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

[tonequester]

tonequester here.

Any and all advice acceptable. Use, blues primarily and blues based rock. Suggestions: pros and cons, brands, experiences, things to be aware of, etc. My strong point is inexperience/ignorance. I'll take all comers with great appreciation. Are Steve Conner, soundguruman, and Enzo in the house ?
tonequester.

[Enzo]

I would say try as many amps as you can. Forget the class A thing. If you find a class A amp you like, buy it because you like the amp, not because it is class A. And you may not care at all for some class A amps. Wanting class A versus class AB, or for that matter tube versus solid state, or any of the other choices, should be based upon a real criterion, something thet YOU HEAR that makes it better. DOn;t let voices on the internet tell you something is "better" because of some particular aspect. If you like the sound of an amp, then you like it. You don;t then decide "Oh I can;t like this one, it isn;t class A." What I like may not be at all what you like.

When you have played through enough class A amps to learn just what the class A contribution to the sound is, then you are better prepared to make a choice. But just hearing some amp that is class A in operation, and really liking it may or MAY NOT be due to its operating class. You may like it because of the speaker configuration, or perhaps the preamp tone. A lot of class A amps have cathode biased output stages, but then non-class A amps can have that too. They are not the same thing, though many people think so. SOmeone claiming to love the sound of a class A amp may be liking cathode bias instead. Cathode bias and fixed bias have differences in dynamics, sorry, they TEND to.

[Steve Conner]

You probably want to make up your mind how much money you want to spend, too. There are lots of amps in the 15 watt range, from Chinese-made ones under $500 (Jet City JCA20H, Orange Tiny Terror, Vox Night Train NT15 for example) to handcrafted boutique jewels that cost thousands (Swart, Kendrick, Mission Amps etc.)

Two classic designs in this power range were the Fender 5E3 Deluxe and the 18 watt Marshall. Both are available as reissues, clones, DIY kits and so on. Both need cranked up loud to get distortion.

I doubt any of them is "true Class A" but as Enzo explained, that doesn't matter in the slightest.

[tonequester]

tonequester here.

Thanks Enzo and Steve for the info. i may have not made myself very clear in my post. i actually have never a heard true class a amp that I was aware of. I have read the sane thing about the cathode bias thing in one of Gerald Webers (Kendricks Amps) books. I also know that I'm going to have to not only listen to any that I might get the chance to, but If I can't personally play with it for an hour, I won't buy. I learned quite a lesson with the HT-1R, plus all the advice you guys gave me on that one. I have learned that far better than half of what I read on the internet is so much B.S. That's one reason that I decided to try this forum, where I could ask quesrtions and at least sort of get a feeling for the people that I post with, like you Enzo, and you as well Steve. I actually learned the same lesson over the course of a few months when i was trying to learn
some new songs on those tab sites that are free. I never saw such blatently wrong stuff in my life. I couldn't get iover the fact that some of those people that offered up transcriptions had the b---s to put them on the internet and sigh their name to them. I must admit that some told you at the end of the tab that "this is probably not right" and "I think this is close". On the amps, Enzo's advice will pretty much be my guide before even thinking of buying. Steve, you gave me some suggetions as to some brands to check out.
The 18 Watt Marshall may be a good place to start for me.......if I can find one some where around Kansas City. Whether class a, ab,single ended, or push pull my main concern is the sound of the amp, and I'm hopeing that I can come up with an all tube amp with a fairly simple circuit. If the sound is there, I don't think that I'll go wrong there. I do realize the price range, and being on disability things like hand-wired and "Boutique" are nothing but a pipe dream for me. I do have patience and(God willing) plenty of time, so maybe I'll find that "deal" we all hope to stumble upon. Thanks to the MAX as usual for your posts. Although we have never actually met, i have a good deal of respect for both
of you, your obvious expertice, and your opinions. I hope that "things" are great in Lansing, Michigan and Glasgow, Scotland. Sure is hot and dry in Spring Hill, Kansas !

tonequester(ampless in Kansas) out.

