There are a couple of quick things to pay attention to on these amps.
when looking at them for guitar or improved bass use.
The good news is that the power amp section runs without a feedback loop
so its a pretty good sounding setup for guitar if we can get the
front end dialed in ...
The Keys:
How the pre amp gain is set up
How the stages are coupled
and how the tone stack works
if you have a look at the available schematics you will probably see your amp
http://www.schematicheaven.com/bargainbin/traynor_bassmate_yba2b_manual.pdf
Interstage coupling:
if you follow the schematic through the first tube you will see
that the audio signal exits the tube on pin 6 of the first pre amp tube
at that point it meets a 100k plate load resistor and a .1 400volt coupling capacitor
that .1 capacitor sets the bandwidth of the signal passing into the next
stage. If we were to do the math .1 puts the amps bottom end well below
guitar frequencies a more typical "guitar value" would be .02 mfd but lots of
values between .047 and 500pf will work between the first and second
stage. I used .02 on my bassmate. All capacitors should be 400volt
The tone stack :
The next thing you see in the schematic is a network of capacitors resistors
and controls. Follow this along and see if you can figure out how this divides
the signal and provides tone controls. With bass mates you should consider
adjusting the slope resistor r5 in the second last schematic and r10 on the
last schematic. The slope resistor adjusts the separation of treble and
bass. On later bassmates they use 220k. Fender used 100k during their
golden era, and marshall used 56k then 33k in their lead amps. There is more
mid gain and growl with a lower value slope resistor, I think I used 33k on
mine.
These two changes alone should tighten up the bottom and boost the
rich mids.
More Gain:
Finally once you have the amp eq'ed with a nice sweep of tonal range suiting
your guitar and style you can look at tweaking the gain.
I suggest you do this last because most people go crazy and choke up their
amp with too much gain.
Looking at that first 12ax7 look for pins 3 and 8. These are the cathodes of
the 12ax7. In most guitar amps the typical value is 1.5k with a 25 mfd
bypass cap. On some bass mates you see a 5.6k resistor with no bypass
cap. This setup keeps the gain low and that gain stage very clean.
If you have the final version of the bassmate with the double gain stage
before the tone controls you can swap the pin 8 5.6k resistor in the first gain
stage over to 1.5k and have all the gain you might want or need.
If you have the 6v6 single gain stage type bass mate you probably want to
drop the existing 1.5k resistor to 820 ohms and leave the 25mfd bypass
cap. If you have the single stage bassmate and you need more gain you
might want to raise the 100k plate load resistor to 220k r8 on that
schematic.
To sum up, these are great little amps and they require very little to sound
amazing. Don't go to wild simply study the schematic tighten up the
tone a little and bump the gain slightly if you want, the key is to drive that
nice 20 watt open loop power amp hard!
here's a guitar mate getting this kind of treatment
http://www.youtube.com/watch?v=hLhGeU4wb2U
Note: in the video the guitar mate power amp is modded to work more like the bassmate version
the bassmate power amp needs no such adjustment
here's the bass mate almost done
in the picture you can see the new yellow mallory 150 .02 400 volt
that replaces the .1 mustard
you can probably make out the "tropical fish" (orange and brown) 300pf treble cap with the new slope resistor
replacing the 220k slope with 33k
you can also see two unused eyelet holes I put a 1.5 k cathode resistor in those holes
and since the 5.6k was located under the filter cap making swapping values to tune the amp a bear
I went with 1.5k unbypassed
In use "the wall of Traynor"
p