Bell Labs HiFi amp rectifier question

[The Dude]

Well, it certainly won't hurt anything having the variac (properly adjusted). If your customer is willing to pay, why not?
On a side note, I think there would be less distortion and more headroom with higher voltages, but nothing substantial or enough to be relevant given the small voltage changes we're talking about. As an example, think of the "brown sound" theory of getting more distortion by using a variac to lower the supply voltage.

[Leo_Gnardo]

I made an outboard bucking transformer box for a guitar player last summer

I recalled you had made that 'bucker box, so you have some experience with that item.

Those old RCA 6V6's are tougher than average too, much more so than the EH/"TungSol" that try to look like old RCA's. I've found 'em in old amps, running over 100% recommended max plate, and still working perfectly.

Power, there's a limit to what you're going to get (I'm guessing 10 to 12 watts each at clip) so your "old hi fi" friend would do well to use some hi efficiency speakers if expects rockin' volume with his rebuilt Bells. Any idea what his plans are?

[Randall]

Power, there's a limit to what you're going to get (I'm guessing 10 to 12 watts each at clip) so your "old hi fi" friend would do well to use some hi efficiency speakers if expects rockin' volume with his rebuilt Bells. Any idea what his plans are?

Not yet, but I have put a bug in his ear that this will likely be a process to figure out which input to use, how to set controls, and what speakers will give the best performance. It's probably not going to be the Earth moving the first time he plugs it in. But, he gets it.

[Leo_Gnardo]

Not yet, but I have put a bug in his ear that this will likely be a process to figure out which input to use, how to set controls, and what speakers will give the best performance. It's probably not going to be the Earth moving the first time he plugs it in. But, he gets it.

Mag 2 input looks ideal for regular phono cartridges. Might want to sneak up the value of its 47K load resistor, to 56K, as its in parallel with that 270K/33K combination from Mag 1. Just a minor tweak, most modern carts like to see a 47K load. There looks to be a phono EQ curve in the following stage, whether it's a real RIAA I can't tell, but close enough for your friend to get started.

General choices for efficient speakers, old JBL, Altec, ElectroVoice, Klipsch get the most bang for the buck with a couple of watts. Paul Klipsch's byline was "what this world needs is a good five watt amp."

[Randall]

Mag 2 input looks ideal for regular phono cartridges. Might want to sneak up the value of its 47K load resistor, to 56K, as its in parallel with that 270K/33K combination from Mag 1. Just a minor tweak, most modern carts like to see a 47K load.

Good idea! I will do that.