"Tweed"
Princeton Clones
I have
built quite a few Tweed Champs and Princetons. The first amp I ever
built was a Champ based on the 5F1 circuit, but it is no longer
in existence. I gutted it for parts for another project. I built
the amp on terminal strips and it seemed to take forever to finish.
I started building amps on eyelet boards starting with the next
amp I built and have used that method of construction ever since.
Since
that first amp, most of the amps I've built have been based on the
Tweed Princeton circuit. It is a great platform for starting out.
If you are beginner and just starting out, I recommend you start
by building the 5F2-A Tweed Princeton amp. It is only slightly more
complex than the 5F1 Tweed Champ, which has two gain stages driving
a single ended power section running in Class A. The Tweed Princeton
incorporated a simple (but usable!) tone control. The Princeton
can be built in a small chassis, the parts count is fairly low and
best of all it sounds really good! At low volumes they sound fat
and smooth, cranked it distorts viciously. However, if you think
that 5 watts isn't very loud, try cranking one up in a small room,
you'll be very surprised.
Downloads:
Original
5F2-A Tweed Princeton: [schematic]
[layout]
Original 5F1 Tweed Champ: [schematic]
[layout]
New:
Updated
Tweed Princeton Schematic (.pdf file, 40kb)
New:
Updated
Tweed Princeton Wiring Diagram (.pdf file, 67kb)
This
diagram is an update of the original. It improves the amp over the
original in the following ways:
- The
filament wiring has been improved
- Two
100 ohm resistors create an artificial center tap
- A
120V neon lamp replaces the 6.3V lamp
- Solid
state rectifiers replace the 5Y3 rectifier tube
- A
three-prong power cord replaces the old two-prong type
- The
grounding scheme is improved
- Standby
switch added
- Some
of the component values have been tweaked to make the amp sound
better
Recommended
transfomers:
- PT:
240-0-240 to 275-0-275 rated for at least 50mA; Hammond
270CAX
- OT:
5K-7.5K primary, 5W, single ended, air gapped, rated for at least
50mA; Hammond
125CSE
A good place
to get Hammond transformers in the United States is Radio
Daze.
Below
are some pix of the Princetons I've built.
Click on the thumbnail to get the larger picture:
One
of my first Tweed Princetons |
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This
is one of the first Tweed Princetons I built. I departed from
the circuit by using a 6SL7 tube, which has the same characteristics
as a 12AX7, but has lower gain and is an octal tube. It takes
the same 8-pin socket that a 6V6 does. I kept the 6V6 power
tube. The output transformer is from a Sundown Rocky amp.
The power transformer is an NOS Triad R6-A. I lucked into
a bunch of these cheap, and they are great to use in Tweed
Princeton circuits. |
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This
is a view of the underside of the amp. This amp mounts in a
tweed-style cabinet with the tubes hanging down, the controls
on top and the circuit access facing out. I originally built
this amp to use a 6X5 rectifier, but tried out a plug with solid
stated diodes. |
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This
picture shows the circuit board and wiring. It is pretty messy,
I've done lots of experimentation with the circuit values and
it shows. |
Another
Tweed Princeton |
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This
is another amp I built early on. It uses a 12AX7 for the pre
amp and a 6V6GT for the power amp. Again the power transformer
is a Triad R6-A. I'm not sure who makes the output transformer,
I got it cheap when an electronics store sold all their remaining
stock. The original output transformer was a Hammond
125E that I pulled for another project. |
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This
picture shows the tubes. The chassis is a Bud
Industries AC-401
that I got a deal on from a blow-out sale at a local electronics
store. It measures 9.5" x 5" x 2.5' and worked great
for this type of amp. Again, it mounts tweed-style in a combo
cabinet. |
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Notice
that the wiring is much neater. I also used RG-174U shielded
wire to all the grids. The circuit board is G10 glass epoxy
board that I got at a local plastics retailer which has since
gone out of business. |
Tweed
Princeton with a Twist |
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This
is yet another Princeton circuit but with a different output
tube. I substituted a 6AQ5 tube for the 6V6GT. The 6AQ5 has
similar electrical characteristics as the 6V6, but has a smaller
base and a different pinout. It's ratings are somewhat lower
than a 6V6's, but the plate voltage in this amp is only around
300v or so. |
 |
A
shot of the tubes showing the 6AQ5. The actual tube here is
a JAN (Joint Army-Navy) 6005 which was more mechanically rugged
and designed to be used intermittently. The 6AQ5/6005 tube sound
more chimey in this circuit, they have lot of top end. They
sound edgy but creamy when pushed to distortion. |
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For
this amp I used grade XX Garolite from McMaster-Carr
for the circuit board. I had been using G10 glass epoxy board
from the plastics supplier. I bought one sheet and soon after
their price doubled. The Garolite from McMaster costs $2.18
for .062" x 3" x 48" strips. Their part number
is 9322K22. |
Tweed
Princeton to Mount in a Head Cabinet |
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This
was the first Tweed Princeton circuit that I built into a chassis
for mounting in a head cabinet. The chassis sits on the bottom
with the tubes sticking up. I used a Bud
Industries AC-409
chassis which measures 13" x 7" x 2." |
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Again,
I used the Triad PT. The output transformer is a Hammond
125ESE. Up until the 125SE series came out, Hammond advertised
their 125E
series for either push pull or single ended operation. Then
Hammond developed the 125SE series for single ended use only
and the 125E series is now only for push pull. The 125E worked
great for smaller SE amps, but I like the 125ESE better. It
is double the size of the 125E, and has better bottom end. |
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I
used a piece of G10 glass epoxy board for the circuit board.
