Ah... tubes... how can you live without them?...
Alright, there are really thousands of circuits out there, each one purportedly sounding excellent by its diehard advocates. While there is no denying that there are lots of good stuffs out there, there's also no denying there's the extremely "narrow" choice of "audiophile-approved" tubes. Very often, the usual suspects are
for driver stage: 12AX7, 12AU7, 6SL7, 6SN7, EF86...
for PP output stage: EL84, EL34...
for SE output stage: 2A3, 300B, 845, 211...
for rectifers: 6X4, 5U4G, 5V3, 5AR4...
I have no problem here, but I have a lot of problems with the prices these NOS tubes command. A piece of NOS Telefunken/Mullard/Amperex, smooth/black plate, blah blah blah... 12AX7/12AU7 easily starts at USD50, not exactly the price I'm willing to pay for, no matter how many times audio nuts swear how earth-shattering, how orgasmic these tubes are. What the heck? I once saw a smooth plate NOS Telefunken 12AX7 being traded for USD400!!!!! Alright, granted that these specimens might be the best of the bunch but why the hell do they command such high prices?
An Economic student will tell you:
"It's a law of demand and supply."
Very true, but even truer when you can get sexy Italian actress Monica Belucci to say,
"Itsa law of demanda and supplya"
That's right folks. Willing buyer, willing seller. (Willing sucker, willing suckee.) If you think so-and-so specimen is so great after reading so many reviews, and there is a seller fixing your favourite tube at a price so expensive that "it got to be good", by all means, go for it! That's why it's a law of demander and supplier.
Alright, all fine here, but what leaves us DIYers?
Stay away from them! Get away from mainstream!
We DIYers always have this advantage over non-DIYers: control. We are in control of our sound. We can change components, tweak circuits, and of course, change tubes. That's right! Change tubes! Not just change from one make to another but a totally different type! DIYers rejoice! It's time to be hip!
There are lots of great tubes that can not only do the job, but can even do the job better! The list here isn't exhaustive but it should get your grey cells working and stop looking down at tubes you are not so familiar with.
12B4 is one of those very linear tubes. This guy can operate really low from 90V up to even 500V! (some guys tried here!). Mu is only 6 but way low plate resistance of 1kohm makes good preamp duties. Run them at higher current of 30+mA, and you can even use it as a power tube! Yup, a simple 1W tube amp that even got one DIYer complaining, "dang! I can't get my 300B to convey music as well as this guy!" Guys who have built 12B4-based line-level preamps found it to have a very transparent sound. "It just amplifies, and does nothing else." Better still, 12B4A is electrically equivalent to 12B4 with the added advantage of a built-in slow heater warm up. Hey! Even expensive Telefunkos don't have this feature!
The 5687 maybe isn't so "non-mainstream" as the rest. Audio Note uses it in their M7 preamp. The Ongaku has one as cathode follower. Mu is not high at ~18-20 but thanks to its excellent linearity and low plate resistance (~2kohm), it has the making of a good preamp tube.
The 5842 is as similar as can be with the Western Electric 417A. Hey, buddy, anything with a "Western Electric" name on it isn't cheap okay? (I bet you if WE did make toilet paper, it'll cost a bomb too.) Capable of high current up to 30+mA, they make a VERY beefy driver. Actually, if ran with grid of 2V, 36mA through, you have a one-tube, one-stage ~1W tube amp!
The 5965 is actually similar to 12AV7 but cost a fraction of their 12AX7/12AU7 siblings. Cheap and good, this is one of my favourite tubes and I have quite a number of them! Some Joes on Joelist found that they can be used in place of 12AT7/12AU7, which really saves you truck loads of $$! But beware, better check with your schematics first. Likewise, if you don't need the gain of a 12AX7 (mu=100), they might even work in your amp. For your info, since this tube is dirt cheap, even a cheapskate like me has compiled NOS samples of RCA, GE, Sylvania and Raytheon. Try this with a 300B!
The 6C45Pi seems to be the Russian equivalent of the 5842. Specs are pretty similar but construction wise is night and day! This tube has hefty plates. The plates are so thick that Yankee tubes look like anorexic waifs beside it. Look here.
Balanced Audio Technology made a big fuss a couple of years ago saying that the 6H30P is the "perfect" preamp tube, saying that it has a plate resistance of only 200 ohms but it was later found out that BAT achieved an output impedance of 200 ohms only after PARALLELING several stages of 6H30P. What bollocks! Nevertheless, it has a plate resistance of ~1kohm and makes a pretty good driver.
The usage of Russian tubes has increased these couple of years and another good driver is the 6N1P but the 6N1P doesn't belong to only vodka-drinking Ruskies. Seems that they were made in China as well and military grades of the 6N1P is said to be "very very good". With some circuit modifications you can replace the 6922/6DJ8 with the 6N1P. Word has it that these 6N1P smoke the hell out of even premium Amperex 6DJ8s...
