SoLow Watt with ECL86 tubes...simple?

[m3moser]

Hi, I have quite a stockpile of ECL86 tubes and I built the Mini-Bassman amp using them.. What a great sounding amp.  I think I'd like to build this SoLow circuit using these tubes as well.  I was going to proceed by using the circuit as designed but change a few values to the power tubes to match values in the mini bassman.  Any problem doing this amp circuit with these tubes that anyone can see?  7 watts is just about perfect for the home amp room.  And since I have a lot of these tubes, the more projects I can use them in, the better.

[tubenit]

I think that would be another great sounding amp!  

Actually the SoLow Watt was based off Geezer's  SoHo56 & my 56T.  There are schematics in the SCH library of those for comparison.
There is a schematic of the 56T using 6BM8 tubes there.

http://www.el34world.com/Forum/index.php?topic=6176.0

Hope you build it and report back.

With respect, Tubenit

[m3moser]

Well, I found a pair of the ECL84 tubes in my stash (4 of the actually), so I am going to build this per the schematic and layout posted.  I did see that the layout shows the input coming into pin 2 of the 5879 tube and the schematic (which is correct) has it coming into pin 1.  Pin 1 is correct.  I'll report back on progress.  I will be using a mix of whatever I have on hand and this includes using a higher voltage Hammond transformer that I will mate up to an EZ81 rectifier tube.  But I will still have too much voltage and will probably have to zener it down a bit.  I get a kick out of building these low wattage amps- seems more of my playing is me in the amp room about 6 ft from the speaker cabinet.  Just don't need 50 watts all that much anymore.

[TIMBO]

Hi m3. The ECL84 are a great little tube and perfect for a bedroom size amp. I can't believe that they are able to belt out a great sound. I'm i the process of building my version of T's SoLow Watt (Slow Drive 84) and its producing a full on sound. I am at the moment trying to track down some whitenoise/oscillation at higher volume but are not having much success. Thanks

[m3moser]

OK- I got some time to work on the amp.  I am using parts on hand to build this one, so I have a Hammond PT that I had to pad down a bit to get to close to the schematic voltages.  I have it playing ok but there is a lot of "fuzzy" distortion on the decay of notes that is robbing my joy reflex.  Its a gainy amp and I have tried numerous 5879 and 12aV7 tubes just to make sure its not a tube issue (also swapped in different ECL84 tubes as well).  I think there is some tweak I need to make here.
    I am including a few pictures of the guts- maybe somebody can spot something?  I have stuck to the schematic on this one.

[tubenit]

I don't know how much of a difference it would making but I used Orange Drop PS caps in mine. I have found them to be smoother for higher gain amps such as the Dumblish type.  I have NOT had success using Mallory caps in these type amps because they sound harsher to me.  You seem to have a variety of brands of caps in the amp?  

And I am mostly using Silver Mica for the pf values.

I have found the caps do make a difference in the tone, IMO.  IF you are using a large ceramic cap off the 5879, maybe change that to an Xicon or something else?

Only other thing I can think of is lead dress, but what I can see from the photos looks good to me.  

This is the schematic you're using ............ correct?

With respect, Tubenit

[tubenit]

Can you take a look at what I circled & maybe give a response, please?

What value is that one cap?  It looks sort of large for a 120p cap?

I'd like for this build to work out for you and have the smoothness that you want and that I think mine does.

Double check resistor values also, please.

with respect, Tubenit

[tubenit]

I'd like for you to try something please ................. 

Try a 47uf to 220uf range cathode cap for the ECL84 pentodes.  IF you can safely wire clip that in, give it a shot. Does that change the fuzziness in a way that you like?  Maybe the fuzziness is in the bass response & a larger value cap will tighten that?

What kind of speaker are you using?   I am using a Cannabis Rex with mine?   Maybe that is a factor?

with respect, tubenit

[andrew_k]

Hi, I have quite a stockpile of ECL86 tubes

Sell them to the hifi guys for $$$.

[jojokeo]

I have it playing ok but there is a lot of "fuzzy" distortion on the decay of notes that is robbing my joy reflex.  Its a gainy amp and I have tried numerous 5879 and 12aV7 tubes just to make sure its not a tube issue (also swapped in different ECL84 tubes as well).  I think there is some tweak I need to make here.
    I am including a few pictures of the guts- maybe somebody can spot something?  I have stuck to the schematic on this one.

Layout could be improved and your lead dress is your likely culprit for sure - especially with higher gain amps. The higher the gain, the more important these details become. Too many wires too close together in many places. Before redoing anything - space everything apart from each other as much as you can, especially anything close to your heaters and output tranny wires for starters. Another thing is you should mount your power tube's grid resistors directly on the sockets and the wire length should be kept as short as possible. It appears your resistors are on the board, then the wires run to your ppimv then under the board very close to other stuff especially the OT wiring? This also could be it. Run those wires over the board away from everything to your grid resistors.

[tubeswell]

What jojokeo said.

The more gain, the more possibility for unwanted coupling between signal wires. Keep the circuit layout sensible so you avoid unwanted coupling. It can help to keep high-gain parts of the circuit separated for other high gain parts of the circuit by having intervening low potential wires (such as cathode resistors or wires at ground potential) in between. Avoid unwanted coupling by keeping different stages plate signal wires apart etc.

That is just the signal wires. You also want to be careful with the wires which are logical AC pairs, by keeping them twisted together, and by either laying them hard against the chassis where the ground potential 'swallows' up any stray EM field surrounding the wires, or keep AC pairs at least an inch away from signal wires (especially signal grid wires), and if its necessary to have them near each other, then make sure they cross each other at right angles in order to minimise the possibly of inducing EMF from one set of wires into another. Otherwise keep all leads as short as practicable.

And so on.

[m3moser]

OK- when I get some bench time I will go over the amp with your suggestions in mind.  As mentioned, I did only use parts on hand so maybe a few component choices could be changed.  The cap circled in the picture is a large Mica cap- it is a big boy, buts its 150pf.  I did not have a 120 that the schematic calls for.  Also, the 100k resistors leading into the master volume show in the schematic as feeding the master volume, not after the master volume at the power tube inputs.  Do I have this right?

[m3moser]

Oh- I forgot to mention the two small pf caps on the V1 tube are because I live about 1/4 mile from a radio tower and if I don't snub out the RF I get classic rock station in all my amp builds.  I have learned to live with it by using these small caps to ground at the front end of the amp.  Nothing like 50K watts blasting "More than a Feeling" when you are playing "Sunshine of your Love" on your amp.  They do not mesh well.

[Willabe]

the two small pf caps on the V1 tube are because I live about 1/4 mile from a radio tower and if I don't snub out the RF I get classic rock station in all my amp builds.

There's another way to do this that might be worth trying out, if you haven't yet. It might sound better.

It's on Aiken Amps site, but it's under reconstruction at this time.

IIRC, the input jack is insulated/isolated from the chassis and then the ground tab of the jack is then grounded to the chassis (right at the jack) through a .01 (or was it a .1?) ceramic cap, keeping the leads as short as possible.


                                    Brad