FrankenstAmp build

[Paul P]

I googled the 'net figuring that this name had already been taken by someone
or other but no, it doesn't look like it. So FrankenstAmp it is, the name
chosen to reflect the fact that the design is a quiltwork of bits of existing
designs, much like the monster. Hopefully my amp will be a bit more civilized.
Time will tell.

The highlights of my design are :

- two channels, one clean and one with tremolo (vibrato) and reverb
- Fender's patented 'harmonic' tremolo circuit
- spring reverb with an Accutronics medium delay type 9 tank
- power section configurable as one single ended 6v6, or two 6v6's in push-pull
- bias switchable between fixed bias and cathode bias individually for each 6v6
- separate fixed bias supplies for each 6v6
- 6 Tung-sol 12ax7s, 2 JAN Philips 12AT7s, 2 Tung-sol 6v6GTs, NOS RCA 5Y3GT
for single ended version and a NOS RCA 5U4GB or JJ GZ34 for push-pull

The preamps and tremolo circuit are from Fender's (brown) 6Gn-A series,
the reverb and phase inverter for the push-pull configuration from Fender's
(blackface) AB763 series, the output sections from the Fender Champ, 5E3 Deluxe,
and Deluxe Reverb, and the bias circuit from a Marshall 1987. The overall
chassis layout is similar to a HiWatt. About the only thing that's mine are the
front and rear panel layouts.

Today I cut the circuit boards from 1/8" G-10. This stuff is incredibly durable.
A piece 1/8" x 1/8" x 3" (3mm x 3mm x 75mm) I can hardly bend, let alone
break in two.



I drew up some drilling templates for the holes and turrets :



The drilling template for the chassis top :



I plan to spray glue this to the top to hold it in place while I center punch
and drill the holes. I have similar drawings for the front and rear panels.

Full size drawing of the inside (still to be taped together), and the circuit
boards placed on top of the drawing :



I'll post updates to this thread as work progresses.

Paul P

[bulldogguitars]

Your drawings are very nice. What software did you use. Cant wait to hear it when you complete it. Danny

[Paul P]

See the tenth message in this thread for details :

http://music-electronics-forum.com/s...ead.php?t=4742

If anyone contemplates buying this make sure it comes with the manuals.
There is so much stuff in these programs, I don't use a quarter of everything
it can do. I'll never understand why the company stopped selling this
product. It's full of really nice features like the dimension lines/arrows
above that are drawn automatically and if you change their length the
value changes automatically. And the drawings are layered so for example you
can put dimensions on a different layer and then display them or not.

Paul P

[Paul P]

Here's what the inside of the chassis should look like when it's done. Note that
the ground wires are absent from the drawing.

[ATTACH]1709[/ATTACH]

I figured I better check to see that the drawings were correct before glueing
them to the chassis. I did find that the cut-out for the power transformer bell
was too small. The transformers and choke are all from Allen Amplification.

This is with the push-pull output transformer :

[ATTACH]1710[/ATTACH]

And with the single-ended output transformer :

[ATTACH]1711[/ATTACH]

Drilling templates were then glued to the chassis. From the front :

[ATTACH]1712[/ATTACH]

The rear :

[ATTACH]1713[/ATTACH]

As can be seen here I removed the accessory outlet and fuse that I intended
to have from the rear panel. They were in the way of my bias supply board which
is attached to the rear panel.

I then center punched the center of each hole on the drawing using the anvils
that I showed in a previous message http://music-electronics-forum.com/s...6770#post46770

Top :

[ATTACH]1714[/ATTACH]

Front panel :

[ATTACH]1715[/ATTACH]

Paul P

[Paul P]

I drilled those holes that I could on my small 8" drill press :

[ATTACH]1722[/ATTACH]

and then did the rest with a hand drill with the chassis attached to a small
bench with the block of wood inside.

[ATTACH]1723[/ATTACH]

My vise with the piece of angle iron was too high up for easy drilling of the
front and rear panels so I moved the vise to the bench and clamped the
chassis to it :

[ATTACH]1725[/ATTACH]

Swiss cheese anyone ? All holes are drilled. Still have to punch out the
tube socket holes with chassis punches :

[ATTACH]1727[/ATTACH]

Sorry about the blood. I got off pretty much unscathed considering all the
sharp bits of metal this kind of work produces. Just a very minor scratch
on the end of a finger that I didn't realize had happened.

