Changing a rectifier tube question (Champ)...

[mcinku]

It's my Champ again...

...as I moded it to take a 6L6 tube I was thinking, what would happen if I swap the stock 5Y3 rectifier tube with something bigger like 5U4 for example. Would that be a stupid idea? Would I gain anything?


I sure don't want to blow up my Champ.

[MWJB]

5U4 wouldn't be a good idea, it draws 3A of filament current and typical Champ PTs (125P1B) only supply 2A (unless you have specifically upgraded this parameter).

You'll get more power, whether you like the response is another matter. 5V4, GZ34 or even solid state would be fine. Keep an eye on plate current/dissipation with the SS rectifier.

In most cathode biased amps, simply subbing a 6V6 for 6L6 won't give a tangible change in output, just changes in frequency response & dynamics (which you still might like). The 6L6 draws more current, pulling down B+, the cathode voltage will also rise accordingly and is subtracted from B+, dropping it further. So, normally you need to bump up the B+ with a stiffer rectifier to realise more power.

I'm assuming you have an upgraded OT (10W-ish).

[mcinku]

Originally Posted by MWJB

5U4 wouldn't be a good idea, it draws 3A of filament current and typical Champ PTs (125P1B) only supply 2A (unless you have specifically upgraded this parameter).

You'll get more power, whether you like the response is another matter. 5V4, GZ34 or even solid state would be fine. Keep an eye on plate current/dissipation with the SS rectifier.

In most cathode biased amps, simply subbing a 6V6 for 6L6 won't give a tangible change in output, just changes in frequency response & dynamics (which you still might like). The 6L6 draws more current, pulling down B+, the cathode voltage will also rise accordingly and is subtracted from B+, dropping it further. So, normally you need to bump up the B+ with a stiffer rectifier to realise more power.

I'm assuming you have an upgraded OT (10W-ish).

Thanks for the info...

I didn't just swap the 6V6 for 6L6, I also changed the cathode resistor (made it switchable from 470R=6V6 to 330R=6L6), at the moment the power boost is not huge but it's noticeable. That's why I was thinking about the rectifier.

Will have to check with Nik (Ceriatone) what is the spec on the OT.


thanks

[MWJB]

If you're going to up the B+ with a stiffer rectifier, I'd keep to the 470ohm mode.

Power tube cathode bypass cap should be rated fo 50v at least.

[mcinku]

Originally Posted by MWJB

If you're going to up the B+ with a stiffer rectifier, I'd keep to the 470ohm mode.

Power tube cathode bypass cap should be rated fo 50v at least.

...and probably bigger cathode resistor as well. I was thinking 10W.

Thanks

[Mandopicker]

Not sure if you have considered this, but you might want to change out the output transformer to one that is better matched to the 6L6 tube.

A friend of mine...with great success used a rather large Hammond 125ESE, added an 8 ohm tap in addition to the 4 ohm, an alnico speaker and it sounds great. (Obviously keeping the amp stock was not a question.)

Puts out about 18 watts...unconfirmed. Shocking, actually.

*I suggest this only because you may end up burning out your stock Champ transformer...with the proper trans you could get the most out of the 6L6. The one he used isn't necessary...it is bigger than the power trans!

Just humble observations due to a similar experiment.

Continued success!

[black_labb]

Originally Posted by Mandopicker

Not sure if you have considered this, but you might want to change out the output transformer to one that is better matched to the 6L6 tube.

A friend of mine...with great success used a rather large Hammond 125ESE, added an 8 ohm tap in addition to the 4 ohm, an alnico speaker and it sounds great. (Obviously keeping the amp stock was not a question.)

Puts out about 18 watts...unconfirmed. Shocking, actually.

*I suggest this only because you may end up burning out your stock Champ transformer...with the proper trans you could get the most out of the 6L6. The one he used isn't necessary...it is bigger than the power trans!

Just humble observations due to a similar experiment.

Continued success!

im hoping that that 18 watts was a typo, and it actually meant to say 8 watts, because i doubt very much that it would put out that much. i think thats around what you get from a 5e3 when you put 6l6's in it (along with the correct mods to the power section) which runs 2 6l6 in push pull.

[mcinku]

Originally Posted by Mandopicker

Not sure if you have considered this, but you might want to change out the output transformer to one that is better matched to the 6L6 tube.

A friend of mine...with great success used a rather large Hammond 125ESE, added an 8 ohm tap in addition to the 4 ohm, an alnico speaker and it sounds great. (Obviously keeping the amp stock was not a question.)

Puts out about 18 watts...unconfirmed. Shocking, actually.

