Upgrades to the (made in China) AC50 and AC100

June 19, 2016

VOX China P1020388Hello and welcome back to the blog. This week we discuss an upgrade project for Sydney indie band guitarist, Cameron Birt. Cameron and the boys have built their guitar sounds around the Chinese-built VOX AC50 and AC100 amp heads, but they are well aware that these amps could be significantly improved from stock with some important component upgrades.


VOX China P1020384

We put together an upgrade project scope and quotation for the band, which would deliver maximum results for the $$$$ spent. Our recommendations were accepted and orders placed to source the agreed upgrade components.



VOX China P1020385

Our agreed upgrades were as follows:  output valves – current production Mullard EL34, a pair for the 50W and a quartet for the 100W, suitably matched and the amp rebiased accordingly. Preamp valves – current production Mullard 12AX7 (‘large plate’) for the V4/PI stage positions, and Mullard 12AX7/CV4004 (‘short plate’) for positions V1 to V3 inclusive, in both amps. At the time of this project, Evatco (Queensland) had a good stock of these valves. Transformers – replacement of output transformers and filter chokes in both amps. Power transformers left in situ.


VOX China P1020386While we install and recommend Mercury Magnetics transformers for their lush tone, for this project we chose to use transformers and chokes by Magnetic Components of Chicago, USA, marketed as ‘Classic Tone’. This choice achieved a cost-effective solution. The chosen transformers provided the closest physical dimensions as well as the required electrical specifications.

VOX China P1020387For the 50W head, we installed the Classic Tone part # 40-18025, and for the 100W head the part # 40-18026. The latter is the same transformer used in the Landry made in USA boutique grade heads, previously discussed in this blogsite. For both heads we installed the part # 40-18058 filter choke, which required the drilling of new mounting holes.

We avoided the complication of replacing capacitors in the signal path for this project – upgrading components on double sided boards is time consuming and not much fun at all. Apart from that, there is insufficient space allowed for our favourite caps. Magnetic Components provide detailed dimensions, etc, on their website which is of great assistance with these projects. Never underestimate the impact that a good filter choke can have on an amp’s performance. We have installed the Marshall style 3H (3 Henry) choke by either Mercury Magnetics or Classic Tone in many many projects now, always with positive results (yes, even the dreaded Marshall JTM600/JCM600 series amps).

We should point out that the recent production (China) VOX AC50 and AC100 have absolutely nothing in common with the famous amps of the 1960’s that the British Invasion groups conquered the world with. The current amps are definitely ‘modern’ designs with multiple gain stages and channel switching, more akin to a Marshall amp than a VOX. The end result on these two amps was a big “thumbs up” from Cameron and the boys with the VOX amps sounding great and exceeding expectations. We offer world-class service/MODs/upgrades on all VOX amps in 2016 and beyond ! Thanks for checking in to the blog – see you next week. IR.

Service centre for the Little Big Muff

June 13, 2016

Little Big Muff P1020477Hello again. This blog refers of course to the original Little Big Muff pedal by Electro-Harmonix from the 1970s, and not the more recent version which is basically a Big Muff in a smaller enclosure. This pedal is much loved by its owners, including our customer Adam, for its rarity and its outrageous sound. The Little Big Muff circuit comprises four NPN transistor cascaded gain stages, with each stage filtering and shaping the guitar signal before sending it to the next stage. The “Tone” switch allows two only extremes of either treble or bass tonality. The circuit component values are very similar to the well known Big Muff pedal.

Little Big Muff P1020471Adam shipped his LBM down to us from up in Lismore, Northern NSW. The ongoing problem with his pedal has been massive amounts of hiss – the hiss is of a “whooshing” nature, and renders the pedal unplayable. This pedal has been the subject of attempted repairs at least twice previously. Our immediate impression from trying out the pedal was that there was some instability in the circuitry in addition to the excessive levels of white noise. Please note – there is always going to be some white noise with the LBM as the design is very similar to a vintage Big Muff with the “Fuzz” control turned fully clockwise.

Little Big Muff P1020470First things first !! There were several electro-mechanical issues with this pedal to be corrected before we concentrated on the circuitry/PCB. The “Tone” switch, bypass footswitch, and input jack were all going intermittent, very much confusing the issue. The input jack was also wired incorrectly (!). We replaced all three items plus the DC IN jack (3.5mm min. jack socket) and the battery clip. All were at the end of their useful life.