The 8532 first came to my knowledge as the driver in the original Darling amp. So far, haven't heard any negatives being said about this tube. With mu ~40s, if your circuit needs a lot of voltage swing, you know which number to dial.
Alright, the JJ ECC99 isn't NOS as it's still in production. Nevertheless, it's worth considering. Specs pretty similar to 5687 BUT said to be 3 times less noisy.
I can't thank Bob "Papa Darling" Danielak enough for discovering the excellent 1626. Thanks to its availability and low prices, it's truly a "poor man's 300B". The only complaint is its low power of only 0.7W. Read them all here at the Darling Club. Please visit Papa Darling's website from a link there. By the way, the Darling Club, at time of writing, has members in the US, Canada, Germany, Netherlands, Philippines and Malaysia!
Oh yeah! If you fancy shortest signal path, you can't go wrong with a one-tube, one-stage 1W tube amp! Build the one-tube, one-stage 5842 or 6C45Pi amp! You can't go a shorter signal path then having this tube INSIDE your CD player. This way, all you need is just a CD player with enough space to accomodate 2 tubes (for stereo), a few resistors/caps, a transformer for providing the appropriate B+/filament juice and you are done! Yes, use your CDP volume pot! See? No interconnect! Once you build this, bring it to a friend's place and surprise him with your "mini compo".
The 6C33 is not mainstream yet but slowly becoming so. Lamm and Graaf has amps built around them. First discovered by the Western world in a Russian MiG! Yeah! This tube rocks! Built like a tank, it can give you 15W of SE power, enabling it to drive LOTS of speakers. A DIY friend once had his coupling cap shorted, so full B+ was on the grid but the tube survives! Just goes to show how durable these tubes are. However, there's 2 factors against them. Extremely current hungry filament (6A!) and terrible input capacitance. The latter can be solved by using a beefy driver or a cathode follower but the former requires a chassis with very very good ventilation. Otherwise, fried eggs anyone?
And then there is the rest of the bunch, more obscure ones like 813 etc of which a visit to the excellent Joe's list is a necessity for the adventurous DIYer...
I first learned about TV damper diodes after reading Lynn Olson's work on his Aloha Audio website. (Lots of good stuffs there!) Lynn Olson is a fan of TV damper diodes and according to him, they (the tubes, not Lynn) give the lowest switching noise of any rectifier ever made, be they sand rectifiers, or tube rectifiers like 5U4G etc. Ever. Better still, they are relatively cheap and comes with impeccable specs! The 6CK3/6CL3 can do almost 1000VDC and up to plate current of 250mA! Serious stuff! The 6CG3 can even go up to 350mA DC! There you 6C33 fans can even use this in your amp. My main gripe with them is that they need lots of filament juice. The 6CK3/6CL3 needs 1.2A while the 6CG3 needs 1.8A. Not a big deal but it is when you realize that you need TWO of them for full wave rectification.
Surely this isn't problem for a DIYer right?
Oh yeah, the only TV damper diode still in production these days is Svetlana's 6D22S. See? DIYers have CHOICES.
What if you JUST have to use 6SL7? Still, there is an alternative. Use 12SL7. 12SL7 is equivalent electrically to 6SL7 EXCEPT that it uses a 12.6V filament while 6SL7 uses 6.3V. So, get the 12SL7 and use a transformer that has this 12.6V filament rather than 6.3V. Remember you are now unable to use 6SL7 in your amp anymore but this is a small price to pay! Pun more than heavily intended! However, you can easily implement a switch like what some DIYers do to go from 6V heating to 12V heating. This way, your amp will be able to cater for both the 6V and 12V versions of your favourite tube.
As these are at much lower prices than their more popular "audiophile approved" brethrens, pick them up while you still can! Remember, one day when all NOS 6SL7 is no longer available, people will turn towards the 12SL7!
Suffice to say, there are quite a number of tubes that have electrically equivalent versions but with different filaments. Visit Duncan Amp to download the excellent Tube Data Sheet Locator (TDSL) and try to find your favourite equivalents! You will realize how the hell you lived without this great tool all this while.
For non-DIYers, you have a choice here as well. Get someone to fit in a separate filament transformer (provided there is enough space in your amp chassis) that can give you the appropriate filament voltage, rewire a little and you are done.
That's all, folks! Just a little ditty to show you what DIY can bring you. CHOICES. Better stop here, it's time to go back to my seductive-and-wallet-friendly tubes...
*In the great George Orwell classic, "Animal Farm", after the farm animals ousted the farmer from their land, they had the famous decree, "all animals are equal". However, after the pigs, leaders of the farm animals, began to exert their influence, the decree then had an extra line "but some animals are more equal than others". I don't know about animals, but one thing for certain, the pigs are right about tubes!
