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.

VOX: AC-4 Guitar Amplifier Schematic (original version)

This is the original Vox AC-4, not much like the current line-up at all, apart from the low wattage.

• Volume
• Tone, on/off
• Speed
• Foot switch for trem (vibrato) - no depth control 
• 8" 3ohm speaker made by Elac
• ~3.5 watts RMS
• EF86 preamp pentode
• EL84 power pentode
• EZ80 rectifier
• ECC81 for trem

VINTAGE VOX AC-4 AMPLIFIER SCHEMATIC  V-1-1

VOX: AC4C1-12 Transformer Upgrade

Before I completely rip this Vox AC4 apart and rebuild the amp on tagboard, I thought I'd try swapping the output transformer (OT), just to see if it made any difference to the sound of the amp, as I've read conflicting views online.  

Cutting a very long post short - yes it did make a difference, it sounds much better in my opinion.  I'd already snipped the bright cap (C20) on the master volume and installed a vintage alnico speaker.  The transformer upgrade rounds things out very nicely.  Running 16ohms @ 5k:  No fizz, it sounds bigger and more open sounding.  The amp is cleaner sounding and the breakup is nicer.  It somehow sounds less boxy, which I can't figure out - maybe increased frequency response??  16ohms @ 10k is closer to the stock transformer spec, so some of the original tone returns - I much prefer 16ohms @ 5k.  

VOX AC4 OUTPUT TRANSFORMER SPECS

There's almost no information available on the stock Vox OT apart from the factory part number and that it's made in China.   I did a quick test after I pulled it out, and I found that it has a ~22:1 wind ratio.  With a 16ohm speaker, this puts about 7.4k on the EL84.  An 8 ohm speaker will drop this down to about 3.7k.  

A few forums posts say that it's 10k, I can only go off my own measurements. 

Wattage unknown - safe to say that it has to be at least 4 watts given the rating of the amp.  I'm going to take a guess and say that it's a little over-rated as it's a similar size to the Hammond, which is 8 watts.  Unlike the Hammond, there's no additional taps on the secondary.

HAMMOND 125CSE OUTPUT TRANSFORMER SPECS

I decided to use a Hammond 125CSE as it was available locally at a reasonable price, and the specs looked right.  Hammond transformers are made in Canada and seem to be quite well regarded (completely unrelated to Hammond organs by the way).  

The Hammond 125CSE is an 8w transformer - it has similar dimensions to the stock OT - conveniently the mounting is the same width, so no additional holes were required.  The Hammond felt a little bit heavier and generally speaking seems to be a better build quality.  It certainly sounds better.

There's plenty of information available on Hammond output transformers, the most important of which is on the diagram below.   By way of comparison to the stock OT, the 125CSE can run at 16 ohms with 5k on the EL84.  This is closer to how an EL84 is designed to operate.

NOTE:  See comment attached re biasing - you should check bias after changing the transformer. 

VOX AC4C1-12 OUTPUT TRANSFORMER UPGRADE

WARNING:  VALVE AMPS CONTAIN VERY HIGH VOLTAGES - LETHAL VOLTAGES CAN BE PRESENT, EVEN WHEN THE AMP IS DISCONNECTED FROM THE POWER.

I've marked up a few relevant items on the AC4C1 circuit board.  Both the 10" and 12" version are the same.

In very simple terms,  I disconnected and reconnected P2, P8, P10 and P11 on the schematic below, with a replacement transformer and the addition of a rotary switch to allow three options on P10.

The first step is to remove the back of the amp - I like to leave the chassis on the back of the enclosure, as I find it easier to work on this way.  Naturally the amp is not plugged in at this stage, and hopefully has not been used recently (hot valves and potential for stored DC in caps).  Note that this mod involves the B+ supply to the EL84 - we're talking a 320V connection.  

The output transformer is connected to the board using fully insulated 1/4" 6.3mm female spades - these slide off, however some force is required to do this and the circuit boards are flimsy.  If you try this, take it slow and work very carefully.  

The primary connections to the output transformer are directly either side of the EL84 - there's very little room here.  I removed the EL84 before attempting to remove the spades connected to P8 & P2 using a combination of my fingers small pliers - a bit of gentle wiggling and force was required.

Same again for the secondary connections which are attached to the external speaker jack.  This board feels like it wants to snap off, and the spades face the large filter cap on the circuit board - not a great combination.   

Note that there are actually 2 x P10 and 2 x P11 connections on the small circuit board that the extension speaker jack is mounted on - they're linked.  One pair from the OT, the other pair to the speaker.

After the wires were removed from the circuitboard, I removed the stock transformer.  Quick test placement of parts, before drilling the hole for the 3 way rotary switch.  Need to be really careful to make sure no waste from drilling the hole remains, as you don't want bits of metal sliding under that circuit board - boom!   