Little Big Muff P1020472The pedal was now working as intended, but still with mega amounts of white noise. Turning our attention to the PCB (printed circuit board), we found that the 1st gain stage had been modded. We restored this stage to original spec, which included replacing the BC239 NPN transistor. The BC239 hasn’t been manufactured for donkey’s years, so may be difficult to source, but we have kept a private stock for these repairs. If you substitute a higher-gain device for the BC239, then the pedal probably won’t sound the same.

Little Big Muff P1020473Still noisy ! We ended up replacing all four NPN devices with BC239’s. A number of signal path capacitors had been previously replaced and we weren’t happy with what we saw, so we replaced them again with known types plus a few carbon composition resistors that we suspect had gone noisy and drifted off value.

Little Big Muff P1020476Now the PCB needed a tidy up and repair. We can’t help but notice that some PCB repairs to vintage pedals these days are not working out very well due to the application of too much heat and definitely too much solder. Surely everyone these days is using a temperature controlled soldering tool ?? The tracks and pads are being damaged by too much heat, or else taking too long on each solder joint. Too much solder might create the impression of a long lasting solder joint but in fact is  creating leakage paths across tracks or even the occasional short-circuit. It’s important to clean up after a job like this, in other words all the solder flux residue on the PCB and excess solder. This particular PCB had so much flux residue we couldn’t clean up completely – much of it was probably from original manufacture, but various attempts at repair through the decades have added to the mess.

Little Big Muff P1020481So – in the end, how did it sound ?? Pretty awesome, no wonder these pedals are so collectable. We did a direct A/B comparison with a Big Muff clone, with the “Fuzz” (aka “Sustain”) control set to max clockwise, as per the description above and the level of hiss was very similar, as was the performance of the pedal – taking into account the different “Tone” settings. Our favourite was the very fat bass setting of the “Tone” switch. We hope that Adam is enjoying his Little Big Muff, the pedal is now as quiet as we could achieve. See you next week for the next blog. IR.

MODs to the Fender ‘Super Twin’ amplifier

May 22, 2016

Super Twin P1020234Howdy there folks – welcome back to the world of valve (tube) amps. This week we look at servicing and especially modding a (relatively) rare Fender amp introduced in the mid-1970’s: the 180 watt (!) Super Twin 2×12 combo. The marketing people at Fender must have decided that higher power amplifiers were the way of the future as several models were redesigned for an increased power output during this time, including the “Twin Reverb” and the “Bassman”.  The Super Twin employs a sextet of 6L6GC output valves, with a HT voltage of over 500V DC, in ultra-linear configuration, to achieve the rated 180 watts output. This amp is not recommended for anyone with a bad back – it is seriously heavy !

Super Twin P1020236The design of the Super Twin features an elaborate EQ system that includes the conventional Fender 3-band passive EQ located between two 12AX7 preamp stages as per the Twin Reverb, plus a 5-band graphic EQ and a presence control, both active, driven by a 12AU7 valve. This is not a parametric EQ as is sometimes suggested on user forums.  The EQ is also footswitchable. The power amplifier is driven by a conventional long-tailed pair 12AX7 phase-inverter stage, followed by a 12AT7 cathode-follower stage to provide a low impedance drive to the sextet of 6L6GC output valves. There is also a distortion control which uses both halves of a 12AX7 valve, which is so awful that nobody ever uses it.

Super Twin P1020232Unfortunately, this amp is just too loud to be of any practical use for most guitarists. It would make a great bass amp if it was a bit more powerful. The amp stays clean until you reach the rated power and the overall tonality is rather glassy. BUT, we have a solution to offer which halves the output power and warms up the tone somewhat. Our standard MOD for these amps is to rewire 4 out of the 6 output valve sockets to reconfigure 2 pairs of 6L6GC to triode mode of operation. The remaining pair stay wired as tetrodes. At 90 watts this amp will still be very loud, but useable with a warmer, more musical sound.

We have implemented this MOD recently for Heath Crawley of Aussie indie bands Children Collide and Vanuatu Scalps, and for Nash Chambers, well known as a music producer and artist manager. In both cases there were numerous other issues to be addressed, as might be expected in a 40 year old guitar amp. General servicing includes replacing the high voltage electrolytic filter capacitors, replacing noisy and microphonic preamp valves, cleaning of pots, jacks and valve sockets, electrical safety compliance, and noisy or leaking capacitors in the signal path, including the graphic EQ which employs inductors and capacitors in five series resonant circuits.

