Suggestions for a low watt amp

[liddokun]

Hey y'all,

So I'm looking for my next amp project.  I picked up a smallish chassis not too long ago to transplant an amp into for a friend, but that project fell through. 

At any rate, I'm looking for something to build into this chassis.  It's not too big, so something SE low wattage with 3 or so tubes would be cool. 

I've got a JCM2000 and a Fender Princeton, as well as an AC15 on the bench.  So preferably something a little different flavoured. 

I was thinking about maybe a Supro/Valco/Gretsch?   I thought about a Vibrochamp as well, but the Princeton I've got does as whole lot of Fender. 

If there's a turret layout for the project that would be rad, but schematics are also ok. 

[labb]

Take a look at the P1 or one of its variants. You may find something you like. http://www.ax84.com/static/p1/AX84_P1_101004.pdf


ax84.com/classicprojects.html

[tubenit]

I am super happy with my HoSo56 "the minimalist" using 6BM8 tubes.  This thread has schematic, layout, photos and sound clips IF you're interested.  (see replies #20  thru #24 on the thread)  Only 4 tubes and it has an active FX loop. 

http://el34world.com/Forum/index.php?topic=23013.0

And then there is the SoLow Watt amp using ECL84's which has only about 3-4 watts output but is still push/pull.

https://ampgarage.com/forum/viewtopic.php?f=6&t=17599&hilit=12AX7+SoLow+Watt&start=15

With respect, Tubenit

[tubenit]

And did you know we have an entire thread in SCH library on "low watt push/pull" amps where Pete (aka Dummyload) provided some excellent information and amp designs.

http://el34world.com/Forum/index.php?topic=12526.0

With respect, Tubenit

[bmccowan]

I was thinking about maybe a Supro/Valco/Gretsch?   I thought about a Vibrochamp as well, but the Princeton I've got does as whole lot of Fender.

Is your Princeton the tweed single ended, or a later PP? If a PP, a SE Valco will sound different, but will sound pretty similar to a Champ/Princeton SE. I built a Valco SE 6SL7>6V6 with a 10" speaker. Pretty cool amp. I think its the schematic labelled 1947. Keep the B+ voltage around 300 for that Valco sound.
And, Tubenit helped me with a HoSo 56 minimalist - I went super minimalist - very nice amp!

[rafe]

Check out the GA5T
with the 6BM8 schematic . I love mine

[sluckey]

You start with an old toaster...   

[liddokun]

And did you know we have an entire thread in SCH library on "low watt push/pull" amps where Pete (aka Dummyload) provided some excellent information and amp designs.

http://el34world.com/Forum/index.php?topic=12526.0

With respect, Tubenit

Woah I had no idea this existed !  Time to lurk! 


@bmccowan It's not a the original single ended kind, it's a later PP (brownface 6g2 circuit). 

Everyone else: Thanks for the suggestions, please keep them coming! 

[liddokun]

You start with an old toaster...   

Funny enough, as I was scouring the web for ideas on low wattage amps yesterday, shortly before starting this thread, I read through your toaster oven build! 

[bmccowan]

It's not a the original single ended kind, it's a later PP (brownface 6g2 circuit)

That's a great circuit. If you build a SE amp it'll sound different enough. I confirmed that it is the 1947 schematic I used for the Valco SE amp I built. The 6SL7 preamp has a certain warmness that is really nice.
But, all the ideas here are good ones. Especially the toaster oven which has a very entertaining write-up on Sluckey's website. Some people say that you can reform electrolytic capacitors by baking them in an oven, so I want to build a Sluckey hybrid Smokey amp/cap reformer: just pull the tubes and crank up the heat!

