VOX: Vintage AC15 Schematic

Ignoring the gigantic and overly complicated trem section - this is one of my favourite sounding AC amps, which is most likely the inspiration for the Matchless DC30 pentode channel.

VINTAGE VOX AC-15 SCHEMATIC

Version:  NO V-1-5 / OA/031

Apparently this schematic is a v3, redrawn by Thomas Organ, with some different component numbering.   I can understand why they redrew it - a lot of people, including me, struggle with some of the original Vox schematics.   It appears that they may have done the same thing for the AC10 (which practically shares the entire output stage as the AC15, with a couple of minor differences)

Below is the original, which isn't the most confusing Vox schematic that I've ever seen, but I still prefer the one above. 

SUMMARY

In the Normal channel, the AC15 is an EF86 voltage amplifier feeding a volume control, which then drives an ECC83 long-tail pair phase inverter and a cathode-biased EL84 push-pull output stage.

It's nice and direct, with limited tone shaping along the way - there is of course the bright switch, and the traditional Vox Top Cut, but apart from that, this is a fairly bare bones signal path.

I'm not going near the trem channel - just too complicated for me, and I'll never build one.  

Inputs: 

• Two jacks wired High / Low 

• Each jack feeds the EF86 grid through a 68k series resistor (R5, R6)

EF86:

• Grid leak: 1M to ground (R1)

• Plate load (Ra): 220k (R15)

• Plate supply / filtering: from +315V through 22k (R14) to the EF86 supply node, filtered by 8uF (C3). Plate voltage is marked ~90V on the schematic

• Screen supply: 1M (R20) feeding the screen, with 0.1uF (C8) bypass to ground

• Cathode: 2k2 (R13) bypassed by 25uF (C5)

• Coupling cap to volume: 0.01uF / 10nF (C12)

Volume, Brilliance, Top Cut

• Volume pot (Normal): 500k (R29)

• Brilliance switch: SW3 inserts a 250pF capacitor (C17) as a “bright” bypass around the signal feed, letting extra treble through when switched on

• Tone: Vox “Top Cut” placed after the phase inverter — a 250k pot (R49) with a 0.005uF / 5nF capacitor (C36) working across the two opposite-phase drive signals

Phase inverter (ECC83 / 12AX7)

• Type: Long-tail pair (LTP) using both triodes (V5A, V5B)

• Normal volume feeds V5A grid via 10nF (C27)

• Trem channel volume feeds V5B grid via 10nF (C28)

• Plate loads: 100k each (R44, R48)

• Supply to PI node: from +315V through 22k (R43), filtered by 8uF (C26). PI node is marked ~220V

• Shared cathode / tail: 1k2 (R42) in series with 47k (R38) to ground

• Coupling caps to power stage: 10nF each (C32, C33)

Power stage (2 x EL84 / 6BQ5, push-pull, cathode biased)

• Grid stoppers: 1k5 each (R56, R57)

• Grid leaks: 220k each (R53, R54)

• Screen resistors: 100 ohm each (R62, R63)

• Shared cathode resistor: 130 ohm, 5W (R60)

• Cathode bypass: 50uF (C39)

• Plate supply is marked ~310V

Output transformer

• Secondary taps: 15 ohm, 8 ohm, and common

• Primary: 8k p-p

Rectifier and power supply (main)

• Rectifier: EZ81 (6CA4)

• Filtering: 16uF reservoir (C10) → choke L1 (10–20H) → 16uF smoothing (C15) to the main +315V source

Speakers

• A few variations of single and twin speakers - all 12" 

• Goodmans Axiom, Fane and of course Celestian blues

EL84 OPERATING CONDITIONS

Operating conditions are similar to the EL84 datasheet. 

EF86 OPERATING CONDITIONS

The preamp circuit is almost identical to the EF86 datasheet

VOX: Vintage AC6 Schematic

The Vox AC6 is a departure from the Vox AC2 & AC4, in that it has a 12AX7 preamp, negative feedback, no trem, and for some reason, the tone control is before the first triode - it's a bit of an odd-ball in the Vox lineup from the time. 

The 12AX7 preamp arrangement would give the amp a different flavour to the EF86 versions, but it's still an EL84 driving an alnico speaker in about the same size cab, so similar to its friends in that sense.

