Another Amplifier Project - The Grinder

[MarkE]

This article is also posted on: http://www.diy-music.com (http://www.diy-music.com/)

As you guys probably know, I’m into tube amps in a big way. If you have read my other thread you know that I have a Fender Deluxe Reverb clone kit on its way and I should have that in a week or so. In the meantime I have been running several circuit simulations on the computer trying to work up my own design…..the amp I would have built for me if I ordered a custom one that way I did with the Carvin.

Well…I decided to scratch build one. I spent several weeks on the computer working out the design and finally parted with the bucks to order all the parts. About 70% of the parts have arrived and I have started the project.

I plan on writing a full construction article and will use this thread as a scratch pad. Please feel free to comment if you like even though I will be writing several technical notes here. I will later use the text and photos to start an article.

HAWK'S GRINDER (yes, that's what I chose to call this thing)

CONCEPT
I wanted to design an amp chassis that I can use as a design bed for experimenting with several circuit ideas. It is not intended to be a complete amplifier as I am only focused on a workable chassis now. I could easily install the chassis in a standard amp head as they are widely available. My goals with this project are:



Use a fairly wide and open chassis with plenty of board space for circuit experimentation, especially with preamp circuits.
Give it a very flexible power supply whose configuration can be easily changed with plenty of voltage and current options.
Have plenty of tube sockets available for experimentation.
Give it a standard working output section running in the vicinity of 30-45 watts.
Output transformer and output tubes selected that will allow me to achieve that power output goal and also have a rotary switch to allow output impedance of 2, 4, 8 and 16 ohms to match any speaker configuration.
Dual, switch selectable preamp sections. One will be mainly used for experimentation.
Use a standard long tail pair phase inverter section with presence control.
Use an “active” tone control. Not just a passive treble, mids, bass EQ but an active one with its own tube with gain. This will increase the range of the controls considerably.
Switchable overdrive circuit to be inserted into the signal chain after the preamp and before the active tone section. This stage will have predrive, overdrive and OD level pots.
A master volume control after the phase inverter and before the output stage. This will allow driving the preamps into distortion and lowering the volume to "apartment" levels or off altogether.
Install another tube (12AU7) to act as an effects loop (send and receive). Effects send will have its own gain control and also act as a line output to feed directly into the board for recording purposes.
To have a flexible bias setting scheme. I plan to permanently install two 1 ohm, 1% tolerance resistors from the output tube's cathodes to ground, then run lines to a stereo 1/4" jack on the rear of the cabinet. I can then use a standard volt meter to adjust/set the bias on the output tubes. The bias supply itself will be zener regulated and adjustable via two 50K linear pots on the rear of the chassis.
The 6.3VAC heater voltage will be elevated to ride on about 40VDC. I will generate the DC using a voltage ladder off the screen (B) supply and have it well filtered. This ladder will also serve to slowly discharge the power supply capacitors when the unit is switched off. The elevated heaters are necessary for both the cascode section and also the two cathode followers in the effects send/return section. Voltages on those cathodes well exceed the maximum heater to cathode rating and will certainly fry the tubes. An elevated filament supply is definitely necessary.
To have fun :)

THE BASIC DESIGN
I chose to call the beast “The Grinder” because I’m relatively certain that is how it will sound. The combination of gainy preamps and a dedicated overdrive channel should really give this thing some real edge and bite.

Preamps: There are two separate preamp sections switchable via front panel switch.

Preamp #1 will be based on a 12AX7 in cascode configuration. I wanted to try something different here rather than the standard multi stage 12AX7 preamp. Cascode amplifiers can be configured in several ways and I thought this would be a great test base for experimentation.

Preamp #2 will be based on an EF86 pentode. This pentode is a gain monster and I know that I have to be careful with the design here. I only plan on driving it to a gain in the range of 125 to 150. I am aware of the idiosyncrasies associated with this pentode such as microphonics but I simply cant resist experimenting with it. I am confident that I can tame the beast with the correct design, tube dampers etc.

