Needed ! Advice on buying an all tube, true class a amp. If possible, minimum 15 Watt

[printer2]

Oh wow, you're good at copying spec sheets...
Now try "working" with amplifiers for a while. (you might learn something useful)

Oh, you missed the math portion of my post? More than just a copy of the datasheet. And I would think that a datasheet can be useful in determining how parts operate, kind of why manufacturers put them out.

Nice to see Chuck understands the different way amps can be operated. Going to keep an eye on that guy, might learn something useful.

[printer2]

AX84 20W SE amp.

http://ax84.com/static/corepoweramps..._Schematic.pdf

[tonequester]

Need "class A", but my brain is push-pull. I also need to win the lotto !

AX84 20W SE amp.

http://ax84.com/static/corepoweramps..._Schematic.pdf

Gentlemen, I don't fully understand this "reply with quote" thing. To tell the truth, I don't fully understand the computer thing. I'll try my hand at a quote.
" The forum experience can be a very humbling thing. I now realize that I know the half of what I thought I did, and it's the easy half." I wish to thank everybody who has posted to my query. I've already done quite a bit of "research" on the suggestions given me. In all honesty, I don't know for sure what type of amp
will give me what I want. The only thing that I know for sure is that it will be all tube as far as the "signal amplication pathway" is concerned. I don't have a problem with something like a digital reverb, if it sounds good. You folks have consistantly reminded me that it's about the sound, and I really never forget that.
I still have alot of 'checking up" to do on all of the suggestions, but I'm already of a mind that I'm going to have to do my first tube amp build.......IF, I find out that "class A" is the sound I'm after(considering cathode bias or not as well). The amps that I checked into(new or new reproductions of vintage amps) are
about twice the price that I had expected. I should have expected as much. If you wan't to play(quality), you have to play. My problem is that I'm stuck in the
'60s. Thanks once again to printer2, for the schematic, and for the AX84 info. There is alot to absorb from that ongoing project, but it IS a possibility. Even if I
have to "drop" a thousand bucks to build my own, I believe that the experience and what I could learn would worth more than the EXTRA thousand that I'd
most likely have to spend to buy most of the brands/models that I've looked at. I will admit that I haven't even tried to find a bargain, yet. I don't see how I can try out a 5E3 "repro" or an AX84 but I'm sure that I can find a demo or two on the internet. I plan to take a day to visit a large guitar/amp shop that's not too
awfully far away, and play the others suggested. Once I have heard all that I can, you all can bet that I'll have more to ask and say.

May we all be succesful in all our endeavors, whether tone related or not. Thanks for keeping me on my toes. tonequester.

[Amp Kat]

Class A has a completely different sound, because there is less distortion, until the power tubes are over-driven.
Then when the power tubes ARE over-driven, the sound is different too.
The decay of notes is perceptibly different, cleaner for sure.
So it depends if you want to overdrive the power tubes, OR if you are going for the preamp distortion / master volume type sound.
Over-driven power tubes in a small amp, Class A probably sounds better. Class A is a sweeter sound. It is the true vintage sound.

Class A amp runs much hotter, and requires more frequent power tube replacement.
Although the cathode bias of Class A amp is fixed, it should really be adjustable, with a wire wound resistor.
Every power tube is a bit different, and the amp would sound better if it was adjusted (just right) instead of fixed.

"Just because we are egocentric sociopaths does not mean we can not be helpful."
Don't forget that we are also Mal-adjusted, technically obsessed misfits, in addendum.

PS Don't buy amps made in China. The lack of support is appalling.

As a builder of a two channel SE Class A Cathode Bias amp (Fender clean and Marshall mean) I have to agree with everything SG says and until you really get into a tweaking build there are things you may not notice that you would just playing one. There is a definite sweetness to a class A amp and they definitely run hotter and obviously so. They are biased at around 110% dissipation and can be even more if you want them too. Many of these amps back in the day also used very stout NOS rectifiers and solid power tubes which are much better than our current production tubes and could take the extra heat. The difference in tube and solid state rectification in these Class A amps are a stunning difference especially at higher wattages as are the tubes used. They do have a really beautiful sound and the speaker and SE transformer used makes a huge difference. The drawback to the SE amp is getting them hum free because of the SE transformer but enough filtering and done the right way can take care of that. IMO SS diodes help in that department because you can add more filtering in the front end where a tube rectifier you need to keep the 1st cap around 33uf or so. Just depends how anal you are about it but it still sounds awesome with SS rectification and a 6V6.

