your favorite simple clean circuit

[riffanvil]

hi--i'm new here but not new to tube amps.  not by any means up to the level of many of the posters here but have several simple amps still pumping out sound for small gig musicians, myself included.  lately i have been building a simple straight forward 18w 1x12 combo amp for myself and other musician friends and have gigged mine for 4 years now without any problems.  i have been considering building another amp for myself that might better suit my needs, though i have no complaints about the 18. 

i build a hexaphonic guitar that uses graph tech saddles and circuit with a single dual humbucker that is made by kent armstrong (motherbucker).  when i gig i mostly use the hexaphonic output and would like that to run through a very clean (hi fi) type of circuit instead of further fuzzing up the signal coming out of the hex effects processor with a more traditional guitar amp circuit.  i considered solid state but tubes sound richer and i want to build what i use and i just get turned off by overly complex ss circuits and tiny components.  besides i don't really understand them well enough nor do i have the interest in learning.  tubes still rule in my music world. but i appreciate not typing this on a tube laptop  ;)

important things to me are simplicity, fairly standard tubes, light weight as possible (if you gig and are over 60 you know what i mean) and as low a watt rating as possible (questionable power in mexico makes smaller amps a better choice) while still having the ability to remain clean at medium volumes (up to 200 person gigs).  i could go either way on the rectifier (ss or tube).  i have been using a fw diode bridge on the 18w amps i build to keep them simple and more reliable, but have pentode (ef86) amp that uses an ez81 tube rectifier i am very happy with as a rock guitar amp. but i built it as a 2x12 and it is getting heavier every year so it stays in the studio.

i would like to know what are some favorites re tubes and architecture for a circuit you might think would fit the bill.  i have a few old hi fi trannies for both a pair of 6l6 style amp and another couple of pairs for el84 based amps so that would be a possible starting point.

it's 2am ---i guess i had better call it a night---thanks---riffin

[topbrent]

Simple loud clean amp.

Single channel AB763 Fender, No Reverb, No Vibrato.

Uses the common 12ax7 preamp, 12at7 phase inverter.  Fixed bias, SS rectifier, 6L6 power section.

4 tubes total, not much that can go wrong, guaranteed to sound great.


Sluckey has a great 6V6 version of this.  Follow it and you will be just fine.

http://home.comcast.net/~seluckey/amps/misc/AB763_Deluxe_Lite.pdf

[riffanvil]

thank you--a couple of years ago i did a cap job and a few other repairs on an AB 763 deluxe reverb with a tube rectifier (gz34 if i recall ).  it was a 4x10 and i must admit even with the original oxford speakers it sounded great.  i wondered at the time if the 2 ohm load and 4x10 had anything to do with the tone..  for me a 1x12 with an efficient quality speaker is the ticket for weight (i like the redfang alnico for the price).  what are your opinions on transformers?

riffin

[rzenc]

Hi,
Don't know if you decided topology towards AB763, but I would suggest 5F6-A.
Hoffman has proven layouts for both amps:

http://www.el34world.com/Hoffman/images/AB763New.gif

http://www.el34world.com/Hoffman/images/5f6ANew.gif


Regarding iron, I would use Hoffman stuff. just look here: 

http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Transformers&ORDER_ID=!ORDERID!

P.T., choke, O.T.

Hope this helps
Best Regards

Rzenc

[phsyconoodler]

Either circuit will work.But change the slope resistor,drop the gain down and use high-powered speakers.The AB763 breaks up early as is.
   Consider using 6550 power tubes and an ultralinear OT.

[DummyLoad]

i like the sound of traynor YVM-1.

--DL

[stingray_65]

thank you--a couple of years ago i did a cap job and a few other repairs on an AB 763 deluxe reverb with a tube rectifier (gz34 if i recall ).  it was a 4x10 and i must admit even with the original oxford speakers it sounded great.  i wondered at the time if the 2 ohm load and 4x10 had anything to do with the tone..  for me a 1x12 with an efficient quality speaker is the ticket for weight (i like the redfang alnico for the price).  what are your opinions on transformers?

riffin

Ever try the "wizard"

Super efficient, very neutral tonally. It's my go to speaker for most builds.

