5E11 Vibrolux, lowering plate voltage

[Randall]

I have a knowledgeable customer who knows quite a lot about vintage amps. He thinks he wants to lower the plate voltages on his Vibrolux to "hit the sweet spot sooner". He thinks it is too clean and pristine as it is now. I asked him to let me disconnect the OT center tap and connect it to my Heath IP-32 PS to see if lowering the plate voltages will even do what he wants. He runs his old Fenders on a Weber 'browner" at 115 - 117v, and says he thinks he is getting 420v on the plates, which if true is way high. (He has "the correct vintage type Mercury trannys in it").

So I'm wondering, if it is in fact lower plate V's he wants, what would be a safe way to do this? I know it depends on how much drop we are talking about, but can this be done by adding plate resistors on the 6V6s?

[Leo_Gnardo]

You forgot to put the quotes around "knowledgeable".

Perhaps your crustomer is trying to replicate the electrical conditions of yesteryears, with his Weber "browner". I dunno what's in the browner but it's true AC supply tended to be lower back in the day, typically 110-117V. Now if he's "knowledgeable" he'll understand it's not just the plates, but the filaments that should be brought into line. After all tube cathodes are heated by those filaments and in the grand scheme of things, it's the cathodes that are the source of electrons. Too hot = too many. I'd have a look at filament voltage first, and whatever line voltage it takes to get it to 6.3VAC would be a good starting point for getting things "the way they use'ter be." Then letsee what the hi voltages are.

I wouldn't go about sticking R's in plate circuits to try & panel-beat hi voltage to what the schematics show. And I wouldn't exactly trust Mercury for anything but removing excess cash from people's pockets.

Variac away, dial down until you have proper filament supplies & then maybe make your own line-bucking "browner" rig to match.

[J M Fahey]

I wonder if MM , trying to make a "period correct" PT wound the few extra primary turns necessary for the modern Mains voltage .

Maybe they believe the Mojo lies on the ***exact*** number of primary turns instead of the ***exact*** secondary voltage.

[elipsey]

I wonder if MM , trying to make a "period correct" PT wound the few extra primary turns necessary for the modern Mains voltage .

Maybe they believe the Mojo lies on the ***exact*** number of primary turns instead of the ***exact*** secondary voltage.

I have wondered this as well, and also about MCI/ClassicTone. I haven't ever touched an old Deluxe Reverb or Princeton Reverb, so I have no idea if my clones are "supposed" to have 425Vp. It seemed higher then I would like, but I shrugged and got on with my life.

EDIT: Discussed here: http://music-electronics-forum.com/t10884/
I think I figured this out a while ago, but forgot; MM "ToneClone" line seems not to be compensated for modern line voltage, "Axiom" line is.

[loudthud]

A NOS 5Y3 will give lower B+ than current production types available. I agree with Leo about dialing down the line Voltage until heater Voltage is correct.

[Randall]

I believe he has all NOS tubes in it. But, so far comments are what I was trending towards.

[elipsey]

I wonder if MM , trying to make a "period correct" PT wound the few extra primary turns necessary for the modern Mains voltage .

Maybe they believe the Mojo lies on the ***exact*** number of primary turns instead of the ***exact*** secondary voltage.

This kind of reminds of the empiricist parable by Eliezer Yudkowsky about the shepard who figures out how to count sheep by tossing pebbles into a bucket. He is then interrogated by an official wise man who demands that he explain and surrender the magic bucket:

“I watched you carefully. You looked in your bucket, checked the level of pebbles, and called that the magic level. I did exactly the same thing.”

“That’s not how it works,” says Autrey.

“Oh, I see,” says Mark, “It’s not the level of pebbles in my bucket that’s magic, it’s the level of pebbles in your bucket. Is that what you claim? What makes your bucket so much better than mine, huh?”