6AQ5 output amps that you really like how they sound

[Paul1453]

I'm playing with my prototyping setup and have successfully set up a number of different output tubes.  I did one simple 6AQ5 circuit and it sounded pretty good to me.  It didn't have the gain to overdrive the 6AQ5 enough for me.  It was just barely starting to get that breakup I'm looking for when I dimed the one control pot.

Can any of you recommend a 6AQ5 design that you really like the sound of?  I'm looking for a low output circuit that can go from nice and clean, to full metal distortion with screaming harmonics.  Any ideas for a circuit like that that I can try to build?  I think I'm ready to build something with more than 2 tubes and 1 control pot, hopefully.   

[HotBluePlates]

I've never played any 6AQ5 amps. However, the tube is exactly the same as a 6V6 except it is in a 9-pin miniature bottle. So any 6V6 design you like will also work with 6AQ5's, with due regard to the pin-out change.

[Paul1453]

Yes I kind of knew about the 6V6 6AQ5 connection, but I am not too confident in changing a 6V6 design to use 6AQ5 tubes.  My other posts notes my 5 6V6 inventory.  I only got 3 6BQ5s, 2 premium tubes 1 Bugleboy and 1 Miniwatt made in Holland, and 1 Zenith USA I think.  4 6L6s with 1 potentially bad.  But I've got like 15 6AQ5s to play with, and only one of them tests low.  It seemed wise to me to use these as cannon fodder in my getting up to speed learning stage.  Of all the simple circuits I've successfully built and tested so far, I actually liked the sound of the 6AQ5 best.     If I can find a design to copy that I can use my most plentiful and inexpensive tubes to play with I will be quite happy.   

[HotBluePlates]

I would suggest a design which doesn't push way beyond published limits for the 6V6/6AQ5. My thinking is the smaller bottle means less capability to dissipate heat, as well as closer pin spacing means greater potential for arcing.

This doesn't mean you have to be overly cautious, but 6V6's in later amps were run way, way beyond their published ratings. Why bother with that with a 6AQ5 amp, when you'll probably not need a couple-extra watts from pushing things.

[tubenit]

This is one that I built that I wished I had NOT sold.  It was a very nice sounding amp!  There is a layout for it also.

It had VVR.     It was based on Geezer's HoSo56 which is a very touch sensitive articulate amp, IMO.

  With respect, Tubenit

The Gibson Scout 17RVT used 6AQ5 power tubes at around 300v.

http://el34world.com/charts/Schematics/files/gibson/Gibson_GA-17RVT_SCOUT.pdf

[Paul1453]

I've never played any 6AQ5 amps. However, the tube is exactly the same as a 6V6 except it is in a 9-pin miniature bottle. So any 6V6 design you like will also work with 6AQ5's, with due regard to the pin-out change.

You are absolutely correct again.     Except for the 9 pin part.  It's actually a 7-pin mini bottle.  I have quite a few new ceramic 9 pin sockets, but I need to order some 7 pin sockets from China now.
I proto'ed the Champ model 5C1 with the 6SJ7 and 6V6 design.  Played around with it, changing signal caps and tubes, just to see how the sound changed.  Then I got bold and checked the 6V6 and 6AQ5 data sheets.  Noted the pin changes:
     6V6       6AQ5
      2-7         3-4    heater
        3             5      plate
        8             2      cathode
        5             1      grid 1
        4             6      grid 2
Swapped out the 6V6 for the 6AQ5 carefully making the appropriate pin reassignments.  I didn't change anything else in the circuit, other than to adjust the 6V6 B+ 320 VDC down to the 6AQ5's stated 250 VDC.  The 6AQ5 played like a Champ just like her big brother 6V6.  I actually prefer the sound of the 6AQ5 over the 6V6.  It sounds warmer and overdrives and sustains better when I put a distortion box on the input.  It draws about 50% less current and seems to have only slightly less volume.  Now to see if I can do the same thing with a 6V6 PP output design.   