Ray

[riffanvil]

thank all of you for the responses so far.  i had considered the 5F6A since it is one of leo's best and being for bass it was designed to be more clean.  i guess i really don't have enough experience with hi fi amps to really know the distinct differences between them and most guitar amp circuits to know what is or isn't coloring the signal too much.  i know i will find some answers if i dig deeper through the topics here but i have found that sites dedicated to amps that play recorded music and others that are dedicated to guitar amps have differences in the approach.  the price difference is too far out to try to build the equivalent of a macintosh--it's like yachts and working fishing boats. 

i also have repaired a few older traynor amps and was impressed with the overall quality of the build and components.  leo and pete were on the same page.  they seem to be rugged and pretty straight ahead until they started using pcb's and overly complicated circuits to do simple tasks.  like the standby circuit on a "stuck in on" ycv40.  the customer had asked traynor for a solution and bought several parts to fix it to no avail.  i bypassed the complete factory standby circuit and put a simple spst toggle in it's place to interrupt the B+ (like the good old days).  it has worked fine ever since.  simple is at the top of my "good" list.


i have an emminence wizard in the box for a future project.  if i didn't have a redfang when i built my 18w gig amp i would have used it.  now i will try it for sure.i also used a tonkerlite (neodymium) from that same red coat series and liked it.  it was for a boaters amp and every pound made a difference to the customer.  i know it doesn't match up very well watt-wise for an 18 watt amp but it sounds pretty darn good.

i think something closer to a keyboard amp would work well and is recommended by both roland and axon for using with their gear.  an ideal amp would have one very clean and linear channel for the hexaphonic/synth/acoustic signal and another dirtier channel more suited for the humbucker that could both be blended without phase cancellation. but that might come later after i get the first half figured out. 

has anyone here built an amp here for hi fi use? could you explain what simple straight ahead changes will get me closer to hi fi from guitar amp architecture? (no $100 oil caps for this musician--a little more tequila for the listener is a better solution and on their tab ;)

 could you explain the slope resistor values and the technical reason for doing this?  once i see it in my head it will make more sense. also the 6550 tubes seem to often be  in bass amps.  not having  worked much with them (other than replacement) i don't have much experience with design around them for a smaller amp.

thanks guys, you are a great group here.

once again--2am and bed time.

[JayB]

Gibson GA-5 is a fun one.

[The_Gaz]

1+ on the AB763 - can't get much simpler without getting too simple. I would not build a 5F6A, which is not a clean amp! Maybe in like in the 1800's when it was invented! Bust seriously the 5F6A does not have as much headroom in the front end as the AB763. Plus the latter's more lossy tonestack with have more range.

[riffanvil]

i guess i am trying to understand why, for example, the ab763 is a cleaner amp than the 5f6a when to a guy like me there are many similarities.  think of me as a guy who knows oso buco is a great dish but doesn't know why the oso buco at frascatti is better than the olive garden. while i can build and repair an amp from a schematic and layout i am wanting to understand more about the finer points.  like the slope resistor value earlier mentioned here, or why a hoffman, heyboer, or chino special trannie all sound different.  maybe this is why decade boxes are among my most used tools.  i hunt and peck till i get what i want but would really like to know more about the theory behind what certain points in an amp make it cleaner of fuzzier or more distorted etc.  probably way beyond the scope of a single thread but probably everyone that reads this has or will be at the same point i am right now.  i'm just having so much fun and satisfaction building and repairing tube gear i feel it is time to learn to be a better cook---and come up with a few more of my own recipies.

thanks, riffin

[topbrent]

i guess i am trying to understand why, for example, the ab763 is a cleaner amp than the 5f6a when...there are many similarities.

The similarities between the AB763 and the 5F6A are limited to the simple fact that both amps use tubes, capacitors, resistors, transformers and wire.  Beyond these sundry items, there are no other similarities shared in those circuits.  Worlds apart. 

The topology is totally different, the gainstages are different, the preamp voltages are different, the tonestack is voiced differently, cathode follower vs plate fed tonestack...ect.

AB763 was designed after the 5F6A to satisfy players needs for a louder and cleaner sound. 

I even like the Silverface 12AT7 PI values, as it sounds nice and punchy.

