Derby details, the long version
The"brown" Derby is an amplifier who's foundation is that of the
Fender brownface Deluxe amp, AKA a 6g3 circuit.That circuit, which was in production only from around1961 to 1963, is brought into the
modern world. A rebirth if you will.
We dealt with the common safety issues of the original design.
Added a heavy gauge 3-pronged grounded IEC power cable.
Removed what is known as the "death cap" from the design.
Added screen resistors to help protect your precious tubes and transformers.
Added standby switch the original design so that you may use a variety of rectifiers
other than the GZ34 without danger of cathode stripping.
Added a simple Slave/D.I. output with a level knob. This circuit is based on what
old pickers may know as a "pigtail". It uses the speaker as a reactive load, giving a
more natural vibe to it's response. It is perfect for driving into the front end of another
tube amp for thick saturation of that amps first tube gain stage, or running into a mixing board,
or for direct recording.
Did away with the fixed bias of the original design and replaced it with a functional
common blackface era bias network. Also added were bias test points to make bias
adjustment safe and easy.
I include a new meter with the amplifier and instructions for bias adjustment of the amp.
Let's talk about the amp construction!
Chassis is made of aluminum, not steel for three reasons.
1) Heat dissipation. Ever see a heatsink made of steel? Me neither. Aluminum dissipates
heat much better than steel and in a tube amplifier where there will indeed be some heat.
A chassis that doesn't hold heat is a good thing not only for your tube life but for your ampslifier circuits as well.
Less heat=Longer life.
2)Aluminum is a non ferrous metal. Much more impervious to hum related issues.
3) Aluminum has less resistance to flowing electrons. The result is a sensitive response to your playing.
4) Non corrosive. Steel can form rust over time and cause grounding issues.
Aluminum cost nearly four times or more than that of steel, and the cost keeps climbing
but it's well worth it in my opinion.
If you look at the pictures of the internals of our Derby you will see our lead dress is
top notch. We followed Leo's examples by pictures we had taken of vintage brownface deluxes.
No spaghetti bowl mess of wires here.
Our boards are made of 1/8" thick Garolite. This is a fire retardant fiberglass material
that will never warp or gather moisture like the "fishpaper" boards used in vintage amps.
Virtually indestructible, shock absorbent, fire retardant, and extremely repair
friendly.
Soldering techniques and skills are perfected. Nothing even close to a cold solder joint in these amps.
Each joints is first mechanically connected. This means you could nearly run one of my amps with
virtually no solder what so ever! Solder is not meant to conduct electricity. It's job is to help keep in place
a solidly formed mechanical joint.
Only the best caps for this particular circuit are used, mostly Mallory 150's, for signal caps
and Sprague Atoms for cathode bypassing and power filtering caps.
Unlike most other amp builders we take the higher longer road in construction and ensure the caps
outer foils are properly oriented throughout the amp.
In Leo's days the cap companies clearly marked the end attached to the outer foil making
placement a snap. If you look inside an old Fender you can see the caps are marked with a line
denoting the outer foil.
Nowadays each cap must be tested on an oscilloscope to determine which end has the outer
foil! Then the amp builder must know how to orient the cap properly in the various places
of the circuit.
Do it right and you have an amp that is properly voiced with less noise and better tone.
Do it any other way and the amps tone will suffer.
Our power filtering caps and bypass electrolytic caps are all Sprague Atoms.
Hands down the best sounding cap, and yes caps used to filter your power most certainly affect the
amps tone.
Mostly metal film resistors are used throughout. They have less thermal (johnson) noise, and have
far superior temperature co-efficient. Meaning when they heat up, as will happen in tube amps, they
don't lose their ability to hold their resistance value. I will by request (and $40 price increase) use a few
carbon composition resistors in the signal path. They do tend to drift over time, and also with heat. I do
a number of tests to weed through the ones that are not long for this world.
I use a combination of CTS, PEC and N.O.S. Centralab brand pots depending on what the pots function is.
Most of current production pots frankly are junk. Even if the construction is the same the tapers are not
correct. What was once a true Algorithmic pot is now made by cutting the tapers of two different value linear
pots the result is usually a nasty jump where these two taper are spliced together. I try and source the best
pots I can find. Allen-Bradly are by far my favorite but they no longer turn up much anymore, and when they
do they are often priced accordingly.
