18W combo tweaking options

[bvayling]

Now that the bias is mostly settled on my now assembled GDS combo trem 18W, I am thinking of the following small mods that I stumbled on searching the site:

1./Switch R18 and R19 PI anode load resistors to same value carbon composition. Sweeter sound?

2./I'd like a slower tremolo. Still fast for me at slowest speed. Change C8 from stock .01uf value to .015 considerable difference or .022uf more noticeable? Or better to change resistors? I read that changing the speed with the resistors can slow it down the trem "without loading it down."
Is this a concern?

3./The tone controls work better on both channels now that I lowered the value of the cathode resistor. (At least it seems that way.) I still think there is room for improvement there by increasing the tone control's cap value (hopefully increasing the range) but I'm on the fence about it, I don't want to change the character of the amp.

It does sound great! Can it get better or?
I welcome thoughts on the above.
Thanks.
Bernard

[Daviedawg]

1. My personal preference is for same values there. It gives a slight mismatch on the two PI signals and more harmonics. I think.
2. I just experimented on mine until I got reliable immediate start up and the range of oscillation I was after. Or simpler - change the valve and you may get what you want. Different valves even with the same label can affect the trem performance
3. Not sure about that. I did not experience (or perhaps more correctly observe) any tone control changes as I changed the cathode resistor. But I was not looking of course.

Dd

[Bieworm]

Replacing the third oscillation cap from .01uf to .022uf is a proven mod to slow down the trem. Going higher in value than that might result it the oscillation coming on too slow...kinda starting up slower and taking a few seconds before it's at cruisin' speed. Make sure you use a good quality tube. I have good experience with the 12AX7AC5 high gain tube FWIW.

For tone control you might give a thought of the VOX AC15 tonestack. In my memory I think the AC15 HW I once had did have a better range in the normal channel than the 18W. But me thinks the limited range an 18W has keeps it in character of an 18W... too much tweaking that tone stack will drift away from the true tone and will end up in an unbalanced OD. That might result in you wanting to add a cut control or presence control... don't you wonder you'd better build an AC15 or a plexi instead?

I suppose you're like me and need a tremolo. If that's the case you can keep the classic 18W and build an extra amp called the JMP designed TMB tremolo, which I did. Now I own 2 18W amps with tremolo...1 classic 18W with single tone control an 1 18W TMB with tremolo (hail Josh, who did the design)

The TMB tremolo you can find in the download section.

Here's a few samples of mine:

https://www.dropbox.com/s/k8skj0rgslu54 ... r.m4a?dl=0

https://www.dropbox.com/s/yp2gp6khutfph ... g.m4a?dl=0

1585906037885352210472703187407.jpg

Note:
* the white knobs are trem controls--> will be making a custom controlplate for that issue
* the only operational input is the one with the jack plugged in. The rest are dummies, so not connected. Maybe an idea for an effects loop?

[JMPGuitars]

The TMB tremolo you can find in the download section.

Tremolo TMB: viewtopic.php?f=25&t=25550

Maybe an idea for an effects loop?

files/JMPGuitars_18_Watt_EF86_Xtra_Schematic.pdf

I included my FX Loop in my docs for the EF86 Xtra if you want to put it in the Tremolo TMB, it should work fine. the schematic!

BTW- this is how simple the FX Loop is: https://www.instagram.com/p/B8pHMHfHWwP/ (obviously the last resistor is on the turret board)

[bvayling]

1. My personal preference is for same values there. It gives a slight mismatch on the two PI signals and more harmonics. I think.
DD, just to be clear, same values but CC resistors?

Thanks for the feedback DD.

bva

[bvayling]

Replacing the third oscillation cap from .01uf to .022uf is a proven mod to slow down the trem.

Bieworm, which is the third cap? C8 or C10?

add a cut control or presence control... don't hou wonder you'd better build an AC15 or a plexi instead?

AC15 is on my list to build, I want to keep the 18 as close in character to the original as possible with respect to tone.

I suppose you're like me and need a tremolo. If that's the case you can keep the classic 18W and build an extra amp called the JMP designed TMB tremolo, which I did. Now I own 2 18W amps with tremolo...1 classic 18W with single tone control an 1 18W TMB with tremolo (hail Josh, who did the design)
Here's a few samples of mine:

Nice amp! I haven't built a TMB amp yet, but I love building these things.... 2 18's and counting...

Thanks for chiming in Bieworm!

Bernard

[Bieworm]

Replacing the third oscillation cap from .01uf to .022uf is a proven mod to slow down the trem.

Bieworm, which is the third cap? C8 or C10?

->C8, the one between the 1M and 2.2M resistors

add a cut control or presence control... don't hou wonder you'd better build an AC15 or a plexi instead?

AC15 is on my list to build, I want to keep the 18 as close in character to the original as possible with respect to tone.

