Fender Deluxe AB763 design flaw? Or better tubes available back then?

[mikepukmel]

Im looking to do mod's on a 6L6 amp. I have found a few versions (scans) of this schematic, and they all have GZ34 rectifier and 2 6V6's. The plate voltage is 410V



But every 6V6 data sheet I can find have the plate at 250 to 285, which corresponds to what most people talk about in blog posts



Im far from having the engineering chops to explain this, or identify it as a typeo that was maybe fixed in release versions of the amp.

Can anyone shed some light on this??
Thanks!!!

[nickb]

Guitar amps were designed for low fidelity and maximum power output for the the buck. The designers routinely used (and still do use) higher plate voltages than the datasheet implies.

[Dave H]

Im far from having the engineering chops to explain this, or identify it as a typeo that was maybe fixed in release versions of the amp.

Can anyone shed some light on this??

It's not a typo or a design fault and it wasn't 'fixed' in in released versions. As I understand it they did it deliberately to get more power out of two 6V6 and got away with it with old 6V6s. If you want to run 6V6s at those voltages with current tubes I think JJ are your best bet. The high plate voltage is OK. It's the high screen voltage that's the problem. I'd increase the value of the screen resistor.

[mikepukmel]

It's not a typo or a design fault and it wasn't 'fixed' in in released versions. As I understand it they did it deliberately to get more power out of two 6V6 and got away with it with old 6V6s. If you want to run 6V6s at those voltages with current tubes I think JJ are your best bet. The high plate voltage is OK. It's the high screen voltage that's the problem. I'd increase the value of the screen resistor.

Thanks, this is really great info. So, all those people shelling out a bunch of money for a nice old BF/SF Deluxe will for the most part, be sincerely disappointed with the tube life. I just dug up a Princeton Reverb AA1164 schematic, and the same thing: GZ34 410/400 v to plate/screen.

[Leo_Gnardo]

So, all those people shelling out a bunch of money for a nice old BF/SF Deluxe will for the most part, be sincerely disappointed with the tube life.

Those folks with 40-50 and more years old Deluxes and Princetons get plenty of mileage out of their 6V6's, unless they choose the "weak sister" varieties (in recent years installed by the manufacturer (!) ensuring permanent employment for me ). They also have the option of using 5U4 or 5Y3 rectifiers, dropping the B+ noticeably, as well as the power output, that can work out very well especially for blues players. Then there's those who use 6L6's in those amps, and they last a good long time. Happy audiences, nobody knows nor cares what's in those tube sockets as long as there's a good show, they just enjoy the music and that's what counts, right?

[mikepukmel]

Thanks for the tip on the JJ's. They have absolute max 450v/500v on their site

JJ Electronic - 6V6S

and even state that this tube can be used in some 6L6 amplifiers.

[mikepukmel]

Those folks with 40-50 and more years old Deluxes and Princetons get plenty of mileage out of their 6V6's, unless they choose the "weak sister" varieties (in recent years installed by the manufacturer (!) ensuring permanent employment for me ). They also have the option of using 5U4 or 5Y3 rectifiers, dropping the B+ noticeably, as well as the power output, that can work out very well especially for blues players. Then there's those who use 6L6's in those amps, and they last a good long time. Happy audiences, nobody knows nor cares what's in those tube sockets as long as there's a good show, they just enjoy the music and that's what counts, right?

Oh yeah, for me, as long as I don't have to change the tubes every 2 months, and the unit sounds good, I'd be happy. Also, I did not know that we could just swap in the 5U4 or 5Y3 without some other component changes.

[mikepukmel]

I found some guy on a Marshall forum, who had a fairly recent Marshall tube head. He said he had to change the power tubes every two or three months! It was a little older thread, that he wasn't watching anymore so I could not get more information. I hope to avoid multiple tube replacements a year.

[Leo_Gnardo]

I found some guy on a Marshall forum, who had a fairly recent Marshall tube head. He said he had to change the power tubes every two or three months!

Oh yeah, "some guy", that's an authority. Why not ask Yngwie Malmsteen, back in the day, when he was a legend in his own mind, and could afford it, 3 hundred watt Marshall heads, he had his output tubes changed for every show. A dozen GE 6550A's. A fortune in the trash can. Don't worry, local stage hands picked 'em all out.

To be fair, there is a sort of "edge" quality to fresh output tubes. They lose it and settle down to a long run after say 20 to 100 hours of break-in. If you are sensitive to that "edge", have ears young enough to hear it, not battered from years of abuse, and you can afford it, be my guest, change tubes often as you'd like. For the rest of us, we'll settle for years of good audio from our amps, without breaking the bank.

Keep looking at the interwebs, you'll always be able to find "some guy" who says - anything you can imagine - sometimes right here on MEF. Some tweet it out at 3 to 6 in the morning, but we shan't talk further about that...

[mikepukmel]

Interesting task. Only a few reviews on, say, TheTUbeStore web site for 6V6's, but, several say TungSol's popped after a few minutes or a few months, in a Deluxe. Glad I asked! Thanks again fro the tips on JJs.

[mikepukmel]

Oh yeah, "some guy", that's an authority. Why not ask Yngwie Malmsteen, back in the day, when he was a legend in his own mind, and could afford it, 3 hundred watt Marshall heads, he had his output tubes changed for every show. A dozen GE 6550A's. A fortune in the trash can. Don't worry, local stage hands picked 'em all out.

To be fair, there is a sort of "edge" quality to fresh output tubes. They lose it and settle down to a long run after say 20 to 100 hours of break-in. If you are sensitive to that "edge", have ears young enough to hear it, not battered from years of abuse, and you can afford it, be my guest, change tubes often as you'd like. For the rest of us, we'll settle for years of good audio from our amps, without breaking the bank.

Keep looking at the interwebs, you'll always be able to find "some guy" who says - anything you can imagine - sometimes right here on MEF. Some tweet it out at 3 to 6 in the morning, but we shan't talk further about that...

Not meant that he was any authority, just a kid who practices in his bedroom at home, and he has to shell out $$ for tubes every few months because they cook themselves.

[nosaj]

Interesting task. Only a few reviews on, say, TheTUbeStore web site for 6V6's, but, several say TungSol's popped after a few minutes or a few months, in a Deluxe. Glad I asked! Thanks again fro the tips on JJs.

Well how about an analogy. If you have an old car and redline it all the time your gonna have to replace stuff more often than if you drive it normally. Of course higher than recommended voltages could be an issue in the amp also.

nosaj

[Enzo]

Some kid who has to replace his tubes all the time may have other issues. Intermittent circuit failures could be killing his tubes. Deluxes are not known as tube killers.

[J M Fahey]

Agree and add: that Marshall user might have been using it with all knobs on 11 , which certainly sounds killer, and with the output attenuated so as not to be thrown through the window, but amp is running full power, heavily overdriven, all the time.

On tbhe other extreme, there is a MEF member, Stan Jacox, who moved to Saint Petersburg in Russia a few years ago, and lately started repairing amps again.
He gets Russian made amps, which are used by local "wedding" musicians, those who have 7 dates a week, with original 20 or 30 years old 6L6 in them, still working reasonably well

He couldnīt believe it .... until he started measuring: those tubes were used exactly "by the book" , say 350V plate voltage, 250V screens, reasonable idle dissipation, etc.
No Heavy Metal of course, rather think Uncle Igor playing all those wonderful Folk songs on his accordion , pulling 25W (which are more than enough) out of a pair 6L6 instead of blistering 50 to 60W ... and they seem to last forever.

That might change, of course, if some day these guys go electric