Power Supply: I chose a power transformer meant for international sale and thus has many taps on the primary winding. This should allow me to swing the voltages around at will. The secondary winding is standard and has 720 and 640 VAC center tapped windings as well as 6.3 and 5VAC filament voltages. The 5VAC is for the 5AR4 rectifiers.
I have circuit breakers (instead of fuses) mounted on the rear of the chassis. There is one for the mains and another for the B+. I’m sure I’ll be popping these like crazy…especially the B+.

After several hours of soul searching I decided to use tube rectifier(s) instead of silicon diodes. I will wire two octal sockets for a pair of 5AR4s running in parallel. Using one or both I should be able to supply all the current I need and have some control on sag. I can always solder diodes under the sockets later down the line if I want/need to. I want to stay completely tube for this design. I will however need to find a chassis punched for 4 octal sockets, two for the 5AR4s and two for the output tubes., which brings me to……

THE CHASSIS
Selecting a chassis was a little more difficult than I expected. I wanted wide open spaces, something pre-punched and hopefully finished with front panel lettering. I found a chassis at Weber called the 6SX which was perfect for my application (pictures below). It is pre-punched for 5-9 pin tubes, 4 octal sockets and transformers. It is finished in a nice white powder coat with no burrs etc. This is a finished chassis. Forgive me but….its friggin’ beautiful.

THE BUILD
Given that this is a scratch build there is a lot of planning to be done here. Once I received the chassis I spent several hours and cups of coffee staring at the chassis considering a low noise layout for this thing. One thing that distresses me a bit is that the 9 pin sockets are in the front of the chassis near all the control pots. This would make the installation of a ground bus vs heater wiring problematic. I plan on wiring low on the heaters and elevating a thick wire ground bus above it. I’m hopeful that this will give me appropriate noise immunity. I will install a 14ga square tinned copper wire up on standoffs as far from the filament wiring as possible.

I then came up with a plan to get the maximum building area in the chassis without cramping myself too much. The pictures below show the configuration that I finally chose. There is plenty of board space here.

Once I had a plan, I started the metal work on the chassis, installing standoffs, drilling holes etc.


http://www.thehawkstudio.com/picts/grinder/IMG_1399.JPG



http://www.thehawkstudio.com/picts/grinder/IMG_1403.JPG



http://www.thehawkstudio.com/picts/grinder/IMG_1406.JPG



The pictures really don't do this thing justice. It is a very nice white color although the pictures yellow it a bit.

Here is a shot of how I will install the two boards.

http://www.thehawkstudio.com/picts/grinder/IMG_1409.JPG


I have never been a fan of brass plate grounding, however I decided to install it in the chassis simply to aid in grounding the potentiometer casings.

Now that I'm done (hopefully) with the metal work Im starting to install the main components.

The power transformer is installed temporarily with strap ties. I don' have the correct bell housing. I have a set coming from Weber and will install the transformer at that time.

Many of the potentiometers, jacks, circuit breakers, pilot light, power and standby switches are installed. I also installed five of the tube sockets. I will install the rest when I receive my next shipment of parts.

Here are shots from several angles

http://www.thehawkstudio.com/picts/grinder/IMG_1413.JPG


http://www.thehawkstudio.com/picts/grinder/IMG_1416.JPG


http://www.thehawkstudio.com/picts/grinder/IMG_1417.JPG


http://www.thehawkstudio.com/picts/grinder/IMG_1421.JPG


http://www.thehawkstudio.com/picts/grinder/IMG_1422.JPG



LINE EM UP!!!

With a project of this magnitude, making sure that I have all of the parts and organizing them properly is very important. I want to make sure that I have ALL of the primary parts in my shop. I hate having to stop a project like this for a week waiting for a 25 cent capacitor that I forgot to order.

Here I organize/inventory the components using plastic tubs. There is a tub for every section in the amp. I reconcile each one against the schematic I developed. I will post the schematic later once I get it off paper and on to the computer.

http://www.thehawkstudio.com/picts/grinder/IMG_1411.JPG

More to come. Comments appreciated.








http://www.thehawkstudio.com/picts/IMG_1399.JPG

[MarkE]

IT IS ALIVE!!!!!!

