Valve Jr and the Hum

[Baltar]

valve jr interests and modders, i did a nice recovery ..

I was always wondering, why so many Valve Jr fans recommended to
do mods to improve hum and noise, because i judged mine always to be
quite ok at moderate volumes. in deed it may become noiser cranked up
especial when using a dist pedal, but that's tolerable.

I started preparing myself to mod my valve jr head and was very suprised,
when i found a complete different pcb layout, than shown on most
mod pages !!
my valve jr head already has ...
- one more 22µF capacitor
- dc filaments
- improved nylon guitar cable plug (not perfect, but acceptable)

so, if you buy a valve jr head now, you don't need to mod that much for
hum/noise reasons. I can't tell you if this applies for head only or not, but may
be interesting for somebody who considers to buy one.

my mod plans are reduced to the following ...
- champ like input impedance mod (just a try)
- treble boost in two steps switchable (i really need this for clean playing)
- add another 47µF for smoothing (just a try)
- reduce bias, which seems to be quite hot
- build a nice front (i really hate the original one)
- add a little practice speaker

i will post pics, when i'm done with this ..

cheers
martin

whoever wants to do something similar, i'd like to copy that warning for you...

Be forewarned that there are potentially LETHAL voltages within these amps, even when unplugged! Filter capacitors should be fully discharged before working inside the amp to avoid the possibility of a serious or even FATAL shock. If you don't feel comfortable with doing this work yourself, take the amp to a qualified technician.

 

[Baltar]

Re: Valve Jr and the Hum

i spent two evenings now with my top and gained nice results.

what i did sofar was an input inpedance change, which actually did a lot.
i replaced R1 with 1MOhm and R2 with 22kOhms, which i read on a mod site.
not even the loudness-behaviour changed, it changed the voicing slightly
and even with the useage of the standard sovtek tube (the jj i bought
yesterday was dead on arrival) it transports the attack much better now.

mod 2 is reduced bias. i read, somebody reported the little buddies are auto
biased much to high and he was right. i corrected it, by adding 22 Ohms more
to the 220 Ohm resistor responsable for that

mod 3 is a two step treble boost. in parallel to R6 i added a switch and cos
with the following options ... 1) light boost 68pF 2) open 3) good boost 68pF+22pF

if anybody else did mod expirience on that buddy, i'd be interested.
hope you enjoyed it an overlook evt broken english

 

[Kommerzbassist]

Re: Valve Jr and the Hum

so, if you buy a valve jr head now, you don't need to mod that much for
hum/noise reasons. I can't tell you if this applies for head only or not, but may
be interesting for somebody who considers to buy one.

It does apply for both but for the combo only for those released about at/after the release of the head.