A Slew of Beginer Tube Questions

[JPeitzman]

Hello once again to everyone! I have spent a lot of time in the forum learning and posting a few, usually useless comments and threads. I spent a while in the Pass forums, watching, learning, what not. But now it has come time to jump back to my first true audio love, tubes. I have built a JLH Original, the first amp I built, I love it, but there is just something missing. Well I also built a pair of Gainclones, and well... I must say the hype didn't justify the sound, but I am new so I could have done something wrong...though I doubt it with such a simple circuit. I have very grand and expensive plans for some Pass amps, but they are years away. It is time for tubes!

Basically I have a bunch of questions I would like to bounce off some of the tube guru's, I am sure though that these kinds of posts get annoying, I am sorry. I need a pre-amp, and I want to build a couple power amps as well, but questions abound regarding these subjects. I have tubes that I got from my dad, and I am slowly buying on my own. For this reason I have lots of some and few of others.

1. I don't know what to build for a main preamp, I am thinking 12AX7 and 12AU7, but I am open to suggestions. I have a RCA 12AX7 and a couple 12AU7's (RCA, Sylvania, and one unmarked, I think Tung-Sol). I also have quite a few RCA 6SN7's and 6SL7's, so I could do something there as well, any ideas?

2. I have a beautiful pair of Western Electric 264B's sitting on my desk in front of me that I really want to hear sing. Has anyone ever used these before? I would also really like to build a 56 based preamp, I have one but am going to buy more...any idea how the 2 would compare?

3. Any other ideas, keep in mind there are two things I really really really like. Keep in mind the constraints...low distortion, good to high frequency response, blah, blah, you know. I love old tubes, ie: old RCA, Western Electric, Cunningham, etc... I also like really weird tubes, either something not normally used that shines, or something that is physically strange looking, tube wise.

Power Amp:

1a. I am thinking of doing either a 6L6 PP UL, or an 807 PP UL amp as my main, and kind of reference amp of this style. If I go 6L6 is 300V good or should I go a little higher. I have no idea what is good for 807's. I have a few RCA 6L6's, but am considering buying some Sylvania or RCA 6L6GC's. For 807's I have 4 that are RCA and 5 that are Amperex stamped "Made in England". The RCA's I believe may be used, I haven't tested, but the Amperex's are brand new still wrapped in paper.

1b. I don't know what topology to use, or input/driver stage for that matter. Williamson would be the easiest, but I was thinking of running it fully balanced, balanced input and a transformer for the unbalanced input. I was thinking a pair of 6SN7's or a 6SL7/6SN7 Input/Driver combo. Any other ideas for tubes?

2. This amp above and probably a few others will be used for music, movies, games, etc... A general purpose high end amp. I assume PP with 6L6's or 807's would be a good choice. I could move to KT88's or 6C33's though just to get a little more power output I guess.

3. I really want to do a SET amp as well, same principal, high quality to judge other creations. I am leaning towards 300B's, but I have one 2A3 and one 50. I have no idea what to use for a driver or input, or really what output tube to use either.

Thanks for any or all feedback. Thanks to for putting up with my long and sometimes pointless posts. I will go back to lurking and building for a little while.

[Sheldon]

Those 264b's have very nice plate curves. They would probably make a wonderful low gain preamp. Not too good for driving an amp with low input impedance, but that shouldn't be a limitation with most tube amps. Other possibility is as an input tube for a SE DHT. For a two stage amp, you'd need to pick the opt that didn't require a lot of voltage swing.


I would guess that others will suggest that they are worthless, even dangerous. That's no problem as certainly someone will generously offer to dispose of them properly.

Sheldon

[Jeb-D.]

For your first amp build I'd do something that can all be ran off one power transformer per channel. So picking output and driver tubes ect. that run in the same voltage range on both the plates and fillaments needs to be considered. Something self-biased as well, to avoid a biasing circuit. Chose tubes that have readily available power and output transformers.

Right now I'm building an OTL that requires 5 transformers per channel. It has really given me an appreciation for the minimalist designs.

If you like odd looking tubes check out the 829B. It would be cool to make a push pull amp out of these. Since each tube has two penodes it would only require one output tube per channel.

[JPeitzman]

Thanks so far!