I crimped new spades onto the Hammond transformer leads and bolted it onto the chassis - I did not trim the leads to the correct size, as I plan on rebuilding this amp at some stage.  I didn't want to cut anything short.  I used heat shrink to terminate the end of the unused orange secondary wire.

The primary windings (blue and brown wires) attach to P8 & P2 on the circuit board.

I'm using a 3-way rotary for the secondaries to increase output options as shown below.  I wired the three secondaries that I needed to a 3 way rotary (white, yellow & green).   The common pin on the rotary connects to P10.  The black secondary connects directly to P11 on the external speaker board. 

I have no plans to detail this process any further - if you can't work out what I mentioned above on your own, it's probably not advisably for you to be playing with high voltages.

I'll add proper labels for the rotary at a later date - while I know what the coloured dots mean, if I ever sell the amp, this will need to be clear to avoid issues.

  

VOX: Vox AC4 C1-12 Guitar Amplifier

I picked up a Vox AC4C1with a 12" speaker recently, as it was selling really cheap second-hand, and it looked like it was straight out of the box.  I have a sneaking suspicion that the previous owner hated it - he seemed glad to be rid of it.

Note: comments below relate to the stock amp - no mods.   I wrote this post just after buying the amp.  

VOX AC4C1-12 GUITAR AMPLIFIER

How does it sound?

It sounds truly awful running at low levels - I think this is what has earned its bad reputation on several forums.  However, this little amp sounds pretty damn good when you crank it.  Turn the volume up, and set it on the edge of breakup (or further) with the gain, and the amp comes alive.  

I was running the volume at full for a decent amount of time - I measured 110dbA at one metre on the leq setting on my meter (that's an average, not peak).   I don't think the previous owner gave it much use, so I thought I should crank it to break the speaker in a bit, and it was a fun way to get to know the amp.  

I think some people assumed that the AC4 would be good at low levels because of the low wattage, and the spiel from Vox refers to it as "Famous for its ability to achieve classic VOX tone at low volume levels" which should perhaps include the disclaimer, when compared to how loud a cranked AC30 is.  If you want a small Vox amplifier that can sound good at low levels, buy a Pathfinder 15R or something along those lines.  

VOX AC4C1-12 SPECS

•         Gain, bass, treble and volume 

•         2 x 12AX7, 1 x EL84 (solid state rectifier)

•         4-watt RMS into 16ohms

•         Weighs 10.6 kilograms

•         Vox VX12 12-inch speaker. Which is a Celestion Seventy 80 more on that below.

VOX AC4C1-12 MODS

Warning number 1.  Valve amps contain lethal voltages.  Don't go poking around in there if you are not sure of what you're doing, as you might just end up dead.

Warning number 2.   Upgrading cheap valve amps can be an expensive exercise, with no financial return when you decide to sell. 

The Infamous Bright Caps

OK, so if you have read anything about Vox AC4 mods, you’ll read a lot about bright caps.  My view is that people buy the amp, decide they don't like it, and then try to mod their way out of it.  I think these are the same people who run it at low levels and regret their purchase, then desperately try to fix it (a huge assumption on my part, but there it is).  

The capacitors in question are C6, the 120pf cap across pins 3 and 2 on the gain pot, and C20, the 100pf cap across the same pins of the volume pot.   If the description I just gave and the schematic don't mean anything to you, the small capacitors are similar to a treble bleed on a guitar volume pot - when the gain or volume is low, the caps let high frequencies through (bypassing the pot).  The effect reduces as the pots are turned up.  

C6 is present on the gain pot of a regular Vox Top Boost channel.  As far as I'm aware, C20 on the volume pot is not used on any of the traditional lineup of Vox amps - in fact, the opposite occurs with the AC30, with a treble cut following the master volume in the power section.   

The Cab

After bright caps, the next "fix"' for the AC4 is taking the back off the cabinet, or enlarging the bass port (which is tiny).   I tried it - taking the back off did make a difference, but not as much as I was led to believe it would on the forums.  It was a little more open-sounding - there's a surprise.   Again, the biggest improvement that I can find is turning it up, to the point where the room starts to play a larger role in the sound that the amp is producing.

The Speaker

The VX12 is a rebranded Celestion Seventy 80, which is described by Celestion as detailed and crisply defined with a tightly controlled low-end and punchy aggressive upper mid-range. The top-end response is also subtly increased. 

The Seventy-80 is a much-maligned speaker, with ample hate online compared to Vintage 30s and Greenbacks etc, although they do have their fans, and a fair number of people thinking they don't deserve the poor reputation they have.  