It has been suggested on some user forums that the Super Twin was designed by Paul Rivera, but this is definitely not the case. Thanks for checking in to the blog, and we offer world-class service, repairs, restorations and upgrades to most Fender musical instrument amplifiers. I.R.

MODs to the Fender ‘Super 60’ amplifier

May 14, 2016

Super 60 016Hello again. The Fender Super 60 was introduced in the late 1980’s as one of the dreaded ‘red knob’ series of amps, which weren’t always favourably received. This model caused some confusion for people who purchased one, as it sounds nothing like the traditional Fender amplifier models. It has a few admirers, to be sure, but the model was eventually deleted. On the plus side, this is a 60 watt 1×12 amp in a compact combo (although quite heavy as a result), with ‘clean’ and ‘overdrive’ modes plus reverb (solid-state driven, not valve/tube). The ‘clean’ tonality is good, it’s just not quite the same as a ‘blackface’ Fender.

Super 60 011On the minus side, the ‘overdrive’ mode is not that great, and the clean/overdrive tonalities and levels really don’t match up. This is due to the amount of shared circuitry, which is re-configured using opto-couplers. The bias supply voltage is not adjustable, leading to complications when installing a fresh pair of 6L6GC output valves. So, the service tech has to change resistor values as required to achieve the desired result. This is really tedious ! However, the PCB can be modified to accept a bias trimpot.

Super 60 012Which leads us to serviceability issues with these amps. As you can see from the 2nd and 3rd photos, all components (apart from transformers) are mounted to either the large main board (PCB), or the smaller front panel board. Unfortunately for the service tech, these boards are kind of ‘back-to-front’ with the solder side of the board facing upwards, and the component side facing downwards, so they cannot be inspected without stripping out the boards. The valve sockets are mounted direct to the main board.  The three preamp valves are not especially a problem, but the heat from the pair of output valves will to some extent end up being absorbed into the chassis and the main board.

Super 60 013This customer’s amp was delivered to us with low output level, a couple of badly damaged pots, and broken jacks. The input and footswitch jacks on this model are the very brittle and easy to break PCB mounting types from the 80’s and 90’s. The pots have a solid shaft with a flat section, and the original knobs naturally match this shape. The ‘clean’ mode level was considerably lower then the ‘overdrive’. We would have to completely strip out the boards anyway, so this was the perfect opportunity to implement some MODs to try and improve the ‘overdrive’ qualities plus balance up the two modes a bit better. This ‘balancing act’ doesn’t achieve absolute perfection, but is a definite improvement over the stock amp. We would suggest leaving the 3-band EQ as it is, to maintain the ‘clean’ tonality, even though the EQ is less than ideal for the ‘overdrive’ mode.

Super 60 015For those of you who have access to a schematic we modded the following components: R167 to 82K, C102/C105 to 0.01uF, R103 to 100K and R158 is the resistor to be changed for different bias levels, or else remove altogether if a trimpot is to be installed. We rebiased for 2 x 35ma Ik at B+ of 487V DC. Biasing this amp to run much hotter would be a mistake, as per the preceding paragraphs. The end result is still a compromise, but the changes will result in a fuller signal range and also more saturation available for a more modern ‘lead’ sound. Upgrading the preamp valves will improve the tone of the amp in both ‘clean’ and ‘overdrive’, and will smooth out the spiky distortion characteristic and reduce hum/noise. We have more Fender MODs to be published soon. IR.

Super 60 017p.s. the previous owner of this amp discarded the red knobs, but installed some really cheapo looking ones in their place; we ended up matching up some Fender vintage reissue black knobs, which look much better.

p.p.s. some comments on the web forums mistakenly attribute this amp to the Paul Rivera era at Fender – this is not the case, this design is dated 1988 – well after Rivera moved on to manufacture his own products. IR.

Warning !

Valves [vacuum tubes], transformers, capacitors, amplification circuits found within a guitar amplifier operate at high voltages that can cause permanent injury, disability or death. Valves [vacuum tubes] operate at high temperatures that can cause severe burns. Never attempt to repair, modify, test, work on or touch electronic equipment unless you are trained or otherwise qualified to do so. Likewise, never remove a protective cover from electronic equipment unless you are trained or otherwise qualified to do so.

Warning !

Do not remove the amplifier rear panel, the amplifier chassis, the amplifier fuses, the valves [vacuum tubes], or any other part of the amplifier with the 240V AC mains supply connected.