Notice the orange drop capacitors on the left side. |
Universal
Octal Tweed Princeton |
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I
built this amp as an experiment. I wanted to be able to use
most common octal power amp tubes, 6V6, 6L6, EL34, and 6550.
I used the Hammond 270EX and 125ESE. The best sounding tubes
to me were the 6V6 and the 6550. The plate voltage is a little
high to use 6V6, but I haven't had a problem using NOS 6V6s.
Notice the boost switch on the front of the amp. |
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One
great thing about the 125ESE is that it can match up a variety
of primaries and secondaries. I put three jacks on the back
just for that reason. |
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This
is my cleanest wiring yet. Again I used the G10 glass epoxy
board for the circuit board. I didn't use shielded wire for
this project, and I didn't notice any extraneous noise. |
All
Octal, All Triode Tweed Princeton |
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I
built this amp as an experiment. The pre amp tube is a 6SL7.
The power tube is a 6BX7 which is in the same family as the
6SL7, 6SN7, 6080 and 6AS7. All are octal dual triodes with different
electrical characteristics. All have the same pinout. The amp
sounds fat and smooth clean, but gets ragged and mushy when
pushed into distortion. I've also tried a 6SN7 in the amp as
it has the same pinout, and it worked well. The distortion was
smoother and less mushy. Even though the output power is less,
the amp sounds almost as loud with the 6SN7 |
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Again
I used the Hammond 125ESE for the output. The PT is the Triad
R6-A I have been using all along. The 6BX7 is a dual triode
so both sections are in parallel single ended. I used the output
section of this schematic.
The pre amp is the same as the Princeton's with adjusted plate
and cathode resistor values for the 6SL7. |
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Since
a triode does not have a screen grid, I decoupled the first
node of the power rail to the second with a 100 ohm resistor.
The power tube plate supply is from the second node, and the
pre amp tube plate supply is the last node of the power rail.
Notice the 68µF cap across the first 22µF capacitor.
The amp had a lot of power supply hum, but it all but vanished
when I soldered the bigger cap into the circuit. |
| Another
Universal Octal Tweed Princeton |
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This
is a close up of the board. The board itself is made from G10
glass epoxy board. I like this much better than the Grade XX
Garolite, but Garolite is much cheaper and works well. I usually
solder the leads to the eyelet bofore installing the board.
The recitfier diodes on the left are UF4007s, which are the
ultra fast recovery version of the 1N4007. They are supposed
to reduce power supply switching noise. |
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This
is the first amp that I've used a face plate. I chose yellow
since this amp will eventually be housed in a black head cabinet.
The PT is an NOS Stancor PC8404. The OT is a Hammond 125ESE.
This amp can use a variety of octal power tubes: 6V6, EL34,
and 6L6. Notice the large, blue 330uF, 450v snap in cap. This
amp is a lot stiffer sounding than a vintage amp with a similar
circuit, but is dead quiet. Additionally, the amp has a master
volume. |
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The
back of the amp shows the three jacks for the OT. Different
power tubes can match up to different speaker cabinets. The
power tube is a Russian Sovtek 6V6, which sounds surprisingly
good in this amp. |
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The
wiring is much neater in this amp as it is being built for a
friend. This is my neatest and most carefully wired amp yet.
All grid leads are RG-174U sheilded wire. This amp is dead quiet.
One interesting thing to note is that the master volume pot
casing was not connected to ground at first. This caused extraneous
noise when the MV was turned all the way up. It drove me crazy
for several hours until I grounded the pot's casing and the
noise went away. |
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