Changing Plate resistor question.

[Shawnobi]

Thanks Dave.
So I guess I'm back to wondering how I make this thing overdrive a bit more when I wind the gain knob up....

[Jazz P Bass]

How about a pedal out in front?

A simple 'boost' pedal should do it.

Or a Tube Screamer.

[eschertron]

Thanks Dave.
So I guess I'm back to wondering how I make this thing overdrive a bit more when I wind the gain knob up....

With a complement of 3 each 12AX7s, I'm guessing that your amp uses 1 for the PI, and the other two are used for gain functions - but that may not be the case. Without knowing exactly what the signal flow through the amp looks like, we're all blind men poking at an elephant. Changing a resistor can make drastic (that is to say, noticeably audible) differences in an amp's gain, but it has to be the *right* resistor in the *right* location. As has been posted above, the resistors at the plate or cathode of stage 1 or 2 can have an effect on the sound, but it won't take an amp from clean to crunchy, and may not even be the effect you're looking for.

A drawing that shows the signal flow through the preamp tubes, with the plate and cathode component values, AND any interstage divider component values, AND the tone stack, will go a long way to bringing the issue you propose here into the light.

Many amps will have a "boost" function that is nothing more than a component that bypasses some or all of the tone stack, allowing a substantial increase in gain. The best part of that is it can be put on a switch!

[Shawnobi]

I'm tempted to build a tubecaster. My problem is that I'm a compulsive tinkerer. I like the idea of tuning the amp rather than adding additional hardware. Also modifying will help my understanding of how amps work.

[big_teee]

I'm tempted to build a tubecaster. My problem is that I'm a compulsive tinkerer. I like the idea of tuning the amp rather than adding additional hardware. Also modifying will help my understanding of how amps work.

I have a prototype head amp that is not in a case, that I experiment with.
If you are going to change the preamp components often, I would use a Turret board.
They are the easiest to change resistors and caps on.
I'm changing and adding Cathode bypass Caps all the time when I'm looking for a particular sound.
Good Luck,
T

[Shawnobi]

With a complement of 3 each 12AX7s, I'm guessing that your amp uses 1 for the PI, and the other two are used for gain functions - but that may not be the case. Without knowing exactly what the signal flow through the amp looks like, we're all blind men poking at an elephant. Changing a resistor can make drastic (that is to say, noticeably audible) differences in an amp's gain, but it has to be the *right* resistor in the *right* location. As has been posted above, the resistors at the plate or cathode of stage 1 or 2 can have an effect on the sound, but it won't take an amp from clean to crunchy, and may not even be the effect you're looking for.

A drawing that shows the signal flow through the preamp tubes, with the plate and cathode component values, AND any interstage divider component values, AND the tone stack, will go a long way to bringing the issue you propose here into the light.

Many amps will have a "boost" function that is nothing more than a component that bypasses some or all of the tone stack, allowing a substantial increase in gain. The best part of that is it can be put on a switch!

I'd love a scheme for this thing! It's quite hard to draw my own from the PCB, things get quite confusing. I understand what you are saying though, I'm just a typical Mod-Newbie wanting the moon on a stick It does have a boost switch. I should look into the circuit that is on.

Big-Teee - Not a bad idea. I have a fear of track lifting on the PCB if I start pulling components in and out quite often.

[Shawnobi]

For reference - here she is with a few 'beautification' mods!

[dwmorrin]

I've taken the liberty of redrawing your partial schematic here.

I'd love a scheme for this thing! It's quite hard to draw my own from the PCB, things get quite confusing.

When you get back in there, there should be a capacitor connected to the first plate (pin 6) and R3. I've labelled where that should go "A" on my schematic.

Try to get as far as connecting point "A" to point "B" and we should have much better info for you.

While you're at it, jot down the voltages at the tube terminals too.

[Shawnobi]

That's really kind of you, thank you. I should have chance to open it up tomorrow evening with a bit of luck.

[kingswayguitar]

For reference - here she is with a few 'beautification' mods!
[ATTACH=CONFIG]26524[/ATTACH]

regardless, she looks like a beauty!

[Shawnobi]

Here we go. FYI C3 is a 100pF Ceramic disc capacitor.




Kingsway Guitar - Thank you

[dwmorrin]

Here's the schematic for the Strauss SVT-H50R. See if it matches your subzero.

[Shawnobi]

Here's the schematic for the Strauss SVT-H50R. See if it matches your subzero.

Amazing! I tried Strauss but never got a reply. That certainly looks the same. Its even stamped Belcat which is the other brand its sold under. Thank you.

[pdf64]

There's an unused 12AX7 gain stage! Tinkerer's heaven!

'I have a fear of track lifting on the PCB if I start pulling components in and out quite often'

Consider fitting small turrets/solder pins into the pcb holes, once components are removed.
Then the trial replacement parts can be easily fitted and swapped out, all done on the component side of the board, with minimal stress to the pad / track.
Pete

[Shawnobi]

There's an unused 12AX7 gain stage! Tinkerer's heaven!

'I have a fear of track lifting on the PCB if I start pulling components in and out quite often'

Consider fitting small turrets/solder pins into the pcb holes, once components are removed.
Then the trial replacement parts can be easily fitted and swapped out, all done on the component side of the board, with minimal stress to the pad / track.
Pete

I've got some breadboard type turrets at work.

I noticed that V2B seemed to be empty. So how do I best rope that gain stage in to my preamp circuit? That could be exactly what I'm looking for!