Further reading:  VoxAC30.org.uk   

VINTAGE VOX AC6, GUITAR AMPLIFIER SCHEMATIC

SUMMARY

In simple terms, the circuit uses two 12AX7 triodes feeding a volume control, which then drives the EL84. The first triode is cathode-bypassed, the second is unbypassed and receives negative feedback from the output transformer, and the tone control sits ahead of the first triode.

Some of the schematic values are hard to read, so hopefully this is close.  That said, apart from the unusual placement of the tone control, the 12AX7 stages are biased cooler than a typical Fender-style preamp.  

This cooler operating point doesn’t so much reduce gain as it shifts the clipping behaviour, with the stage tending to run out of headroom on one half-cycle first, giving asymmetrical clipping when driven.

The 220 kΩ input resistors are also a little unusual.  As drawn, they don’t just act as isolation resistors — they form a voltage divider with the 1 MΩ grid leak on the first triode.  The result is a small amount of input attenuation, so some signal level is lost before the first gain stage even begins to amplify.

The 12AX7 Preamp

Inputs:  

• Two jacks.  

• Each jack feeds the first triode's grid through a 220k series resistor

First Triode:

• Grid leak: 1M to ground

• 12AX7 plate load (Ra): 100k

• Cathode resistor (Rk): 4k7

• Bypass cap: 25uF, 50v

• Coupling cap to next triode: 0.01uF (10nF)

Second Triode:

• Grid leak: 470k to ground

• 12AX7 plate load (Ra): 100k

• Cathode resistor (Rk): 4k7

• Negative feedback from the output transformer to the cathode, 47k series resistor

• Coupling cap to volume pot: 0.05uF (50nF)

Volume & Tone control:

• Volume pot: 500k (wiper feeds the EL84 grid via a 4k3 grid stopper)

• Tone: 250k pot with a 0.005uF (5nF) cap in series to ground from the grid of the first triode

Power stage: EL84 (6BQ5) single-ended, cathode biased

• Grid stopper: 4k3

• Grid leak: via the volume pot

• Cathode resistor (Rk): 150 ohms (2W or 3W)

• Cathode bypass:  25uF, 50v

Output transformer:

• Secondary: 3 ohms

• Primary: Probably 5k or 5.2k, which was common with Vox at the time

Rectifier: EZ80 (6V4)

Power transformer:

• HT secondary: 250V-0-250V (as shown)

• Heater winding: 6.3V

• Primary shown with 250v, 230v and 85v

Power supply filtering:

• 32uF reservoir (C1) → 1k (8W) series resistor (R3) → 32uF (C2) main B+ node - likely to be 270v

• From +270V:  47k dropper (R5) → 8uf feeding 12AX7

Speaker: 

• Elac 8" alnico, 3 ohm

VOX: Vintage AC2 Schematic

Another early Vox model is the AC2.  It’s often described as being the same as an AC4, but there is one key difference — the tone control.  

Instead of sitting in the preamp like the AC4, the AC2’s tone control is wired in the power stage, between the EL84 plate and the B+ supply (effectively across the output transformer primary).  

It obviously works, but no one does this anymore - the tone control is sitting at just short of 300 volts DC, which isn’t ideal for a number of reasons.  Curiously, they chose the opposite direction for the AC6, with the tone control before the first triode of the preamp.    

Further AC2 reading:  AC2 on VoxAC30.org.uk 

VINTAGE VOX AC2, GUITAR AMPLIFIER SCHEMATIC

VOX: Vintage AC4 Schematic

Despite the name - and even the familiar look - the original Vox AC4 has very little in common with the modern “AC4” amps wearing the same badge.  The cabinet and the single EL84 output stage are about all they share.

The AC4 started life as the AC2 in 1958.  Fair to say that the AC4 is probably best known due to its modern counterparts, despite being a different beast.

The circuit, layout and feel are very much of their era — the preamp and power stage are almost text box examples from valve datasheets - and if you want the deeper backstory, the Vox Showroom & AC30.org both have an excellent history of this little amp.  

VINTAGE VOX AC-4 GUITAR AMPLIFIER SCHEMATIC

SUMMARY

It's a classic single-ended amp design, point-to-point construction, valve rectifier.  High gain from the EF86 firing pretty much straight through to the EL84, into an open back cab with an alnico speaker.   

There's very little loss in terms of low-end or with almost no frequency shaping along the way (at least before it hits the output transformer and small alnico speaker).  The tone control just rolls off some treble; no other shaping takes place. 