*I suggest this only because you may end up burning out your stock Champ transformer...with the proper trans you could get the most out of the 6L6. The one he used isn't necessary...it is bigger than the power trans!

Just humble observations due to a similar experiment.

Continued success!

18W of Champ power - sounds good.

I must ask Nik what is the spec on my OT. I actually already have impedance selector for 4,8 and 16ohm load but I doubt that it can take 18W.

thanks

[mcinku]

Originally Posted by black_labb

im hoping that that 18 watts was a typo, and it actually meant to say 8 watts, because i doubt very much that it would put out that much. i think thats around what you get from a 5e3 when you put 6l6's in it (along with the correct mods to the power section) which runs 2 6l6 in push pull.

I was thinking the same. I think my Champ already drives around 7W with 6L6.

[Mandopicker]

Consider the power that a single 6L6 is capable of...

18 to 20 watts...check the tube specs.

Set up everything perfectly and you'll get as much as 18 watts out of a single 6L6 run all out in true Class A.

Remember, the output transformer has been changed to a 125ESE which is pretty huge. in addition to a complete overhaul.

We did not mathmatically calculate the wattage, but based on the design, we know it can put out as much as 18 watts and is much more powerful than a stock Champ.

[Mandopicker]

Definitely check out some of those Hammond models transformers...a single ended version with the appropriate primary impedence to match a 6L6.
(These things are used in medical equipment among other important equipments that has to run all the time and be very stable.)

The bigger they are and better match to the tube(s), the more efficiently you will run the tube...getting the maximum rated wattage. The experiment was to get power...and it seems to work.

All in all...definitly the most powerful 1971 Champ I have ever seen or heard.

[Bob M.]

I have always liked a 5V4 rectifier tube in Champ/Vibro Champ amps. My best sounding one has a 6L6, 5V4 rectifier and a Weber speaker. I use it for all sorts of rehearsals and small volume situations - it sounds great.

[mcinku]

Originally Posted by Bob M.

I have always liked a 5V4 rectifier tube in Champ/Vibro Champ amps. My best sounding one has a 6L6, 5V4 rectifier and a Weber speaker. I use it for all sorts of rehearsals and small volume situations - it sounds great.

What else did you change... - what is the value of your cathode resistor

[Bruce / Mission Amps]

Originally Posted by black_labb

im hoping that that 18 watts was a typo, and it actually meant to say 8 watts, because i doubt very much that it would put out that much. i think thats around what you get from a 5e3 when you put 6l6's in it (along with the correct mods to the power section) which runs 2 6l6 in push pull.

I've used lots of Hammond SE OTs in Champ like amps and they NEVER, EVER EVER make more then 5-6 watts of clean'ish class A power.
+8 watts of raw, distorted total power is possible.

[Mandopicker]

Originally Posted by Bruce / Mission Amps

I've used lots of Hammond SE OTs in Champ like amps and they NEVER, EVER EVER make more then 5-6 watts of clean'ish class A power.
+8 watts of raw, distorted total power is possible.

To understand...it is not possible to get more than 8 watts out of a champ with a 6L6 and a 125ESE? I guess my understanding of the power output that a single 6L6 is capable of needs more study. I know that the output transformer is rated at 15 watts and the tube was biased pretty high.

On the subject...is it then necessary to change the output transformer when using a 6L6? Long term...

Anyway, my apologies to all for mis-speaking or causing confussion...but I guess that's what a forum is all about. Sharing knowledge.

It is a very loud Champ, though.

Thanks.

[Bruce / Mission Amps]

Originally Posted by Mandopicker

To understand...it is not possible to get more than 8 watts out of a champ with a 6L6 and a 125ESE? I guess my understanding of the power output that a single 6L6 is capable of needs more study. I know that the output transformer is rated at 15 watts and the tube was biased pretty high.

On the subject...is it then necessary to change the output transformer when using a 6L6? Long term...

Anyway, my apologies to all for mis-speaking or causing confussion...but I guess that's what a forum is all about. Sharing knowledge.

It is a very loud Champ, though.

Thanks.

No, my bad I didn't realize the whole amp was modified to run a single 6L6.
A SE 6L6 amp with proper transformers and clean drive should be able to get somewhere around 12-15 watts output.
Fully cranked and allowing for massive 20%-30% distortion levels could easily get you 18 watts.
Sorry.

[Mandopicker]

Thanks for that Bruce...(my name is David)

No worries...it does seem hard to believe...but as you pointed out massive mods were required to make the amp be what it is today. Keeping it stock was not part of the equation of course.

Anyway...I appreciate your insights.

Just goes to show that with a little elbow grease and a few bucks...a SF Champ is the best Class A amp value out there.

Kind regards and Happy Holidays!