Two Things: Toroidal Transformers; And No Chokes?

[nico22]

There's not much mystery about chokes or their substitute by a resistor.

The biggest advantage of a choke in respect to a resistor is its very low DC resistance, while its AC resistance is very high (what's required, to smooth out the remaining ripple as good as possible).
This allows to have the screen supply voltage not to far off of the B+, a difference of 2...5 volts usually, what gives the output stage some higher output power. But the output stage then also is rawer sounding due to some more K3 (odd order harmonic) - the rawer, the less the choke's inductivity. Example: Late 60's Marshalls have a 10H choke -> smoother sound. Early 70's Marshalls have a 3H choke -> much more rawer soundwise. Of course that's not the only difference, but contributes not negligible.

Now use a resistor, i.e. a 470 ohms or even a 1K like in the Trainwreck Express. Result, much more voltage difference between the B+ and the screen supply - a smoother sound, more 'touch sensitivity' of the power stage, but a reduced power output.

But the major advantage of a resistor is costs and its small physical size in respect to an adequate choke.
A disadvantage of a choke - if choosen too small in respect of current capability - is, that it might saturate. In this case spontaneously its inductivity is dropping to zero and the choke is acting like a simple resistor with its usually very low DC resistance with the result of enhanced ripple and hum.

There are some other ways, to get a 'smoother' sound and a higher touch response, even by using a 3H choke - but this post shouldn't become a small booklet

Larry

Larry,

How a choke campare in sound with a capacitor multiplier (i saw that in merlin blancowe book)?
Have you ever tried them?

 

[talltxguy]

Finally got my TA-15 back with a MM choke installed. There is no myth about chokes in my mind. The amp sounds better and plays better. I noticed more of a difference on distorted than clean settings for whatever reason. The choke costs @ $40 with an hour of labor at your local tech. I think it's one of the better mods for the money.