Carling switches, and Switchcraft jacks are used throughout. Industry standard for decades.
Mercury Magnetics Transformers
The heart of good tone in an amp is the transformers. If you have weak transformers
made of sub par materials your lost. No guitar, no tube, no speaker, no tube, no cap,
no bag of mojo, or other combination of part will make things right.
Lots of companies can make transformers. But no one does it better than MM.
They are by far the best sounding iron made for this circuit. I know because I have ran the
gamut with every other name brand under the sun.
I used a lowered B+ power transformer. This voltage correction accommodates for the simple fact that line
voltages were once lower then todays standards. Thus all vintage Fender amps are running much hotter then they did
in the 60's whereas my Derby amp is running on the actual design specified voltages internally. The result is my Derby sounds
like a brown deluxe did in the 60's. It's basically a time machine back to the golden era of rock and roll.
Mercury Magnetics transformers are not cheap but what's your tone worth to you?...Exactly!
They are the best money can buy and Quinn Amps is proud to use them in every amp built!
Speaker speak... Tone Tubby Alnico's have proven themselves to deliver the
voice of my Derby amp in the finest way. They are uncannily remarkable to my ears. I have also
seen eyes light up and old grumpy men shine with big grins after a
few notes through one of these. Other sizes and configurations available.
The tremolo circuit in this amp is worthy of very particular mention. It is known as
bias vary (sometime called bias wiggle, bias trem, bias modulated trem, etc.)
Most popular during the "brownface" era. Almost all the later "blackface" era amps
went with the "roach" trem (an LED and LDR coupled together beneath shrink tube.
The majority of those in the know will tell you brownface trems are far better sounding
then the later roach types. This is do to how they operate. The vary the bias of the power tubes,
causing them to modulate between cuttoff and saturation. This causes the amplitude to rise and
fall naturally. With the "roach" trem the signal is simply set repeatedly to ground and the result is an
abrupt and stepped sound. With the Derby it's a nice smooth waveform.
The sound is truly hypnotic and three dimensional. Not choppy at
all. So smooth an natural. It is a feature you will only find in very few rare amps.
Tremolo footswitch included.
Quinn amps are outfitted with some of the finest NOS tubes available.
Tube compliment is GZ34 rectifier, Two 6V6 power tubes, Three 12ax7's
6V6 choices include: 5992 redbank bendix aircraft division, mazda greys, rca navy '44 to '51 production,
kenrad vt107, brown base military raytheon or sylvania.
12ax7's are RCA Black/longplate '61-'62 production.
All fully tested and exceptional tubes.
Let's get into the cabinetry.
All cabinetry is done here on site! Not many amplifier companies can make this claim.
Quinn Amps can and indeed, do so with pride!
Speaker cabinets are a hybrid design based somewhat on Fender combo amp cabinets
with a Howard Alexander Dumble designed style rear port.
Cab is constructed using half-blind dovetail joints.
3/4" #2 or better Pine top, bottom and sides. The pine adds some woody warmth and clear mids.
3/4" void less Baltic Birch speaker baffle. The Baltic baffling makes sure to get the most from any speaker you load into it.
Much less transfer loss then thinner baffles made of lesser wood. Tight and crisp tone.
The combination of the two gives that great old aged tone, but without flubbing the bass and losing speaker tone.
Rear panel is also 3/4" Baltic Birch. The port is based on Dumble cabinets and is designed to better align the front and rear
emanating sound waves resulting in warm rounded notes that bloom and fill the room.
With the front and rear vibrations in better phase your working more efficiently.
Solid as a rock, these cabs will hold my weight (140lbs) with one corner edge to the ground and me
balancing on the opposite corner edge and not even flinch at the corners!!
Our amps are made to withstand a touring life, gigging nightly, moving from climate to
climate, and give great tone reliably night after night, and consistently for years to
come. There is no type of damage one could inflict upon this amp that would put it
beyond basic repair save perhaps a drop in a vat of acid!
Simple Volume and Tone controls, no fumbling, just easily dialed sweet tones.
For less than you would pay for a sickly, uncared for vintage amp you can have "That same old
tone", in a far more reliable rendering. This is superb amplifier circuit with fantastic tone that truly is built to last.
Pure, simple, unadulterated, raw, blues and rock and roll of tone!
