Best tubes for under 4watt se type amp

[Tone Junkie]

Just day dreaming about useing the reverb pt from weber and a flea output transformer with 1.4 or a 4k
Any thoughts .Bill

[bigdaddy]

I really liked the sound of the 6K6GT, that can run on about 300+v on both plate and screen. That was my last build, I took a 6V6 BF champ amp I built using an Allen PT18 and popped the 6K6GT in there. I used a little over 1K bias resistor and it sounds better then with the 6V6, it's loud and screams but not as loud as the 6V6. Much better overall tone then an el84 as either pentode or triode. Next would be a 6AK6, from what I under stand they also sound great and are the little brother of the 6K6GT so to speak. It's a mini 7 pin tube based on the 6G6G. The progression is 6V6 12 watts max, 6K6GT 8 watts max and 6G6 3 watts max dissipation, similar tubes from what I have read. The 6AK6 and 6G6G are the same tube. SE operation says 180volts but I have read 300V on the plates and 250v on the screens max. Those tubes all like to see about 10K on their primaries on the OT. So the Hammond 125s are perfect.

I was going to build a 6G6G BF champ but I just got too ill to do it. I might still in the near future if I can.

[Tiny_Daddy]

There's the good old 12FX5.

[PRR]

What is "under 4watt"?

Three Watts? (Not a lot less than a 5W-6W Champ.)

Then at 30%-40% efficiency, you need to dissipate like 8 or 10 Watts.

What is "a flea output transformer with 1.4 or a 4k" ??

If that is 1.4K or 4K primary impedance, then for good matching to 10 Watt dissipation the tube drop should be 118V with 1.4K or 200V for 4K.

> useing the reverb pt

So use the reverb OT as well. Fender reverb OTs are speaker-impedance secondaries (they were universal replacements for small 250V radios). The stand-alone uses a 7K or so for big drive, the built-in reverb models used 15K (or so) and a triode for less than a Watt.

300V at 20mA and 15K load is 6 Watts dissipation, say 2.5W output. The Fender onboard RT is small but it is no flea, and we know it does nothing nasty to guitar. At 300V the choice of 6W tubes is small, you are "forced" to use one of the 8W-12W tubes such as 6F6, 6K6, or 6V6 (6AQ5). Oh, you could grub around and find a smaller pentode, but... why? If you need it to WORK without fuss, if you need a spare tube on a hot Saturday night, 6V6 is the choice. If you want "different", look at the Video Amplifier pentodes: you can get more gain (but not enough more to omit one premap stage).

The next step down from Champ/Junior ~~5W level, to my mind, is One Watt. And if you can score a quarter-decent 2K OT, then you go 110V B+ and either king 25L6/6Y6 or the killer-cheap 12FX5. However you have to re-scale preamp gain: a full-out 12AX7 preamp with 100V B+ will gag on hot guitar.

[Tone Junkie]

This was what I really had in mind I have 6or7 6aq5 I would love to use them in single or parallel . the reverb pt i can get cheap is 260v 100ma I could use the champ output at 7k or an se output with 5k and it has 2,4,8,16 ohm outputs cant I fudge one of those over  and get a 10k match up if need be. dont mind me my friend everytime I get an amp about done Im daydreaming two amps down the line. Im open to other odd tubes also . Thanks Bill

[tubenit]

How about a 6V6, 6Aq5 or 6BM8 and then a  VVR?  You can get it at a pretty low wattage and still maintain good tone.

With respect, Tubenit

[birt]

ecl80 (3,5W and you get an extra triode)

[darryl]

There are a number of very inexpensive Compactrons which also fit the requirements. http://www.junkbox.com/electronics/CompactronTubesIndex.shtml

The 12-pin socket can cost more than the Compactron though...

[JB]

I can vouch for single ended ECL82/6BM8.  Gets you about 3W out with a free triode for driver, CF, tremelo or whatever. Into a decent 12" speaker mine is loud enough in our jam room with a drummer.  Little bit heater hungry for a small bottle at 700mA, but you are getting a triode in with that.

Not tried ECL80, but I think in those the triode and pentode have a common cathode which is perhaps not ideal.