If you have just bought this amp or have purchased one second-hand with very little use, the speaker will not be broken in.  Get some solid hours on it at a decent level to loosen things up before deciding you need to replace the speaker (over 20 hours).   It's not the high end that changes; it's the mids and lows that start to breathe - the balance will shift, which may help with one of the complaints about the sound of the amp.  

Don't take my word for it, check this from Ignazio Vagnone from Jensen speakers.  This advice is not specific to Jensens, according to Ignazio, all speakers, all brands need break in.

If you still don't like it after breaking it in and decide to try a different speaker, it's important to note that there's very little space between the output transformer and the speaker magnet - we're talking about 10mm...  a lot of common speakers will not fit without moving the output transformer.  There is room to do this, however, the leads connecting the transformer don't allow much movement, at least on mine anyway, I'm assuming others will be the same. 

As a reference, the Seventy 80 magnet is 134 mm wide and the speaker is 119mm in depth. 

The Output Transformer 

The AC4 has an unbranded output transformer.  Some say that upgrading to a Hammond or similar transformer will remove the fizz that can be heard at times. 

Hammond 125BSE (rated 5 watt)

Hammond 125CSE (rated 8 watt) 

The internet says the stock transformer has a 10k primary running the 16 ohm speaker (forum post, not an official Vox spec).  Others have mentioned that an EL84 likes to run with 5k on the primary, as per their datasheet.  I measured the stock output transformer and it came in at 7.4k @ 16ohms.

Valves

Like any amp, swapping valves may or may not make much difference.  I think despite the stock valves just being labelled as CHINA, there's nothing inherently wrong with them.  For me, if I'm swapping out or replacing valves, I buy NOS or vintage ones that test well and are reasonably priced.  Why - cause I like reusing old things.  I never spend more than the price of a new valve on an old one.

Most modern valves come from just a handful of remaining factories.  Popping Mullard on a new valve and selling in a box with vintage style artwork is just marketing.  

So what’s a stock AC4 good for?

I think it would make a great little recording amp, if you’re chasing the sound of a Vox working hard.  Possibly OK for small gigs if you only have variations of one tone, with that tone being a juiced Vox.

Pairing with another larger AC for a stereo rig.  Paired with my AC15 with a Alnico blue it sounds great.  The larger AC lifted the smaller amp, and the AC4 was in no way detrimental to the AC15.

What is it bad at?

It does not sound good at low levels, the clean tones are especially bad..

How does it compare to the 10" AC4 model

The 12" version is noticeably better - do not buy the 10" AC4 unless you plan on plugging it into an extension cab.  The 10" is really boxy sounding.   They're tempting cause they're often going cheap and they look cool.

What mods have I done?

Note:  all comments above relate to the un-modded AC4. 

• replaced the stock speaker with a MSP vintage alnico speaker

• cut the C20 bright cap on the volume control

• swapped a pre-amp valve for something vintage I had lying around

• replaced the output transformer - details here

To my ears, it's a much better sounding and more versatile amp now - still very much a Top Boost Vox.  The bright cap on the volume was only a minor change, as I don't run the amp quietly, and it's bright enough as it is for me.  Preamp valve change was noticeable, but not major - a change, but not necessarily an improvement.  

Collectively, the biggest result was the combination of the output transformer and the vintage alnico speaker.  Apart from the cab size which is inescapable, the combination of an EL84, the speaker and output transformer really has a lot to do with the voice of the amp.  

There's no fizz, it sounds bigger and more open.  The cleans are better and the breakup is smoother.  

VOX: BM1 Escort Transistor Practice / Busking Amp

I just bought this rather beat-up Vox BM1 Escort practice amp from the seventies, or maybe early eighties today.  I'm thinking seventies, as it doesn't have an IEC power connector, and the grill cloth is the red/brown colour. 

The back panel looks different to the one on Vox showroom and other photos that I've seen, so not sure what’s going on here - maybe it’s from a different production run or regional difference?  The rotary battery/power selector switch has been replaced with a standard toggle switch, and the volume pot doesn’t look original; apart from that, all working as it should.

My first thought on this one - it's a little monster.  Way louder than I thought it would be, and the driven sound is cool.  I really punished my ears testing this...  slightly regretting it now.  It seems to like running somewhere between half and three-quarters volume, with the tone in a similar position depending on the input used.  It's also pretty happy with the volume on full - it really fires off some attitude.  I think it would be interesting to record this little thing running hot.

Clean sounds? Can't say I spent much time in this area of the amp.

VOX BM1 ESCORT - SOLID STATE PRACTICE AMPLIFIER

• One channel, two inputs.   Normal and Brilliant

• Single tone and volume control

• Battery or mains power switch

• 5” Elac speaker (Elac were used in a lot of Vintage Vox amps, quite sought after)

• Powered by a single TB810S IC amplifier

• Output for extension cabinet

• Manufactured from the mid-seventies to early eighties

• The cabinet is approximately 33cm x 22cm x 13cm, and it probably only weighs a couple of kilos without a battery

• Battery is a PP9 - 9v, 5aH, 6cm x 5.5cm x 8cm

The batteries are large, expensive and are reported to not last long, which I believe is why Vox created this version with the option to run off mains power.  As a busking amp, you would want to make money petty fast, as you would need to make $20 just to break even with the cost of the battery.

