5F8-A HIGH POWER MOD FOR BASS

[DaveWell]

OK ! thanks Sluckey !

Is the treble cap, 250pF must be adjust to 500pF ?

remember , this amp have to be MOD for Bass player

And a qestion about the 0.047 600V on the standby switch... is this necessary, or that this old spec... ?

[didit]

Heretic here: discourage "standby"; and encourage grounding on signal path for anyone the really wants to "quiet" an amp---cathode stripping etc.... If you insist, put the first block of capacitance directly on the rectifier side of the B+ switch, and other side into the OPT center & choke; and then you can forego the small one. This is common approach in later designs, and has no audible effects. Using silicon rectification, which is a fine plan, likely requires higher voltage for primary filters---600V was OK at 380V B+. Targeting higher, I would want 700V or even a series stack.

For a bass amp recommend increases in signal coupling capacitors, from stock 0.02uF to 0.047/0.05uF or even more. Would also recommend a "fat" OPT.

As already noted, that 250uF bias bypass make a mess, or no sense. Always a bit puzzled by it. 50uF more than adequate. Increase the voltage to 35v or even 50v.

Best .. Ian

[DaveWell]

Hi didit

Witch of the 0.022 should up to .047 ? all of them ?

[xtian]

+1 ditch the standby switch.

[didit]

Witch of the 0.022 should up to .047 ? all of them ?

Using this schematic as reference: 5F8-A.

Between first preamp & volume, and then entry into PI. A 0.05/0.047uF moves high-pass freq down toward "bass" range. This has worked for me and others. Try it. Something for experimentation, maths simulation or both.

Also, schematic calls for 400V, with the power supply changes 600/630V or greater is advisable.

Best .. Ian

[DaveWell]

Hi Didit, thanks for the Infos

So according to your suggestion, if I'm right, the .022 circle in Green, must be up to 0.05Uf

[didit]

Go with "should" rather than "must". And yes, those are three to tweak. Be prepared to adjust to taste, and also to the bass response of whatever output transformer is used.

Best .. Ian

[DaveWell]

didit, sorry my english....

I Must go with those mods !

Thanks you all helping me throw this project !

This mean a lot to me !

[DaveWell]

Thanks All Fou You help !

The Amp Work Like A Charm !

Regards

Dave

[didit]

Nicely done. Bass is firm we assume.

Best .. Ian

[DaveWell]

Hi,
yes it's firm , but a hole in Mid between 125hz and 500hz

any idea ?

Thanks

[didit]

Hard to say from here.

Tone stack values are same as the schematic?

Component values tested & confirmed before assembly?

Does your "mid" control help, but not enough?

Best .. Ian

[DaveWell]

Hi Ian
nop, not the original layout.
The one that gose to the volume pot have been change to a 0.05 and the treble to a 0.05.
Gonna bring it back to 0.022 for sure.
That was a good suggestion on paper , but not in practice... !