8/2/09
I did all the preliminary wiring on the power supply today. IEC socket, through breaker, main power switch to the transformer.
I constructed the power supply board and wired everything up including the 5AR4.

Now for the dreaded smoke test. I fired up the scope and meter, dug out my safety glasses, crossed my fingers and hit the switch. The 5AR4 lit up normally....no smoke. A nice full wave signal of the appropriate level on the scope. I let it sit for a few minutes then pulled the power.

After bleeding out I brought it back up again, and once warmed up I crossed my fingers and hit the standby switch. Beautiful....straight line DC on the scope at 377VDC. No smoke, no explosions, no ripple on the scope. I let it sit for a while while watching it closely. All normal. I shut it down and bled it out.

I then hung a 39K resistor across the D output to load the supply down at about 10 milliamps. I fired it up again and all normal. I let it run like this for about 30 minutes.

Here are some shots from the smoke test.

http://www.thehawkstudio.com/picts/grinder/IMG_1430.JPG

http://www.thehawkstudio.com/picts/grinder/IMG_1432.JPG


Nice clean signal on the scope with a 10 milliamp load down

http://www.thehawkstudio.com/picts/grinder/IMG_1426.JPG



This design is loosely based on the Weber Kelsey so I followed the Kelsey power supply with some minor modifications. I changed the capacitors on the C and D supply from 16 to 20 microfarad. Here is a copy of the schematic for the power supply.

http://www.thehawkstudio.com/picts/grinder/powersupply.jpg


The bias supply will be redesigned for regulated, dual output controlled by the two bias pots on the rear of the chassis.

Now I can move on to setting up the dual bias supply and heater elevator. Things are looking real good.

PM
Okay, here is a picture of the completed power supply board. A resistive ladder for the filament elevator and a dual regulated bias section has been added. The elevator chimes in with about 48VDC and has a capacitive filter. It will be tied directly to the heater center tap.
That's it for the power supply. I still have room left over for more stuff if necessary.

http://www.thehawkstudio.com/picts/grinder/IMG_1437.JPG

I cant do much else in here until the transformer bell housing arrives from Weber. Until then its a mish-mosh.

It's time to start working on the preamps but I'll save that for another day.

[babayaga]

Hi Mark...

This is fascinating stuff matey....

I grew up around my Dad who was always tinkering about with something electronic.. he even built me a couple of effects pedals along the way. He tried to teach me about this stuff but I never quite listened hard enough - too many distractions, whether it be from the music (or the girls!). He was a cinema projectionist and would take me along to help him run the shows....I remember I'd be lacing up projectors, and splicing header acetate onto the front of the ads supplied with the main feature, while he was sitting at the back of the booth with an open circuit board and a soldering iron in front of him on the bench.

Tom's cellar is also an education...with tools left over from when his Dad used it as a workshop.... one of his CS80's is laid bare in one of the rooms as he works on it, and I just can't get over the feeling that my Dad would be thrilled to check out either of you guys and the projects you undertake!

Great respect matey....! G.

[MarkE]

Thanks man
I've been doing this stuff since I was a kid. My Mom had to hide stuff to keep me from pulling it apart.
Here's a little story you might enjoy. When I was really young...oh about 12 or so...I used to have this tube clock radio and I went to sleep with it on every night. This was around 1967 or so, so I was listening to the Beatles, Stones etc. Anyway, in the dark I could see this eerie orange glow coming from the back of the radio, so I turned it around and stared through the cooling holes. I was fascinated by what I could see in there...these glass envelopes all glowing...and they gave off heat and sound....it was almost as if it were alive somehow. I remember wondering how John Lennon could be singing through those glowing glass tubes. Believe it or not, that is what hooked me initially on electronics. I studied it quite a bit as a teenager. When I went into the Navy I went to school for it. Actually, that's why I signed up was so that I could go to one of their schools. I was trained initially on tubes but spent most of my career up to my ears in computer circuits. Now I'm back into tubes again....I've gone full circle. Now it will be me and my bass playing through those eerie warm orange tubes :)

[SilverHamer]

How cool is THAT!? Mark did you ever build any of the Heathkit stuff when you were a kid?

