How to get my plexi clone sound like a orginal?

[Ukko75]

Hi!
I have built this amp and it sounds little different like orginal. Orginal sound is little bigger and more 3-dimensional. This is more rounder, dull and "on your face".

I have done lots of experimenting different caps and resistor values but nothig helps this broplem.

I have classictone transformer in it, could it help if i try some expensive transformer?

Or is it just that old marshalls just get better when they get older.

Please let me know if someone have struggle with same problem.

[M Fowler]

I don't think it is the Classic Tone transformers I have used them in Plexi and JCM800, and JTM 45 builds no problem.

You might need to adjust grid stoppers to each stage or treble peakers, so many things to adjust. Even the screens and grids on the EL34's. Tube type and speaker type.

Just about any quality coupling caps work well.

There are some really good Marshall builders on this forum and I hope they stop in soon to help you out.

[Reeltarded]

Which amp have you built?

A few tweaks and we can get it screaming, bet ya.

[martin manning]

What kind of tubes are in it? Have you tried different ones?

[Jana]

There are a lot of versions of "originals". If you have an original there that you can measure, document it for components and voltages and try to get your clone as close to that as possible.

B+ voltage is a factor. Most of the replacement power transformers for the 50 watt marshalls give a B+ of about 470. The best sounding 50 watters I have had only had a B+ of about 380.

The NFB is another area that changed over the years. The earlier ones had much more NFB that later models. I personally like 27K to 47K to the 16 ohm tap!

Compare the circuits between your clone and the originals. A simple change of a fizz cap or bright cap can make a huge change.

Check the resistor values in the B+ string. Earlier ones had 20K between the screen node and the PI node. Later ones and many clones have 10K. This makes a huge difference (because of which clips first, the PI or the power tubes going into saturation). PI clip is good--power tube saturation sounds like elephant farts.

That should keep you busy for a while.

[Ukko75]

Here is the layout wich is with same part values as mine.

I have tried various diffrent tubes. Best that i was found is GT12ax7 m V1
tung-sol V2 JJ ecc803 V3 and power tubes jj el34.

I must measure the B+ voltage i don´t remember it. Power tubes pin 3 has a 433V

Can i drop the B+ voltage with out changing power transformer?

[xtian]

Can i drop the B+ voltage with out changing power transformer?

Not easily. Though I was just checking out a 50watt Reinhardt that has a London Power scaling unit in it. Pretty cool.

[Zippy]

I must measure the B+ voltage i don´t remember it. Power tubes pin 3 has a 433V

Can i drop the B+ voltage with out changing power transformer?

Check 'round the site for The Zener Trick - you use a 50V Zener to lift the ground reference. The hardest part is sourcing the correct stud-mounted Zener.

Before you go through all that trouble though, you might try using a Variac to drop the voltage and see whether that is sufficient for the effect you think you need to hear.

Alternatives to dropping the B+1 include leaving the B+1 as-is, and adjusting the dropping string to lower voltages to the preamp and PI. What you are looking for, may also be in tweaking other components in the amp rather than relying on the OT as the cure.

There are many cats, and even more ways to skin them.

[statorvane]

Your speakers can make a big difference here too. What speakers / cab are you playing through?

[Reeltarded]

Dull but rounder and forward. Aha. You want it brite brite. Gritty.

Swap the 47k NFB to the 4 ohm tap. Is that better? Need more?

Swap in 56k slope resistor in place of 33k. Did that help? This scoops out a little bit of boxy/chesty sounding fur.

Change NFB resistor to 100k on the 4 ohm tap. That is brite and the amp is angry now. Grrrrr..

I like lower B+ but it's actually the opposite of what you are asking for. It makes it more smooth instead of brite. Your amp is in range for original type amp, even a little low.

Speakers make a big difference. 25/30s are good and so are 75s. The G-12/75s do a little more of what changing the slope to 56k does. I don't like much else besides Celestions. 4x12 better than all others for the sound you expect too. You'd like 25s I think.

[Ukko75]

I have Celestion G12M speakers in Harley Benton 4X12 cab. The cabinet may not be the best. It is made of quite thin polywood, maybe the cabinet with thicker wood can be better choice.

I will try that 56k slope resistor. That boxy/chesty sound is that i like.

[Reeltarded]

Oh I see.. what is missing in your amp's tone then?

[Jana]

Well, you can't get much pleasure from thin wood--er--I mean, um--I'm going back to the heater thread.

[Bob S]

Minds me of an old chat up line.
"It might be thin, but it's very. very short"
Works like a charm.
Apparently.

OK - where's the heater wire thread...

[cbass]

It might be small but it will grow on ya.