Paul P

[Casey4s]

It might be a little late now, but I always cover all the places on the paper where holes are to be drilled with clear packing tape, it keeps from shreading the paper template.

[Paul P]

Good idea, thanks Casey4s. I'll remember that next time 'round.

Paul P

[Paul P]

I punched the holes for the tube sockets with a couple of (vintage )
Greenlee Radio Chassis punches. A 1-1/8" one for the Amphenol octal
sockets and a 3/4" one for the Belton 9-pin sockets :

[ATTACH]1732[/ATTACH]

You turn a bolt to bring the two halves together which then shear out a
washer-shaped piece of chassis :

[ATTACH]1733[/ATTACH] [ATTACH]1734[/ATTACH]

The holes drilled for the bolt don't always end up exactly where you want
them. Having the drawing glued to the chassis helped to position the
punch at the right spot before tighening it.

All holes are now done :

[ATTACH]1735[/ATTACH]

Next will be finishing the openings for the power transformer and AC inlet
and deburring all the holes.

Paul P

[Paul P]

I was going to say that I'd finished my chassis but while uploading the
pictures I noticed that I'd forgotten something. So here it is in most of
its glory. Looks like some old military radio equipment :

[ATTACH]1746[/ATTACH] [ATTACH]1748[/ATTACH]

Since my chassis is painted I had to scrape through it in places for the tube
shields to ground properly. Looks like I forgot one :

[ATTACH]1749[/ATTACH]

I wonder what kind of metal the tube shields are made of. They are very
light and are somewhat attracted to a magnet, but not much. Shouldn't
they contain as much iron as possible for proper shielding ?

I added a lamp to my chassis vise :

[ATTACH]1750[/ATTACH]

So now the fun can begin...

Paul P

[Casey4s]

Looks like you are well on your way here Paul, looking forward to your progress reports.

[Paul P]

Here is a picture of all the ingredients to be shaped into an amp. The only
thing I forgot to include is the speaker, which is an Emminence 12" Red Fang
(I just had to try out a speaker with an Alnico magnet).



Most of the stuff fits nicely in my workbench's tool tray/drawer :



Paul P

[Paul P]

Here is a bit on turrets. I'm using two sizes of turrets, seen here with the
staking tool :



The small one is a Keystone 1540-4 and the large one a Keystone 1509-4.
They're hollow so you can stick a wire in them which is good for connecting
jumper wires from underneath. Turrets aren't cheap so I use the big ones
only for those places where multiple wires are to be connected.

Here's a close-up of the business end of the staking tool :



There is an anvil piece that I hold in a small vise :



You stick a turret upside down in the anvil :



Place the circuit board over the turret so it sticks through :



(The piece of metal is there just to keep the circuit board horizontal.)

Apply the staking tool and hit lightly with a hammer :



The underside of the turret tube is nicely rolled to firmly hold the turret in
place :



Paul P

[Paul P]

This circuit board will be the dual bias supply :

[ATTACH]1795[/ATTACH]

My setup for populating circuit boards :

[ATTACH]1798[/ATTACH]

The finished bias supply board :

[ATTACH]1796[/ATTACH] [ATTACH]1797[/ATTACH]

[oops, looks like I forgot the diode]

The first filter stage board :

[ATTACH]1799[/ATTACH]

The decoupling filters board :

[ATTACH]1800[/ATTACH]

The resistors are missing since I still want to work a bit on their values.

And this little guy is the single-ended output board, which mixes the signals
from the two channels before sending it off to the power tube.

[ATTACH]1801[/ATTACH]

I've learned a couple of things so far. First, a turret can only receive so
many wires, especially inside the tube. I had a couple of places where two
jumper wires were to go into the same turret underneath and I found out
that they may not fit. Secondly, I placed my turrets too close together
which leaves the leads on the components pretty short. Not good for heat
dissipation while soldering.

Paul P

[Casey4s]

It looks like you are making great progress Paul.

You have a really nice bench and tools, my shop is in my garage and it is soo cold out there I can only work about an hour or so before I have to quit.

Do you have a drill press? That is how I do turrets, just unplug the drill press and use it as a press with the anvil under the chuck and the flaring tool IN the chuck.


Good luck and keep the pics comming...

[Paul P]

Haven't had much time to work on this in the last few days...

Normal channel preamp board :



The circuits boards are now done for the first version of my amp,
the world's biggest Champ :



I'll get this much working properly (hopefully) before adding the
second channel. Then I'll add the push-pull output stuff after that.

Paul P