changing classic 18 watt to 18 watt modern classic

[JMPGuitars]

Yes, you should drop your B+, and bias the power tubes better.

What's your current cathode resistor value?

[Bieworm]

Yes, you should drop your B+, and bias the power tubes better.

What's your current cathode resistor value?

180 Ohms
For dropping the B+ I might just as well wire the powertrannie back to 240V.. Same result as zeners.. the b+ was 342V with the 240 V wiring

[JMPGuitars]

180 Ohms
For dropping the B+ I might just as well wire the powertrannie back to 240V.. Same result as zeners.. the b+ was 342V with the 240 V wiring

Figure out what's different between your build power sections:

download/file.php?id=12268&mode=view

download/file.php?id=12328&mode=view

They both have similar tube complements. If they're both running the same PT setup, why the voltage disparity?

[Bieworm]

180 Ohms
For dropping the B+ I might just as well wire the powertrannie back to 240V.. Same result as zeners.. the b+ was 342V with the 240 V wiring

Figure out what's different between your build power sections:

download/file.php?id=12268&mode=view

download/file.php?id=12328&mode=view

They both have similar tube complements. If they're both running the same PT setup, why the voltage disparity?

Comparing the voltage charts I don't find them so much different... what's critical in your opinion?

Well let's look at the differences from power transformer to preamp:
1.
TTMB runs through a SS rectifier and a 150R25W resistor to the first 32uf cap, meets a 2.2k 5W resistor to the 2nd cap. It feeds the EL84 with 2 x 1k 3W resistor. Also feeds the PI plates with a 6.6k 3W resistor. The plates of V2 see that voltage through an 82K resistor and the preamp plate of V1 sees that through a 100k resistor.

MCL runs through an EZ81 rectifier to the first 32uf cap and goes to the second through a 1.5k 5W resistor. That feeds the power tubes through a single 100R 5W resistor and feeds PI plates through an 8.2k resistor. The plate of V2 sees the voltage through 91k resistance and the plates of V1 through 100k.

Must say the power tubes of MCL give higher values than those in TTMB. If I swap them between the amps it's vice versa. Then TTMB reads lower values and MCL higher...

[Bieworm]

Also read in some thread that the position of zeners in the B+ line is variable. I think I saw somebody state that in some position it will do a 50% voltage drop of it's value... (if I understand that correctly)
well I have the 24V 5W zeners... where do I put it to decrease voltage by 12V ? That would be an option... (see attachment for the source)

dropping B+ voltage zener position.png

[JMPGuitars]

I would first focus on your tube bias. Just get it down a little closer to 9 watts, and see what the amp sounds like.

Your B+ being slightly elevated means you have slightly more headroom, and later break up. I get the impression this is probably okay with you. But you might need to adjust it after improving the bias.

IF you decide to use the Zener(s), the part of the conversation you're referring to is placing the Zeners before the first filter cap. So right before or after the standby switch would be an example of this.

[Bieworm]

I would first focus on your tube bias. Just get it down a little closer to 9 watts, and see what the amp sounds like.

Your B+ being slightly elevated means you have slightly more headroom, and later break up. I get the impression this is probably okay with you. But you might need to adjust it after improving the bias.

IF you decide to use the Zener(s), the part of the conversation you're referring to is placing the Zeners before the first filter cap. So right before or after the standby switch would be an example of this.

By adjusting bias you mean raising the cathode resistor I presume?

I have an idea... suppose I reset to 240V PT primary winding, lower the value of the 8.2k resistor after the cap can. That should raise the voltage to the PI and give me better values there? The preamp would be in the same ballpark as with the 230V PT winding as a consequence of that? The bias was better with the 230V and honestly the earlier OD overall too...

[JMPGuitars]

By adjusting bias you mean raising the cathode resistor I presume?

Correct.

[Bieworm]

By adjusting bias you mean raising the cathode resistor I presume?

Correct.

I only have a 220k 5w at hand...wouldn't that be too dramatic?
The plate to screen voltage difference is very small.. how do I modify that?

[JMPGuitars]

I only have a 220k 5w at hand...wouldn't that be too dramatic?
The plate to screen voltage difference is very small.. how do I modify that?

No good. That's way too high. We're talking about going up maybe 20 ohms or so, not 220,000 ohms.

If you have 180R, get some 200R and 220R. If you don't already have 180R, get some of those too. 5W is fine.

BTW- I would also raise that 100R to 1K on the screens.

[Bieworm]

Did some changes...
240V primary
1k to screens EL84's
5.6K from B to C
Voltages are pretty ok I think:

15888605897381702027779575520318.jpg

[JMPGuitars]

Did some changes...
240V primary
1k to screens EL84's
5.6K from B to C
Voltages are pretty ok I think:

They do look okay. You're at 11 watts per tube, which is better than what it was.

Your voltages are in a higher headroom range, but as I mentioned, I'm guessing you're okay with that. The next time you're ordering parts I would still consider including 200R and 220R 5W resistors. But...

How does it sound?

[Bieworm]

Did some changes...
240V primary
1k to screens EL84's
5.6K from B to C
Voltages are pretty ok I think:

They do look okay. You're at 11 watts per tube, which is better than what it was.

