Brett takes delivery of his custom Blue Mood 30W EL34 head

December 1, 2013
Blue Mood EL34 head in rough blonde tolex

Blue Mood EL34 head in rough blonde tolex

This blog showcases a customised “Blue Mood” series amplifier designed & built by the Richards Amplifier Company – Australia, for our good customer Brett Lowe. Brett has been playing guitar & bass on the local Central Coast (N.S.W.) scene for many years and was a pupil of the late, great Don Andrews, so he knows his stuff. When Brett was looking for specific voicing for his next amplifier acquisition, he came to us and we recommended a custom design based on our successful Blue Mood series amps.

Blue Mood 30W EL34 head

Blue Mood 30W EL34 head

Brett was looking for a hybrid Brit/USA voicing, so we kept the layout and gain structure of the Blue Mood amps, but substituted a pair of EL34 output valves (tubes) in lieu of the 6V6 & 6L6 family of output valves we would normally employ in this series of amps.

Blue Mood EL34 amp head

Blue Mood EL34 amp head

We rejigged the choice of output transformer and its primary impedance & also revoiced the 3-band passive EQ for a more Brit tonality, all of which contributed to the final result. The amp retains the Blue Mood features of a bypassable master-volume, and a pull-shift on the bass control for fine tuning of the bottom end, plus a “bold/vintage” switch on the rear panel to reconfigure the EL34′s to cathode-bias operation for a nominal half-power output.

Blue Mood 30W EL34 head

Blue Mood 30W EL34 head

Brett chose “rough blonde” tolex & “wheat” grille cloth to match one of his speaker cabs. Brett has acquired (and sometimes moved on) many amps over the years, including DR-Z, Swart, Bad Cat, Budda & so on, ie many of the top boutique names in the business – but his band mates are of the opinion that this is the best sounding amp he’s ever owned. We love to hear that !

rear panel - Blue Mood

rear panel – Blue Mood

You can see in the photo opposite, we have employed an output transformer by Mercury Magnetics - we are one of their recommended installers, by the way. The choice of output transformer was a key ingredient in the design of this amp. Our next project for Brett will be a replica of the “Brownface” 2×10 Vibroverb amp of 1963, once again employing transformers & choke by Mercury. We will report on this success of this project in a few weeks. Regards – Ivan.

rear view - Blue Mood

rear panel – Blue Mood

rear panel - Blue Mood

rear panel – Blue Mood

burn-in test @ the Rock God Music School Wyoming

burn-in test @ the Rock God Music School Wyoming

burn-in test @ the Rock God music school Wyoming

burn-in test @ the Rock God Music School Wyoming

Pedals & amps by Ivan Richards Audio at work in the Australian music industry

November 26, 2013
Rich Blues live on Sunrise TV CH-7 Sydney. Marcus Catanzaro NOV 2013.

Rich Blues live on Sunrise TV CH-7 Sydney. Marcus Catanzaro NOV 2013.

Rich Blues. Recording session - Slow Chase.

Rich Blues. Recording session – Slow Chase.

Class-A Distortion. Hoodoo Gurus on tour. NOV 2012.

Class-A Distortion. Hoodoo Gurus on tour. NOV 2012.

Richards 15W Expressionist amp. Recording session - Slow Chase.

Richards 15W Expressionist amp. Recording session – Slow Chase.

Richards 15W Expressionist amp. Recording session - Slow Chase.

Richards 15W Expressionist amp. Recording session – Slow Chase.

Raw Brit. Melbourne, Australia.

Raw Brit. melbourne, Australia.

Raw Brit. Melbourne, Australia.

Richards 15W Expressionist amp. Recording session - Slow Chase.

Richards 15W Expressionist amp. Recording session – Slow Chase.

Ivan’s guitars & pickups by Pete Biltoft

November 24, 2013
Ivan's '52 Tele Reissue

Ivan’s ’52 Tele Reissue

Welcome back to the blog ! Recently I discussed my intention of upgrading one of my favourite guitars – my ’52 Telecaster Reissue (late 1990′s USA manufacture), with our good customer Chris. In appreciation of some labour intensive work that we have done this past year, Chris presented me with a pair of Tele pickups from Vintage Vibe Guitars, by Mr Pete Biltoft, wound to my preferred specifications. Chris had previously had some custom work done by Pete Biltoft, with geat success. All the photos that accompany this blog were taken after completion of the upgrade work.

USA '52 Tele Reissue

USA ’52 Tele Reissue

According to the Vintage Vibe Guitars website, Pete Biltoft has a strong background in chemistry, metallurgy & precision fabrication. Add to the fact that he is guitar enthusiast, and those are pretty good qualifications for a custom pickup winder. Pete’s designs aren’t a copy of any one specific vintage pickup, but rather they are considerably enhanced & evolved designs for today’s player, while retaining the very best characteristics of the original pickup. If anything, they are somewhat over-engineered for the job at hand. It’s not often that we endorse products to this degree in these blog pages !

Ivan's '52 Tele Reissue

Ivan’s ’52 Tele Reissue

The original Fender Vintage pickups had previously been replaced by a pair of Seymour Duncans. The original neck pickup as usual was totally underwhelming, and the original bridge pickup had loads of character but a very spikey top end which rendered it unsuitable for some styles. I chose the Seymour Duncan Jerry Donahue bridge pickup and Alnico II neck pickup. The neck pickup would have suited a solo jazz guitarist but not a rock’n’roll band context, and the JD pickup curiously was not a stunning success in this guitar, although in theory it should have been. The bridge assembly is standard, but the saddles are from Acme, by Callaham, for improved intonation. The choice of saddles does have a significant impact on tone & sustain – even brass saddles from different suppliers can sound different, so every variable has some impact, however subtle that might be.