[jojokeo]

Paul,
Geezer's amp Tubenit posted is really nice. However, it won't go into "full metal distortion" and most tube amps you'll come across will not either. That kind of gain takes a number more gain stages and even then will not exactly get to the same territory for that. Not do you want that in a tube amp unless you're looking for a 1-trick-pony of an amp. These kind of amps may be fun in your bedroom but are not what you want if you intend to play anywhere at volume. The more you turn things up the more mud & compression you'll get which masks tone & technique both.
Not sure you're aware of V1 and V2 in T's schematic but it's using a 5879 for V1 and likely a 12ax for V2? Build yourself a nice sounding versatile amp and get your distortion fix from a stompbox or two would be my suggestion to you. That's what's in most of the modern metal amps today or even the usual Marshalls, Fenders, etc. - built in stompbox channels is all. On another note your thread was an interest to me cause I too like the el90s and will soon be getting some use out of these minty little bottles:

[HotBluePlates]

I've never played any 6AQ5 amps. However, the tube is exactly the same as a 6V6 except it is in a 9-pin miniature bottle. So any 6V6 design you like will also work with 6AQ5's, with due regard to the pin-out change.

You are absolutely correct again.     Except for the 9 pin part.  It's actually a 7-pin mini bottle. 

Ha ha!! I guess I shoulda looked at the data sheet... Yep, hadn't played any 6AQ5 amps. 

[Paul1453]

Thanks for the input.  I am not a gigging musician, so playing at volume actually would cause problems on the home front when I'm just plinking around on my guitar in the basement.  I am enjoying getting back into my old electronics training.  I wouldn't mind a cheap and easy one trick pony to start with.  Even with scavenging most of my parts, and the amount of money I'm spending setting up my bench, accumulating tubes/resistors/capacitors/transformers etc.  I could have probably already bought a couple of low watt amps to plink on.  With my limited guitar skills half the fun of playing is just making the amp I am using.
 

[Paul1453]

Paul,
Geezer's amp Tubenit posted is really nice. However, it won't go into "full metal distortion" and most tube amps you'll come across will not either.

Build yourself a nice sounding versatile amp and get your distortion fix from a stompbox or two would be my suggestion to you.

On another note your thread was an interest to me cause I too like the el90s and will soon be getting some use out of these minty little bottles:

If I can end up building myself a nice low power bedroom versatile amp that can get the tones like the ones on most of the songs on this link I will be ecstatic!

https://www.youtube.com/watch?v=0Zze1RHhR34

   The tones Joe gets on these quiet songs really float my boat.   

That's quite a nice stash of EL90s you have there.   

[printer2]

First amp that actually worked when I got into tubes.



Got the feel of a Tweed amp, throw in a BF tone stack for fun, output to one of the P-P pair for a semi-single ended feel. Nothing much special, just a Fender Harvard using 6AQ5's. As the guys said, just think of the tube as a 6V6 except for the voltage and power limits on the tube. I found no problem going up to 300V supply.

[jojokeo]

First amp that actually worked when I got into tubes.

What program did you use to make this schematic printer? Do you still have the amp? What do you think is the total wattage output when in pushpull at the voltages listed?

[Paul1453]

I tried a slight deviation of the Hoffman Tweed Deluxe circuit this weekend.  Subbed in the 6AQ5's, didn't have any 12AY7s so tried AU, AV and AT's instead.  Dropped the 2nd input and tone pot part.   It was working, sort of.  It was much louder than the SE circuit.  It had horrible hum issues though.  I only adjusted my B+ up to about 150V and I was getting guitar signal through the circuit but the hum was overwhelming.  Seems I have serious hum issues whenever I try to use 12XX7 tubes in my circuits.  On the bright side the 6AQ5s seem to have no issues being swapped in for 6V6s with the proper pin reassignment and voltage adjustments.

[printer2]

I use Tinycad, not properly mind you.


http://tinycad.en.softonic.com/


I would guess about 5W. Used a 70V line transformer for the output transformer, a PA paging transformer. The power transformer is a Hammond 1:1 / 1:2 isolation transformer. I used a wallwart power adapter for the heaters. Actually think they are 12AQ5's not 6AQ5's. A cheap build, transformer free from some renovations at work, wallwart $2 from a thrift store, power transformer under $20, 12AQ5' are cheaper than 6AQ5's.