6L6GC conversion for the DeLuxe Reverb Reissue (DRRI)

April 24, 2016

DRRI Project P1020347Welcome back ! Hopefully we are now back into a routine of publishing a fresh blog every week. In this week’s blog, we discuss a major upgrade project recently completed for the (Fender) ’65 Deluxe Reverb Reissue, which we will refer to as the DRRI. The guitarist in one of Sydney’s best loved and longest surviving blues bands has been playing through a Twin Reverb for decades, but decided to downsize to a lighter amp for the smaller rooms, which makes complete sense, and invested in a new (2015) DRRI.

DRRI Project P1020345As you can see from the photos, this particular Limited Edition DRRI looks very smart indeed, with the early ’60s Brownface amps cosmetics. Also included in the Limited Edition package was a Jensen (new production) speaker. All other aspects of this amp were identical to the standard edition DRRI.

DRRI Project P1020346Unfortunately, the tonality presented by this amp was very thin and rather shrill. Overdrive characteristics when the amp was turned up (no pedals) were actually pretty awful. We attribute a lot of this to the choice of speaker. Just as critically for our customer, the lack of headroom with this amp and speaker combination defeated the whole purpose of investing in this particular amp, as it was virtually unuseable even for the smaller gigs.

DRRI Project P1020343The first step in this project was to upgrade the speaker, as is so often the case with combo amps. Choosing a speaker is not as easy as it sounds – there are a bewildering number of specialist guitar speaker options out there now. WGS offer some excellent choices at very reasonable prices, and we ended up choosing the G12C from their American Vintage range. We could just as easily have chosen the G12C/S for a smoother, softer top-end, but this model does seem to complement the DRRI voicing and adds a couple of dB in efficiency which will help with the headroom problem. Most importantly, the G12C fills out the missing lows and mids of the DRRI and behaves itself very well under overdrive conditions. The 75 watt rating of this speaker allows a healthy overload margin.

DRRI project P1020322Having restored the basic tonality of the amp with our new speaker, in consultation with the customer we devised a major upgrade project to increase the headroom available by implementing a conversion from the existing 6V6GT output valves to the larger 6L6GC output valves. To take full advantage of the larger valves we also replaced the existing transformer set.

DRRI project P1020320The available space and the need to allow clearance for the 12-inch speaker restricts our choices somewhat, but by re-orientating the output transformer and choke just slightly, we could install the power transformer, filter choke and output transformer set as per the 60’s Vibrolux/Tremolux series 6L6 amps. Such a reproduction transformer set was available at very reasonable pricing from Magnetic Components of Chicago, USA, although the cost of shipping adds quite a bit these days.

DRRI Project P1020337Such an upgrade will increase the power output of the amp to between 30 and 40 watts, as per the original amps of the abovementioned series, without a huge increase in the weight of the DRRI. It will be necessary to modify the bias circuitry slightly (one resistor) to increase the range of the bias adjustment to accomodate the 6L6 output valves. We also upgraded the main high-voltage filter capacitor to the good quality F&T brand.

DRRI project P1020321This was not an inexpensive project by any stretch of the imagination, but much, much cheaper than selling the amp on and reinvesting in a more suitable amp. We have replaced the shrill and brittle tonality, as presented by this example, with a very warm, full sound, still characteristic of the best examples of the Fender Deluxe Reverb, and increased the headroom significantly. This is now a fine performance amplifier which will serve our customer well !

DRRI Project P1020344

Correcting electrical safety issues in a Bad Cat ‘Classic Cat’

April 9, 2016

Bad Cat 0159Hello again. In this week’s blog we look at correcting some electrical safety issues in a Classic Cat 1×12 combo from Bad Cat amplifers, of the USA. This particular Bad Cat would appear to be a limited edition, maybe even a one-off custom order, and we could find no reference to it at all on their website.

Bad Cat 0163Most Bad Cat and Matchless amplifiers are derived in some way from (or inspired by) vintage 1960’s made-in-UK VOX amplifier circuits. This model is completely different, and is obviously derived from 1950’s Tweed/Fender and Valco/Supro amplifier designs. Classic Cat controls and functions are really sparse – just a pair of input jacks plus volume and tone controls. That’s it ! The design follows the classic Supro pattern of a pair of 5881 or 6L6 output valves, cathode-bias, for a nominal output of 24 watts rms at the onset of clipping.