[Steve Conner]

I agree, I think it is well worth trying a small single-ended amp. High powered ones can be very expensive though. My solution to that, as I keep harping on about, was to use a small SE amp as a driver for a push-pull transistor output stage. If you want lots of clean headroom, or to play loud at a gig, you turn the extra output stage on. If you want lots of dirt, or to play quietly, you turn it off and let the tube amp drive the speaker directly.

To be fair, this struggles with "in between" settings. In practice, it works out like having a master volume with only two clicks. But it's still more versatile than an ordinary amp. Power scaling helps to fill in the gaps between the power ranges.

The SE hum issue is even worse in this design, because the transistor output stage amplifies the hum from the tube stage, so I had to be super-anal about it. I used SS rectification and a CLC filter with big caps. A good choke can really kill the hum in a SE amp, and you can use a small capacitor before the choke and a large one after, to keep a tube rectifier happy.

I already had the screen supply going through a MOSFET for power scaling, so I arranged that as a capacitance multiplier to filter the screen supply even more. Hasta la vista hum!

[Austin]

I have had a THD Univalve, I think they are really nice. Single ended cathode bias, you can switch tubes from kt90/kt88 all the way down to 6g6 and all tubes in between with the same pinout to try out different tones. You can try out any preamp tube with the same pinout as the 12ax7, there are lots of them. It comes with a built in attenuator, so you can play quieter and stil get a cranked up sound. It has a good sounding transformer isolated line out and a built in dummy load so if you want you can unplug the speaker alltogether. It comes in a cool looking industrial strength metal cage that lets you see the tubes and is built like a tank. I used mine for years, it is plenty loud enough to play over a full band without even miking the cab or useing the line out to bi-amp if you have a sensitive speaker. You could probably get one used on ebay for 400 bucks. Somebody mentioned the THD bivalve, I always wanted one of those too. They are double the price tho..

THD Electronics

http://www.thdelectronics.com/pdf/univalve.pdf

http://www.thdelectronics.com/pdf/univ_manual.pdf

[printer2]

Would not mind learning more on the amp, not crazy about some of the documentation though.

“Class-A” is a term given to an amp that
runs its tubes at full current all the time, unlike most tube amps that alternate between
running one set of tubes and the other set, each for one half of the wave. The set not in
use is turned off by a positive swing of the grid voltage.

Each for one half the waveform? Sounds like Class B to me. And the full current all the time thing? I sure hope the tube does not run full current all the time, not much sound out that way.

Most push-pull amplifiers, including the venerated Vox AC-
30 operate in Class-AB when overdriven, even if they are in Class-A while clean.

Well at least they acknowledge that AB amps do spend time in A.

There is no point at which you will be waiting for the tube to
receive its full current for the best sound—it always will.

God I hate waiting.

[Enzo]

And the full current all the time thing? I sure hope the tube does not run full current all the time, not much sound out that way.

Not full current as in the most the tube can possibly conduct, but full current as in the tube current doesn;t drop away in partial cycles. It is conducting the full amount designed for its circuit. In a similar sense to driving at the speed limit on the freeway. You can drive full speed - whatever the speed limit might be, not the fastest your car can go. Not driving full speed would be like going 20mph slower than everyone else, the bastards.

[printer2]

Not full current as in the most the tube can possibly conduct, but full current as in the tube current doesn;t drop away in partial cycles. It is conducting the full amount designed for its circuit. In a similar sense to driving at the speed limit on the freeway. You can drive full speed - whatever the speed limit might be, not the fastest your car can go. Not driving full speed would be like going 20mph slower than everyone else, the bastards.

Your words inform, theirs is just advertising copy.

[Austin]

http://freestompboxes.org/members/ba...tic%5B1%5D.pdf

Here is the schematic.


For whatever it's worth I really like the amp. I like the 12ax7 in front and a 12av7 in v2 with a 6k6 or if I want to be a little louder a 6f6. A 6550 in there rattles the plates in the kitchen cabinet when I play at home and I have never needed to be that loud at a jam but then again a big tube like 6550 might work well for country chicken pickin'. I use a celestion gold with a avatar 1x12 deep(they make a thinner one too) sealed box speaker but have a really old traynor ysc-4 that I use alot too. People have often complimented me on the tone it gets!