BTO IN A CASHBOX

[TIMBO]

Hi guy's, Thanks to HBP for the NOD on the SPLIT PI, it's worked a treat  .

This rebuild of the rebuild of the original build that was the "MINI BASSMAN" (isn't that what this amp building stuff is all about) has got me    with joy.

At first i was not going to rebuild again as it seemed that there was a lot of factors (layout etc.) that could have an effect on the final outcome.With the other builds they worked OK but the buzzers,hum and static was a kill joy.
I built this amp as per the schem that is close to the BTO LB260D preamp with the LIL ROCK (B90L) Split PI and Tubenit's ECL84 Power Amp
This of course is always going to have its problems, but has turned out to be a LITTLE MONSTER.
I can see now why the BTO was held in high regards.

With the amp ON,nothing plugged in, absolutely no hum or buzz at all (Had major buzz with controls turn to 10 in the other builds)
With guitar plugged in, all controls turned to 10, minute hum that you would expect but nothing like i was getting in the other builds  still getting a little buzz but again so minute that with volume turned to 8,could not hear it at all (so far this will be my quietest amp)The buzz that i get from my guitar (ongoing problem)will disappear when touching the strings.

I did not change much of the grounding but what i did do was solder a buss on the back of the pots and grounded all preamp grounds to it but DID NOT ground that buss to anything.The only ground is the pot bodies grounding themselves to the chassis. Maybe this has made the amp so QUIET 
I found the James TS to be very responsive and i don't think it will need any tweaking (was not getting much joy with the other builds as the treble control would make the hum/buzz worse 
There are three switches, one is a treble boost that does chime in with not only treble but with different settings on the guitar gives some MIDS as well. The other two switches add some drive and distortion when engaged.I kept the values around these switches the same as the original schem as they were only small values that were bypassed by the switch and the difference is unbelievable. 

The only down side is that there is early breakup even though i have a 12ay7 in V1, i tried a 12au7 (very cheap chinese)and it did not sound too good and a 12ax7 that was too distorted, the ay7 sounded the best and i think the cathode could be tweaked a bit. Thoughts???
HBP informed me that the original has a 6SN7 in the PI that was close to a 12au7 and the ECLs triode was a higher Mu. This i think could also be pushing the Pentodes a bit.
I am getting some very smooth breakup/distortion playing the high end notes but the bottom end gets a bit loose and flabby. THOUGHTS??
With the last build i was getting a lot of feedback (on feedback connected) not getting any as such but i did hit one note and the feedback was great , it did not change pitch or volume and was constant for a long time.
I think this one was a great leaner and i think building the BTO with 6L6s or 6V6s (the power stage are similar in a couple of there amps)is a must do because i NEED another amp.

I think some values need the be changed just to tame it a bit  Thanks

[TIMBO]

Hi guy's, been having fun with this one. The three on board switches are great but are more like a FUZZ type sound and lack a bit of BITE so i thought a treble boost might give it a bit more grunt.I built a boost pedal (SHO) and found it gave a bit more EDGE to the amps sound,so i tried it with this amp and it boosted the volume and gave some sharp EDGE to the sound (BITE).

I built the AMZ treble boost and and added it to the front end and found it to work well. It improves the sound of the other switches as well and does not overdrive the amp.
But i am still getting a little "looseness around the bottom end" so how can i TIGHTEN it up a bit.I was thinking that maybe changing the .047 caps off the PI may help as Tubenit has these as .01 in his SoLow Watt. Hopefully someone could give some direction on this, as it is a little hard to get into as it is a small chassis.
I'm using a hammond 125d universal transformer so could a different tap arrangement help with the loose bottom end
OK, now that these items are being addressed,i do like reverb, so i have been wanting to try this SS IRF820 reverb circuit.

[tubenit]

I think the ECL84 tubes are really bass heavy in tone ............. I found going to lesser values like  .01 to be pretty important.

with respect, Tubenit

[TIMBO]

Thanks Tubenit, I tried .02s and they were alright so i'll give the .01s ago.