[Wittgenstein]

You can't go wrong with a 5E3 Deluxe

[printer2]

Built a Class A P-P amp with 12AQ5's (12V version of a smaller 6V6 equivalent) putting out about 6W and it turned out OK, built a SE Class A amp with about the same wattage. Both are Class A but different animals due to the different circuit. The difference is mainly in the way they distort. A class AB amp would sound a bit different yet, actually I think it might even be more of a R&R sound with the output tubes load line being shifted.

No problem getting 15W in Class A. Two 6L6's in SE parallel at 350V will get you an easy 20W or P-P around 300V.

[diagrammatiks]

the thd bivalve is great and it's confirmed class A. The Laney Lionheart is another.

[tonequester]

tonequester here.

Much thanks to Wittgenstein, printer2, and diagrammatiks for enough info to research for hours. I must say that I,ve read some impressive things about the
5E3 Deluxe, and some modifications that have been done with them. By the way the pics of your work(Wittgenstein) looked pretty impressive, and I'm assuming that the
resulting tone was as impressive. printer2, I like your idea about class a, using parallel 6L6's for 20 Watts. That hits my output power needs dead on, and the "right" 6L6
can have just as sweet a tone as a 6V6. I've had experience with both, although only in push-pull configuration. Did you use cathode-bias, and pardon me if I show my ignorance by asking. I don't have the "build" experience of most of the guys that have replied to my posts. Beginning to feel awful humble ! I've printed off everybodies ideas and WILL
check them all out before spending a buck. diagrammatiks, I most definitely will check out the Bi-Balve. I actually know a dealer not too far from my usual haunt, where I remember seeing the THD brand on display. I didn't have the time to try anything out that day as I was busy with P.A. problems and this outfit works on everything, unlike the
small shop I usually frequent(very close to home, good friends with owner). I will call Guitar World(not a chain store) tomorrow and find out if they have a Bi-Valve I could
"test drive". I'll be suprised if they don't. They must have fifty amps on the floor. Once again I "doff my hat" to all of you for your speedy replies. Great to "meet" you Wittgenstein, and printer2. Until i joined this forum, I used to think that most folks who did so were probably egocentric sociopaths. You all continue to prove that thought
idiotic. I've already profited greatly on about a dozen problems and projects, for having made your aquaintences, and read your comments. BEST WISHES TO ALL IN EVERYTHING ! tonequester.

[printer2]

Just because we are egocentric sociopaths does not mean we can not be helpful.

Did a quick search for a 20W SE transformer.

Doberman 20 Watt Single Ended Output Transformer

Looking up the datasheet of the 6L6 tubes (can use a GB along with a C, might even be worth going inexpensive Russian as in Class A you would be running lower voltages compared to regular guitar amps) one tube is looking for 4.5k, the above transformer with a 2.5k tap should be good for two tubes. The Hammond 125GSE might be another option. Not that I am pushing a SE amp but it is a easy option. No reason you can not do a P-P Class A with the pair of 6L6's, the difference between the amp is the SE will have a higher second harmonic distortion when pushed while the P-P will cancel it out giving you more third. Depends on the flavor you want.

I used Cathode bias on the amp. I did not mention it before but since it was a Class A P-P amp I put a switch in to turn off the signal to one of the tubes. The off tube still was biased for center operation so the idle current balanced out the current through the transformer of the other tube. So now only one tube was working (sort of SE) and I got out about half the power.

[soundguruman]

tonequester here.

Any and all advice acceptable. Use, blues primarily and blues based rock. Suggestions: pros and cons, brands, experiences, things to be aware of, etc. My strong point is inexperience/ignorance. I'll take all comers with great appreciation. Are Steve Conner, soundguruman, and Enzo in the house ?
tonequester.

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.