--> I had 2 AC15's: a HW (vietnamese) and a CC1. The CC1 was a lifeless amp. Sounded great at home, but at practice it lacked complexity. The HW was a fine amp, especially with the blue alnico speaker. It really kicked A$$ in overdrive!!! But the pale tolex and the brass strip in the front made me a little " not feel like it"..not to mention that cheap plastic generic goldplated logo. I never liked the color gold, unless it's real gold. Attempts to recreate that color are just plain cheap

I suppose you're like me and need a tremolo. If that's the case you can keep the classic 18W and build an extra amp called the JMP designed TMB tremolo, which I did. Now I own 2 18W amps with tremolo...1 classic 18W with single tone control an 1 18W TMB with tremolo (hail Josh, who did the design)
Here's a few samples of mine:

Nice amp! I haven't built a TMB amp yet, but I love building these things.... 2 18's and counting...

--> 2 18's will do it for now. I'm running out of space here. Me having the 2 18W's, a vibroking, a vibrolux and a marble clubreverb. The dilemma's I have to go through when going to practice... which amp? Which guitars?... ah man! I'm really jealous at people who are satisfied with just 1 amp and 1 guitar...Imagine your bank account!!!

Thanks for chiming in Bieworm!

Bernard

[bvayling]

Thanks, the .022 is going in today!

[bvayling]

I want to build a replica of the vintage early 60's AC15 with the EF86. "Sluckey" has built one with a Marshall style board, I saw it on Hoffman's site. I have to figure out what kind of iron to use. Haven't really gotten serious about it yet. More to it than an 18.

6 tube guitar amps around here......room for just one more!

[Bieworm]

I want to build a replica of the vintage early 60's AC15 with the EF86. "Sluckey" has built one with a Marshall style board, I saw it on Hoffman's site. I have to figure out what kind of iron to use. Haven't really gotten serious about it yet. More to it than an 18.

6 tube guitar amps around here......room for just one more!

Ooooh...the EF86 adventure... good luck
Nice drive valve though

[bvayling]

I had a Dr. Z Route 66 for a few years, it was a great amp. No problem with the tube in that amp....but not all amps the same obviously.

[Bieworm]

I had a Dr. Z Route 66 for a few years, it was a great amp. No problem with the tube in that amp....but not all amps the same obviously.

IMHO preamp distortion is rarely satisfying. The only amp I had with great preamp distortion was my bogner shiva EL34. That amp was only useful at high volume and sounded thin on low volume. But the overdrive that thing had...oh boy!!!
Again, too heavy to haul around

[bvayling]

Yes, of course I did eventually sell the Route 66. As you say, there has to be that satisfying balance between all the stages of amplification to have the end result be just like you want.

Last night I put carbon comp PI anode resistors in the 18 to replace the stock ones. I wonder how much of a difference it will make?? I’ll have to wait a bit to crank it up, I’ll have “kranky” neighbors otherwise......

[zaphod_phil]

IMHO preamp distortion is rarely satisfying. The only amp I had with great preamp distortion was my bogner shiva EL34. That amp was only useful at high volume and sounded thin on low volume. But the overdrive that thing had...oh boy!!!

From my own experience it's largely a matter of how the preamp tubes are biased. Many amps I've come across have 12AX7s biased a little too cold with 1k or higher cathode resistors (and 100k typical load). When overdriven, they hard clip, yielding a harsh, somewhat fizzy distortion. The higher the cathode resistor value, the worse it gets.In my Superlite TMB design the 2nd preamp stage is biased asymmetrically warm, with a cathode resistor of around 600ish ohms. This makes it soft limit instead of a hard cut off, when overdriven, yielding a thick, warm Marshally crunch. Way better IMO. A DC-coupled cathode follower also has a similar effect. I tend to think the best sounding preamps have several differently-biased stages, which clip or limit on different parts of the waveform, so that you get a rich, layered distortion effect.

[Bieworm]

IMHO preamp distortion is rarely satisfying. The only amp I had with great preamp distortion was my bogner shiva EL34. That amp was only useful at high volume and sounded thin on low volume. But the overdrive that thing had...oh boy!!!

From my own experience it's largely a matter of how the preamp tubes are biased. Many amps I've come across have 12AX7s biased a little too cold with 1k or higher cathode resistors (and 100k typical load). When overdriven, they hard clip, yielding a harsh, somewhat fizzy distortion. The higher the cathode resistor value, the worse it gets.In my Superlite TMB design the 2nd preamp stage is biased asymetrically warm, with a cathode resistor of around 600ish ohms. This makes it soft limit instead of a hard cut off, when overdriven, yielding a warm Marshally crunch. Way better IMO. A DC-coupled cathode follower also has a similar effect. I tend to think the best sounding preamps have several differently-biased stages, which clip or limit on different parts of the waveform, so that you get a rich, layered distortion effect.

Man I did the wrong engineering studies. I'm a mechanical engineer... should have done electronics.. The way you guys understand and comprehend this matter is making me jealous..filled with awe:)