Chokes vs resistor

[E biddy]

These are the two schematics I was looking at.

https://drtube.com/schematics/ampeg/b12nf-jp.gif

http://www.thevintagesound.com/ffg/s...b165_schem.gif

[J M Fahey]

Canīt read their minds but it may very well boil down to cost and "tradition" to give it a name.
From my point of view, and I mentioned something similar 1 or 2 days ago, I see Fender evolution and designs as starting with very basic, straight from the book designs in the 40's and then endlessly tweaking and tweaking and tweaking intil they arrived to later designs step by step.
Often very small steps.
If you put a (long) line of Fender schematics side by side from oldest to newest, you wonīt see *dramatic*changes from one to the next; although jumping 4 or 5 steps shows big differences.
I also think theu sed the principle "fonīt fix whatīs not broken" so in a way Fender circuits tend to keep some older features or tricks, simply because they worked well before and for a long time.
Really canīt fault that and gave us good sounding and trusrty reliable amps, whatīs not to like?

So my guess is that since Fender comes non stop and step by step from a very early age, when Electrolytics were expensive, I remember early Fender using ludicrous 8uF filter caps and of course needed every help they could get from chokes, which way back were cheaper than electrolytics, so were used a lot.
So this Bassman amp does use a choke ... because it uses small electrolytics: acceptable (for the 60īs that is) 35uF main filter followed by: *choke* - 20 - 20 - 20 - 8 uF while Ampeg which was a "new design" used a similar 30uF main cap (made out of 2 x 60uF caps in series, go figure, no *real* 600V Electrolytics available, Chemistry simply was not that advanced) followed by : *resistor* - 40 - 40 - 40 uF
I bet both amps have similar hum levels and of course work very well; Ampeg spent a little more on Caps and saved on achoke, Fender did the opposite but I also guess that since that choke is small/simple to begin with , it must have been relatively inexpensive to begin with and to boot, since Fender had been using them for long and probably ordering thousands at a time must have had an extra discount, so *for them* it was a good option.

Like it or not, Economics plays a lot into decisions.

FWIW I *started* making amps in 1969, by 1970 was cloning Fender amps, and guess what? ... being in Argentina those chokes were not easily available (thatīs an understatement ) having them custom wound was beyond the resources of a poor Student (is there any other kind?) so I used resistors instead and simply doubled Cap values, since by then larger electrolytics had become very affordable.

[Justin Thomas]

Hey Juan,

The frickin' 5E1 Champ and 5E2 & 5F2 Princetons used chokes for a little while, all 3 of which were still single-ended at the time. Granted, we were back to a resistor for those two models when the first filter cap went from 8uF to 16uF on both...

I mean, to me it shows Fender wanted to do what was best even for their "munchkin" amps... since the C & D series both had resistors and 8uF caps throughout. Looking for that ever-elusive balance between managing costs and putting out the best product possible, because a student amp that is hum-free will sell before student amp that isn't...

Justin

[Malcolm Irving]

A big difference between a choke and a resistor is how they respond to transients. I think this would affect the dynamics and 'playing feel' of an amp.

If there is step change in voltage across a resistor, the current through it will instantly step up. If there is a step change in voltage across an inductor, there is no instant change in current, rather the current just begins to ramp up. In amplifiers there is usually (always?) a shunt capacitor at each end of the choke, which prevent any step change in the voltage anyway, but the transient dynamics will be different nonetheless.

I would think the 'sag' in a choke power supply must be significantly different to a resistor power supply.

[E biddy]

Thank you ! This is the discussion I was looking for.

[Zozobra]

I've read lots about choke/LC preference for high gain designs elsewhere, I have no direct experience myself, but there is a consensus that if you overcook it then the amp can feel too tight at which point you may as well use an RC filter. As for the effect on tone I suspect that it's another one of those user preference things and you'd just have to try a few things out, granted you can get a fair bit of mileage from one choke by adjusting the caps to suit within reason. Roberto who occasionally posts here has a lot of experience with this king of thing. In my next high gain amp I'm going to give regulated screens a go as I want it to be tight and dry for one, but also because it's running KT88s and I don't want 500V on the screens when all that is going to do is cause unnecessary stress.

[Enzo]

One suggestion is to look at it as systems and not as parts. Step back a ways. Quit looking at 100 ohms versus 200 ohms or whatever. When they designed a Champ, they were thinking how can I make a CHAMP sound best at a certain price. They were not thinking how can I use a 100 ohm resistor better.

Look at Champ. 5C1 has two filter stages, plate and screen. Then 5E1 added a full CL filter stage up front. Reservoir, plate and screen. And then they woke up and kept three stages, ditched the costly choke, and moved plate back to the first cap. This resulted in acceptable performance, and no choke.

In push pull amps, the output stage has natural hum cancellation, so they put a choke between plate and screen. SIngle ended Champ has no cancellation. They can look at a Champ circuit, wonder what to do about the hummy little thing. They try changing the number of stages, whether they add a choke or more caps. And they end up where they end up.

[J M Fahey]

One suggestion is to look at it as systems and not as parts. Step back a ways. Quit looking at 100 ohms versus 200 ohms or whatever. When they designed a Champ, they were thinking how can I make a CHAMP sound best at a certain price. They were not thinking how can I use a 100 ohm resistor better.

Thatīs the point.

I see tons of people **agonizing** in endless Forum fights to death over such details ... which are analized minutely ... out of context.

Or claiming (and believeing) myths such as "this pedal is the secret of Larry Carlton/Robben Ford tone", "Jimi Hendrixīs Strat is unique" (he went to Sam Ash or Mannyīs and asked the shop assistant: "how much is that Strat hanging there?") and so on?
Yes, it was *one* element in a looooong chain of factors; by itself pretty unimportant.
Oh well.