 

VOX ESCORT SCHEMATIC

IC AMPLIFIER DATASHEET

I've seen the amp mentioned as being 3.5 watts, but I can't see this anywhere on the data sheet - looks like 2.5 watts when running at 9v.

VOX: Pathfinder 15R Transistor Guitar Amp

Like others, I had read the hype about the Vox Pathfinder 15R and thought, really?  I'd never paid any attention to them until I saw an article in Premier Guitar recently.  So when I saw a Vox Pathfinder 15R pop up on Facebook marketplace at a reasonable price, I thought it would be worth a shot.  

VOX PATHFINDER 15R - SOLID STATE GUITAR AMPLIFIER

Positives

• It’s really loud for 15 watts of solid state amp with a little 8" speaker - surprisingly loud in fact

• You can get a few decent sounds out of it tonally, which hasn’t always been the case for some Vox amps that I’ve played

• I don’t mind the reverb, which a few people complain about.  It is a bit weak, as I think it’s a small two-spring reverb, but it works for me

• For an 8" speaker, it sounds big.  This may have something to do with the size of the cabinet, as it's way bigger than needed for an 8” speaker.  Vox may have been lucky with the speaker construction too.  Normally at this price point no-one expects anything from the stock speaker  

• It feels decent.  It certainly doesn't have a premium feel, but it doesn't scream cheap amp either 

• Trem is a bonus

• The foot switch is handy (boost and trem only, not reverb)

• Looks like a traditional Vox - which I guess I didn't need to tell you

• Some people have bad things to say about the overdriven sound - I actually like it, but I can see how some might really hate it.   It's a bit raggedy and rough around the edges at times.   It's in no way a tight, polished modern distortion/overdrive sound - I'd say it has character.   The flip side of this as that most amps that do a good polished modern distortion can't do a rough around-the-edges sound at all.  After playing with it for a few days and trying different guitars, my assessment is that the overdriven sound is not great with low-powered single coils, but it worked well with everything else.   Results may vary, as they say.

• I've also heard people saying just leave the boost on all the time, or otherwise, it doesn't sound any good - not my experience, I like both options.   The boost is really quite a loud boost too.   Almost too loud in terms of balance between the options (especially on clean settings).  Not having the boost on provides more range at low levels with the gain and volume controls

Negatives

If I had to mention downsides, I could only think of three when it comes to my needs;

• The boost level is way higher than the regular level on clean settings - so much so it may be too different from being useful.  Care factor - we all build pedals right?  This is also much less of an issue if the amp is already overdriven.  The boost is appropriate when driven.  

• The overdrive can get a little dark compared to the clean tone, but given that there's no way to switch between the two, it's not a big deal.   Maybe being a one-channel amp is a downside, but it is an inexpensive amp...  how much can one expect for the price?  And to repeat myself, we all build overdrive pedals yeah?  So not a deal breaker for me.  

• Despite liking the reverb for what it is, it's obviously not an awesome reverb.  No surf sounds from the Pathfinder.  I use a Carl Martin Headroom spring reverb pedal with my other Vox, which doesn't have verb - the Headroom costs more than this amp, so maybe nor a fair comparison    

Occasionally you will hear its limitations, but whether you find that to be the charms of a small amp struggling or the sign of it not being a great amp is up to you.  These are cheap enough to buy two, for a dual rig.

SPECIFICATIONS - VOX PATHFINDER 15R

Dimensions:        396 x 400 x 193

Weight:                8kg

Output power:    15 watt RMS into 8 ohms

Speaker:            1 x Vox Bulldog (8", 8 ohm)

Inputs:                Input jack, foot switch

Outputs:            Extension speaker, headphones, line out

Controls:            Gain, Master volume, Treble, Bass, Tremolo speed, Tremolo depth, Reverb, Gain boost switch

Options:            VFS-2 dual foot switch for boost and tremolo (not reverb)

CONTROLS

EXTENSION CAB

The extension cab works a little differently from some larger amps - the stock speaker is bypassed when an extension cab is used.

note: you must use a cab of 8 ohms or more.  Lower than 8 can damage the amp.  16 is ok, but it will reduce the output level.  

LINE OUT

This output carries a specially filtered signal for direct connection to a soundboard or recording console. This gives you a good-sounding signal for recording or live work without having to mic up the amp.

HEADPHONE OUT

Guess what plugs into this?  Yes, headphones....