Single ended tube amps...

[bruno]

Hi,

lately I've been wondering about the marvels of having a small tube amp to carry around, and play at home.

Gave single ended amps some though, checked some of the existing ones on the market.

Most seem to have ratty characteristic to their sound, especially when pushed above 5 on the volume, most sound boxy (which I attribute to smaller cabs and some times 8"-10" speakers).

Do you guys sugest any amp schematic, maybe one discusses here in the forum, for a single ended tube amp, that actually sounds bigger, and keeps it together, with some headroom?

cheers

[labb]

go over to the AX84 site and take a look at the P1, HO and the SEL. They will be in the Classic Amps Projects. Should be sound clips of all.

[PRR]

Push-pull 6AQ5 will be a smaller better "big" amp than a single-end job.

The OT will be smaller/lighter even at twice the power out.

Single-end guitar amps are prized for NOT having the good quality of push-pull.

[stratele52]

bruno ,

It is because they are build with cheap components . It is possible to built a very good one.

[tubenit]

Bruno,

I personally have given up on building single ended amps for low wattage.  I can't seem to get a tone that I like?  They never have the smoothness that I like.

I'd rather do a push pull with a 6K6, 6BM8 or ECL84.  Then use a PPIMV or VVR to get it down to champ type volumes.

In the SCH files, we have a low watt push/pull gallery:

http://www.el34world.com/Forum/index.php?topic=12526.0

Geezer's HoSo56 with 6BM8's is a very nice amp also.

I built a SoLow Watt 12AX7 amp using ECL84's that turned out really nice, IMO:

http://www.el34world.com/Forum/index.php?topic=13438.0

And JBP built a better looking version of it here:

http://www.el34world.com/Forum/index.php?topic=13151.0



with respect, Tubenit

[jjasilli]

My hot-rodded VibroChamp (SE) sounds great clean (10" speaker).  Overdriven it's a bit ratty; but so was my Princeton (Push-Pull ).  Actually those two amps sound pretty much identical.  Clean tone should be no problem for an SE power amp.  And, so long as your at 10W or under the SE OT should not be a major weight issue.

Overdrive is more complex and comes with hidden user expectations. Some people like "ratty" overdrive and may take umbrage at that description.  Back in the day, smooth or creamy overdrive was a major feature of (though it did not originate with) Mesa Boogie.  The design was to have (at least) two consecutive preamp stages to produce the overdrive tone.  The reason is that when overdriven, a gain stage distorts one leg of the sound wave significantly more than the other.  This results in a raspy overdrive.  Putting the signal through another gain stage reverses the phase, and results in an evenly distorted signal on both legs of the curve.  Most SE amps have the simplest preamps.  There's often only one stage to overdrive, resulting in raspiness.  Hence, one solution is a Mesa Boogies style overdrive in the preamp with a clean boost in the power amp.  BTW: KOC in his TUT series recommends that all overdrive be generated in the preamp with only a clean boost in the power amp.

Of course it's also possible to overdrive the power tube.  But only one power tube may generate a lopsided signal curve and raspy overdrive.  However, I'm not sure of the curve shape out of an overdriven power tube.

[SILVERGUN]

Hey Bruno,
Back in Dec. '12 I built this for a friend as a present.... http://www.el34world.com/Forum/index.php?topic=14765.msg141156#msg141156

I originally borrowed a 10" "designed for fender" speaker to test it with,,,and HATED IT.....thought the amp was crap...
But, I soon plugged it into my 2x12 cabinet and that was a huge improvement.......so I built a small 1x12 cab with a Celestion G12H-30 and it sounds great..
So I put it up against a Fender Champ 600,,,and the difference was night and day......this amp blows that Champ 600 away---hands down---no contest

So here's the punchline...
About a month ago, I contacted Mark Huss (http://mhuss.com/), who I recently found out lives about 1/2 hour from me, and asked him if he would be OK answering some questions in person if I came out to see his band.....he agreed
One of my last questions was "Have you ever done anything SE?"......he said "Yeah, I collaborated on an amp called "The Beast"......"
I laughed, and told him that I had built The Beast and was very happy with it,,,,,and he wasn't surprised, because he had gotten other positive feedback on that amp  

I had just blindly picked that schematic off the internet about 6 months prior, and had no idea where it had came from (other than Google),,,,,and now I was standing in front of the co-creator,,,,,and didn't have the heart to tell him that I had omitted one component and changed the name of the schematic (take a look at the "BOOST" switch),,,,,because I didn't think "The Beast" was an appropriate name for this amp......so I called it a Custom Champ......
I still feel guilty, especially because of what a nice guy Mark was and is, and how accomodating he was with my questioning....funny coincidence

So anyway,,,,this is a solid design with a proven good schematic, if you'd like to try a SE build.......listen to your gut and go with a 12" speaker if you want a nice big sound.

jjasilli posted as I was typing,,,,so to address the OD on this amp,,,I would say it was/is better than expected, and actually does a nice sustain into feedback trick pretty easily, when cranked.....
I had recently built a Trainwreck Express style PP head, and this amp kinda reminds me of that raw OD,,,,,,which doesn't surprise me now that I know that the design came from TAG.
And to agree with Tubenit,,,I would say, "there is nothing smooth about this amp"

[eleventeen]

jjasilli, I have a request for you, since I gave a pal a SF Vibro Champ for doing me a favor. He really likes it, I bot it 35 years ago and never used it for anything but a signal tracer and 5Y3 tester. It's not at all my kind of amp.