There is one unusual thing about the preamp - a huge 5.6meg screen resistor is taming the EF86: it starves the screen to drop gm and gain, improves linearity, and when you push it the screen current dynamics produce that soft ‘screen compression’ feel pentodes are famous for.  By comparison, 1meg is the datasheet value when paired with Ra 200k.

The trem wiggles the bias of the EF86 (cathode coupled), which is a fairly typical design from the era, not unlike a Vibro Champ.

The EF86 Preamp

Inputs:  Two jacks.  Each jack feeds the EF86 grid through a 100k series resistor

Grid leak: 1M to ground

EF86 plate load (Ra): 220k

EF86 screen supply: 

• 5.6M (Rg2) from the preamp B+ node

• Screen bypass: 0.1uF (100n) to ground

EF86 cathode:

• Cathode resistor (Rk): 1k5

• Bypass cap: 25uF

• Cathode voltage: ~2.7V

• Trem oscillator connects to the cathode

Coupling cap to volume/tone network: 0.047uF (47nF)

Volume & Tone control:

• Volume pot: 1M (wiper feeds the EL84 grid via a 6.8k grid stopper)

• Tone: 1M pot with a 0.001uF (1nF) cap in series to ground from the signal node (treble-cut)

• Power switch is shown as part of the tone control assembly

Power stage: EL84 (6BQ5) single-ended, cathode biased

• Grid stopper: 6.8k

• Grid leak: via the volume pot

• Cathode resistor (Rk): 150 ohms (2W)

• Cathode bypass:  25uF

• Cathode voltage: ~8.5V

Output transformer:

• Secondary: 3 ohms

• Primary: 5k / 5.2k as stamped on output transformers 

Rectifier: EZ80 (6V4)

Power transformer:

• HT secondary: 250V-0-250V (as shown)

• Heater winding: 6.3V, 2A (as shown)

• Primary shown with 230V / 115V options via selector plug

Power supply filtering:

• 32uF reservoir (C1) → 1k (5W) series resistor (R3) → 32uF (C2) main B+ node labelled +270V

• From +270V:  22k dropper (R5) → 8uF cap, ~260V node feeding the EF86 & 12AX7

Vibrato oscillator: ECC83 (12AX7)

• Cathode resistor: 3.3k with 25uF bypass (cathode marked ~1.7V)

• Speed pot: 1M

• Coupling caps shown: 0.02uF and 0.01uF, plus 0.01uF to ground in the network

• Footswitch shown to switch vibrato on/off

Speaker: 

• Elac 8" alnico, 3 ohm, sometimes Goodmans

EL84 OPERATING CONDITIONS

Operating conditions are similar to the EL84 datasheet.  I included both the 5.2k and 7k primary impedance conditions, as some modern transformers offer both options (or at least 5k and 8k).   

Many AC4s had transformers stamped with 5000, or 5200, indicating their primary impedance.  Given how common EL84 based amps would have been at the time, a stock transformer from any number of manufacturers would have been readily available.

EF86 OPERATING CONDITIONS

The circuit is very similar to the EF86 datasheet, but that massive screen resistor is hardly textbook.

AWA: Model PA1001 Valve Amplifier Schematic

 AWA MODEL PA1001 PA HEAD SCHEMATIC

 AWA MODEL PA100B VALVE AMPLIFIER SCHEMATIC

BELL & HOWELL: Model 385 Amplifier Schematic

The original schematic for the 385 was killing me - just too many part numbers listed, so I cleaned it up a bit.  I also removed the projector circuits.

I think there are two versions of this amp - this is the 6V6 version, while the other uses EL84s (which is nearly impossible to find a schematic for).

BELL& HOWELL - FILMOSOUND MODEL 385 SCHEMATIC

After the clean-up, I redrew the schematic in LTspice.  Seems to work as expected, so hopefully no mistakes...

The tone control is unique, as it uses a dual pot for the James EQ instead of separate pots for bass and treble.  Bass is cut while treble is turned up, and vice versa - or you could wire it so both bass and treble go up and down at the same time, leaving the midrange alone...  interesting.  

The dual 3meg pot is not easily found these days - in theory, resistor and capacitor values can be scaled to work with a 1meg pot, however, after spending some time on this, I can't get the response to match.   It's roughly the same, but there are obvious differences.  

