SoLow Watt 12A_7

[tubenit]

Guys,

I am embarassed to admit this ............... but I've concluded the 5879 pentode in V1 in the original SoLow Watt was overkill gain. I've learned you can still get the great overdrive but with a MUCH lower gain tube.
 

Because I have two D-style amps with high gain already, I decided that I would change the pentode out in the SoLow Watt and put in a
12AV7 to have a cleaner tone small watt amp more geared for playing rhythm. I figured I'd use a tube screamer for any overdrive.

It only took about 30-40 min to rewire the V1 from the 5879 pentode to 12A_7.  And I was anticipating an amp with very little overdrive and a pretty clean sound even when cranked.  I was wrong.

I plugged in a 5751 to V1 & tried it.  AND .................. oh my gosh, it sounded great!!!!  

So then I plugged in a 12AV7 and it sounded absolutely beautiful with really sweet harmonics and a very very creamy tone. The 12AV7 is in between a 12AY7 and 12AU7 with gain.
 

Thing of it is,  I can NOT tell any significant loss of sustain.  Sitting in front of the amp using a guitar with humbuckers, the amp will still sustain into feedback on some notes.

My conclusion is the 5879 gain was probably too much for these ECL84 tubes in this design. The 5879 does have MUCH MORE chime to the tone, so if that's your gig, then I'd stay with the 5879.

The 5751 and 12AV7 are MUCH creamier in tone with better harmonics and sweetness in my opinion.  However, the tone is not as FAT and there is not nearly as much chime.  I think the 5879 perhaps is more touch sensitive in playing, but I think the 12AV7 is a more transparent clearer  overdrive.

My goal was to simply get a cleaner tone.  I ended up with a clearer tone in both clean and OD with improved harmonics, sweeter & creamier tone,  & more transparency.  

I do like the ability to use a range of 12A_7 tubes in a V1 and V2 position. It does allow versatility.

So unless you like the chime tone alot and need super touch sensitivity,  I'd skip the 5879 tube and use a 12A_7 in V1.  To those of you who built the SoLow Watt with 5879 already,  you might want to consider rewiring the V1.  It was easy to do.

I attached the original SoLow Watt schematic to show how little the changes were from 5879 to 12AV7.

I would describe the tone as 75% Marshallish and 25%  D-style transparent creamy OD.

With respect, Tubenit

[Willabe]

Tubenit you've had a lot of great success with fine tuning an amp build with the R's&C's. I'd bet you could get a lot of that chime back if you wanted to.     

I count at least 4 pF bleeder caps, 5 if you include the 120pF across the PI drive lines. IIRC, you did fine tune that amp with those caps/values to smooth out the distortion, but now you've changed the 1'st tube, so some of those might not be needed? Or their values lessend?



                                 Brad     

[JBP]

I was affraid this would happen. Will report back. JBP

[bruno]

Hey tubenit, cool experiment.

Just thought I should share with tou, yesterday I finally tried the cascode circuit.  I tried it on a "blackface champ clone" test bed, but I will eventually put it in a larger prototype amp with a push pull output stage.

I used the 2.2k/25uf combo for the cathode and plate to cathode connections, went with the self adjusting circuit too. It sound brilliant, has some of the punch of a pentode but with richer/creamier mids. I used a 12AU7, which appears to be perfect for the application.

Got very little noise ratio, and some nice gain.

Maybe you could try it out one day, you might like it.

Cheers

[tubenit]

I used the 2.2k/25uf combo for the cathode and plate to cathode connections, went with the self adjusting circuit too. It sound brilliant, has some of the punch of a pentode but with richer/creamier mids. I used a 12AU7, which appears to be perfect for the application.

Got very little noise ratio, and some nice gain.

Hey that's good to know!  Thanks!

With respect, Tubenit

[tubenit]

OK, I did a quick one take demo of the amp.  I think the overdrive has a decent smooth tone to it. The OD is further towards the end.

http://www.soundclick.com/player/single_player.cfm?songid=11515063&q=hi&newref=1

With respect, Tubenit

[DummyLoad]

tubenit, nice sounding amp! :-)

--DL

[Tone Junkie]

Tubnit sounds real nice. I keep hoping one day to do one of these. This would be all I would play at home, maybe my wife and kids would quit complaining Im to loud  
After I get done with the 2 in my amp stands I will have go for it. OOPS my addictions showing again.
Maybe I just need another amp stand.
Bill
                                                                  
              I love these things

[proaudioguy]

May I ask how loud is this guy?  Is there a page on this with all the details of parts to order for transformers and such?

[tubenit]

It's maybe 3-5 watts max.

No parts list.  You have to make your own.  Just use the schematic for parts/components.

I think I used a 12" x 6.5" x 2.5" blank chassis.  A blank 18 watt chassis would work fine too and perhaps be easier to work with.  Since Doug doesn't carry blank chassis, check out ebay for one.

I would recommend a 250-0-250 PT (using a 5Y3GT)  and a pp OT that's good for 10-14 watt and has an 8 ohm tap.  Something like a Princeton Reverb trannie would work, IMO.

With respect, Tubenit

[tubenit]

This SoLow Watt 12A_7 is proving to be a reasonably versatile amp.  The cleaner tone has the volume at about 3-4 and PPIMV around 7.
The overdriven tone has the volume about 7 and the PPIMV around 5.5.

Compare this cleaner tone:

http://www.soundclick.com/player/single_player.cfm?songid=11526416&q=hi&newref=1

to the more overdriven tone:

http://www.soundclick.com/player/single_player.cfm?songid=11515063&q=hi&newref=1

with respect, Tubenit

[jjasilli]

 

[sdp1234]

Looks a bit like a lower power rocket\AC30.  Would you say it responds or sounds a bit like the rocket\AC30?

[tubenit]

It is not nearly as chimey as a Vox.  Closer to Marshall, IMO.

With respect, Tubenit

[bakerlite]

thats a crackin sound for blues! and at very manageable volume levels too by the looks of things.
have you posted gut shots of this amp in a build thread other to this one?

[tubenit]

The SoLow Watt was either the 4th or 5th? build in the same chassis.  I would NOT win any points on neatness even though the amp is very quiet at idle and there is no oscillation issues.
 

However, here is the way it should be done. Absolutely beautiful work w/ chassis interior shots :
http://www.el34world.com/Forum/index.php?topic=13151.0

With respect, Tubenit

EDIT:  added a VVR version