Jose Plexi mods

[Spencerleehorton]

I’ve made the transition over to SLO50 now and everything sounds pretty good apart from the bias, I changed the dual bias to this version


Can’t seem to dial in the left hand EL34?
I have several different tubes so will move the tubes and see if the problem swaps sockets or stays where it is.

 

[Spencerleehorton]

Have got two JJ EL34 and have got 35mv on one and 28mv on other with the above bias, will try changing bias again to dual bias.
Going to change the 1uf cathode caps to 2.2uf to bring a bit more bottom end back as there doesn’t seem to be much bottom end, when I turn the bass pot nothing much happens.
Will try and improve the OD channels noise floor.

 

[BIASKING]

Sounds like you may have a leaky coupling cap ofsetting your bias voltage. Did you check (with no output tubes) the DC voltage at pin 5?

 

[Spencerleehorton]

I will thank you
I’ve just spotted my mistake before the tone stack, pretty sure that’s why the tone stack isn’t really working but the presence is!!

 

[Spencerleehorton]

Having a nightmare with this bias again!!
Have gone back to 150k then diode then 15k, 56k then 50k pot, 2 x 10uf/100v either side of 15k to gnd.
Getting -50v at bias output so this seems right but when measuring at the 1R resistors I don’t get any readings!!
I’m going to go over it all tomorrow again as I’m sure I’ve made some mistakes in the wiring.
I have only put in one cathode follower as I have a metro fx loop pcb which I put last in line before going into the phase inverter, just hoping it’s ok to do that with this SLO50 design?