The preamp could be simplified a little, and you would most certainly want to get rid of the 1meg resistor on the input.  

Hard not to notice all the little caps rolling off some highs from plates of the 12AX7 gain stages.  Something to experiment with and tune to taste.  

LTspice sim of the eq range

Original pages below

 

UNCLE DOUG CONVERSION VIDEOS

FENDER: Deluxe 5E3 Amplifier

Some reference notes on the Fender 5E3 Deluxe amplifier, possibly the most famous and widely copied variation of the Fender Deluxe, produced from about 1955 - 1960.

TWEED ERA FENDER DELUXE 5E3 SCHEMATIC

POWER

Transformer:  Triad 6452, 380–0–380 V

Rectifier:    5Y3GT

B+ ~360V  

Filtering:    B1 - 16uf,    B2 - 5k / 16uf,    B3 - 22k / 16uf

OUTPUT

OT:   8k P-P,  8ohm secondary.   Triad 108 (pre 60's).   Schumacher 125A1A.   Note the option to add another 8ohm extension speaker, which implies that the amp can handle a 4 ohm load

2 x 6V6

Va ~340 - 350

Cathode biased.  Rk 250hm, 50uf bypass capacitor

Grid stop: 1k5.  Grid leak:  220k

CATHODYNE PHASE INVERTER - 12AX7

First stage, boost:

Ra 100k,  Rk 1k5 ohms / 25uf bypass

22n coupling to grid of inverter

Second stage, invert:   

Ra 56k,   Rk 1k5 in series with 56k 

Rg 1meg to 1k5 / 56k resistor node

100nf coupling to 6V6 from cathode and anode of 12AX7

PREAMP - 12AY7

Ra 100k,  Rk 820 ohms shared / 25uf bypass.   (1,640ohms per cathode)

Grid stoppers 68k (in parallel, for high).   Standard Fender input wiring

Rg 1meg.  100nf coupling caps to volume

Normal and Bright channels

A1M VOLUME & TONE

A1M volume and tone pots.   

In tweed circuits, the volume pots are wired in an older style: the wiper (pin 2) is the input, while the outer lug (pin 3) serves as the output.  Do not change it to the modern pin 3 in, pin 2 out convention, as it will not work the same way.  

In terms of tone control, it is essential to note its position in the circuit.  On the Bright channel, treble can be increased via what is essentially a variable bright cap on the volume pot.  This does not occur on the Normal channel.

On both the Normal and Bright inputs, the treble can be turned down.

A 500 pF capacitor from pin 3 connects back to the preamp’s coupling capacitor (on the bright inputs). This acts like a variable bright cap—its effect diminishes as the volume is turned up.

A 4.7 nF capacitor from pin 1 goes to ground, providing a simple treble cut by shunting high frequencies away.

Pin 2 (the wiper) carries the combined signal forward to the grid of the phase inverter (also connected to the output of the volume pot).

One hallmark of these amps is the interaction between the two volume controls and the tone. Both volume pots connect directly to the grid of the first phase inverter stage, so even if only one channel is in use, adjusting the unused channel’s volume will still alter the response of the active channel.  There are tonal variations all over the place - be sure to experiment with extreme settings.  Mixing resistors were introduced in later models to remove this interaction.

12AY7 x 12AX7

Parameter	12AY7	12AX7
Amplification Factor (µ)	40	100
Plate Resistance (rp)	22.8 kΩ	62.5 kΩ
Transconductance (gm)	1750 µmhos	1600 µmhos
Typical Plate Current	≈ 3 mA @ Va=250 V.  Vg = –2 V	≈ 1.2 mA @ Va=250 V.    Vg = –2 V
Max Plate Voltage	300 V	330 V
Max Plate Dissipation (per triode)	1.5 W	1.2 W
Heater Current	0.3 A @ 6.3 V	0.3 A @ 6.3 V
Typical Bias for ~1 mA	–2 V to –4 V	–1.5 V to –2 V

6V6

Parameter	6V6
Type	Beam power tetrode
Plate Resistance (rp)	~62 kΩ (effective in Class A)
Transconductance (gm)	~4100 µmhos
Typical Plate Current	34–45 mA (idle, Class A)
Max Plate Voltage	350 V (design centre)
Max Plate Dissipation	14 W
Heater Voltage	6.3 V
Heater Current	0.45 A @ 6.3 V
Typical Bias	–12 V to –15 V (Class A)
Typical Load Impedance	8 - 10 kΩ  P-P
Typical Output Power	≈ 14 W (push-pull, Class AB)

