The best output tube you've (probably) never heard of... 

Just need the red subaru now...

6aq5 and el84 are interchangeable.

My grandpa’s did.

and R2R tape recorders....

@@skullheadwater9839, interestingly, Voice of Music portable phonographs and reel-to-reels (a favorite of mine for scavenging parts from) typically used single-ended octal output tubes (usually 6V6, occasionally 7591) and not miniature tubes like 6AQ5 or EL84.

Just don't put a 6V6G into an amplifier like a Deluxe Reverb that was designed for a 6V6GB and runs the tube at 70 volts over its rating!

@@goodun2974 That's right ( same with 6L6 etc ).............I know the ratings ........the issue of my comment was the sound quality . kind regards

Hi I would use 6BQ5/EL84 instead , nice tube in SE configuration both for hi fi and guitar. For Hi Fi you need global negative feedback.

Hah! I knew someone would catch my error in haste, couldn't imagine it would be Mr. Carlson himself. Thank you for yet another lesson in the need for attention to detail 🤣

Well yeah, but there's just something about how the GE 6AQ5 breaks up. They are also very cheap and very well made.

I can see that in the sense of the fact it handles more voltage but as an amp builder you are the one who controls that so you can design the power supply to put the ideal voltage for this tube as well. They have a different tone, the sound very smooth compared to a 6V6, I actually prefer them to 6V6's and have built a handful of amps with 6AQ5's. I actually built an amp using all 12volt tubes using 12AQ5's which I want to say I got a sleeve of 5 NOS for $25. It is one of my favorite sounding amps.

I like it too

367V would be about right if it was solid state rectification, but don't forget the 6CA4 drops about 60V. Plate voltage is right around 305V. That's still in excess of the 250V or 275V shown on 6AQ5 datasheets, but the handful of guitar amps out there run the plates at ~300V no issue.

So true, good news is they tend to be ~$10 for high quality tubes... for now 😉

Agreed! I know Gibson had no problem running 6AQ5 at 300V, 400V might be pushing it in the smaller tube package.

Due to the smaller size they physically can't dissipate the heat of and octal tube with all other things the same.

Can't ask for more than that!

How so? It has a DC coupled cathode follower into a tone stack, a master volume into a Cathodyne PI into Push Pull power tubes. A champ is literally two preamp stages into a power tube. This is sort of a mixture of a Brown face Fender deluxe front end with a master vol added into a 5E3 tweed power section with some component values changed.

Hard to get quiet, non -microphonic EF86 these days, and vintage EF86 are expensive; I'd be tempted to use 5879 low-noise pentodes instead (often used as a mic preamp in vintage PA equipment); not super common these days, but available as NOS, and not terribly expensive. Or perhaps even 6AU6 which are common and cheap as chips; you could buy a dozen of them for about 3 bucks each and select the quietest ones. BTW, I have a big Webster PA/paging amp with 4 !!! 5879 inputs, 4 6L6's, and two 5U4's, which is just begging me to build a guitar amp out of it....

The series diodes are protecting the power supply from a shorted rectifier tube. Without those diodes, the filter caps could potentially see very high AC voltage and fail spectacularly! See Robrob's info on "backup" diodes: robrobinette.com/Generic_Tube_Amp_Mods.htm#Protection_Mods

Not only do the diodes add protection for the power transformer and rectifier tube, as described here, but you still get the sag and compression of a rectifier tube when you play hard (a fully solid state power supply would be much stiffer feeling) and it also still gves a gentle time delay of the B+ feed to the tubes and caps at turn-on.

My exact 💭 thoughts

I guess if you are using off the shelf transformers made for a deluxe but, a builder can make whatever he wants. I have built amps out of control transformers that put out 240v, with a bridge you get about 325v before load, you just use a separate 6.3v filament transformer. The cool thing is you can usually get both for less than you pay for one of those "fender" replacement transformers. It just depends on what you want to build vs how much you have to spend. If you are building clones, I suppose it may be the safe option to buy a kit or individual parts made for your clone but every amp I build is a unique entity. I generally do use modified existing concepts for successive stages. For instance, the last amp I built was sort of using the idea of a 5E3 preamp but instead of using a 12ax7 I used two separate tubes a 6SJ7 pentode and a 6SF5 which is an octal triode with 100mu, using the same basic interactive V,V,T, scheme of a 5E3 but then I used a 6SL7 set up as a paraphase inverter into a pair of cathode biased 6V6's. This thing sounds phenomenal, like nothing else. I used the chassis/PT out of a 1954 Revere R2R with a OT from a 59' Conn Organ. It is mounted in an upright 59' Magnavox record player console with a 57' 12" magnavox alnico speaker out of a different console.

