#1
I am looking to mod a 6505+ head to have a better more tapered scaling from the volume knob so audibly it goes 1,2,3 not from can't hear to too loud. Is there a pre-existing mod for this? I'd like to get into amp modding for personal use is this an ok thing to take on as a beginner or am I better having someone else do it?

Or anything else that'd be good to know.

Thanks.
#3
Not sure how many people call the 6505 a serious mod amp, but sounds like upgrading the pot might not be a bad start for what you want. Or possibly pulling the inner/outer output tubes to lower the power a little bit. (you may have to rebias if you do this)

If you want a good amp to start modding, start solid state. If you want to do tube amps I've heard a lot of good things about the epiphone valve jr and blackheart for messing in the guts.

And of course make sure you know what you're doing when it comes to tube amps and their innards. lethal voltages, even when they're unplugged.
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Last edited by metalhead352 at Apr 2, 2012,
#4
is it the pre and post gains on the lead channel you're having issues with? the rhythm side looks fairly normal, but the lead channel has a few resistors around the gain potentiometers that would affect the taper of the control.
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#5
I don't know the actual mechanical parts that are problematic, I know that the practical application is that the amp jumps in volume instead of scaling correctly like a more expensive amp.
#6
It's not as simple of a concept as you might initially think. Perceived volume is not linear, but rather logarithmic, and this is exacerbated by the fact that the amplification is achieved with non-linear valves. This is the reason why, generally speaking, a 50 watt valve amp is not half as loud as a 100 watt amp. In fact, there is only a 3 decibel difference between the two.

There is a 1 meg resistor (R162) electrically in parallel with the 1 Megohm Post volume pot on the lead channel, effectively reducing its overall value to around 500k. This could be limiting your volume sweep efficiency, but it's also serving the purpose of attenuating some of the high frequencies coming out of the tonestack. You might find that clipping this resistor would make your highs thinner and more shrill. Not a good thing to most people's ears.

Now, what i would suggest is lowering the value of R81 from 2.2M to 1M and seeing where that gets you. You can do this by soldering A 2 megohm resistor across it, effectively reducing the resistance to around 1 meg. If this limits the overall volume sensitivity enough for you, cool. If not, you may want to try going a little lower, such as 470k. This resistor also affects the Clean/Crunch channel.
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Last edited by ConfederateAxe at Apr 4, 2012,