[printer2]

Not wanting to sound contrary but a Class A does not have to run hotter. The datasheet for the 6L6C gives an output of 11W running at 350V and idle of 54mA. Without standard loses that is about 18W plate dissipation. With a 30W plate dissipation the tube is running at 63% which is less than the 70% many fixed bias amps are set at or the 90-100% cathode biased amps are run at. Also going for preamp distortion compared to power tube distortion makes no difference between what class amp you run. And even a Class AB amp runs in Class A until you get close to full output anyway. A small amp can also run Class AB, no reason it has to run A.

[soundguruman]

Not wanting to sound contrary but a Class A does not have to run hotter. The datasheet for the 6L6C gives an output of 11W running at 350V and idle of 54mA. Without standard loses that is about 18W plate dissipation. With a 30W plate dissipation the tube is running at 63% which is less than the 70% many fixed bias amps are set at or the 90-100% cathode biased amps are run at. Also going for preamp distortion compared to power tube distortion makes no difference between what class amp you run. And even a Class AB amp runs in Class A until you get close to full output anyway. A small amp can also run Class AB, no reason it has to run A.

Class A ALWAYS runs hotter, class A uses tubes faster, and uses more electricity.

[printer2]

From the 6L6GC datasheet,

Push-Pull two tubes Class A1, 270V plate voltage - 134mA idle current -140mA max signal plate current - 17.5W output, -17.5 bias voltage

Idle plate dissipation 33.8W - full output plate dissipation 35W

Push-Pull two tubes Class AB1, 360V plate voltage - 88mA idle current - 155mA max signal plate current - 18W output, -22.5 bias voltage

Idle plate dissipation 29.7W - full output plate dissipation 52W


Push-Pull two tubes Class AB1, 450V plate voltage - 116mA idle current - 210mA max signal plate current - 55W output, -37 bias voltage

Idle plate dissipation 47.9W - full output plate dissipation 87W


And if you run the tubes at a lower voltage yet they can dissipate a messily 20 - 25W. If you want to run at a lower voltage and put out lower wattage you pretty much have to run more current otherwise the amp sound anemic. The way to do that is run Class A rather than Class AB. The tubes will last a lot longer running at 270V rather than at 450V.

[soundguruman]

From the 6L6GC datasheet,

Push-Pull two tubes Class A1, 270V plate voltage - 134mA idle current -140mA max signal plate current - 17.5W output, -17.5 bias voltage

Idle plate dissipation 33.8W - full output plate dissipation 35W

Push-Pull two tubes Class AB1, 360V plate voltage - 88mA idle current - 155mA max signal plate current - 18W output, -22.5 bias voltage

Idle plate dissipation 29.7W - full output plate dissipation 52W


Push-Pull two tubes Class AB1, 450V plate voltage - 116mA idle current - 210mA max signal plate current - 55W output, -37 bias voltage

Idle plate dissipation 47.9W - full output plate dissipation 87W


And if you run the tubes at a lower voltage yet they can dissipate a messily 20 - 25W. If you want to run at a lower voltage and put out lower wattage you pretty much have to run more current otherwise the amp sound anemic. The way to do that is run Class A rather than Class AB. The tubes will last a lot longer running at 270V rather than at 450V.

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

[Chuck H]

SGM, it really depends on how the amp is used. A class A amp set for center bias at some moderate voltage, ending up below the tubes max dissapation and played distorted (often drawing a tad less current than idle) will likely have longer tube wear than an AB1 with some 600Vp biased hot. "Runs hotter" is relative. In the above example I'd bet the AB1 runs hotter per tube capita and wears out tubes more quickly. Remember that AB1 just means that each side is handling half the duty cycle. If that duty cycle is twice the tubes max then it's actual "work" is the same as class A. More if it's biased hot.

EDIT: It's worth noting that in all practical cases a class A amp WILL run hotter than an AB1 amp. But amps don't make music idling. And, other than bias supply faults, most heat related failures will occur while an amp is amplifying.