Your voltages are in a higher headroom range, but as I mentioned, I'm guessing you're okay with that. The next time you're ordering parts I would still consider including 200R and 220R 5W resistors. But...

How does it sound?

It sounds really good! Nice crunch and stuff.
When effects are ran through the fx loop the drive backs down noticable...that's a little bumming, but allright ... if that's the sacrifice for eliminating the digital hiss noise..so be it
You want to hear samples ofcourse?
Will record it later on...
Somehow it differs from the former 18w classic build..less beefy but still pretty up there. It's just different. Maybe I have other tubes in it.. don't remember exactly..

[JMPGuitars]

It sounds really good! Nice crunch and stuff.
When effects are ran through the fx loop the drive backs down noticable...that's a little bumming, but allright ... if that's the sacrifice for eliminating the digital hiss noise..so be it
You want to hear samples ofcourse?
Will record it later on...
Somehow it differs from the former 18w classic build..less beefy but still pretty up there. It's just different. Maybe I have other tubes in it.. don't remember exactly..

Well, that's good! Yes, obviously need some demos. Both channels, with and without the effects loop please.

What do you mean about the drive backing down? Are you putting distortion pedals through the fx loop?

My guess regarding the beef is that the voltages are playing their part in the sound. I think these were your old classic voltages, and most are closer to the chart: download/file.php?id=12215&mode=view

[Bieworm]

It sounds really good! Nice crunch and stuff.
When effects are ran through the fx loop the drive backs down noticable...that's a little bumming, but allright ... if that's the sacrifice for eliminating the digital hiss noise..so be it
You want to hear samples ofcourse?
Will record it later on...
Somehow it differs from the former 18w classic build..less beefy but still pretty up there. It's just different. Maybe I have other tubes in it.. don't remember exactly..

Well, that's good! Yes, obviously need some demos. Both channels, with and without the effects loop please.

What do you mean about the drive backing down? Are you putting distortion pedals through the fx loop?

My guess regarding the beef is that the voltages are playing their part in the sound. I think these were your old classic voltages, and most are closer to the chart: download/file.php?id=12215&mode=view

Nope, just delay and reverb. Tried the dirtortion too, but...no, no not that one
I'm building it in my tremolo TMB too. But I have only got the standard neutric jack inputs at hand, so they ground directly on the chassis. Am I looking for trouble this way? I'm using shielded wires and intend to connect the single grounding side at the input jack. The metal inputs make it more obvious which inputs are FX loop and what input is the guitar IN...since I have the loop inputs on the frontpanel.

Is it normal for the loop working in both ways. It doesn't matter which input goes to either side of the effects.. I thought the send and return should stand for something?

[JMPGuitars]

Nope, just delay and reverb. Tried the dirtortion too, but...no, no not that one
I'm building it in my tremolo TMB too. But I have only got the standard neutric jack inputs at hand, so they ground directly on the chassis. Am I looking for trouble this way? I'm using shielded wires and intend to connect the single grounding side at the input jack. The metal inputs make it more obvious which inputs are FX loop and what input is the guitar IN...since I have the loop inputs on the frontpanel.

Is it normal for the loop working in both ways. It doesn't matter which input goes to either side of the effects.. I thought the send and return should stand for something?

That's odd that you have less gain when using the loop. Maybe this is related to not paying attention to which jack is the send jack?

Yes, you're potentially looking for trouble not using isolated jacks. Did you know, that you can label things on the panel?

Send and Receive does matter. If you reverse them, then you're relooping your loop. But yes, I would expect the loop to be audible regardless of which way you insert your effects.

[Bieworm]

Nope, just delay and reverb. Tried the dirtortion too, but...no, no not that one
I'm building it in my tremolo TMB too. But I have only got the standard neutric jack inputs at hand, so they ground directly on the chassis. Am I looking for trouble this way? I'm using shielded wires and intend to connect the single grounding side at the input jack. The metal inputs make it more obvious which inputs are FX loop and what input is the guitar IN...since I have the loop inputs on the frontpanel.

Is it normal for the loop working in both ways. It doesn't matter which input goes to either side of the effects.. I thought the send and return should stand for something?

That's odd that you have less gain when using the loop. Maybe this is related to not paying attention to which jack is the send jack?

Yes, you're potentially looking for trouble not using isolated jacks. Did you know, that you can label things on the panel?

Send and Receive does matter. If you reverse them, then you're relooping your loop. But yes, I would expect the loop to be audible regardless of which way you insert your effects.

Dang! In that case I shall isolate the inputs with heatshrink and plastic washers for now..

[Bieworm]

https://www.dropbox.com/s/78nko8k9k85g3 ... p.m4a?dl=0

I think this one needs the ruby mod too...
And notice the gain of grind when the FX loop is unplugged

[JMPGuitars]

I think this one needs the ruby mod too...
And notice the gain of grind when the FX loop is unplugged

What's your cathode capacitor value in this one?

[Bieworm]

I think this one needs the ruby mod too...
And notice the gain of grind when the FX loop is unplugged

What's your cathode capacitor value in this one?

1000uf 63V
I have a 2200uf in stock, but it's not axial and looks weird if I stick it on the board... it has to look nice too huh

In the tremolo TMB it's 1500uf