Yeah I like the 829B, I think I have seen an amp using one around, but I don't remember for sure. I have seen a lot of amps. I really like the 833 as well! My favorite so far though has been here:

http://www.teresaudio.com/haven/

Hit "Friends Systems" then check out Orey Block's 450TL SE amp!!! 150-watts of single ended power! But with the plates at 4200 volts and dissipating 400 watts!! They all have great systems, but I really like Ken Schei's Audio Note DAC with 56's at the outputs, and Grant Gassman's amps. Western Electric 417A's and 205B's driving Telefunken RV-218's, pure awesome! That and Mr. Gassman's horns are drop dead gorgeous.

So do you think the 264B's would sound good in front of 300B's, 2A3's, 50's, 45's, the like? Or would it be better to use something like a 417A, ½ 6SN7, 205, 101, etc...?

[Sheldon]

Originally posted by JPeitzman
So do you think the 264B's would sound good in front of 300B's, 2A3's, 50's, 45's, the like? Or would it be better to use something like a 417A, ½ 6SN7, 205, 101, etc...?

I don't see why not. You could make a flea power amp with the 264 in front of a type 10/801, or 45, or the like. Or the flea power section could be the driver for a bigger triode. I'd try the 264 over a 6SN7, just because it's much less common. Here's an SN7 example. I built an amp based on this circuit, but with current regulated DC rather than using the hum reduction method shown: http://members.aol.com/sbench/humbal.html. Gain with the 264 is marginal, but if you are driving it with a preamp with gain, you might get away with it. Note that I haven't really thought this through, but I'd find a way to use that tube in front of a DHT amp just for the coolness factor.

Sheldon

Thinking a bit more, the gain is light for a two tube amp, but a 264 into a 10/801/45/2a3 into a 300b would work.

[ray_moth]

Firstly, there's nothing wrong with 6L6 and 807 as good, gutsy OP tubes. However, if you don't like flying leads going to a top cap at high voltage, that would rule out the 807, I suppose.

Secondly, I believe the 6SL7 and 6SN7 are much better (more linear) than the 12AX7 and 12AU7. If you read Morgan Jones's 'Valve Amplifiers', you'll see that, from testing many examples, he found the 6SN7 and like tubes (12SN7, 7N7) to be very linear.

A 6SL7/6SN7 combo would be an excellent choice. The high-mu 6SL7 is not suited to driver duty but makes a very good voltage amplifier. The medium-mu 6SN7 is a good driver for most purposes.

MJ also found the 12AU7 to be very consistent - consistently bad! It's a non-linear TV tube that has somehow found its way into audio circuits and people still keep using it! If you want a 9-pin true equivalent of the 6SN7, there are two choices: 6CG7 or 6FQ7. The 12AT7 is also reputed to be a good choice in the right application, e.g. for an LTP splitter/driver.

[JPeitzman]

So here are the designs I was considering for a line-stage:

1. One half of a 6SL7 connected to one half of a 6SN7.
2. An 6SN7, both halves as a common cathode, connected together.
3. One half of a 6SN7 as a common cathode, that's it.
4. An 6SN7 SRPP, for some reason this is my favorite, but I know almost nothing about SRPP design.

I am wanting to use little to no feedback. Again I am wanting detailed, dynamic, low distortion sound, but I don't mind the small colorations that some have said the 6SN7's add. Example, some have said that they don't like the 6922 because it is almost harsh in sound, yet some do like it over the 6SN7, the tube that is, not the harsh sound. I am going to use a regulated B+ supply, around 200v, give or take a little. So far I am planing to use a 5AR4, 5U4, or 5R4, ie tube rectifier. I don't know if I will see (or hear) much of a difference between choke loaded or capacitor loaded PSU's, so it is an either or thing to me. The only other stipulation is that I want it to sound good, but I also want to be able to tweak and change it as time goes on with little to no difficulty.

As for power amp I am thinking of a couple of different things:

1. Build a simple and publish amp to kind of get my feet more wet. I was thinking something like the EL-84 "Baby Huey" or I have a schematic for a Balantine (old theater amp company) 6V6 monitor amplifier. All it uses are 6V6's in push pull and a 12AT7 (if I can remember right) driver. I was wondering how it would sound with some warm n' smooth Marconi 6V6G's with a sexy Mullard ECC32 driving it (slight circuit changes of course).

