Transformer question for Liverpool

[chibby]

I'm planning on trying to pull iron out of an old seymour duncan 84-50 head for a Liverpool clone. But the PT has a 12Volt winding instead of the 6 volt or 6.3 volt winding for the lamp and tubes. Is there a way to setp that voltage down with a resisitor? I know this is probably a stupid question and very basic, but I've never run into this before.

[dave g]

No resistors needed - I drew up a little diagram to show how you can do it.

Leave pin 9 on the 12AX7s disconnected.

[C Moore]

You are going to have to explain the EL84 wiring to me, I understand the 12AX7's. Doesn't that put 12 volts on the heater of the EL84?
Thank You

[dave g]

It puts 12 volts across each series pair of EL84s - from Kirchhoff's laws, the voltage drop across each individual EL84 is then 6 volts.

[C Moore]

It's funny how I can look at something for 5 minutes, and not really see it. But 2 seconds after you say Kirchhoff, I suddenly see a series connection that was there the whole time.
Thank You (again)

[Buschman]

The 84-50 ran very high plate voltages. You will need to drop almost 100 volts for it to sound like a Liverpool. I had an 84-50. Man it was harsh sounding.

[chibby]

So if I follow you right, then disconnect the Ht wires I would normally put into pin 9 of the 12ax7's and put them into pin 4, then leave the EL84's as normal.

[chibby]

and if the plate voltages were 100volt higher on the SD 84-50, how do I get rid of that voltage? Can I change resistor value to get there? What else could I do? Yes, the SDwas harsh and it's OD channels unuseable in my mind.

[chibby]

Here's the rectification for the SD 84-50 what's weird is you can see it's got IN4004 diodes for the filaments full wave rectifier, but going down the page you can see there are IN4007 diodes for the primary's. And it's not full wave - right? Isn't that drawing depicting just two IN4007's? Yes-it is...because I'm looking at the SD boards diodes as we speak. I've never seen anything like this before. Why would they use two separate rectifiers like this? Is the first rectifier just to get the filaments to 12Volts? Then the two 4007's to get the primary's to 335v on one side and275v on the other? Looking up from the 330UFx350vdc cap shown there, they show 350v. The caps I'm using are the normal 22 and 47 UF caps for the Liver pool. But it looks like I still might be needing to deal with fairly high voltage off the primaries. If thats 350v is downstream of only one IN4007 diodes, wouldnt it be less than that runing through four or more. So if like the one person that remarked that the SD 84-50 had such high plate voltages is true, what will I end up with. Those plate voltages don't look that high to me, especially if I add two more diodes. I have two IN4007 and four IN4005's ...could I just use what I have?

[dave g]

So if I follow you right, then disconnect the Ht wires I would normally put into pin 9 of the 12ax7's and put them into pin 4, then leave the EL84's as normal.

No, the EL84s have to be divided into two pairs and then each pair connected in series - see the diagram.

[chibby]

Actually, the larger question now becomes completely different than my original one. Looking at the schematic I attached, that winding isn't 12volts at all. It ends up being 12 volts after running through diodes and resistors right? What I really need to know is what the actual voltage is right now with the tranny on it's own. I can't find any info on this PT or OT even though they are not that old really. They have serial numbers on them, but that's all. The OT looks pretty standard, but the PT is a make I've never seen. Please look at the schematic at filament 1 and 2. Do they mean it's 12 volts where it originates, or 12 volts after running through diodes and resisitors - pretty beefy resistors at that. If they atarted out at 12 volt then maybe they were looking to get them to 6.3v already. Please help the mathmatically challenged

[dano-rator]

I'll take a stab here, but PLEASE don't listen to a thing I say until someone who knows what they're doing agrees or more likely corrects me...

Me thinks the HV secondary is a doubler arrangement. a
At least it looks like it to me in my very limited experience

And likely the filament winding is 12v that is rectified to provide power for the op amps in the FX loop and also preamp heaters.

Best bet I'd say is to measure the voltages at the secondaries of the trafo. Than you know what you got for sure.

Dan