Supro S6606 - first post here - need advice to thicken the tone/add gain?

[Harvester]

Hi all,

First, I would like to thank Doug Hoffman for creating this space (and selling me many of the parts for this build) and SLUCKEY for the layout.   I built a MOJOTONE 5e3 kit last fall and settled on this little amp as a second but wanted to scratch build.

I was able to make this little circuit in a box.  Will post a bunch of pics.  Worked first try just like my 5e3 (I do have a doorstop pedal project that has been set aside tho...), and I have had great fun running it through different guitars and speakers.

The verdict: compared to my 1973 Bronco amp, this thing is a dog.  But cute, like a puppy.

Including the schematic which shows that the preamp cathode goes directly to ground and a few other unorthodox bits.  I am guessing that if I add a resistor and bpass cap I will get more gain, but will need to change a few other values like that 6.8m resistor and the cap next to it?

Any advice on improving, modding this little circuit welcome.

Thanks much.
Darrin

[Harvester]

pics

[Harvester]

+ pics

[tubeswell]

What would your goal(s) be in modding the amp?


'Thicker tone' can be got by running the tubes hotter - especially the output tube, which running in SE cathode bias, can be safely pushed to Pmax.


Running a low-efficency, low power speaker and help this too, esp an Alnico 10-15W.


The input stage is grid-leak bias, and changing to cathode bias with fully bypassed cathode will increase gain, as will increasing plate resistors to 150k or 220k or 330k. But losing the grid-leak bias will make V1 run colder.

[Harvester]

Thanks tubeswell for taking the time.  I thought I was clear on my points of dissatisfaction in my head, but I just played it for an hour and I am fairly pleased.  I had been using hotter pickups and just tried some less heat humbuckers and still think a little more gain would be great.   I will leave the input stage alone and experiment with the bias to add heat.

I have a Heppner 15 watt alnico that is good as you suggest. I also found that the outtake speakers from modern "Supro" amps are really fun as they are voiced like a field coil speaker.   I have never used a field coil speaker but this 10" Supro dk10 is a nice blurry match as well.

[bmccowan]

Have you tried swapping in different tubes? Worth a shot before firing up the soldering iron. I'd try bypassing the 6V6 cathode resister with a 20 to 50 uf cap. Exact value is not critical. Although it seems counter intuitive, I'd try a 5751 or 12ay7 for the preamp.
And if you do decide to change V1 to cathode bias, I think the values used in the Gibson GA-5 (the single ended 6V6 variety - Gibson used the same model number on several amps ) are a good place to start.

[scstill]

have you seen this thread
https://el34world.com/Forum/index.php?topic=27455.0

I discovered that I cannot access the Sluckey amp site anymore. Too bad was a great place.

[Harvester]

Thanks for the guidance.   Will order some more tubes for trial.

Also, I saw that thread long ago and should have gone back to it.  Fixes the hi/lo inputs.