@@skullheadwater9839 HI, I put " Fender Deluxe Reverb" not as a brand or specific model, It cuold be any clon with similar circuit, It´s not an unusual one , didn´t mean to put "Fender" in the context of cost or status as vitage or valuable device.

I would generally reject the idea that output tubes have an inherent sound. Even if it was true, being able to separate it from difference in circuit design, actual component values vs. marked values, and subjective listening would be impossible. I don't think I do.

​@@graybenchelec, In general I would tend to agree with you, but I also had an experience with a Kalamazoo Model One that I had recapped which sounded kind of tame with 3 or 4 other strong-testing American and Japanese 6BQ5's but when I installed a good used European Amperex Bugle Boy EL84 into it, the amp turned into a tiger and sounded very much like a miniature Vox AC30. The difference was staggering! In hindsight I am guessing that the Amperex EL84 was a true pentode with internal suppressor grid, and the American and Japanese tubes I tried were beam power tetrodes, not true pentodes.

The 807 was often used in Williamson amp designs. They're still fairly common and affordable today whereas the 6146A is rare and pricey and perhaps should be saved for use in original early Ampeg SVT bass amps.

@@goodun2974 The 807 is just a 6L6G with a plate cap, (not the GC version.) The 6146A and B versions are a nice powerful compact tube for RF and modulator service, along with the S2001, 6883 and 8298.

@@MrCarlsonsLab , If I remember correctly, the 807 could handle significantly higher plate voltage than a 6L6G, which is why it was favored for use in small RF transmitters (6L6G was rated for only 300 volts). The 6146A and B are very different animals, of course.

@@goodun2974 Yes, the reason the 807 could handle more plate voltage is the plate connection is on the top of the bulb, not in the octal base like the 6L6G. The internal structure between the two is identical.

@@MrCarlsonsLab , Of course, 807 were usually used in class B as transmitters and therefore coul handle even more voltage than you might expect, compared to what they can handle as class AB audio amplifiers.....

Hah not so sure about that. You could use 6AQ5 in a 5E3 kit, just have to do something about the plate voltage. There's solutions out there!

It is a cool tube but many of us amp builders know about them and have already been using them for years. No disrespect intended to Mr. Gray.

My first interaction with 6AQ5 was a Gibson Scout I bought a while back. GA-17RVT I believe. But I do enjoy his videos as well, yes.

Fair point! I think I was trying to leave a little context clue for anyone who might have been confusing 6AQ5 and 6BQ5, but yeah EL84 is probably the more common part# overall.

@@graybenchelec Thanks for the quick reply. I take your point about 6AQ and 6BQ tubes and it's a valid one. BTW, love the channel, keep up the great work!

Yes EL84 tubes tubes have it hands down. Lol.

American-made new-old-stock 6BQ5 and 6CA7 are likely to be beam-power tetrodes and not true pentodes like European EL34 and EL84 tubes. Phillips held the original patent on Pentode tube design and most American manufacturers didn't want to pay Philips to manufacture their own pentodes, so they developed beam powered tetrodes which have beam forming plates to direct the electron stream. 6BQ5 and 6CA7 are pin-out plug-in compatible with EL84 and EL34 respectively, but the performance might be a little different in some cases. Towards the end of the tube erar, of course, many American manufacturers such as RCA were importing tubes from Europe and rebranding them, and so you might see true pentodes bearing American brand names ----- And it's possible that the Phillips patent may have run out and allowed American companies to produce their own pentodes, but would manufacturers bother to retool for this in the 1960s when it was clear that the era of vacuum tubes was ending soon?

@@goodun2974 probably not but you misspelled era, so...can I trust you? Lol.

Just a bit of self-deprecating humor 😉I haven't measured the output wattage, probably about 10W.

The first tube was a 6V6GT, the second tube, and subject of the video, is 6AQ5.