5Y3

Parameter	5Y3GT
Type	Full-wave rectifier
Maximum DC Output Current	125 mA
Peak Inverse Voltage	1400 V
Typical DC Output Voltage	~350 V DC (at 100 mA load).
Max Input Capacitance	20 µF (first filter capacitor)
Heater Voltage	5 V
Heater Current	2.0 A
Typical Voltage Drop	≈ 60 V at 125 mA load

VOX: AC2 & AC30 Schematics, EL34 based

 The little-known EL34 Vox amps from the late fifties, one of which is fixed bias.   https://www.voxac30.org.uk/vox_ac2_30_1957.html. 

VOX AC2, 30 WATT AMPLIFIER.  OS/003 (FIXED BIAS)

VOX AC30, NO2.  OS/007  1960 (CATHODE BIASED)

EL34: individual 470 ohm cathode resistor and 50uf bypass caps.  5k output transformer

VOX: Vintage AC10 Schematic

From what I can see, the only difference between the two schematics below is the 200ohm resistor after the rectifier (shown on the V-1-3 schem).  There are some variations of cap values that can be ignored, such as 4n7 vs 5n etc.  I think this may be similar to the AC15 schematics, where Thomas Orgain in the US redrew the schematic.  

Further reading:  https://www.voxac30.org.uk/vox_ac10_overview.html

Note: Like many Vox guitar amplifiers, there have been iterations over time - this is the last version that was in production from about 60 - 66.

VOX AC-10 SCHEMATIC, OS/008 1960

VOX AC-10  NO. V-1-3

FENDER: Tweed Princetons

I'll start with the Fender 5F2A Princeton, as this is generally considered to be "the one" for a lot of people.

Basically take a tweed Champ, and add the classic Fender one knob tone control, which has no insertion loss, and you're in business.  It's hard to go wrong with this formula, which is why it appears in so many amps.  

FENDER TWEED PRINCETON - 5F2A, SCHEMATIC & LAYOUT

• 12AX7, 6V6, 5Y3

• Classic Fender hi / lo input stage

• Standard Fender preamp component values / biasing 

• Preamp is cathode biased

• Volume 1M, Tone 1M

• 22n coupling caps

• 22k negative feedback from OT secondary to second triodes cathode 

• Simple heater wiring - one side grounded

FENDER PRINCETON - 5B2 SCHEMATIC

• Preamp is grid leak biased

• Simple heater wiring - one side grounded

• 6SL7, 6V6, 5Y3

• Jensen P8T

• Volume & tone 1M

• OT 7765

• PT 6500

FENDER PRINCETON - 5C2 SCHEMATIC

• 6SC7, 6V6, 5Y3

• 2 x triodes in preamp - the first feeds the second via a voltage divider to reduce gain

• Shared cathode resistor

• Volume & Tone 1M

• Volume & Tone control is sitting on the grid of the 6V6

• Simple heater wiring - one side grounded

FENDER PRINCETON - 5D2 SCHEMATIC

• 12AX7, 6V6, 5Y3

• Preamp grid leak biased

• Volume & tone 1M - 1meg resistor in series before the volume pot

• No negative feedback

• Simple heater wiring - one side grounded

FENDER PRINCETON - 5E2 SCHEMATIC

• 12AX7, 6V6, 5Y

• Classic Fender hi / lo input stage

• Preamp is cathode biased

• Volume 1M, tone 250k

• Slightly more complicated tone control - tone control sits on the first triode's plate, before the coupling cap

• Simple heater wiring - one side grounded

• Choke on power supply

• 22k negative feedback

FENDER PRINCETON - 5F2 SCHEMATIC

Almost identical to the 5E2 - no bypass cap on the first triode

• 12AX7, 6V6, 5Y3

• Classic Fender hi / lo input stage

• Preamp is cathode biased

• Volume 1M, tone 250k

• Slightly more complicated tone control - tone control sits on the first triode's plate, before the coupling cap

• Simple heater wiring - one side grounded

• Choke on power supply

• 22k negative feedback

FENDER: Tweed Champ Schematics

I know these are everywhere, but humour me - this is mainly for my own reference.