Bad Cat 0164There is a single 12AX7 gain stage followed by interactive volume control and single (“tweed”) tone control. The effectiveness of the tone control depends on the position of the volume control and also offers no control at all over bass or lower midrange frequencies. This stage is followed by a 12AX7 valve employed as a “paraphase” (self-balancing) phase-inverter, very similar to some mid-1950’s Fender (“tweed”) designs. However, this type of phase-inverter is not known for achieving perfect balance or low distortion, and so adds to the raw vintage character of the amp’s performance.

Bad Cat 0154Our good customer Danny brought this amp into the workshop to resolve some electrical safety issues. The most obvious sign of trouble is the broken IEC 240V power inlet. Further investigation revealed a lost earth connection, plus a loose mains fuseholder which could not be tightened. This latter component was also not compliant for 240V in the first place. We replaced the IEC inlet and installed a dedicated chassis earth point. We replaced the dodgy fuseholder with a compliant component and installed a T1A fuse.

Bad Cat 0155The amp now passed the Workcover NSW electrical safety test with flying colours, meaning that we achieve an earth test of less than 2 ohms from the earth pin of the 240V plug to any exposed metal part on the amp. You can see from the next photo the IEC inlet and fuseholder wired correctly, plus the dedicated earth connection to the chassis. The final photo shows the internal layout of the chassis, and hand-wiring Bad Cat/Matchless style.

Bad Cat 0158We would like to thank Danny for his continued custom, and for supplying us with the subject matter for this blog. We offer world-class service, restoration, repairs and advice re most boutique level valve (tube) musical instrument amplification.  It HAS been a lifetime obsession.


Bad Cat 0156Please check out our earlier blogs re amplifiers by Matchless, DR-Z, Landry, Jackson, Morgan, Matamp and others, plus our own Richards custom design amplifiers.

Repairs to the Peavey Classic 50 in Australia

April 4, 2016

Classic 50 P1020263Welcome back to the blog, everyone. We have been servicing the Peavey Classic Series 30 watt and 50 watt combo’s since their introduction back in the 1990’s and we are in fact still the A.M.I. authorised Peavey warranty repairer (valve/tube amps only) for NSW. Since the 1990’s the 30 watt 1×12 combo has overtaken the 50 watt models in terms of popularity as they provide reasonable performance in a compact package. Reliability has been questionable at times – we have had to repair printed circuit boards (PCB’s), replace transformers, valves and 9-pin valve sockets, and so on. Bias for the EL84 output valves is non-adjustable, which means some amps run rather hot.

Classic 50 P1020262The subject of this blog is a more recent 2×12 model delivered to us by a local music shop, reported as losing output and nil reverb level. It may not be immediately obvious from the photo, but the speaker connection tagstrip, normally pop-riveted to the speaker basket, has come adrift, causing unreliable operation. This is a problem we have witnessed many times with the cheaper OEM speakers supplied by Eminence of the USA to various amp manufacturers. The only reliable solution is to carefully drill out the remaining body of the pop-rivet and refasten the tagstrip by other means.

Classic 50 P1020264In the meantime we isolated the ‘nil reverb’ problem to the reverb tank itself, which is mounted in a vinyl bag at the bottom of the cab. The only way to gain unrestricted access to both the problem speaker and the non-functional reverb tank is to remove the speaker baffle completely from the cab. This is what is known as a ‘floating baffle’, with mounting screws along the top and bottom front of the cab, which must be removed. The amp chassis has to be removed before this can happen, of course.

Classic 50 P1020267Once the baffle is removed and placed face down on the workbench, we can repair the speaker. We choose to refasten the tagstrip with nut/bolt/lockwasher rather than another pop-rivet. It takes longer but will survive the demands of rock’n’roll guitar. The other speaker on this 2×12 baffle is checked OK.

Classic 50 P1020269Before we re-install the baffle into the cab, we will repair the reverb tank. One of the transducers tests open-circuit (O/C) and is not repairable, so we will replace the unit altogether. This is not a bad thing as we will upgrade the reverb with one of the ‘MOD’ tanks, The reverb will sound much better than it did previously.

Classic 50 P1020270Reverb tanks are available in various combinations of impedances and delay times, so it is important to select the correct unit for the individual amp. In the Peavey Classic Series, the reverb tank is driven by an IC, requiring a different input impedance than for example a Fender ‘Deluxe Reverb’. The replacement tank is placed within the vinyl bag, which provides some degree of isolation from vibration, which in turn is screwed into the bottom of the cab. The baffle and amp chassis are each reinstalled into the cab, and the reverb cable reconnected within the amp.

