Bluezmeister

[TIMBO]

Hey guys,
The Vadis to Dumble was a great success and the dumble sound is so unique.
I'm on a mission to complete my non starters and rebuild them into something else.
So sifting through my trays of parts.....
Tweedy Bluesmeister non-HRM
So I will be following Geezer's final schematic but there is going to be a bit of a twist to this build.
1) If I don't have the capacitor component I'll graft whatever I have to get close to the value required
2) Resistors will be comprised of metal oxide and carbon film to achieve close value
3) Large filter caps is what I have on hand
4) At this stage it will be fixed bias
5) Power transformer was for a project that never flew
6) Output transformer is 10K/15 vintage A&R taken from a old stereo
7) Cabinet and chassis, ready made sitting on the shelf
8) 14GW8 valves
9) The phase inverter/power amp PBC is also a project that had a flaw, so the preamp was cut off

[bmccowan]

Love the idea of using what's on hand to build an amp. Way too often I am ordering new parts when I have a whole pile of everything sitting around.
Not knowing much about Dumble type amps I had to look up HRM. I was not expecting Hot Rubber Monkey
About that chassis - is that a length of glavi-steel framing?
I went back and listened to the clips of Geezer playing that amp. Great tone and great playing.

[TIMBO]

About that chassis - is that a length of glavi-steel framing?

Correct!!

[bmccowan]

What a great idea for a cheap chassis. This is going to be interesting to watch. Have fun.

[TIMBO]

A bit of progress...

[TIMBO]

Hey guys,
Some rainy days have given me some time in the shed.
Wiring completed and fired up with a few issues..

First issue is the unbalance of the pentodes of the 14GW8's
They both have the same voltage on the plates, same negative voltage on the grids, same voltage on the screens.
But the cathode voltage has 15mAs difference between them.
Swapped the valves around to see if it was the valves themselves, but the cathode voltages remained the same in each position.
Now the OT is old and measuring the resistance of each leg from the CT there is a difference of 40ohms.
Could this be the reason I'm getting a difference between the two cathode voltages.
With a previous build using 6GW8's there was a definite overload of the grid due the excessive gain in the preamp/ phase inverter.
I have a few tricks I'll perform to try to tame the blocking distortion I encountered on the previous build.

[TIMBO]

Happy Easter Guys.
This one is moving along nicely.
As you can see there is a vacant socket hole that NEEDS to be filled
I built a Fuzznikator some time ago that used a 6GH8a capacitor coupled reverb circuit that worked really well.
So using parts I have on hand, I have a couple of tanks that are maybe 4E/4F type.





I have used both tanks and each product plenty boing.
You may have or have not noticed I have used 1UF bypass caps on the preamp and OD.
I used these values as a starting point cause I had plenty of them.
The idea was to increase the value by parallelling another cap, I have not increased any of them for the moment as the circuit is producing plenty of gain.

[TIMBO]

Hey guys,
Got the amp sounding pretty good for now.
Time to get a bit fancy,or completely stuff it up...


Going to give "piping/beading" a crack

[tubenit]

I sure hope you will give us a sound clip to hear of this amp!  Watching with interest!


Thanks for sharing.   With respect, Tubenit

[kagliostro]

Ciao TIMBO

Nice job

what are those intakes on the cabinet for ? Do you want to insert a colored pipe there ?

A friend used to insert white covered electrical wires forcing it with a small hammer, does you do the same ?

Franco

[scstill]

Do you reinforce your butt joints? or just glue?

[TIMBO]

@Franco
DIY Cabinet Building - Fitting String piping
@scstill
Glue nail and a timber dowel

[kagliostro]

Thanks TIMBO

that is near what my friend do, only seems he use a wire a bit larger that the intakes

Franco

[DummyLoad]

Happy Easter Guys.
This one is moving along nicely.
As you can see there is a vacant socket hole that NEEDS to be filled
I built a Fuzznikator some time ago that used a 6GH8a capacitor coupled reverb circuit that worked really well.
So using parts I have on hand, I have a couple of tanks that are maybe 4E/4F typ



I have used both tanks and each product plenty boing.
You may have or have not noticed I have used 1UF bypass caps on the preamp and OD.
I used these values as a starting point cause I had plenty of them.
The idea was to increase the value by parallelling another cap, I have not increased any of them for the moment as the circuit is producing plenty of gain.

Nice work Tim. Schematic has two references to V2; a 12AX7 and 6GH8. Would a 6GN8 work better for a reverb driver/recovery? Have you ever experimented with one? I experimented with a 6T9 and was impressed with the results, although I suspect that compactron may be scarce in NZ. Fiddle with a 6AC10 if you have some, bond a pair of the triodes exactly as done in Fender SR/TR AB763 amps, the third triode is recovery - All three triodes are similar characteristics to 12AT7; very pleased with the results of that experiment as well.

--pete 

[TIMBO]

Hey Pete,
Just copied and pasted the reverb in and didn't change the valve numbering.
I'm willing to try and valve that will produce a good boing, I try to stick to the known working ones as I don't have the time these days to tinker like I used too.

[TIMBO]

Hey guys,
Tolex completed and ready for the white string piping


So far so good

[scstill]

that tolex looks great
How do you get it sewn so perfect and the seams to lay so flat?
Do you have any pictures during the process?

[tubeswell]

that tolex looks great
How do you get it sewn so perfect and the seams to lay so flat?
Do you have any pictures during the process?

See Timbo's earlier post

DIY Cabinet Building - Fitting String piping

[scstill]

unless I missed something, That video does not show how the red and the black tolex are combined
Maybe its in reply #7 are the different tolex colors simply cut neatly and glued...
In reply #15 it looks like its folded over at the joint yet there is no rise at the joint.
Its a really clean & artsy tolex joint (as it is w/o piping) that I'd like to try sometime.

[TIMBO]

@scstill
Hey mate, the process is similar to the video.
That first photo of the red tolex has it lapped over the 3mm grove
I then trimmed the red tolex to the far side of the groove, this gives me a flap of 3mm to fold into the groove.
I went on and did all the red tolex this way
Strips of black tolex then glued in place over lapping the red tolex on either sides
In the video the guy used a paint scraper to push the tolex into the groove
This was the tricky bit was trying to squeeze the layers of tolex and the scraper into the groove
Once I got it into the groove, it was the same process as the video of trimming the excess tolex
A cab this size would normally take around 2 hours to do, this has taken twice that.
Tolexing is a fairly simple process, with some KEY items
1) you use TOLEX if you want a professional finish
2) you use contact cement, I only use Selley's  SELLEYS KWIKGRIP Horizontal Contact Adhesive 1L | eBay Australia
3) the contact IS touch dry
4) you have a sequence in the cutting and folding corners, unfortunately this comes with doing a number of cabinets.
So give it a CRACK

[scstill]

Thanks Timbo and Tubeswell
I get it now
I missed the groove earlier
I guess that is pretty standard for piping as well
Having only done wood cabs I guess I have to set out with a tolex focus
My problem is that once the cab is made I fall in love with the wood...
Maybe I need to get ugly wood as a starter  :-)

How do you cut the groove around the rounded edge? is groove cut before assembly and router?
Assumming since its a cross cut you use either a sled or a mitre guide

[TIMBO]

The grooves across the ply were done with a power saw with a guide screwed to the ply
I finished the small grooves on the edges and curves with a junior hacksaw
No fancy machinery here.....

[TIMBO]

String piping done

[tubenit]

Stunning!  What a superb job!  Thanks for sharing.


With respect, Tubenit