IIRC, there were 3 or 4 versions of the Skylark: single EL84, dual EL84 push-pull, dual 6AQ5 push-pull, and perhaps another version with single or a pair of 6BM8/ECL82....

How do you know?

fair point, I get annoyed sometimes when a content creator comes out and say," Did you know that you can get blah blah which is better than blah if you just blah" Sometimes I am like damn dude stop telling our secrets so dudes on ebay jack up the prices even stupider than they are. Not long ago I could go into a second hand/thrift store and buy a tube radio or R2R for $10 now people think they are worth $150 if you get to charge $50 to ship them. I keep having to remind local dealers " just because someone on ebay is asking $100 doesn't mean it is worth $100"

The EL84 equivalent is a 6BQ5. The EL90 is the equivalent to the 6AQ5 tube shown in this video.

I stand corrected! And only 7 pins ..?

@@cliverkay , yup, 7 pins. Pretty much the same specs as a 6V6 except for lower plate voltage handling and lower power dissipation. A pair of them in push-pull can still put out 10 watts or so, perhaps more. I have about 50 of the uprated, ruggedized, military 6005WA version, which I bought at a ham fest for about $2 each a while back; I really need to build some amplifiers with them!

🤔Do you build amps? I do, you are mistaken on several things IMHO. The only thing that I agree with is 6V6's and 6L6's are the most popular in America. They are also still made today in Russia, Czech Republic and China so there is that, but when you can buy a pair of these 6AQ5's vintage RCA NOS for about the same as 1 brand new Russian 6V6 or but a 60's tube reel to reel recorder with a pair of them, a 6CA4 rectifier and a couple RCA 12AX7's for like $40, I am not sure how this is overpriced. I literally buy vintage tube gear cheap, gut them and build stuff equal in tone to a legit 50's or 60's vintage amps for less than $100 all in regularly. Just sayin' don't be a hater bra.

@@skullheadwater9839 RCA tube manual says that the 6AQ5 has a max plate voltage of 275 volts and the same for the screen grid. The 6V6 is rated at a max plate voltage of 350 volts and a max screen voltage of 315 volts. Apparently that it the operational difference between the tubes. Obviously, we know that a 6V6 will operate above that voltage because Fender has been putting 400 volts plus on them since the late 1960s... I know that Gibson used the 6AQ5 in some of their little amplifiers with pretty good results.

@@skullheadwater9839 The 6V6 / 6AQ5 schematic is only basically similar (The 6V6 /6AQ5 in U.L. mode requires an 8k impedance for the OT the larger tube of the 6v6 takes heat better as well as higher voltage. I been in the electronics field industry since the 70s yes I built and repaired many Tube amplifiers even a few Dumbles . As a matter of fact I recall some manufacturers used the 6aq5 in vertical deflection circuits in TVs . The 6AQ5 is a power beam type tube, like a 6L6. The 6BQ5 is a power pentode, like a EL34. Like I said before 6v6 has a lower input impedance which has more headroom which equates to nicer cleans also 6V6 is a larger tube which equates to better heat handling and higher plate voltage so that's why I prefer it plus I have stock piles of vintage RCAs just sitting around NOS since the 70s . No Hate here and no I am not into bras ? 🤔

@@skullheadwater9839 Some of the JJ teslas 6V6 Power Beam tetrode that performs flawlessly at up to 475 volts! No 6aq5 will touch that !

Actually, a proper EL84, at least if New Old Stock and made in Europe, would almost certainly be a true pentode, but an American 6BQ5 might be a beam-power tetrode instead. American manufacturers developed beam-power tetrode versions of European pentodes so they wouldn't have to pay the Phillips pentode patent. Similarly, the American 6CA7 is analogous to the European EL34 and pin-out compatible, but the 6CA7 might not be exactly the same internally or performance-wise because it doesn't have a suppressor grid like a true pentode does.

I sorta did, EL84 and 6BQ5 are interchangeable.

@@graybenchelec Yes, that's true. Sorry I didn't catch it when you said it. Considering that it's the tube used in amp designs just as historically and musically important as the EL34 and 6L6 (vox, matchless, victory, marshall, hiwatt, fender, etc.), I guess I just was missing equal love shown for the type I use for 5 out of 6 amp builds I do. 🙂 Thanks, again, for the info on the 6AQ5. I'm always looking for something new to play with. Have fun!