[Fresh_Start]

I can vouch for single ended ECL82/6BM8.  Gets you about 3W out with a free triode for driver, CF, tremelo or whatever. Into a decent 12" speaker mine is loud enough in our jam room with a drummer.  Little bit heater hungry for a small bottle at 700mA, but you are getting a triode in with that.

Not tried ECL80, but I think in those the triode and pentode have a common cathode which is perhaps not ideal.

Do you have a schematic and transformer specs for that build using the 6BM8?

Thanks,

Chip

[JB]

Lets see how well this drawing posts.

You'll see that I put VVR in it to wind the power down when the drummer isn't present!  Thats why there appears to be a master volume in there - it's actually more of a drive reduction to stop the pentode getting clobbered when the VVR is turned right down.  If you don't need to lower the power then build it without VVR and the 'master'.  Sounded fine that way to me, maybe not to my neighbour.

It's actually in bits at the moment as I re-used the chassis for a smaller EL91 output stage amp (just over 1W) for home/recording use.  I'll be rebuilding it soon and may do something more imaginative with the triode half of the ECL82. There wasn't a great benefit in having a CF in there so maybe use it for trem, reverb recovery or something.

I found it a little hummy, hence the dc heaters which improved things.  I did have the ECL82 right next to the PT on a very small prototype chassis so that may have been an issue.

[Fresh_Start]

Thanks JB!  The schematic looks great.

It looks like the pentode would get clobbered no matter what with those cathode resistor values on the preamp triodes and the CF.  Might be able to get a nice, lower wattage Vibro Champ out of just two tubes.

Cheers,

Chip

[JB]

It did have a reasonable amount of gain and had many different cathode resistors, bypasss caps, coupling caps etc.  Can't remember if that drawing represents the final version exactly but the topology is what sounded best to me - i.e. tone stack at the end.  Lots of loss in that tone stack though so not as dirty as it looks.

In the refined EL91 version I've got it running nicely with the output pentode starting to bend before the pre-amp does likewise and as and when I re-build the ECL82 version I'll be aiming for that gain structure.

Those little Hammond transformers sound good!

   

[mackie2]

WAY BACK I USED 6Y6--NICE SOUND

PIN OUT IS SAME AS 6V6
   

6Y6 Substitutes
Close or identical   CV515, VT168A
Warning: Substitutes are given as a guide only - please refer to original manufacturers data sheets to ensure that a substitute is safe and appropriate for your application.

 

6Y6 Application Data
Class   Va   Vg2   Vg1    Ia   Ig2    Ra           S        Zout     Pout
A S/E   200   135   -14.0    61   2.2   18,300   7.1   2,600     6.0W            Z was 2.5 to 4.5 k  (lower voltage with lower Z)


HAS LOW B+:   200V MAX


MACKIE2
 

[Tone Junkie]

So because Im a newbie humer me a little.
 what type of impedence would this tube like to see on the output trannie single or 2 in parallel. By your data on it, Im trying to learn a little here. Thanks Bill

[DummyLoad]

6CM6 - a 6V6GT in a 9 pin package and cheap (~~$10 NOS).  180V B+ makes 2 watts into 5k5 load w/ ~~ 17Vp-p drive.

[Tone Junkie]

Isotone what type of b+ can it handle I have a tube reverb pt with 290 and a good 5y3 should bring it down a ways remember Im a newbie and dont really have a good grasp yet. So

[Tone Junkie]

I just looked i think plates are 315 max could work with that pt.

[jojokeo]

The reverb trannies have a primary Z of 20k - 25k w/ 8 ohm output depending on which model you buy. To get down to a better match you'd need to run a 2 ohm load for that 6V6 or 6Y6.

I personally really like using a JJ ECC99 in push-pull. You can run a pi if you want but self split sounds great and w/ about 3 crankin watts too. I use this in a firefly-like build which is much louder & sounds WAAAY better than a 12au7. It would be a little overkill to run a tube rectifier but you could to get some sag going while you're crankin it up and "slappin da bass" (-strings ). This little amp is lots of fun & has a lot of tube mojo.