[shooter]

you can reform electrolytic capacitors by baking them in an oven

I've reformed a few, but in the end troubleshooting or cleaning cap guts got old, want a good amp, start with good parts.
fwiw, I re-formed by limiting current to very close to zero then letting them "bake" with 70% of their rated voltage for 24hrs, If they didn't explode or get real hot they got a green sticker 

[jjasilli]

Hey y'all,

So I'm looking for my next amp project.  I picked up a smallish chassis not too long ago to transplant an amp into for a friend, but that project fell through. 

At any rate, I'm looking for something to build into this chassis.  It's not too big, so something SE low wattage with 3 or so tubes would be cool. 

I've got a JCM2000 and a Fender Princeton, as well as an AC15 on the bench.  So preferably something a little different flavoured. 

I was thinking about maybe a Supro/Valco/Gretsch?   I thought about a Vibrochamp as well, but the Princeton I've got does as whole lot of Fender. 

If there's a turret layout for the project that would be rad, but schematics are also ok.

I'm baffled.  Just watched a youtube video with Joe Bonamassa getting perfect Bluesbreaker tone through a Champ.  So, I agree with the Supro/Valco/Gretsch approach; not to mention Silvertone, Garnet, Traynor Bassmate or Guitarmate.

[shooter]

Joe Bonamassa getting perfect Bluesbreaker tone through a Champ

I don't get many sales by using this comment, but I use it often  ;
If you can't make my amp sound good, maybe you need more practice 

[jjasilli]

Whoops, forgot Alamo.  The irony!!!

[liddokun]

It's not a the original single ended kind, it's a later PP (brownface 6g2 circuit)

That's a great circuit. If you build a SE amp it'll sound different enough. I confirmed that it is the 1947 schematic I used for the Valco SE amp I built. The 6SL7 preamp has a certain warmness that is really nice.
But, all the ideas here are good ones. Especially the toaster oven which has a very entertaining write-up on Sluckey's website. Some people say that you can reform electrolytic capacitors by baking them in an oven, so I want to build a Sluckey hybrid Smokey amp/cap reformer: just pull the tubes and crank up the heat!

Do you have a link to the schematic?  I scoured the schematic database and found the following two SE 6SL7 based circuits (they're pretty similar circuits too):

https://el34world.com/charts/Schematics/files/Valco/Suprospectator_1950.jpg
https://el34world.com/charts/Schematics/files/Valco/Supro_1948.jpg

Lastly there's this one, which is also similar in design but uses a 12ax7 as the preamp:
http://www.oldfrets.com/Valco/Schematics/Gretsch6150.jpg

[bmccowan]

Sure - its attached. BTW all of these are pretty similar. I used the Valco style Classic Tone transformers. I have also used those for older Gibson circuits too, as the B+ voltage is lower than the typical Fender style transformers.
I have quite a pile of Valco schematics; at some point I need to go through them and see which ones are distinct from what is on this site, so they can be uploaded. But its confusing as the schematics are repeated across Valco, Supro, National, Gretsch, Airline, and some house brands. 

[shooter]

Once you're built, happy n finding out xSE sound is mobetter than pp, check out SG's, DL's, n my big brother versions, Pete wins of course but he lives in Texas n it's like built in the DNA 

[bmccowan]

Folks, If you speak Shooter, please translate.

[sluckey]

Just show up at the beer 'n bait shop about closing time.   

[DummyLoad]

richard and i built one of these... well, sort of. we added a 6SJ7 to the front end and bypass jack to plug direct into the 6SL7 1st stage. i'll post the schema shortly - need to find it. 


--pete

[shooter]

please translate.

google translates for me 

[1blueheron]

I am in the same boat deciding what my low watt Silvertone organ chassis will become. 

Candidates so far are:
Kalamazoo Model 1 or Model 2
SoHo56
Gibson GA5
Micro Champ
Alamo Challenger
Silvertone 1481

In my case, the power tube will be 6AQ5

[dunner84]

Hi, I don't mean to hijack the thread, but I am also starting a low watt build, and I don't know much about these micro amps.
I am leaning between SE el84, or SE parallel 12au7/12bh7... Can anyone chime in who has had experience with both?

