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I have a YRM-1 reverb master and its schematic which I can read fine..
I would like to try some of the recommended mods but my problem is identifying the actual components on the chassis as they are no labelled.
Parkhead wrote
"There are two simple ways to add gain that do not disturb the other features of the amp.
#1 cathode resistors
if you look at the schematic of the amp you are looking for v1a and v1b
the bias for that tube is set using a 1500ohm resistor on each half of the tube PINS 3 and 8
you could probably drop that resistor value down to about 820 ohm giving a bump in gain
FWIW I would only do the cathode resistor on v1b (the output of the tone stack ) and I would use 1k as the value
this will give the amp a little more internal gain range ...without losing what you already like
#2 plate load resistor
if you follow v1a you will notice its power supply feed is a 100k resistor ... this is also known as the plate load resistor
you can change its value to 220k as used in the guitar mate ....
while this adds apparent gain by sending more signal throught the attached coupling cap to the next stage
there is way more going on ... A... you are dropping the operating voltage of the tube
B... you lose some headroom in that tube C... the tube has more apparent growl
I like a little growl so I would change the plate load on V1a to 220k ...if you like Fender style headroom skip this mod
both of these tweaks are fairly subtle and would result in what you describe ... the amp sounds the same and has all stock features
but has a little more gain incorporated into the sweep of the volume control so the amp is a little more fun to play
in some ways the effect is similar to a slight boost but since it built into the amp the amp will still respond to a booster pedal
your friends will think your playing has improved, and your guitar is made of magic vintage wood
do not do this if you don't know what you are doing
do the tweaks stepwise and listen and evaluate the changes by playing as you go
the 100k plate load is in line with the power supply so you can get zapped
#3 if and when you decide to recap the amp with new power filters, probably more important than new tubes in beasts of this age
consider lowering the filter values in the pre amp ... this will also enhance the growl and touch of the amp
the 40mfd cans that filter the pre amp sections can be replaced with filters as low as 20mfd
the first B+ filter should stay 40mfd however in an amp like this I often double it to 80mfd (both sides of a paired can ) if I am lowering the filters in the rest of the amp
the raised B+ filter improves the initial noise reduction effect and the bass output of the power amp ... lowering the pre amp filters improves the touch of the pre amp
and tightens the pre amp bottom end (this filter scheme is a bit radical and you won't see it described elsewhere.. but it sounds a lot more Tweed/Plexi )
c6 is already 10uf in these make sure you stay at that value and do not add capacitance killing the tone you like
also r42 is a big sandbox 470ohm choke/ screen resistor can be changed out to 2 or 3k to better protect the output tubes
and shave a hair off the power output, the power amp becomes warmer and the screens react a little more slowly protecting the tubes and almost imperceptibly cutting output the power
(in reality you hear this as less loud brash edginess in the power amp) "
If someone could label the components (in bold ) mentioned on the picture I would be so grateful
Thanks
![IMG_2003.JPG]()
I would like to try some of the recommended mods but my problem is identifying the actual components on the chassis as they are no labelled.
Parkhead wrote
"There are two simple ways to add gain that do not disturb the other features of the amp.
#1 cathode resistors
if you look at the schematic of the amp you are looking for v1a and v1b
the bias for that tube is set using a 1500ohm resistor on each half of the tube PINS 3 and 8
you could probably drop that resistor value down to about 820 ohm giving a bump in gain
FWIW I would only do the cathode resistor on v1b (the output of the tone stack ) and I would use 1k as the value
this will give the amp a little more internal gain range ...without losing what you already like
#2 plate load resistor
if you follow v1a you will notice its power supply feed is a 100k resistor ... this is also known as the plate load resistor
you can change its value to 220k as used in the guitar mate ....
while this adds apparent gain by sending more signal throught the attached coupling cap to the next stage
there is way more going on ... A... you are dropping the operating voltage of the tube
B... you lose some headroom in that tube C... the tube has more apparent growl
I like a little growl so I would change the plate load on V1a to 220k ...if you like Fender style headroom skip this mod
both of these tweaks are fairly subtle and would result in what you describe ... the amp sounds the same and has all stock features
but has a little more gain incorporated into the sweep of the volume control so the amp is a little more fun to play
in some ways the effect is similar to a slight boost but since it built into the amp the amp will still respond to a booster pedal
your friends will think your playing has improved, and your guitar is made of magic vintage wood
do not do this if you don't know what you are doing
do the tweaks stepwise and listen and evaluate the changes by playing as you go
the 100k plate load is in line with the power supply so you can get zapped
#3 if and when you decide to recap the amp with new power filters, probably more important than new tubes in beasts of this age
consider lowering the filter values in the pre amp ... this will also enhance the growl and touch of the amp
the 40mfd cans that filter the pre amp sections can be replaced with filters as low as 20mfd
the first B+ filter should stay 40mfd however in an amp like this I often double it to 80mfd (both sides of a paired can ) if I am lowering the filters in the rest of the amp
the raised B+ filter improves the initial noise reduction effect and the bass output of the power amp ... lowering the pre amp filters improves the touch of the pre amp
and tightens the pre amp bottom end (this filter scheme is a bit radical and you won't see it described elsewhere.. but it sounds a lot more Tweed/Plexi )
c6 is already 10uf in these make sure you stay at that value and do not add capacitance killing the tone you like
also r42 is a big sandbox 470ohm choke/ screen resistor can be changed out to 2 or 3k to better protect the output tubes
and shave a hair off the power output, the power amp becomes warmer and the screens react a little more slowly protecting the tubes and almost imperceptibly cutting output the power
(in reality you hear this as less loud brash edginess in the power amp) "
If someone could label the components (in bold ) mentioned on the picture I would be so grateful
Thanks