FENDER CHAMP-AMP,  5C1 (WIDE PANEL TWEED)

Note: The Fender Champion 600 and 800 are said to use the same schematic (or at least extremely similar).

Preamp: 6SJ7 pentode, grid-leak biased (no cathode resistor)

• Inputs: two jacks, each 75k in series with 0.02uF (20nF) into the grid

• Grid leak: 5M to ground

• Plate resistor (Ra): 250k

• Screen feed: 2M, bypassed with 0.05uF (50nF)

• Coupling cap to volume: 0.02uF (20nF)

• Volume pot: 1M

Power stage: 6V6 single-ended, cathode biased

• Cathode resistor (Rk): 500 ohms, bypassed with 25uF

• Grid leak resistor = volume pot

Output transformer:  Triad 70189 

Note: I can't find a definitive source of original Champ OT measurements.

• Small single-ended output transformer

• OT Secondary 3.2 ohms 

• OT Primary, usually quoted as ~5k-7k  (some modern replacements offer 5k & 8k primaries). 

Turns ratios

• 46.8:1 = 7k @ 3.2 Ω    15VAC on primary = 0.3205 on secondary

• 39.5:1 = 5k @ 3.2 Ω   15VAC on primary = 0.3797 on secondary

Rectifier: 5Y3

Power supply filtering:

• 8uF reservoir → 500 ohms → 8uF (plate/OT node) → 25k → 8uF (screen + preamp node)

Power transformer:  Triad 6500

Typical Voltages:  Actual voltages vary a lot with wall voltage, rectifier condition, and transformer, but the commonly quoted targets for a 5C1 are roughly:

Rectifier DC output (first B+): 340V

B+ after the 500 ohm dropper / main supply node: 320V

6V6 plate: 300V

6V6 screen: 280V (lower because it’s fed through the 25k drop)

6V6 cathode: 16V across the 500 ohm resistor (so ~32mA cathode current as a rough check)

6SJ7 plate: 130V

6SJ7 screen: 21V

6SJ7 grid: -5V

Heaters:  Simple wiring, one side grounded (not twisted pair, no centre tap)

Speaker (stock): 1x6" alnico - commonly Permaflux 6-L (EIA 395), though other 6" period speakers exist due to Fender’s supplier variability and decades of replacements.

FENDER CHAMP 5D1

FENDER CHAMP 5E1

The classic Fender 12AX7 input stage and preamp values are used.  Negative feedback appears.  Choke on the DC power supply.  Changed to a regular component board, controls now on the top of the amp.

Preamp: 12AX7

Inputs: two jacks in the classic Fender input network.  When using input #1, the effective grid-stopper is about 34k because the two 68k resistors end up in parallel

• Each jack feeds the grid through 68k

• Grid leak: 1M to ground

First gain stage (V1A):

• Plate resistor (Ra): 100k

• Cathode resistor (Rk): 1k5, bypassed with 25uF

• Coupling cap to volume: 0.02uF (22nF)

Volume control:

• Volume pot: 1M (between stages)

Second gain / driver stage (V1B):

• Plate resistor (Ra): 100k

• Cathode resistor (Rk): 1k5, not bypassed

• Negative feedback: from OT secondary back to this cathode via a 22k resistor

• Coupling cap to 6V6 grid: 0.02uF (22nF)

Power stage: 6V6 single-ended, cathode biased

• 6V6 grid leak: 220k

• Cathode resistor (Rk): 470 ohms, bypassed with 25uF

• Screen supply: taken from the main B+ node, after the choke

Rectifier: 5Y3GT

Power transformer: Triad 6500

Power supply filtering:

• On 5E1, the choke sits where the 5F1 uses a 10k dropping resistor

• 8uF reservoir → choke → 8uF (main plate/screen/OT node) → 22k → 8uF (preamp node)

Typical voltages (ballpark):

• Main B+ node often lands around ~305V in many examples (varies with wall voltage and rectifier condition)

• 6V6 cathode: ~19V across 470Ω (≈40mA cathode current as a rough check)

• Preamp supply in many references is around ~260V

Speaker (stock):

Commonly a small 6" alnico in early narrow-panel Champs, often a Permaflux (though other 6" period speakers exist due to Fender’s supplier variability and decades of replacements)

FENDER CHAMP 5F1

Almost identical to the previous model, with a 10k resistor replacing the choke.  No bypass on the input triode - less gain.