Cheers

[shooter]

SE el84

I've used the 84's in a single, double and quad SE.  I like them until you want to push them over the edge, never liked, nor did my amp testers like the hard distortion.

That said, the Kalamazoo seemed to do pretty well.  I fixed a few, mostly for harp guys, but a couple guitar guys liked them to noodle on.

 

[liddokun]

Sure - its attached. BTW all of these are pretty similar. I used the Valco style Classic Tone transformers. I have also used those for older Gibson circuits too, as the B+ voltage is lower than the typical Fender style transformers.
I have quite a pile of Valco schematics; at some point I need to go through them and see which ones are distinct from what is on this site, so they can be uploaded. But its confusing as the schematics are repeated across Valco, Supro, National, Gretsch, Airline, and some house brands.

I think I'm going to go with this simple little circuit, then. 

However, looking at the links I've posted, this one:
https://el34world.com/charts/Schematics/files/Valco/Supro_1948.jpg

Seems to be almost the same as the 1947 circuit, but with parallel 6V6's.  Would I be correct to assume I'd just basically be getting a little more power (~10 watts vs 4 watts)? 

Also, would like to add a simple tone control to it.  Could I simply tack this onto the 2nd stage of 6SL7 feeding the 6V6? Is that a proper implementation?

[DummyLoad]

what richard and i built before adding a 6SJ7 to the front end. should take pedals well for more OD. 


--pete

[liddokun]

what richard and i built before adding a 6SJ7 to the front end. should take pedals well for more OD. 


--pete

Pete, how many watts you reckon it puts out? 

[shooter]

how many watts

varies with load, B+ speaker bias........
the 2 PSE 6V6's I did gave ~ 8W at the scope.
At the speaker maybe like having an 11 on a 1SE volume
the bonus was not loud, it was a fuller more confident sound

[DummyLoad]

what richard and i built before adding a 6SJ7 to the front end. should take pedals well for more OD. 


--pete

Pete, how many watts you reckon it puts out?

10W +/-.


--pete

[shooter]

 here's an odd watt  amp that got pretty good reviews from the testers
came in ~~ 9W full grunge mode which sounded pretty good 

[PRR]

> came in ~~ 9W full grunge mode

There's only 5 Watts of DC in the power stage. So either the "9W" is incredibly distorted, or they have violated natural law.

If the load were 15k, it's a fine/clean 2 Watt amp, approaching 4 Watts totally overdriven. With the suggested 5k load, it may peak near 9W over-drive, but for how long? Interesting build.

[bmccowan]

However, looking at the links I've posted, this one:
https://el34world.com/charts/Schematics/files/Valco/Supro_1948.jpg
Seems to be almost the same as the 1947 circuit, but with parallel 6V6's.  Would I be correct to assume I'd just basically be getting a little more power (~10 watts vs 4 watts)?

That should be fun. I have not built that circuit, but I did repair a Gibson GA-9 Discoverer which has parallel 6v6s SE. Its a cool sound - I'd agree with Shooter, its a full sound. When you crank it you have a lot of power tube distortion. It doesn't do a lot of tricks - but that one is enough.
Whatever you build - keep posting so we can follow, please.
And Dummyload - did you find your schematic with the 6SJ7 > 6SL7 > 2 parallel 6V6? I'd like to see that.

[shooter]

9W

I was in my no notes peaktopeak days instead of doc's n RMS 
schemo scribbles show I took 276 plate V 8k load R came up with 34.5mA X 276V = 9.5W
bottom line, it sounded like a  big Champ we were running through a 2X12 JBL cab

[liddokun]

However, looking at the links I've posted, this one:
https://el34world.com/charts/Schematics/files/Valco/Supro_1948.jpg
Seems to be almost the same as the 1947 circuit, but with parallel 6V6's.  Would I be correct to assume I'd just basically be getting a little more power (~10 watts vs 4 watts)?