2. I am very attracted to (maybe sexually...I can't tell) the AE SixPac Amplifier. Well and the AE-3 MkII Line Stage for that matter, the inspiration for my Line Stage, but anyways. I by no means want to outright copy it, that is no fun, but I would like to make something close. The thing that I think I like the most about it is that it will take EL-34's, 6L6's, 6550's, etc..., with little to no problem. The one thing I am not sure about is the input stage (I guess obviously it has worked, but not the point), I was thinking LTP input with triode common cathode stages for drivers (One for in-phase one for out). I was thinking all this a-la 6SL7/6SN7 or a pair of 6SN7's. I was thinking also maybe JFET CCS's, verses the EL-84 CCS in the original. It would be an undertaking, but I think with a few tweaks it would make awesome music, the real SixPac already does!

I am thinking for this too using a 5AR4 CLC or LCC with a regulator to hold B+ at 300v - 350v for the output tubes. Then another circuit for the input/drivers to hold them in that 200v range plus or minus.

Thanks for the feedback!

BTW has anyone used the Jensen 4-Pole capacitors in their PSU's at all? I am planing on using Jensen Copper Foil and Oil capacitors for coupling, but I find the 4-Poles kind of interesting.

[SY]

Just a bit of advice/philosophy from one of the old guys: "some have said" is almost a certain indication that the statement is wrong.

One other thing- there is no reason to use an SRPP in a linestage and lots of reasons not to.

[Majestic]

Just some comments from a fellow beginner:

- the Akido line-stage is garnering good reviews. I've not built one yet but I'm planning to. Worth considering as a first project for yourself (?) especially since circuit boards are also currently available.

- rectifiers have definite (to my own surprise) sonic effects on the resultant amp. Good-sounding GZ34's will cost you money, but as a DIY-er you have other options that may even be better (e.g. Damper diodes are a strong contender, G37's or some of the more obscure Euro varieties {the latter of which which will also cost you $$ unfortunately})

- many (most?) 6DJ8's seem to have an upper frequency 'glare' to my ears. The sought-after brands though, have this to a much lesser degree. Perhaps that's why they're so in demand? The sound of these latter types is quite nice in fact! The current production JJ also doesn't glare; but concedes a little in transparency and detail to the better 50's-60's varieties. Even so, though I might prefer the grander NOS oldies, I can live with the JJ's. So If you can too, then the 6DJ8/6922 could be a contender for you. That said, it might have too much gain for a line-stage anyway. (Phono is another story of course).

- 12AT7's as a family, 'glare' too. But more in the mids - and they sound 'dry'. There are exceptions here too though (eg early Sylvania's) so treat this as a 'broad-brush' comment. But be aware of it. And I've definitely heard nice sounding designs that use them. They can make for good drivers (as someone else commented), so don't discount them out of hand in such a position especially if you already have some in your own stockpile.

- 6CG7's I quite like. A 6SN7 is reputably better (with exceptions) but there are many good-sounding brands of 6CG7 still redily available for not too silly money. There is also current production of them too. So this seems a sensible tube choice for a line-stage maybe. A respected DIY-er (Thorstein) feels that a 5867 is a "more musical" tube however. But I've not yet confirmed this for myself. (I'm just giving you a smattering of other consensus/option). But a good-tube choice to start off with. (applies to 6SN7 too).

- The 6CG7's cousin - the 12AU7 - can sound classically 'tube-y' which is sometimes nice, but I think it's just overall a little too fuzzy in sonics. (Personal opinion) This may be related to it's reputed distortion characteristic. Thus I agree with other's poster's comments about this being overall, a suboptimal tube choice for a new design. (Go the 6CG7 instead)

- as for power tubes: check out the other recent threads about other DIY-er's faves. I found it quite interesting myself. (I'd comment, but I've only used EL34's and EL37's, so not much to contribute really! I've heard KT88 designs and though it's not an even comparison would agree with the general categorization that other posters have made)

I hope some of that might be of some use to you in your own quest

[arnoldc]

May I know what speakers you'll be driving? That would dictate the amplifier you would be building.

If you want to use the 6SN7, a popular circuit would be the VTV 6SN7 linestage. It would be a good place to start.

If you find a brother for your 56, the Berman 76 preamp would ba a candidate. 56 is a 76 with different filament.