What influences darkness or brightness of tone?

[cuffers65240]

I am currently changing some parts in my mostly stock Weber 18 watt TMB. I started playing with changes for two reasons, one is that I think the tone overall is a little dark and that I think the TMB channel has harsh distortion. I have modded this amp with zener diodes to get rid of blocking distortion and given each output tube it’s own cathode resistor and removed the bypass cap to drop the output wattage (this was a great mod for home use).

I have re wired channel one to match the schematic in the downloads section for the 18Watt TMB (Richie’s TMB) which consisted of using 820 ohm cathode resistors on V1 (vs1.5K) and swapping some coupling caps to different values. This did not brighten anything but it did make the tone control work better (turning the knob did not seem to effect tone much before).

What in an amp like this influences tone in terms of bright vs dark? Coupling cap values, output transformer, preamp tube bias, speaker or something else? I am not searching for Vox sparkle but would like to brighten a little.

Thanks

[JMPGuitars]

Everything you listed affects the tone, especially the speaker. 18watters, especially in classic configuration, are typically considered bright amps. What speaker are you using?

[cuffers65240]

8ohm 25 watt Celestine greenback. G12M I believe.

[cuffers65240]

Darn spell check. Celestion

[JMPGuitars]

Those are usually really good with these amps, though with a typical 18W OT, the 16Ω tap is preferred.

You can edit your posts, look at the top right corner of the message for editing options.

Post the schematic you built your amp with, and edit it with your mods so we can see where you are currently.

Also make sure your guitar's tone knob works.

[cuffers65240]

Thanks, will do!

I have taken down voltages and put them into one of the voltage charts from the downloads section.

I will post an edited schematic with the aforementioned voltage chart in the morning.

[cuffers65240]

Sorry, busier Sunday morning than I bargained for.

I have taken the original Weber 18 Watt TMB schematic and marked it up with changes, mods and voltages as recorded today on my bench. Currently the output trans is connected to a 100W 8ohm resistor, volume dials are at zero, nothing connected to the inputs.

Take a look, see what you all think.

I thought of a new term for what I am hearing, the cleans are thick and creamy but on my strat (especially position 4) it is dark to the point of being muffled. The main thing is that from sound clips online and from playing 18 watts in person (no originals, only the reissue Marshall and clones), the distortion is flabby in comparison.

Channel two has not been touched much yet but I was going to start with copying Richie's 18 watt TMB schem exactly and see where I landed tone wise.

6m18tmb_schem_Markups.pdf

[JMPGuitars]

Why is C5 0.1uF? That should be 0.01uF.

[Bieworm]

Why is C5 0.1uF? That should be 0.01uF.

The coupling caps to the PI are changed to .1uf too. Why would he want to muddy this amp?

[JMPGuitars]

Why is C5 0.1uF? That should be 0.01uF.

The coupling caps to the PI are changed to .1uf too. Why would he want to muddy this amp?

Ah, I didn't look that far. Those caps need to be corrected, and his muddy problem should go away.

[JMPGuitars]

I just looked at the rest of your schematic. You definitely need to use .01uF for those 3 coupling caps you changed. C3 and C4 are typically between .01uF and .022uF. C5 should also be .01uF, and those are sometimes even .005uF. If you put in higher values like you did, the expected outcome is muddiness and distortion problems.

The "Carr Vincent" mod, that's up to you if you like it or not. We typically like the shared cathode resistor with a high value cap. Review the 18W TMB Modern Classic schematic and voltage chart.

[cuffers65240]

Thanks all.

I will change the cap values as you have shown for C3, 4 & 5 and see what I get. I may even tweak them later.

[Bieworm]

Thanks all.

I will change the cap values as you have shown for C3, 4 & 5 and see what I get. I may even tweak them later.

If you are planning to run the amp on high volume then C5 would suit better as a .0047uf value. For testing and tweaking you could try this with alligator clips before deciding and soldering

[cuffers65240]

I again want to thank everyone for the helpful replies.

I first made the changes recommended for C4, 5 and 6 to a lower value and did not hear much of a difference. I then followed the tweaker's table on the layout and swapped the 100K resistor between the volume and tone pot for a 47K resistor and voila! I plugged in the thickest sounding guitar I have, an Ibanez 335 copy with a Fred in the bridge and a Gravity Storm in the neck and it retained its thickness but not overly so like before. Volume anywhere up to halfway and the sound was almost chime-y. Volume dimed sounded like a good distorted tone without being muddy, even on the neck pickup. Used to be that it made me hate my Tube Screamer but now it sounds great as well.

On to the TMB channel next.

[JMPGuitars]

with a Fred in the bridge and a Gravity Storm in the neck

Dude. That's one of my favorite pickup combos! I have at least 2 guitars with that combo, and 2 more with FRED in the bridge.

[cuffers65240]

You sir are the person that turned me on to that combo! I am so happy with the results, especially now that some things have changed on the normal channel.

[JMPGuitars]

You sir are the person that turned me on to that combo! I am so happy with the results, especially now that some things have changed on the normal channel.

lol, okay, that makes sense. It would have been a weird coincidence.

So much versatility, and plays really well with touch-sensitive amps. Gotta love that combo!

[cuffers65240]

Update.

I have completely redone the amp to match the 18W TMB design from the Downloads section. In addition, the amp has a variation of the Carr-Vincent mod on the power tubes, the zener diode blocking distortion mod and some adjustments as suggested in the Tweaker's Table. I am blown away at how much better and more "alive" this amp sounds. I had originally faithfully followed the drawings provided by the kit supplier for a TMB 18 watt but was never fully sold on the tone even with the zener mod installed.

I am absolutely shocked by how differently the amp sounds when I kick on my TS9 Tubescreamer. It is a night and day difference. The distortion used to be flabby and unappealing either from diming or pedals. No more, I can dial in lost of different tones and distortion levels. The CH1 tone control is responsive now, CH2 TMB controls actually can be used to shape tone. I can go low on the treble and bass and high on the middle and get a distorted Fender sound, go the opposite with a mid scoop and sound like modern gain.

I am amazed. Thanks again for all the help.