The power transformer can be used as a 120V secondary but it also has two primaries for 240V. Flip the input and output and you get about 100V or 200V (roughly as far as my memory is). Hammond winds their transformers a little hot so the secondaries have extra voltage, if you flip the input and output you get less than line voltage. So you can get different voltages to work with. A voltage doubler gives you a few more options. The proper secondary is also center tapped. You can get different VA ratings, I get the 250 mA version and it is enough for a 15-20W amp. No longer use a low voltage transformer for the heaters, I use the switching power supplies that have been replacing the iron in wallwarts.


Used an old tabletop radio as the cabinet. Need to rebuild this thing one day, the rotary switch is junk and is noisy or just does not work. All the switches were for me to learn how much effect part changes have on the sound. So a good learning experience but the small cabinet size limits the sound from the speaker, an 8" fro the work demo. A quality OT would help also, maybe make another watt or two. The grill cloth is a Dollar Store place mat that has an open weave pattern, I used some fabric dye to give it an aged look to match the cabinet. I think I paid $5 for the radio, it was not working. Had a volume and tuning knob with the frequency dial across the middle. Cut off one side, turned it on it's side and gave it a look of a TV from the time period. One of the knob holes is for the input jack.

[Paul1453]

The simple Fender Champ 5C1 worked the best for me when I subbed the 6AQ5 in for the 6V6.  My only wish was that I could drive the input of the 6AQ5 harder.  Looking at my stock of tubes I have a 6SQ7 who's data sheet shows it can be used as a high gain audio amplifier, and has an amplification factor of 100.  That is the same amplification factor as a 12AX7.  So my question is could I just put this 6SQ7 in front of the 6SJ7 as a pre-amp in the Champ 5C1 circuit?  If that seems to be a reasonable possibility, how would you suggest I modify the 5C1 circuit to properly add the 6SQ7 as my pre-amp?

[Paul1453]

   That build looks fantastic to me!   
You say it was your 1st?  You obviously have other electronics experience.
I also have a few of those 12AQ5s around, just not as many as the 6's.

[printer2]

You should be able to put 6SQ7 in front of a 6SJ7 but more than using a little gain you may not like the sound. The Champ circuit has the 6SJ7 operated in a circuit described as 'grid leak'. There is no cathode resistor and the bias voltage on the grid is generated by the electrons collecting at the grid and having no where to go because the grid resistor is large, 5 M. This produces a sound some like when overdriven but when hitting it hard things fall apart. If you want to put another stage in front of it (does not have to be a tube, could be a booster pedal) you will need to put a cathode resistor in place and lower the plate resistor value. You will not need to milk the last bit of gain out of the 6SJ7 with another stage, don't know what would be good values but if you Google '6sj7 octal fatness' you should get more than enough information.


More to follow. Oh yeah, know enough to get me into trouble, almost enough to get me out of it.

[printer2]

Drew up a schematic of an amp with the triode and pentode in my reverb thread.


http://166.63.127.229/Forum/index.php?topic=19326.0


I have a three way switch in there to change from grid leak to cathode operation. You can ignore it if you like, guessing you might find yourself short of room. Also if you are not careful with the wires you might get some interaction especially with all the gain. It might be a good idea to have a stage of filtering between the triode and pentode gain stages. A volume pot for sure.

[Paul1453]

You should be able to put 6SQ7 in front of a 6SJ7 but more than using a little gain you may not like the sound. The Champ circuit has the 6SJ7 operated in a circuit described as 'grid leak'. There is no cathode resistor and the bias voltage on the grid is generated by the electrons collecting at the grid and having no where to go because the grid resistor is large, 5 M. This produces a sound some like when overdriven but when hitting it hard things fall apart. If you want to put another stage in front of it (does not have to be a tube, could be a booster pedal) you will need to put a cathode resistor in place and lower the plate resistor value. You will not need to milk the last bit of gain out of the 6SJ7 with another stage, don't know what would be good values but if you Google '6sj7 octal fatness' you should get more than enough information.

Thank you, Printer2!
This kind of answer just blows my mind!  The depth of knowledge and willingness to take the time to share that information with others on this site is astounding!  I shudder to think just how long I would be    without all you guy's help.  I sincerely appreciate it.   

