: M15Mk1 mod for 30W?

Hi again.

Would these transformers be good for the 30w mod?

Hammond 1615 output transformer (15W, 5000ohm, 100ma. 4-8-16ohm)

Hammond 370HX power transformer (secondary 275-0-275, 200 ma. D.C. current)

Ok, this project will be starting asap...as soon as I get the parts needed

d95err

Re: M15Mk1 mod for 30W?

Zitat von OscarVein

Hi again.
Would these transformers be good for the 30w mod?
Hammond 1615 output transformer (15W, 5000ohm, 100ma. 4-8-16ohm)
Hammond 370HX power transformer (secondary 275-0-275, 200 ma. D.C. current)
Ok, this project will be starting asap...as soon as I get the parts needed

Some notes:

The OT is 15W, you obviously need one that can take 30W.

The PT is center tapped, so you would need to change the rectifier to a 2-diode setup.

The PT voltages would be significantly higher than with the MADAMP trafo (probably 50-80V higher). You would need to change the main filter caps to ones that can take higher voltages.

Then, you need to decide wether to adjust the voltages somehow (e.g. using power Zener diodes on the PT center tap), or to adapt the circuit for the higher voltages.

If you use higer voltages, you'd have to adjust the bias resistor for the power tubes for the higher voltages.

OscarVein

Re: M15Mk1 mod for 30W?

Yes, I realize that the output tranny is 15W but so is in ie. Vox AC30 , it's a part of the sound that the OT is 15W....or so I've been told :-\ Correct if wrong....

The M15Mk1 manual says the PT secondary gives voltages 265-24-7,4...and the Hammond 370HX gives 275v and has 6,3v taps for the filaments...what is it that I don't understand here?

so...Hammond 260G?

d95err

Re: M15Mk1 mod for 30W?

Zitat von OscarVein

Yes, I realize that the output tranny is 15W but so is in ie. Vox AC30 , it's a part of the sound that the OT is 15W....or so I've been told :-\ Correct if wrong....
The M15Mk1 manual says the PT secondary gives voltages 265-24-7,4...and the Hammond 370HX gives 275v and has 6,3v taps for the filaments...what is it that I don't understand here?
so...Hammond 260G?

The MADAMP trafo has a 230V secondary. The 265V reading is when the transformer has no load connected, so the voltages go up a bit.

Using a 15W trafo at 30W could work (although there is a risk of overheating and destroying the OT), but it would cause more saturation and reduced bandwidth (fuzzy bass and highs). If you want to keep the same sound as the original M15Mk1, you should probably go for a bigger transformer.

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