Classic 50 P1020272We had previously tested all the valves (tubes), external to the amp, and also carried out a power output test and electrical safety test. The final play test revealed a huge improvement, and the amp was returned to the music shop. Thanks for checking out the blog and we are located here in Gosford (Wyoming) NSW for all your valve (tube) amp service needs, including custom design. IR.

Bob’s Solo Album

March 22, 2016

June 2012 005Yes folks – my very good buddy Robert (aka ‘Bob’) Spencer is recording his very first ever solo album, provisionally titled “SAINTS AND MURDERERS”. A solo album has been a long time coming – after albums with Finch, Skyhooks, The Angels, and The Temple Gods, plus countless sessions over the years either as guitarist or producer, the time is right for Bob to record some of his own stuff. In Bob’s own words……….


Unlike my previous recordings, this album will contain songs which are not required to squeeze into a band’s format, set structure, style, agenda, or which will appease a particular target audience or demographic. In short; I want to record songs which I think are cool and interesting, which groove largely and which I hope you’ll dig, too! 🙂


Please take the time to check out Bob’s campaign for the recording of his album here at pozible……….


Here is the link to a “pre-teaser” teaser short video, the result of a collaboration with Laura Davidson……….


We are proud to tell the world that Bob’s choice of amp for the recording of this album, for recording both guitar and bass tracks actually, is the custom-designed-for-Bob KT66 amplifier by the Richards Amplifier Company – Australia. Not the big 4 x KT66 85 watt monster of his, but the very recordable 28 watt custom design. Bob was actually our very first customer who appreciated what the KT66 power output valves could offer (with the right choice of output transformer) in performance and tonality, as compared to other alternatives.

RAW BRIT 2008 001Pedals employed in the recording of this album include our very own Treble Meister, an enhanced Class-A NPN midrange/treble booster pedal, plus an old favourite – the Rich Drive (Bob was the first customer for this overdrive pedal, back in 1997), plus our all-time best seller – the Rich Blues which delivers Bob the extra mids he likes for soloing.


Thanks for checking out our blog again after a long break from writing – but we have heaps more material to publish regarding custom amp builds and interesting amp repairs, so please check us out on a regular basis.

Regards, IR.



Greg’s custom amplifier build progress

March 19, 2015
18W 'British Lead' chassis

18W ‘British Lead’ chassis

Welcome back to the blog after a long break of 3 months. We have been busy !Here is another in our occasional series of blogs where we publish a visual report of a custom-order amp build, in progress. This example shows a Richards Amplifier Company British Lead Series chassis underway for our good customer Greg, of Sydney. Greg has previously purchased our Expressionist and Blue Mood model amps, with matching Tone Cabinets.

18W 'British Lead' chassis

18W ‘British Lead’ chassis

Greg has developed an appetite for vintage ‘British’ tones, but with the output scaled down to a more manageable 18 watts at full power, by employing a pair of 6V6GT output valves (tubes), in lieu of the more obvious choices, such as EL34’s, KT66’s or KT88’s. Rectification of the high voltage supply on this model is handled by a GZ34/5AR4 valve (tube), with excellent current production valves now also available from Tung Sol and Mullard.

18W 'British Lead' chassis

18W ‘British Lead’ chassis

With this project, we are looking to create the broadest range of classic, vintage British tones possible – including those tones recorded by (for example) artists as stylistically diverse as Mark Knopfler (JTM45) or ZZ Top’s Billy Gibbons (JTM45/Plexi/JMP). To that end, we have included a trio of mini toggle switches on the front control panel to reconfigure both the ‘front end’ circuitry and the 3-band passive EQ as required to achieve ‘JTM45’, ‘Plexi’ or ‘Metalface’ voicings. The 2nd mini toggle switch actually switches an additional 12AX7 valve (tube) into the signal path to achieve the more aggressive ‘JMP’ or ‘JCM800’ voicing and gain structure.