[MarkE]

Not when I was a kid. When I was a kid I was more destroying stuff trying to figure out what made it tick lol. Once I got into the service I built nearly the entire Heathkit catalog including a 25" color television, which in those days was top end size. Heathkits are how I cut my teeth on my soldering skills. Damn...it is a real shame they went out of business. I wouldnt mind rebuilding some of their test equipment. I built two of their oscilloscopes, RF and audio signal generators and other stuff. They had Ham Radio stuff too, but I wasnt a Ham in those days (extra class license now) or I would have built that stuff too. I cant believe how much money I spent with them. They got nearly every extra penny I had in those days. I believe the company actually started by manufacturing aircraft. Im curious now...I hafta go back and read on that.

I've been working on the amp all day (well...after my honey-do list). I'm off to write my next installment now.
Thanks for checking in on this thread.
Mark

[MarkE]

8/8/09

During the week all of the remaining parts were delivered including the badly needed transformer bell housings. Now that everything is here in the shop I can rip out all the test wiring and wire for real. I will also install the rest of the tube sockets, output transformer, impedance selector and other items.

I started by drilling a few holes for terminal strips and P clips and then went to work. Here are some pictures from various angles.

http://www.thehawkstudio.com/picts/grinder/IMG_1440.jpg


The yellows are the 5VAC heater wiring for the 5AR4's. The reds and red/whites are the secondary HT taps, the brown, black and blue are the primary with 120V tap.


http://www.thehawkstudio.com/picts/grinder/IMG_1444.jpg


Heater wiring is a real pain in the ass. I have all the preamps on the front of the chassis and the output tubes on the rear. I elected to run the heater tap to the pilot light and then star off two heater runs from there, one for the preamps and the other for the output tubes. I'm still not comfortable having the front heater wiring so close to the pots but there is little I can do about it. I'm hoping that by elevating the ground bus (to be installed later) on stand-offfs it will give me the distance I need to keep sensitive preamp signals out of harm's way. The three stand-offs can be seen. I also configured the stand-offs for the preamp board so that I can screw another set on the existing one to elevate the preamp board a little if necessary. I wont really know how this will perform until I get the two preamp circuits up and running. As I mentioned earlier, there will be a cascode stage and also an EF86 stage switchable from a front panel toggle.


http://www.thehawkstudio.com/picts/grinder/IMG_1442.jpg

http://www.thehawkstudio.com/picts/grinder/IMG_1443.jpg


Initial power up went without incident. I had wired the power transformer's HT secondaries to a terminal strip so that I could easily switch voltages. I also wired the two 5AR4's in parallel, although I'm thinking that I wont need the second one.

I chose to wire the transformer's primary to a terminal strip. The primary on this transformer has 120 and 125 taps. I went to a terminal strip instead of hard wiring it so that I can change taps later if needed. I also wired the unused 45VAC tap there to terminate it.

I hit the switch and the meter reads 673VAC RMS. Very cool. I love it when a plan comes together.

http://www.thehawkstudio.com/picts/grinder/IMG_1441.jpg


Before knocking off for the evening I test fit the power supply board back in its original position. I will get that up and running tomorrow.

http://www.thehawkstudio.com/picts/grinder/IMG_1447.jpg

Okay...its nice to have this part behind me. The wiring was done as neatly as I could make it. I have the heater center tap kind of floating in the breeze because I plan on wiring it to the heater elevator when I get the power supply back up. For now I just have it bolted to the PT. I will need to fix that before I install the cascode preamp.

Here is the power supply schematic from my notebook.


http://www.thehawkstudio.com/picts/grinder/schem-powersupply.jpg

[MarkE]

8/9/09

Today's plan was to get the power supply wired and completed and to do the heater runs. Here are a few pictures.

