OT upgrade recommendation for SF Deluxe Reverb

[Tone Meister]

I want to upgrade the OT in my 76 DR to accommodate 6L6GC types. Looking for more a little more beef, increased sustain, a dab more output, and tighter bass and figure an OT upgrade and some old stock 6L6GCs will do the trick.

I want to do this without having to upgrade the PT. Right now I'm using a 5V4 rectifier and have the voltages right where I want them. Amp is fully serviced and is good to go otherwise. I do not care about retaining its vintage value whatsoever; I am looking to have this one amp do all my Fender stuff.

Looking at the Allen TO-26. Anything else out there I should consider? Any caveats other than the amp won't retain its vintage value? Any tech advice for the swap?

This is a pull-boost model and I disabled the boost circuit and used the pull pot for a tremolo disconnect, if that matters. Schematic attached.

[The Dude]

A couple of things come to mind. Depending on how much use or abuse you're going to put the amp through, the OT you have may work just fine and you might get by with a rebias. I would probably be a bit more worried about the PT. The 6L6 filaments run about double the filament current of the 6V6. All that said, MOST older fender iron is pretty robust. I would see if you can find the specs for the specific transformers in your amp and go from there.

[g1]

Right now I'm using a 5V4 rectifier and have the voltages right where I want them.

The voltages are going to change with 6L6's so you may have to compensate for that.
Also, I'm not sure if a 5V4 will hold up for 6L6's, maybe others will comment on that. And the 5V4 has max. capacitance spec. of 10uF ?

[The Dude]

You may even want to consider a solid state rectifier if you want tighter bass.

[Richard]

I ran 6L6's in my SF Princeton for a couple of years. If you're worried about the heater current draw on the PT you can pull tubes out of the reverb or vibrato to lower the load. I'm pretty sure that the reverb and non reverb versions of the Princeton used the same PT so I was comfortable. I was running into a 4 ohm load (the 6L6's want half the impedance of 6v6's) and it sounded good, the tone was a little bit cleaner and had a little more "heft". I don't think the Princeton phase inverter has enough gain to really make good use of the 6L6's but the Deluxe probably does. I would swap the tubes and if I liked what I heard I would spring for the new iron. I have heard of some people on this forum checking heater voltage with tubes installed, if it's low then the PT can't handle the load. I'm looking forward to hearing how it comes out.

[Tone Meister]

Even though the Fender part numbers are the same (125P23B) for BF, early and late SF, the later SFDR power transformers provide 3mA for the 5V tap to accommodate the 5U4 rectifier and the high voltage secondary was increased to compensate for the extra voltage drop of the 5u4. My thinking is the extra current draw of the 6L6GCs will pull the voltage down and I can install a GZ34 to get it back up where it needs to be.


Primary 117 V, 60 Hz
Secondary 330-0-330 VAC @ 120 mA, 340 VDC @ 120 mA, with 50 V bias tap
Filament Winding 6.3 V, 3 A
Rectifier Filament 5 V, 3 A

[Tone Meister]

... I have heard of some people on this forum checking heater voltage with tubes installed, if it's low then the PT can't handle the load. I'm looking forward to hearing how it comes out.

Good idea. That is exactly what I will do, with a couple of different rectifiers. I'm not sure I want to go the SS rectifier route because of the immediacy of attack on the notes - I've gotten used to a bit of sag. I will test out some 6L6GCs and take some voltage measurements before making a decision. Thanks for the idea.

[The Dude]

I don't think he's necessarily talking about B+ and rectification as much as filament load. With 6L6's in the amp, I calculate around 3.6A total filament current. The filament rating of your transformer is 3A. If that is the actual threshold, you'll be pushing it and filament voltage will likely fall low. If indeed the transformer is underrated, as many old Fenders are (IMO), you'll be fine. You'll want to keep tabs on the PT and make sure it's not getting too hot.

[Tone Meister]

It'll be easy enough to check before spending any money. I ran old stock 6L6GBs in this same amp for several years and it seems like I had measured the filament voltage then to be sure the PT wasn't being overloaded. The GBs draw the same 900 mA as the GCs

[The Dude]

Right, and for clarification, I wasn't saying it won't work. Just a cautionary point.

[Tone Meister]

All caveats duly noted. That's the very reason I'm askin' ...

[pdf64]

Are you looking to crank the amp into heavy overdrive, or keep it clean with a touch of hair for lead breaks?

[Tone Meister]

Pete, as a base sound, I'm looking to keep it pretty much clean and then overdrive it in varying degrees with pedals for rhythms and solos. The amp sounds killer with the 6V6s cranked, but I don't play it that way and never will. The goal is to add a touch of overall volume and headroom and tighten the bass. So yeah, I want it to do more than it was designed to do, but pro and semi-pro players do that all the time.

I am hell bent on trying the 6L6GCs even if I end up upgrading the power transformer. Mojo has just the one I need with 4 A on the rectifier and 4 A on the filament, so go ahead and throw me in the briar patch, Br'er Fox. This amp isn't a collector item and its vintage value is not a consideration whatsoever. I am a player and my amps are tools and are required to work for a living too.

OK, here's the deal: I'm selling off all my amps but two or three and plan to keep one Fender. My collection included two Twins, two MusicMan HD130s, a Pro Reverb, a Vibrolux Reverb, a second Deluxe Reverb, and a Hot Rod Deluxe - and they are already sold or will be sold. I am not gonna "keep the Pro and sell the Deluxe" because all my other amps have more vintage value and will be sold. I plan to keep and play this one.

In a nutshell, I want this amp to handle all my Fender stuff and will expect to use it on 100+ shows per year on medium stages.

[pdf64]

OK, my concern was that I've killed a Weber DR PT running 6L6 cranked (WZ34 and 4kp-p OT).
I would consider a good spec interleaved OT with 8k primary, with 6V6 and GZ34; I think that a Hammond 1650E would be fine, a lot beefier than the stock OT; even though only 15 watts nominal, that's at 30Hz, so the rating can be doubled for guitar.
Also the 1650FA at 25 watts at 30Hz, probably overkill, though it would also support 6L6 so keeps your options open, see http://www.hammondmfg.com/1608A.htm
I've no idea why DR use 6k6 OT, as the power output of 6V6 under DR conditions seems to be a little more into 8k, and the plates should run cooler.
The small '2 hole' Fender OTs tend not to be good if you want a big full sound

[ron vogel]

I used this one for my Princeton/deluxe hybrid build. It handles 6L6's with no problems: http://www.classictone.net/40-18087.pdf

my work is directly across the street from where they are made...I walked over one day and talked to the engineer over there about my project. 40w should be no problem, it's overbuilt.