Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: macula56 on July 10, 2011, 06:36:57 am
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i recently read that 6L6's can be used in a deluxe reverb with just a rebias. does this actually work without changing the OT to a 6L6 friendly version?
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Yes. I've got a Silverface DR I rebuilt with the Hoffman AB763 circuit. Using a 5AR4 rectifier with the Silverface PT brings the voltage up quite a bit, more than I'd like to use with a 6V6. I tried various tube combinations, different 6l6- 6v6- 5881 tubes and the one I liked the best was a pair of Sovtek 5881's, with bias adjusted to get best balance between tone and tremolo depth. If you are using the roach circuit, it should be even easier to find a sweet spot. You should have the 1Ω resistors installed to read the bias. As far as the OT impedance, I am not qualified to say if it should be changed for optimum performance, but it will work, no problems in mine after two years of light usage. Your results may vary, depending on your speaker.
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cool. i was planning on using some 5881's in mine. thanks Mr. Batty.
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I'm still using 6L6s with my Deluxe OT- designed for 6V6 impedance but has 4-8-16 secondary (it's the EXT version- I forget the numeric designation). I have an 8 ohm speaker cab but use the 16-ohm connection. AFAIK this matches the impedance. And it sounds GOOD.
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i'm gonna try it and see what it soumds like.
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You have to make sure your PT has enough heater current for those tubes.
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You have to make sure your PT has enough heater current for those tubes.
...and enough juice for the additional load on the HT winding.
I'm running 6L6s in my DR but I also have a big PT and OT that has multiple secondary taps.
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I should have been more specific in my earlier answer. I have the stock Silverface PT. The Silverface DR used a 5U4 rectifier tube and 2- 6V6.
Filament current for the 5U4 is 3 amps. Filament current for the 6v6s are .45 amps x2= .9 amps. or 3.9 amps for the three big tubes.
I used the 5AR4 (1.9 amps FC) and the 5881's (.9 + .9 = 1.8 amps FC) for a 3.7 amp total- less than stock. The 5AR4 uses less current but also delivers higher voltage, maybe too high for a smooth sounding breakup.
If you used 6l6's or 5881's you would be at 3.7 amps, much more than a stock BF which uses 2.8 amps- almost half again as much!
If you used a stock Blackface PT you might have a problem with current supply. The Silverface PT is a little different than the Blackface- it was designed to have the extra current in the filament taps. . If you are using a DRRI you might want to research this issue very carefully, I doubt that they put any extra capacity in that PT. If you are rebuilding an amp you can adjust for the differences, but if you have a collector-grade original blackface DR you might want to reconsider experimenting on it.
As far as OT impedance goes, you should be alright unless you go lower than 8Ω. The actually speaker makes a big difference. It seems like the most often asked questions about which speaker to use concern DR's or PR's, which becomes a matter of taste.
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I know a guy who ran a 1964 Deluxe Reverb for years with 6L6's in it. No problems and was one of the best sounding Fender amps I've ever heard. They won't work in every DR however. Stick them in and bias them up and see if the filament voltage is still around 6.3v or slightly higher after the tubes have been working away for 30 minutes or so. Also, check and see if the power transformer is too hot to touch or not. If it isn't and the filament voltage is ok, then you should be just fine. JJ 6L6GC's sound great in these btw. The one caveat when using 6L6's in a DR is to make sure to bias them on the cold side.....about 18ma is about as high as I would go...because if you bias them as you would normally, the transformer doesn't have enough to supply that much current and something will blow.
Greg
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Filament current for the 5U4 is 3 amps. Filament current for the 6v6s are .45 amps x2= .9 amps. or 3.9 amps for the three big tubes.
The rectifier is on a separate 5v winding, so it doesn't add up like that. You can take the recto out of the equation.
G
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Uh-oh! :laugh:
Mine hasn't caught fire yet!