I completed the power supply wiring and brought out the A, B, C and D supplies to a terminal strip. Red, White, Blue and Yellow. With the patriotic color selection it will be easy to remember but I labeled the terminal strip with a marker anyway.

http://www.thehawkstudio.com/picts/grinder/IMG_1450.JPG


Next up was the heater wiring for both sides. I hate doing this shit. It's probably the only part of the project that I don't enjoy very much.

http://www.thehawkstudio.com/picts/grinder/IMG_1454.JPG



For a moment I forgot that the first tube is an EF86 and I had the socket wired for a 12AX7. I had to go back and fix it by running the heater voltage to pins 4 and 5. Ugghhh.. I'm glad I remembered this. Its easy to loose track of details when you have so much to do.

Next, I installed the ground bus. It can be seen up on standoffs. I also reinstalled the main board. The ground bus is a 12ga square tinned copper wire. I think this arrangement will work out really well.


http://www.thehawkstudio.com/picts/grinder/IMG_1456.JPG


http://www.thehawkstudio.com/picts/grinder/IMG_1457.JPG


Here we are all tubed up for the heater test. All went normally. The big output tubes are KT66s. Earlier in the day when I tested the power supply I placed the second 5AR4 and they are working well in parallel. Its exciting to see this bad boy finally light up.


http://www.thehawkstudio.com/picts/grinder/IMG_1462.JPG


Tube covers in place.

http://www.thehawkstudio.com/picts/grinder/IMG_1466.JPG

With all the power and heaters completed I can finally continue the project by wiring up the first preamp stage. I think I'll do the EF86 first as I'm anxious to experiment with it. Next will probably be the cascode preamp for channel 2.

Looking long term I think I'll then move on to the other end and wire up the output stage, phase inverter and active tone control in that order. The plan is likely to change but for now that's what Im thinking. When I do those last three sections I will be building from the other side of the board back. When they are completed I should have a blank area between the preamps and the phase inverter. I hoping for a sizable area there as I will be experimenting with an overdrive circuit and an effects loop send/return.

[MarkE]

8/10/09

I managed to get a little bit of work done tonight. I started on the EF86 stage. I have a circuit I'm starting with, its pretty standard. I'm sure that it will come under at least a little bit of modification.

Here is a picture of the board. Its nice to finally get some parts on it.

http://www.thehawkstudio.com/picts/grinder/IMG_1467.JPG


Here's a shot of the startup schematic from the good ol' notebook


http://www.thehawkstudio.com/picts/grinder/IMG_1476.JPG


Here is a nut case bassist with way too many hobbies!

http://www.thehawkstudio.com/picts/grinder/IMG_1475.JPG

[MarkE]

8/13/09

The chronicle of my first amp build continues. Did I mention that this was my first build? Well, it is. I guess a scratch build might be a little ambitious for a first build but a project isn't fun unless it scares you a little.

Ok...all good news. I now have both preamp stages built, a EF86 and a 12AX7 cascode stage. I fired them up tonight and they both operate normally. Oh yeah...the heaters are now elevated to +40VDC. I don't want any unexpected surprises from the cascode tube. More on this at the end of this post.

Here is a picture. The EF86 is on the left and the cascode on the right. The mixer is simply two resistors and a capacitor (scope probe connected to it). That will be the exit point of the preamp section.


http://www.thehawkstudio.com/picts/grinder/IMG_1486.JPG

I'm intentionally leaving a two hole space between each section to give me just a little elbow room for later modifications. The bare area at the right will most likely get an overdrive stage.

The way I have it wired now, there is one input jack on the front panel. The signal is routed through a DPDT switch to one or the other preamp circuits. The unselected one's input gets grounded. The outputs of both preamps go through a dual ganged 1meg volume pot then the signals are mixed to a single point through 220K resistors.

I fired up the signal generator and injected a 200mv P-P sine wave. Here are some scope shots at various frequencies. The probe is attached post mixer. By hitting the toggle switch I can compare both configurations almost side by side.