If you have one, I would greatly appreciate hearing your general opinion/report of sticking a 5751 or 12AY7 lower-gain dual triode in for the preamp tube. This is what I have suggested for him...and I even gave him a NOS 1958 mil-spec 12AY7! He reports as you do, that (with the stock 12AX7) the amp gets ratty early in the vol control rotation.

[floyd]

I built a VibroChamp with parallel 6L6 and a solid state rectifier , Allen PR upgrade PT, and a Hammond 125ESE OT. I use an efficient 12" speaker , and there's nothing ratty or boxy about it.

[woolly]

David Allen's Chihuahua amps sound Great!  He has a new 14W with single 6550, and

also offers the new TO15 used in this amp. Lots of good sound clips also.

[tubeswell]

My favourite SE circuit is the 5F2A. Here's one I made about 5 years ago (with me mangling the guitar). (No NFB loop in this recording, and just a strat plugged straight in)

http://music-electronics-forum.com/attachments/8941d1271393408-tubeswell-tweedway-heaven-.mp3

[jjasilli]

I've been trying to get a handle on the allure of audiophile SE tube amps.  My thinking is that they may be an artifact leftover from the pre-pentode days.  Triode power tubes!!!  Lots of internal "parasitic capacitance". Relatively low power output, requiring very high input voltage  -- calling for the use of interstage transformers instead of preamp tube gain stages - to keep down noise???  Still could barely drive a loudspeaker, so the the mechanical enhancement of horn speakers was added.  I've never heard such a system in person.  Maybe it sounds great.  Maybe it has nostalgic appeal.  I'm not sure they could cover the entire musical spectrum, maybe 100 - 10,000 Hz.  Great for things like chamber music and human voice, like solo opera singers.  Haven't delved into this for awhile. 

[jazbo8]

Triodes are much more linear than pentodes at high power, especially the directly-heated ones. If you want nearly the pentode output power and linearity with the same supply voltage, look at the ultra-linear and/or the cathode feedback designs for the pentodes/beam tetrodes.

[jjasilli]

jjasilli, I have a request for you, since I gave a pal a SF Vibro Champ for doing me a favor. He really likes it, I bot it 35 years ago and never used it for anything but a signal tracer and 5Y3 tester. It's not at all my kind of amp.

If you have one, I would greatly appreciate hearing your general opinion/report of sticking a 5751 or 12AY7 lower-gain dual triode in for the preamp tube. This is what I have suggested for him...and I even gave him a NOS 1958 mil-spec 12AY7! He reports as you do, that (with the stock 12AX7) the amp gets ratty early in the vol control rotation.

Thanks for this great suggestion.  A 12AY7 in the V1 position is a great improvement, which I would not have thought of.  The amp sounds much smoother and "open" compared to a 12AX7, for both clean & overdrive tone. 

NOTE: 
*  I dont' have a 5751. 
*  V1 is input stage + tone recovery stage; V2 is all tremolo
*  The 2 preamp stages are hot-rodded for extra gain.  Stock the amp would barely overdrive with a 12AX7.  Now nearly dimed (guitar dimed too) it has a wonderful hint of overdrive with the 12AY7.  The RAW control dials in more overdrive if you want it.   

My initial guess was that the lower mu preamp tube would simply undo the gain boost mods.  To an extent that's true.  Without the gain mods the 12AY7 would probably be too anemic.  But given the gain mods + RAW control, the 12AY7 stays!!!

[jjasilli]

Triodes are much more linear than pentodes at high power, especially the directly-heated ones. If you want nearly the pentode output power and linearity with the same supply voltage, look at the ultra-linear and/or the cathode feedback designs for the pentodes/beam tetrodes.

Yes, but the key is "at high power".  E.g. I think a 60 - 100 watt tube amp pushing cone speakers with decent SPL in a "normal" cabinet need not be run at signal bending power.  I also think that this thread may be hijacked 

[Platefire]

What happened to bruno??? May have been flooded with too much info.

[jjasilli]

He probably built & sold the amp already 

[jazbo8]

Yes, but the key is "at high power".  E.g. I think a 60 - 100 watt tube amp pushing cone speakers with decent SPL in a "normal" cabinet need not be run at signal bending power.  I also think that this thread may be hijacked 

Actually I should not have said high power, it is more linear period.

[eleventeen]

jjasilli, many thanks fer doing that and I'm glad it worked out nice for you!

I've been hammering him to shove that 12AY7 in...and even GAVE IT to him.....why he doesn't do it...IDK?

Maybe with his stock V-Champ a 5751 (gain = 70 vs 12AY7 gain = 45) would be better. I have a few of those somewhere in my storage space.

These are EXCELLENT things to try with amps. Cheap. (well, the tubes aren't) Easy to try/reverse.

[bruno]

Hey guys,

just read through the posts, sorry it's been a busy week.

Great info, and the beast amp seems unsettling simple.

I've been doing some math, regarding parts costs, and I'll have to follow (as I usually do), PRR and tubenit's comments on this one. It's as cheap at this point to go with a really low volume push pull amp, so that where I'm headed for now.

[SILVERGUN]

Great info, and the beast amp seems unsettling simple.

And that's why I picked it....I always gravitate towards a nice simple schematic
.....this time I got lucky
Just out of curiosity,,,what kind of sound are you looking for? OD or not? Fender'y cleans,,,,Marshally grit,,,,Vox chime,,,Dumblish marshmellowness ???

I'll be curious to hear how it turns out.....keep us in the loop 

[bruno]

Usually stir towards something that has a bit of a blackface cleans with some chime, if possible with a an overdrive that is not too gainy, and keeps some of the chime.