That should be fun. I have not built that circuit, but I did repair a Gibson GA-9 Discoverer which has parallel 6v6s SE. Its a cool sound - I'd agree with Shooter, its a full sound. When you crank it you have a lot of power tube distortion. It doesn't do a lot of tricks - but that one is enough.
Whatever you build - keep posting so we can follow, please.
And Dummyload - did you find your schematic with the 6SJ7 > 6SL7 > 2 parallel 6V6? I'd like to see that.

Yes I'll keep posting as I progress slowly through this.  Classictone luckily makes a 10 watt version of their Valco OT as well so that's convenient. 

[DummyLoad]

here's an odd watt  amp that got pretty good reviews from the testers
came in ~~ 9W full grunge mode which sounded pretty good 

there is NO way that thing is making 9W, peak or otherwise.


--pete

[DummyLoad]

if your numbers indicated in the schema telemetry are true, then the three 6AU6 are idling at 19.5W total. i assumed a 10V drop across OT less the 5V across the Rk, so 6.4W each if closely matched. 6AU6 are rated at 3.5W plate plus .75W g2 so, 4.25W each. really pushing them hard huh?

assume .4- to .45 x 19.5W for class A max power out: or about 7.8W, if you have an ideal load which is about 3.5K. so guestimating about 4-5W max with a 5K load.


--pete     

[liddokun]

Here I am, resurrecting a thread from 2019. 

At any rate, I feel silly as I left this on the back burner for so long.

I planned to build it and then the pandemic started and work picked way up as could imagine, being a registered nurse.

Anyways, I came back to update this.  I ended up building the 1948 valco circuit, and went super basic without much deviation from the stock schematic. The only thing I added was a 14H choke and an extra filtering cap. 

Transformers were all Hammond, as I live here in the Toronto area and getting my hands on any model is incredibly easy.

There's no head cab at the moment, I'm waiting on my cabinet guy to finish building it for me.  But the omission of a power indicator light is because I plan to make a light up logo on the front of the cab.

[bmccowan]

Nicely done. I just had one of those back burner projects too. I had let it go so long that I forgot I had ever started it.
First - We have 4 nurses in the family - you are all heroes in my book. Thanks for the hard work!
Look at that massive choke!
Nice faceplate - did you do that engraving? Purple plexiglass - that's inspired.

[liddokun]

Indeed the choke looks comically massive and likely overspec.  I had some parameters for the specs and I think this particular one was the only one in stock that day, I had not actually anticipated it's size until I showed up to buy it and opened the box. 

The faceplate was done by a local lamicoid and sign maker.  I actually wanted something even flashier, but they didn't have any glitter/metal flake lamicoids in stock.  The amp will eventually be a gift to my friends and their small indie record label, so I was trying to make it super bright and flashy. 

[liddokun]

I'm coming back to post one more photo, as I've often posted in these forums seeking assistance but rarely post final products.

My custom cab came back. There's a local builder here who supplies a lot of the cabs for a bunch of boutique builders. Got this one done by him. Had the addition of a hole cut in the front to do the light up logo, ala Morgan Amps (where I got the inspiration for this). 

It took me a bit to figure it all out, but the logo is 3d printed in two layers, a bottom 2mm thick transparent layer, followed by the logo over top in 3mm.  This was all done for $1 at the public library, which I thought was fantastic. 

Tapped some power off the heaters and rectified to DC with a few diodes and a capacitor, and hooked it up to one of those cheap RGB led strips you can get off Amazon.  They cut to length and have a +V input, and you can turn the each of the red, blue, or green LEDs on or off by grounding their pins on the strip.  Opted for a magenta to match the faceplate.  I built the rectifier on a tiny turret board, and put a 9v dc jack on top of the chassis so I can disconnect the LEDs and remove the chassis easily.  Turned out pretty well.  LEDs are have adhesive backing, and I just lined the inside of a small electric outlet box.