choke filtering

[sniper]

okay, a lot of this amp dohickey business is clear as mud but there are a few things that jump off the page at me. choke filtering is one of those things as well as adequate power, its just not quite as clear as the power requirements.

back to Sunn. the power on the Sunn schematics is awesome for what they said they put out. it seems like they may simply have understated the power output on some make that about all of their amps. what is not so apparent is the choke filters they used vs the values of say a Fender amp or even a Weber clone. looks like Marshalls go really high in values on the chokes they use.

i'm getting the impression that the higher inductance values for choke filters, measured in Henries, tends to be lower for guitard amps than bass amps and that this one fact alone seems to make a remarkable diff in tone. is this correct and could you elaborate on this a bit PBG? has it got anything to do with the chokes acting like a big cap?

[Psycho Bass Guy]

i'm getting the impression that the higher inductance values for choke filters, measured in Henries, tends to be lower for guitard amps than bass amps and that this one fact alone seems to make a remarkable diff in tone. is this correct and could you elaborate on this a bit PBG? has it got anything to do with the chokes acting like a big cap?

Yes.  Chokes were an attempt to make better use of tube rectifiers, which still put out a fair amount of noise, even post-rectification, due to things like heater-to-cathode leakage and high internal impedance. On "dirty" power sources, a tube rectifier will still dump lots of noise into the audio output via the supply rails. To see this in action, use an amp with a tube rectifier and no choke on generator power, which is typically sawtooth, instead of sine 60 Hz. What the choke "did" was filter out the remaining noise, post rectifiers. Its inductance rating is directly proportional to the amount of current it can pass, and since bass is lower frequency, bass requires more current to modulate its output voltage since the period of the output wave is longer. With the introduction of the s/s rectifier, a choke became moot.

[Psycho Bass Guy]

looks like Marshalls go really high in values on the chokes they use.

BTW, I meant to comment on this earlier and just forgot: Marshall's were designed with double the mains voltage, which means the potential for line noise is double, so they needed bigger chokes to filter it out.

[Highlander]

I presume you mean UK built by "double voltage"...?

[Psycho Bass Guy]

Yep.

[sniper]

it appears that might make sense for Sunn also. i was looking at a few schematics for Sunn and noticed a "Marshallesc" 10 Henry value on a 100 watt amp. in comparing the schematic to a Dynaco Mark3 which the Sunn 200S is based on, the Dynaco 60 watt amp originally carried a 4 Henry choke. Dynacos are known for having an overbuilt tranny set as well as Sunn. reading further i found an amp builder that makes a tube "Dynaco clone" ST120 that uses two 4 Henry chokes. it is a stereo amp but he states it is made to be able to bridge easily to use as a mono amp, which i assume would make it a basis for a nice instrument amp. the interesting thing about it is he states the two chokes allow an enormous amount of micro amps through, something on the order of 800ma. it is based on a Dynaco ST70 amp design and layout. it even uses a PA060 power amp which is called for in the original ST70 amp.

1) is that why i have heard (read) the expression that "Marshall watts are 'big' watts" plus probably the fact that Marshall might have under rated their amps like Sunn did?

2) it appears to document the Dynaco/Sunn big watts theory i am postulating and why they are so popular 50+ years after they were both designed. same same.

3) it also gives me the idea why some designs still carry a choke with their ability to use an octal socket for a solid state rectifier and always (usually!) state the voltage will vary when using a tube rectifier instead of a solid state one. the Weber 6S100 design would be a good example as it is in reality a redo of a Sunn schematic in my opinion. the name of it gives me that idea although not formally stated by Weber, or at least that i can find, i did find allusions to that fact in a popular forum.

[the mojo hobo]

the Weber 6S100 design would be a good example as it is in reality a redo of a Sunn schematic in my opinion. the name of it gives me that idea although not formally stated by Weber, or at least that i can find, i did find allusions to that fact in a popular forum.

According to the Weber naming convention:

6= 1960's
S= Sunn
100=watts