First is the EF86, putting out almost 12V P-P. Im taking some signal loss through the mixer but thats normal. This is a 20hz sine wave. There was no low frequency roll off until I got to around 12-15 hz.


http://www.thehawkstudio.com/picts/grinder/IMG_1479.JPG



Here it is at 2KHZ. Same amplitude. I love it!


http://www.thehawkstudio.com/picts/grinder/IMG_1482.JPG


Now, without changing anything I switch over to the cascode. The signal is slightly lower. I think I may be loosing it at the mixer. I suspect that the cascode has a higher output impedance and is being loaded down a bit. I'll look into that later, if only to understand it. This thing is being built as a learning tool.

http://www.thehawkstudio.com/picts/grinder/IMG_1483.JPG


Now we bring the cascode down to 20HZ. Definitely some roll off here.

http://www.thehawkstudio.com/picts/grinder/IMG_1484.JPG

I'll start experimenting with the component values later on after I get the output stage up and running. One of my goals here is to experiment with learning to design circuits with a known frequency response, and get comfortable with it. I spent most of my career as a digital/embedded systems designer. Working with audio circuits is a bit foreign to me. There is much to (re)learn.

I did take the time to lower the volume enough to drive the signal into my studio mixer board and it sounds really good. I know its still early in the game but I couldn't detect any hum whatsoever, even through headphones. That was a relief. I then plugged my Schecter guitar into it and played a while. Everything seems to work just great.

About the heater elevation: I think its obvious why I put it in, as there is a cascode stage and possibly a cathode follower if I can jam in an effects send/return loop. I also wanted to take the heaters more positive than the cathodes to help eliminate hum. I recently read a great article on that and it makes a whole lot of sense to me.

Next up: Output stage. I want to set up the KT66s and phase inverter so I can start driving a speaker, so I will move to the end of the amp and start building backwards.

Thanks for looking in

MarkE

[MarkE]

8/15/09

Well, the weekend is finally here so I made a major push. I started by completing the chassis wiring in the power supply, supply runs, grounding, bias section, output transformer, impedance selector switch and bias monitor jack.

After all that I went to work on the two remaining primary sections. I started with the output section followed by the phase inverter. Once I got these two stages in I jumped a signal from the preamp section to the phase inverter to see if the inverter operates normally. For whatever reason I was worried about this working properly.

Here are the two new sections in place on the opposite end of the board. The output section is on the right and the PI on the left.

http://www.thehawkstudio.com/picts/grinder/IMG_1497.JPG


I once again injected a 1KHZ sine wave, crossed my fingers and hit the switch. The scope showed me exactly what I wanted to see, two nearly identical signals 180 degrees out of phase. This PI is a standard 12AT7 long tail pair with feedback and presence control.

http://www.thehawkstudio.com/picts/grinder/IMG_1491.JPG


The lower side (yellow) is at a slightly lower amplitude. Note/Edit: I changed the 100K plate resistor on the red channel to an 83K which lowered its amplitude and evened up the symmetry (standard fix).

Okay, now I was getting excited. I was within spitting distance of driving a speaker. I checked the bias levels on the empty KT66 sockets to verify that it was operating. A nice clean -60VDC and variable independently. I took a quick measurement of the DC levels on the KT66 plate pins, shut it down and bled it out.

I plugged in the KT66s, connected an 8 ohm speaker, plugged a male stereo plug into the bias test jack and hooked up the meter. Once again I crossed my fingers and hit the power switch (standby mode).

http://www.thehawkstudio.com/picts/grinder/IMG_1496.JPG

The heaters on the output tubes came alive normally. After letting it sit for a minute I took it off standby. Cathode current on both sides was about 5ma. I wanted to initially setup the bias for about 60% of maximum plate dissipation. I did a little math and figured about 35ma should do the trick. I was able to dial it in without difficulty.

Some notes on biasing: For a bias test point I'm using the usual 1 ohm, 1% resistors between the cathodes and ground. I have these wired to a stereo jack on the rear of the chassis for easy access.
I'm not using matched tubes. With independent bias controls I was able to match the quiescent bias currents. I plan to adjust the plate resistors on the phase inverter to make up the gain difference between output tubes. As for rise times, there is nothing I can do about that. Two out of three ain't bad. I'm sure it will be fine.

