Magnatone

[J Rindt]

A friend of mine asked for help with his M8.
He replaced the Elytics, and tried a new set of EL84 power tubes. He says (i do not live near him) the amp seems kind of "lack luster". I was wondering a couple of things.
1.  Is there another option (besides el84) for a pair of 7189.?

2.  After the Volume Knob (channel#1), there is a 1M resistor into the next grid. Can that be omitted, or reduced for more volume.?

3.  Would the amp "benefit" from a more standard value of plate and cat resistors on the first 2 gain stages.? Maybe more of the traditional 100k - 1k5 values, with some sort of cat by-pass cap.?

4.  The 33pf cap at the first triode, is that killing some of the brightness or "perceived" volume.? Maybe that is a component that could be played with.?

I guess I am basically trying to figure out how he can add some life to his amp. I have no idea what speaker he is using. Any suggestions would be welcome.
Thank You
http://www.el34world.com/charts/Schematics/files/magnatone/magnatone_m8.pdf

[jazbo8]

A few things for your friend to try:

1. 6P14P-EV, Russian or Chinese, may be a bit more edgy than the EL84;
2. The 1Ms are large but can't be reduced too much, as they form the mixer for the next stage, may be 470K?
3. The first stage is bias very cold on both channel, I agree they could be changed to more common 100K/1K5 combo, may be add a small cathode bypass cap as well, to bring the gain up a bit.

Jaz

[smackoj]

has he tried hooking up to a diff. speaker?  if his is orig. then it might well be 'lifeless'

 

[Willabe]

That's a good point.


        Brad     

[J Rindt]

Thanks Guys -
10-4 on the speaker.
But THAT is something I can recommend.
Needed your help with the more (for me) technical stuff.
Thanks Again

[SILVERGUN]

The 33pf cap at the first triode, is that killing some of the brightness or "perceived" volume.? Maybe that is a component that could be played with.?

Not really, that's just a "shunt cap" to get rid of some "fret squeal" or very high frequency into the first stage.....you probably won't notice any volume increase if you take it out,,,and I don't beleive it's any part of his problem (it's not a bad idea)

The best way to experiment with the 1M grid stoppers would be to just clip in a paralled 1M which will give you 500K,,,but I'm not sure that's the way to go either..

You will notice a big difference by adding a bypass cap to V1,,,BUT if the amp is "lack luster", compared to how it used to be, we should be troubleshooting to try to find the problem first, and then adding mods later.

If you mod now, you may never figure out where the root of "lack luster" came from

Obviously, all other tubes should be swapped out, one at a time to try to narrow it down

If he just got the amp, and it is "lack luster" to him, then "mod away",,,,,including replacing all tubes

[J Rindt]

Silver -
Yeah, tubes are definitely a concern. That is why I was asking about power tubes. The tube of spec (rather the lack there of) in this amp have been discussed many times. I guess there are no great plans by Mike Mathews, or JJ, or the Chinese to manufacture a modern day equivalent.
I am pretty sure he swapped preamp tubes, but I will 2x check for sure.
Thank You

[sluckey]

I would want to know exactly what "lack luster" means to the guy. It's a vague description to me. It may be that the amp is working as designed but it's just not his 'cup of tea'. Someone that loves the sound of a Plexi might think a Twin Reverb sounds kinda "lack luster".

I have a M10A and it's a clean sounding amp. I would think the M8 might sound similar.

[DummyLoad]

use the russian  6p14p-ev or the sovtek EL84M. should work fine.

--DL

[J Rindt]

I would want to know exactly what "lack luster" means to the guy. It's a vague description to me. It may be that the amp is working as designed but it's just not his 'cup of tea'. Someone that loves the sound of a Plexi might think a Twin Reverb sounds kinda "lack luster".

I have a M10A and it's a clean sounding amp. I would think the M8 might sound similar.

Well Stated...
This kind of "stuff" is hard to do via third party
But yeah, Pat is definitely a BF Fender  kind of a guy. I believe he was saying the amp did not seem as "loud" as it should be, and all the tonal issues associated with volume.
Anyway.....
you guys have given me some good ideas to run by him, and clarify what is "missing" from the amp.
Again, not sure what speaker(s) is being used. He usually tests amps with a 1x12 ceramic EV.
But I will find out.
Thanks Again

[smackoj]

I would think trying diff. tubes and speaker would be an easy way to narrow down what he wants to hear? If he has gotten familiar with a certain sound "BF" perhaps, then the Magna might be too tame for his ears.....sometimes if I don't let the amp settle in for 20 or 30 minutes, I miss hearing the real 'sweet' spot of the amp.

 

[SoundmasterG]

The 7189 is basically a high voltage capable EL84. If the amp doesn't use the higher voltage, then there is no reason to run those higher priced tubes. A lot of the Magnatones used lower voltages so you may have no need to use a 7189 and any EL84 type would be just fine.

Greg