[Paul1453]

I've started to read the threads on octal fatness, and the odd 6SJ7 configuration of the 5C1.  I'm beginning to think that I would want to add the 6SQ7 after the 6SJ7 now.  Many have commented about liking the compression, touch sensitiveness, and overall sound of the 6SJ7.  Maybe one could keep all those desirable attributes by just adding the gain to overdrive the output tube after the 6SJ7 instead of before?  Or maybe I'm just    again?

I'd like to make a little low power 6AQ5 output amp that goes from clean to pretty heavy dirty without the use of any pedals.  Possible, or just not worth the effort?

[Ed_Chambley]

I've started to read the threads on octal fatness, and the odd 6SJ7 configuration of the 5C1.  I'm beginning to think that I would want to add the 6SQ7 after the 6SJ7 now.  Many have commented about liking the compression, touch sensitiveness, and overall sound of the 6SJ7.  Maybe one could keep all those desirable attributes by just adding the gain to overdrive the output tube after the 6SJ7 instead of before?  Or maybe I'm just    again?

I'd like to make a little low power 6AQ5 output amp that goes from clean to pretty heavy dirty without the use of any pedals.  Possible, or just not worth the effort?

I have many built many versions of the 5C1 and even variants.  The 5 meg grid bias on the tube many say causes problems using pedals, but I disagree.  I have found that I can boost the signal more and it has a better feel than cathode biasing.  This old method has much more touch sensitivity to me. 

I am not sure from reading how much clean headroom you are looking for or if you want Power Tube Distortion.  Anyway, I built a 6Sj7 to a 12Ax7 LTPI into a push pull design and it is similar to a Tweed Vibrolux as I used the values of the Vibrolux.  Recently I added another gain stage and it did not work out very well as I had no clean tone.  I converted it to a tube loop that way the octal tube only gets hit with dirt pedals and the modulation is inserted at the PI.  The octal pentode is very worth exploring, but read up on how to install a humdinger.

Sure you can build what you want.  Look at the HoSo 56 and simply lower the voltage for protection of the 6AQ5 and use those if you want.  The EF86, 5879 and 6Sj7 are very similar and I find the 6Sj7 not to be as microphonic as some say.  Then you have an overdrive which is all you will need.  Problem is if you do not use a relay for switching you would need a toggle and then to hit solo overdrive you physically have to switch it.

Search the site for the HoSo 56 sound samples and see if you think it distorts hard enough.  The Fender Musicmaster Bass amp does not get much attention and still can be had fairly cheap and they had the 6Aq5.  Sluckey also built a mini Twin using these tubes.  Add a 12Ax7 and you wil get 2 additional gain stages which can put you heavy overdrive, but unless you can switch you are sort of stuck like Jojokeo said.  A one trick pony.

I also built a Parallel 6Sj7 to 6sn7 PI like in an Ampeg J12 to 2 cathode bias 6V6. Does it sound like Joe Satraini?  Sure, if I put a modded Boss DS-1 in front of it as a lot of his tone comes from clipping diodes.

[printer2]

No reason you can not add a triode after the pentode. But be careful, next thing you know you will make another amp, then another one, then ...

[Paul1453]

I tried a new 6AQ5 SE circuit this morning.  I forgot the name, will post later.  It has a 6U8A using both it's triode and pentode to drive the 6AQ5.  Still having hum issues when using 9 pin tubes, even this new 6V model.  I need to troubleshoot my signal path as I was not getting any guitar sounds out, but it seemed like the 6U8 was driving the output tube much harder and was much louder than the Champ using the 6SJ7.  Seems weird that I don't seem to have the same hum issues when using octal socket tubes.  A quick bout of troubleshooting tonight when I get off of work and then a fresh look at the whole thing in the morning.  Seems like this 6U8 may be able to drive the 6AQ5 hard enough to get that distortion level I'm seeking.  Wish me luck.

Back home now, the new circuit being proto'ed now is called the "Savage Croaker".   Have you guys heard of it and any comments on its performance?

[Paul1453]

I was able to get the croaker to pass guitar signal, but the hum is still unbearable.  Think I'm going to play with some octal designs instead for now.  Maybe it's my proto sockets?  I don't seem to have the hum with the 8 pin sockets.