Keep the preamp voltages up around 250v on the preamp plates, 450+ on the power section. 
Make sure to use the 220k to ground at the Phase inverter entrance as shown in the layout in my earlier post and that will keep the amp a bit cleaner.

It really is a simple amp with a low parts count.

[jojokeo]

I think all you'd need and want is 6V6's they can stay clean and get plenty loud. But use your 6L6 iron and if you ever wanted you could switch in and out which ever you feel that you'd need making it veristile for whatever venue you're playing in or practicing at. Something simple w/ the Princeton's non-reverb specs would be perfect. The reverb version has too much gain and breaks up too quickly.

If you decide to go with any of the AB763 circuits, you should consider going w/ some different biasing & bypass cap values over the standard 1.5k/25uF - I'd put in an on/off/on "voicing" switch to change this because one setting (Fender's values w/ the added bass) sounds better at lower volumes but another (Marshall's values less bass but a bit more drive) sounds better at louder volumes. Make the middle position unbypassed for cleanest setting if playing jazz or using pedals for example.

[bluesbear]

I don't find that 5F6a's are any dirtier than an AB763. Different, yes. I build 2 6V6 amps, one with an AB763 pre and PI, one with 5F6a, identical power section. My 5F6a's are brighter with a bit harder attack. The AB763's are softer and a bit harmonically richer. Two dogs, different tricks. Neither gets dirty any earlier than the other... but that's how I designed them. I believe in headroom. I add a hot switch on a relay for more preamp dirt when needed.
Dave

[PRR]

> as low a watt rating as possible

A NO-watt amplifier is easy.

Elsewhere I am working on 0.2W, 0.035W, and 0.001 watt tube "power" amps. Enough for a radio to be heard several feet away. Batteries eliminate wall-power worries. But 0.001W won't be heard behind the acoustic sound of strings even with a solid-body.

You better get more specific.

Not much wrong with the AA-Champ. Enough tube for flavor, 5 Watts covers a lot of small gigs. For lightness, try to find 200V-240V AC transformer so you can solid-state the rectifier and arrive at around 300VDC for good tolerance against excess wall voltage.

[riffanvil]

by low watt rating i meant as i mentioned {and as low a watt rating as possible (questionable power in mexico makes smaller amps a better choice) while still having the ability to remain clean at medium volumes (up to 200 person gigs.}  the 18 watt i used works fine but a dual 6l6 or 6v6 is ok too since i have transformers for those types of amps in my cache.  those tiny output amps sound like fun.  is it a project to see how small or why such a limited output?

sorry i used such vague terminology as "many similarities".  i meant it in a very general sense as two fender amps running a pair of 6l6's in push pull as opposed to a bassman compared to an ac30 or an old gibson with octyl pa tubes.  thanks for pointing out the differences.  i am slowly learning, bit by bit, (as these boards are about my only school here in the tropics), how these differences can and do affect tone.  a great book would be one that took each stage of an amp and said--if you change component A to this value you could expect THIS change.  or discusses tone stacks for example.  i bought a book on the internet on the 5f6a that is only about that circuit and it is discussed in so much technical detail that i hate to admit i get way more, bit by bit from a forum like this or sifting through the internet's sand pile.

i found the following quote while searching more re the ab763 history-----------it was about the blackface era
  "AA763 was the first circuit that Fender used and didn't last long. Soon after the circuit became the famous one, the AB763. The AB763 had some minor but important updates. Amps such as the Pro Reverb (AA or AB165, came out in late '64)  and the Vibrolux Reverb (AA864, came out in late '64) are identical to AB763 circuits and are still considered the "good" ones. Blackface amps had a brighter, tighter, and more "scooped" sound than the brown amps that came before. Leo was trying to go for a cleaner and more "hi fi" sound. Hi fi may be misleading, because Leo still had his ear to the ground and did what musicians wanted for sound it seemed. "

i have played through and have owned several fender amps and comparing a super reverb with a 5f6a bassman i would choose the first for cleaner harmonically rich country sounds and the bassman for the blues (the 5e3 is a great little small venue blues amp .).  but that might have been the individual amps too.
 
i"ll  measure the voltages on the iron i have from the old hi fi units and see if it will work for one of these projects.  one set is completely potted.