Bright cap on Blues Junior?

[Mark]

I was working on a mate’s version 3 Blues Junior and I wondered why one of the mods on them isn’t to put the 100pF bright cap on a switch?

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The other thing I was wondering about was the 10K grid stopper resistors, I’ve heard they are there to stop RF etc getting into the amp, but I was wondering if increasing the valve from 10K to 220K or 470K bypassed with a 470pF cap might minimise blocking distortion?

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As shown in the first picture the circled 130K resistor is there to stop the amp going into low frequency oscillation when volume, master and bass controls are dimed.

I put the 2.7K cathode resistor in for some Marshall goodness, I have found there is slightly less output (audibly heard) and the distortion is slightly different. If I didn’t have it on a switch I wouldn’t have noticed it.

I have noticed that Fromel have an interesting replacement valve board. I mentioned it as it uses a 12DW7 in lieu of a 12AX7 to use a cathode follower powering the tone controls, it allows the output stage to be made cathode bias which may or not be a good thing, the heaters are elevated via the cathode resistor of the output stage I assume.

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Any thoughts?

[Stevem]

You could do that which is like a bright switch on a BF and SF Fender, but when it’s wired that way as the volume get opened up more and more to 50% the bright effect is reduced until after 50% point it does not take place at all.

If your ok with that then have at it.

[Mark]

You could do that which is like a bright switch on a BF and SF Fender, but when it’s wired that way as the volume get opened up more and more to 50% the bright effect is reduced until after 50% point it does not take place at all.

If your ok with that then have at it.

I typically wouldn’t use the bright switch on a Fender amp unless I had a particularly dull sounding guitar. That’s what prompted me to mention it.

[Mark]

I end up using a three way switch with the 100pF and 250pF value. I liked it.

[stratomaster]

There's also a "dull" cap at the end of the preamp right before the master volume. I tend to pull both out and replace them with a plate bypass cap on the final stage of about 680pF. Gives a more natural high end in my opinion.

[Mark]

There's also a "dull" cap at the end of the preamp right before the master volume. I tend to pull both out and replace them with a plate bypass cap on the final stage of about 680pF. Gives a more natural high end in my opinion.

Thanks for your comment, the dull cap wasn’t in the amp. It may have been removed in a previous mod.

The 250pF cap sounds well suited to funk tones on a Strat using the 2 & 4 positions.