Dropping voltage BEFORE rectifier tube?

[Duncan]

Kind of a weird one that I've got rolling around in my brain.

I've found myself in possession of a pretty complete lot of Leslie Type 25 Booster Amplifier and related parts. I'd like to use as much of these parts as possible to build a Matchless Chieftain-type circuit.

The power transformer, as far as I've been able to find and tell, has a 440v high voltage winding going into the diode rectifiers, and the documentation I've been able to find online of the Chieftain circuit has 350v going into the 5AR4 rectifier tube.

My first question is, has anyone dropped the voltage before it hits the rectifier of an amp? I know the 5AR4 is going to drop the voltage approximately 10v on its own, and I'll be able to drop it further using resistors on the filter caps.

Follow up question, I suppose, would be: would I even need to drop the voltage before the rectifier, and just manage it afterwards?

Thanks in advance!

[sluckey]

You're talking about a voltage drop of 110V. That's a lot! My advice is to get a more appropriate PT for the Chieftain.

[PRR]

Keep the PT and OT together, with similar size tubes (EL34 and 6L6GC are not too different), and it will work good.

[Duncan]

You're talking about a voltage drop of 110V. That's a lot! My advice is to get a more appropriate PT for the Chieftain.

Yeah that’s kinda what I was thinking. I may see how a Chieftain preamp will sound married to something closer to a blackface Bassman power amp (voltages are much closer to that circuit).

Thanks for your input!

[bmccowan]

I think you may be talking apples and oranges. The Leslie schematic shows 410V to the plates. That's likely pretty similar to the Chieftain.

[Duncan]

I think you may be talking apples and oranges. The Leslie schematic shows 410V to the plates. That's likely pretty similar to the Chieftain.

Yeah, from the schematics of the Chieftain I've been able to find, it's 415v to the plates of the power tubes, but 350v to the 5AR4 straight off the HV winding.

That said, from what I've been able to find about the Leslie transformer, there isn't a 5v secondary, so having a tube rectifier might not be in the cards.

[bmccowan]

The 350V is AC - A BF Bandmaster has about 320V AC going to the SS rectifier delivering about 440V to the 6L6s, so I would think with some finessing of the power rail downstream of the rectifier, you would be in a safe range. Another option is to use a Copper Cap rectifier with your choice of sag.
BTW, I built a Clubman and love that thing, although I de-rated it to use 6V6s.
Or build a Hammond B3

[tubeswell]

... has anyone dropped the voltage before it hits the rectifier of an amp? ...

See the stuff about current limiting resistors for tube rectifiers half way down the page on this link. https://www.valvewizard.co.uk/bridge.html


100VAC would be a lot to drop. But if you use Merlin Blencowe's formula to calculate ideal total limiting resistance and see where that might get you in terms of your B+ voltage, that might give you a better guesstimate of whether its worth trying this in your case, or whether you're better off changing to a more appropriate PT or using a bucking x-former for your PT's High Tension winding.

[kagliostro]

I'll go to measure the AC voltage of the secondary of the transformer you have feeding the primary with your line voltage, this before any tehorical guess

If your line is higher than the old time standard of your transformer you will expect a higher secondary voltage

Franco