TMB - No Master

[sruffinc]

If I want to build an 18 watt TMB based on the attached layout (Derived from Ritchie's schematic), can I simply omit the master volume pot and connect the middle lug of the treble pot to the .022 cab that runs to pin 7 of V2?

Or are other component changes needed?

Richies TMB.pdf

[sruffinc]

Meant .022uF cap (not cab)

[colossal]

Sure, no reason you can't omit the Master if it doesn't suit your purposes. You may want to consider adding some padding resistance off your Treble pot, such as 100k in series with the 0.022uF coupling cap going to the PI, if you find you need or want it.

[sruffinc]

Thanks, I'll try that. Definitely getting a lot of hiss from the treble pot and when I turn it past noon it sounds like it is oscillating. I think the gain is too high overall. Normal channel sounds good, but super bright and tons of gain. It's a great sound, but seems too much. Guess I need to double check all the cap and resistors values.

[JMPGuitars]

Thanks, I'll try that. Definitely getting a lot of hiss from the treble pot and when I turn it past noon it sounds like it is oscillating. I think the gain is too high overall. Normal channel sounds good, but super bright and tons of gain. It's a great sound, but seems too much. Guess I need to double check all the cap and resistors values.

It sounds like you need to test your voltages and see where you're actually at before you make too many changes. Ideal B+ is between 340 to 345 VDC. More than that = more headroom, less gain. Below that = more gain (and maybe mud), and less headroom.

Oscillations are usually lead dress related, but sometimes grid stopper values need to be adjusted (or added if there isn't a grid stopper).

Use one of the voltage charts from here and post your results: viewtopic.php?f=25&t=24418

Thanks,
Josh

[sruffinc]

I tried starting the voltage readings with no tubes and testing pins 1, 3 and 7 of the rectifier tube. My reading on pins 1 and 7 of the rectifier with no tubes is 320v. Isn't that supposed to be 290? And I can't seem to get a reading on pin 3 of the rectifier. I'll admit I may not be doing it right.

[sruffinc]

I'm getting a good sound out of the normal channel.

The problem is with the TMB channel. When I turn the treble control up to about noon the sound goes away and a hum begins. Middle and bass controls seems to work as they should.

Any thoughts?

[JMPGuitars]

I tried starting the voltage readings with no tubes and testing pins 1, 3 and 7 of the rectifier tube. My reading on pins 1 and 7 of the rectifier with no tubes is 320v. Isn't that supposed to be 290? And I can't seem to get a reading on pin 3 of the rectifier. I'll admit I may not be doing it right.

Test your voltages with all the tubes in. Unloaded (without tubes) will read differently than loaded. 290 per side is often around 300 with 120VAC at the outlet. It depends on your transformers though and what they're rated for.

I'm getting a good sound out of the normal channel.

The problem is with the TMB channel. When I turn the treble control up to about noon the sound goes away and a hum begins. Middle and bass controls seems to work as they should.

Any thoughts?

Highlighter test, using both the schematic and layout. Also get all your voltages (and post them here).

[sruffinc]

Thanks, will do.

I added the master volume as per the layout and that seems to have corrected the problem. But I'll see what all the voltages are to be sure everything is as should be.

[sruffinc]

Here are my readings:

B+ 307

V6 V5 V4 V3 V2 V1
1 - 306 145 182 173
2 - 31
3 - 338 10.65 10.65 1.04 65 1.6
6 244 175 1.59
7 - 306 326 326 145 30
8 - 147 65 1.58
9 - 306 306

[sruffinc]

Let me try that again (formatting issue)

B+ 307

V6
1 - 306
3 - 338
7 - 306

V5
3 - 10.65
7 - 326
9 - 306

V4
3 - 10.65
7 - 326
9 - 306

V3
1 - 145
3 - 1.04
6 - 244
7 - 145
8 - 147

V2
1 - 182
2 - 31
3 - 65
6 - 175
7 - 30
8 - 65

V1
1 - 173
3 - 1.6
6 - 1.6
8 - 1.6

[JMPGuitars]

Pin 3 of V6 is your B+. 338VDC is close enough for now.

You need to raise the power tube cathode voltage up to 12VDC. Also test the voltage at pin 2 of the power tubes to make sure they're very low mV.

Thanks,
Josh

[sruffinc]

I got around 91.5 mV on pin 2 of the power tubes. Is that right?

[sruffinc]

Josh,

Ok, I have upped the cathode bias. I now have the following:

V6, pin 3 - 345 V
V5, pin 2 - 6 mV, Pin 3 11.80V
V4, pin 2 - 8 mV, Pin 3 11.80V

That's looks better right?

[JMPGuitars]

Josh,

Ok, I have upped the cathode bias. I now have the following:

V6, pin 3 - 345 V
V5, pin 2 - 6 mV, Pin 3 11.80V
V4, pin 2 - 8 mV, Pin 3 11.80V

That's looks better right?

Those numbers are good! How's it sound?

[sruffinc]

Sounds great! Classic Marshall crunch. After years of playing Fenders and trying to get a Marshall sound with pedals I realize there is no substitute for an actual Marshall circuit. Doesn't take much boost from a low gain overdrive pedal to really nail those classic rock sounds - AC/DC, Zep, etc.

Can't believe how quite the amp is. I used carbon comp resistors throughout and there is only the slightest hiss.

I love the Normal Channel, but the TMB Channel seems a bit too gainy, kinda strident on the top-end. Even with the TMB V1 cathode at .68uF/2.7k. I have 2uF/2.2K on the other channel. Maybe I have them reversed? Pin 3 is TMB right?

I also tried using a 2.7k resister on the V3 cathode and that seemed to increase the gain on both channels. Opposite of what I thought would happen. Would that affect the power tube bias?

Most everything I read is about increasing gain, and I'd like to tame it down just a bit. Maybe a 5751 or 12AY7 in V1?

Thanks for the help. This site is awesome!

[JMPGuitars]

Sounds great! Classic Marshall crunch. After years of playing Fenders and trying to get a Marshall sound with pedals I realize there is no substitute for an actual Marshall circuit. Doesn't take much boost from a low gain overdrive pedal to really nail those classic rock sounds - AC/DC, Zep, etc.

Can't believe how quite the amp is. I used carbon comp resistors throughout and there is only the slightest hiss.

I love the Normal Channel, but the TMB Channel seems a bit too gainy, kinda strident on the top-end. Even with the TMB V1 cathode at .68uF/2.7k. I have 2uF/2.2K on the other channel. Maybe I have them reversed? Pin 3 is TMB right?

I also tried using a 2.7k resister on the V3 cathode and that seemed to increase the gain on both channels. Opposite of what I thought would happen. Would that affect the power tube bias?

Most everything I read is about increasing gain, and I'd like to tame it down just a bit. Maybe a 5751 or 12AY7 in V1?

Thanks for the help. This site is awesome!

Congrats on getting a great tone! We often debate the best parts to use in the build, but a clean build is always the best build regardless of the type of resistors or caps in an amp.

I don't have time to look at what you're trying to do right now, but try this out: look at the options for more gain that you've reviewed. Try the opposite. If a resistor is normally 100k, and it says use 120k for more gain, try an 82k instead. Make sure you know what part your modifying before you do tho.

Maybe somebody else can chime in to help more with that.

Thanks,
Josh