Looking at what i have got so far and pretty happy with it BUT :-
The original BTO has a pentode/triode as an FXs called "STINGER" so this got me thinking about some little pentodes that i have 6AU6 and 6AN5.Both have similar PINs and the 6au6 has a bit more watts output.
So i breadboard the little bugger (first the 6an5) with a circuit i pinched from i think was DLs BOGEN K10 HACK that used the 6au6 as the input valve. This did not work when using node "D" of the amp (202v) but when using V1 PIN1 plate supply it worked OK.this gave me about 6v on the plate and screen. 
So i hooked the 6au6 to node "D" this gave me 36v on plate and screen and worked very well (YEAH BABY youno)
I have look at a number of schems and there seems to be a lot of different component combinations for this tube (6au6)
The original has very large plate/screen resistors which i would think that the pentode runs on very low voltage.
So my next thought would be to try the same circuit as the original but halving the plate/screen resistors as the node supply is half of the original. Any input would be great. Thanks STICKTOITNESS

[TIMBO]

Hi guy's, The STINGER circuit works very well and sounds better that the SS stuff.I tried another circuit (another of DLs fine works) so i am going to stick with that one.I have a 6AM5 which i will try while i have the bread board out, just for fun. The voltages may vary a bit cause i haven't setup a proper filter stage yet.Thanks

[DummyLoad]

another of DLs fine works

i see...from the recent CHA10 hack. interesting tone, no? it does have some compression but rings/chimes well. i was happy with that stage but the tone network sucks off too much gain. i may revisit that amp, or just leave it as a gain-y blues amp. so glad you found something useful of all the hacked crap i throw out on here. ;-)
overall, i like the 6AU6: i believe it is a very underrated tube for what we do since every hack i've built around the 6AU6 has pleased me. i've yet to fiddle with the 5879 and it's next on chopping block, so to speak...

happy rosin smokin', timbo! :-)

--DL

[Willabe]

i've yet to fiddle with the 5879 and it's next on chopping block, so to speak...

 

That's good news to me DL!    

I have a set of iron from Merc. Mags. I bought 4, maybe 5 years ago, for a Gibson Les Paul GA-40T after reading a reveiw from Tone Quest Report Mag. They LOVED IT and the TREM TOO! At the time I also bought a 1/2 dozen NOS (RCA?) 5879 tubes and set them aside.

I wanted to build this amp for slide guitar and now I also want to see how this _preamp_ trem compares to (5G9  Fender Tweed) _bias mod_ trem?

Here's the scheme;



http://www.el34world.com/charts/Schematics/files/gibson/GA-40_55_Later.pdf


                
              Brad      

[TIMBO]

Hi guy's, I've hit a bit of a snag,i installed the 6au6 and it's only working at very low volume.I disconnected the 12a_7 at the input jack to see what kind of volume it was putting out and it was very low. I bypassed the tone and volume to rule out them and still very low.I would have thought that it would be as loud as the 12a_7.As said, i used one of DLs schems and thankfully he add voltages and i was able to be close to them. I even tried another tube.I did have it working on the bread board but it did at one stage it did do this ,i just thought that it was because of the flimsy set up. Its pretty straightforward circuit so i can't see what the problem can be.Thanks

[DummyLoad]

 i've had microphonic 6AU6 tube and had to weed through a few before i found a couple that would work, however, i have not experienced a problem as you describe. maybe a wiring error? what happens at higher volume? gross distortion? noise? squeal? silence?

--DL

[TIMBO]

Hi DL, Half of the problem is that i have used a few schems and confused myself with the component values.So after some stuffing around i think that i have found a circuit that works, the one thing that increased the vol was a 47uf across the cathode resistor. I'll rework the TS and hopefully that will get me there. I disconnected the the input to the first triode and it is now loud enough but when connecting the first triode to the input it seems to kill the 6au6 so the desired fuzz is not as full on as i hope this is why i thought that the 6au6 was running at a low volume. Is there any to up the VOL/GAIN or do you think that what is,is what it is.

[DummyLoad]

...that increased the vol was a 47uf across the cathode resistor...

it's a fairly high gain bias that likes to be bypassed for hum reduction. check for wiring errors?

--DL

[TIMBO]

Hi guy's, I'm over the moon with the outcome of this build.I only have a small amount of hum and unfortunately i think if is mainly comming from the SS REVERB but it is only when the level is at max so at a lower level there is plenty of VERB to be had  .I'm hoping a friend will be able to do a sound clip in the near future. Thanks to all that helped.

[TIMBO]

A few more pics,

[kagliostro]

Hei TIMBO Very Nice Build 

K

[TIMBO]

Thanks K for posting the schem