Now set at 60%, I connect a guitar, bring the master volume up and play at low power for a minute. Man, that EF86 sounds really nice, a little growly with nice low end. With the exception of the semi-dead MID control, the amp works perfectly.

[MarkE]

Before adding this installment of my build chronicle I would like to mention Ted Weber. Ted passed away Friday August 14. He has designed seemingly countless amplifiers for the amp kit industry. In spite of being completely overloaded with his work he was always generous with his time and expertise. We will certainly miss him.

This amplifier that I am building at the moment is his design, somewhat modified. The kit is known as the Kelsey and is currently in pre-release. Ted never got to finish it. I finish it in his honor. It's almost eerie that I complete this project as he passes.

Yes, the basic build is complete, and it works perfectly. Today I tackled the one remaining item, installing the tone control amplifier. I went to work installing it and it works nearly perfectly. There isn't really a noticeable change in sound on the MID control but I'll go back and play with the component values later. I still have a little wiring to do here and there but the amp is essentially complete.

Here are the final four shots for now. As you can see, my work area is a shambles after completing this wiring frenzy. I will be picking pieces of cut wire from the carpet for weeks to come. You can see the new tone stack in the middle of the board. The rest of the stack's components are flying on the back of the pots.


http://www.thehawkstudio.com/picts/grinder/IMG_1498.JPG


http://www.thehawkstudio.com/picts/grinder/IMG_1502.JPG



During testing there was good news and bad news. Good news...no hum even with the amp dimed. Bad news...it had a nasty hash/popping kind of noise. I broke out the scope to run it down and it only took about 5 minutes to find it. I had forgotten to solder the filter cap (to the eyelet board) that I use for the heater elevator. Once soldered I couldn't detect ANY noise at ANY volume. It is an extremely quiet build and I cant tell you how happy I am about that.


There was one other small problem. During the testing of the output stage I cranked the volume and was nearly blown from my chair with a LOUD squealing oscillation. I knew right away what to do. I reversed the wires on the output transformers primary and that took care of it.

Lets get this bird upright for a look.


http://www.thehawkstudio.com/picts/grinder/IMG_1507.JPG

http://www.thehawkstudio.com/picts/grinder/IMG_1511.JPG

Man, what a run. It seems that I have completed all of my goals here. There is still tweaking to do but I now have a fully operational chassis with a lot of room for add ons. I will be playing with this thing for years to come. The noise performance exceeded my wildest expectations.

I would like to thank Ted Weber and the crew of Weber VST for making this possible. The Kelsey is an amp I would have chosen to design myself. In the end I ended up following the Kelsey design much more than I originally intended. During the design stage as I was planning each section, I kept coming back to what was the Kelsey design. It was obviously well thought out by Ted and crew.

I would also like to thank all those who frequent Weber's kit building forum. You guys are just simply great sharing your ideas and techniques. I would have never been able to complete this without you guys. I would like to send a special thanks to Steven (LBusters on Weber Forum). He combined information from many thread posts and compiled a great grounding scheme. The grounding technique is marvelous. I'm tellin ya man...NO NOISE...NOT EVEN A LITTLE> Im speachless!!

[MarkE]

Now that I have the Deluxe Reverb behind me I went back this weekend to finish this beast.

I started by tearing the tone control section out and building an active Marshall tone stack to replace it. It works great.

Next, I constructed the overdrive section. It also sounds great.

It could use a tweak here and there but its essentially complete.

http://www.thehawkstudio.com/picts/grinder/IMG_0006.JPG

http://www.thehawkstudio.com/picts/grinder/IMG_0011.JPG

http://www.thehawkstudio.com/picts/grinder/IMG_0021.JPG

[babayaga]

Mark...what a FAB piece of kit! And with the satisfaction of knowing that you've built the baby yourself....great respect matey. I just wish I'd taken more notice of my Dad when he was trying to teach me how to build my own guitar pedals.... too late to ask him about it now. :-(