18W 'British Lead' chassis

18W ‘British Lead’ chassis

The control panel starts on the right hand side with the traditional 4 inputs, arranged as a pair of inputs for each preamp channel – ‘Brilliant’ and ‘Normal’. The preferred method of operation is to plug into the 1st channel, then use a short, high-quality jack-jack patch lead to cross connect to the 2nd channel. The ‘Brilliant’ and ‘Normal’ channels are now connected in parallel. The player then sets the desired balance between the two tonalities with the preamp volume controls. This is probably best done with the EQ set fairly flat (ie, 12 o’clock), then having balanced the volume controls – fine tune the amp’s voicing using 3-band passive EQ and the ‘active’ presence control.

18W 'British Lead' chassis

18W ‘British Lead’ chassis

A mini toggle switch configures the 3-band passive EQ as per the early ‘blues’ JTM45 voicing, or the later (post 1968) ‘crunch’ voicing. The presence control functions as part of the power amplifier circuitry and adds emphasis to the upper-midrange and high frequencies. A good starting point is to set this control to the 12 o’clock position, then fine tune from there according to the acoustics of your playing environment.

18W 'British Lead' chassis

18W ‘British Lead’ chassis

You could consider the balancing of the two channels as your ‘primary’ equalisation, and the tuning of the 3-band treble/middle/bass controls as your ‘secondary’ equalisation. Then the presence control adds further brilliance as required – in effect the amplifier’s ‘final’ equalisation. We think that a master volume control is absolutely essential on an amp like this, even though it was not provided on the original amps that inspired us all.

18W 'British Lead' chassis

18W ‘British Lead’ chassis

Once you have found your ‘sweet spot’, mixing the preamp volumes and refining the EQ and voicing options available on this amp (as discussed in the paragraphs above), there is a reasonable chance that you will be playing at a volume that is considered excessive under the prevailing circumstances, hence the inclusion of our master volume to keep it all under control. The guitarist who prefers to play with the amp running wide open will appreciate the transparency of our master volume design when set to maximum clockwise rotation.

The master volume (MV) control actually functions as part of the power amplifer circuitry – ie, it is located post phase-inverter stage (PPI) in the signal path. The primary function is to manage the output levels as required, but when used specifically to generate distortion, its location means that every preamp valve (tube), including the 12AX7/ECC83 phase-inverter stage, is contributing to the end result. There are other benefits to this design approach as well. With the MV set to maximum clockwise, the amp (up to the point of power amp clipping) is delivering its cleanest, brightest and tightest tones. On the other hand, as the MV is rotated anti-clockwise, the effect of the global negative feedback loop is progressively minimised, and the amp loosens up and behaves much more like a vintage amp design, with a sound full of fat, warm ‘valvey’ character.

The remaining front panel controls include high-quality metal toggle switches for power on/off and standby/play functions, plus a power-on indicator. The rear panel controls/functions include mains and high voltage supply fuses, full-power/half-power switch (once again a high-quality metal toggle switch), output jacks for 16, 8 and 4 ohms, plus an earth-lifted output jack for line/recording, ie DI.

We will now be offering this amplifier model as a permanent fixture in our range of designs, with power output options of 18 watts (6V6’s), 30 watts (KT66’s), 40 watt club amp (EL34’s), 50 or 100 watts (EL34’s), 60 watts (KT88’s).

Thank you Greg, for your continued custom and enthusiasm for our amplifiers !  IR.

the Marshall Class 5 in 2015

December 14, 2014
the C5 head after VVR mod

the C5 head after VVR mod

Hello and welcome back to the blog. Only a couple more weeks now and the year 2014 will be history. Our most popular amp mod’s during 2014, apart from the perennial Fender Blues Junior and Pro Junior mod’s, would have to be to the Marshall Class 5, aka C5. We have completed mod’s/upgrades to a number of these amps now with consistently good results for our customers.


the C5 head after VVR mod

the C5 head after VVR mod

Basic mod’s to the C5 start at $200 inclusive (Australia), and include installation of the VVR module and upgrade of signal path and tone control capacitors. For those who really love their C5, we suggest looking at upgrading to the Mercury Magnetics transformer and filter choke set. For a more detailed description of our C5 mod’s, see our December 2013 blog.

However, to summarise – the capacitor upgrades result in more effective EQ and a tonality more like the favourite old-school Marshalls, for example the “Plexi” series amps. The VVR module works as a power attenuator, reducing the output of the amp to quiet conversational levels. Very handy for apartment dwellers. The most suitable location for the VVR module, both electronically speaking and for user convenience, is directly behind the Class 5 logo. But, at least now we have located a source of traditional looking Marshall style control knobs with set screws, to suit the solid shaft of the VVR control. Many thanks to all our customers from 2014 !!