Pete Biltoft Tele neck pickup

Pete Biltoft Tele neck pickup

My preferred specification for the Pete Biltoft pickups was as follows: both neck & bridge pickups 5% overwound, both neck & bridge pickups Alnico V magnets for E, A & D poles, Alnico II magnets for G, B & E poles; G pole piece slightly raised & D polepiece raised higher to compensate for the thinner core wire in the D string of most string gauges. As an absolute minimum requirement there should be a very good balance between the neck & bridge pickups, unlike the originals. Normally I would prefer the neck pickup to have the usual cover to maintain a vintage appearance, but in this case I accepted Pete’s recommendation of no cover for maximum tone & clarity.

Ivan's ESP Ronnie Wood Telecaster

Ivan’s ESP Ronnie Wood Telecaster

The neck pickup measured 7.4K nominal & the bridge pickup measured 8.3K nominal. The pots are CTS 250K with a 0.047uf tone pot capacitor, with no treble bleed cap, and a standard 3-way switch. Pete has also supplied a 5-way SuperSwitch, to allow two additional pickup combinations – neck & bridge in series, in-phase & out-of-phase. We have yet to install this option. The documentation accompanying these pickups is the best we have seen, and Pete has done commendably well in achieving a balance between the neck & bridge positions, and also a balance between the Alnico V & Alnico II magnets.

ESP Ronnie Wood Telecaster

ESP Ronnie Wood Telecaster

The Duncan Alnico II neck will go on Ebay. But ref the Duncan Jerry Donahue bridge pickup, I had a hunch this one might work a lot better on my ESP Ronnie Wood Signature Model Telecaster – a very handsome fellow with black body, white binding & maple fretboard, a favourite look of mine. This guitar has had numerous pickup changes, mainly because of the problem of matching the neck & bridge pickups. Considering that this wasn’t a cheap guitar at all (over $2000 AUD retail, $1600 AUD street at the time of purchase), the original pickups were really average. The neck has had Fralin & Duncan humbuckers previously, and is now home to the Duncan Seth Lover Alnico II humbucker, which has a nice warm vintage (50′s) sound and is not too hot compared to a Telecaster bridge.

ESP Ronnie Wood Model

ESP Ronnie Wood Model

The bridge has previously had Jason Lollar & Jerry Amalfitano pickups, and once again getting the balance just right has always been my problem. Well, my hunch paid off – I installed the Duncan JD pickup in the bridge and together with the Seth Lover it transformed this guitar with nice vintage flavour tones, but actually although it measures 7.5K nominal, the JD pickup sounds vintage but is quite a bit hotter than vintage. Having both pickups with Alnico II magnets makes good sense, the tones & volumes match up better – the pots are CTS 500K with a 0.022uf tone pot cap, plus a 0.001uf treble bleed cap across the volume pot – this is particularly useful with the humbucker neck position.

ESP Custom Shop

ESP Custom Shop

In conclusion, as well as offering a complete valve (tube) amplifier design/build/repair/modify service centre, we also perform electronic repairs & upgrades to selected models of guitars & basses for local customers, which of course includes installing your choice of pickups & other components. Please contact by email to enquire. info@ivanrichards.com

Restoration of a vintage Sears “Silvertone” practice amp

November 18, 2013
Sears Silvertone 001

Sears Silvertone 001

This week’s blog is about the restoration to good working order of a classic item of Americana – the Sears ‘Silvertone’ guitar amplifier, marketed through the Sears Roebuck chain of stores in the USA, many years ago. This example was recently purchased by our good customer James, who is an enthusiastic collector of low powered valve (tube) guitar amps, including models by Matamp and WEM.

Sears Silvertone 002

Sears Silvertone 002

The Sears Silvertone products have become famous over the years for the entry-level guitar amps that many a successful guitarist first started playing through (in the USA & Canada). This particular model doesn’t appear to have a model number anywhere, but does have a chassis number on display. The schematic diagram is still attached to the inside surface of the cabinet.

Sears Silvertone 003

Sears Silvertone 003

The presentation of the amp is quite appealing, in the style of a vintage radio or record player. The circuit design is broadly similar to the ‘tweed’ Fender Champ models, with a single 12AX7 preamp valve, a single 6V6 output valve, and unusually, a 6X5 rectifier valve in lieu of the more common 5Y3. This last component enabled a simpler power transformer to be manufactured, not requiring an additional 5V AC winding for the rectifier valve. Obviously the cosmetics are very different to the ‘tweed’ Champs, and wouldn’t look out of place in somebody’s lounge-room of that time period.

Sears Silvertone 004

Sears Silvertone 004

The circuitry runs at somewhat lower DC voltages than the Champ, and there is less gain. The amp is very quiet – even at full volume you are playing at conversation levels. This is definitely a practice amp ! There is a commendable lack of hum & noise. This amp would probably suit the higher signal levels from a lap steel guitar. We were pleasantly suprised by the high standard of manufacture, wiring & assembly – one of the benefits of larger scale manufacture (we would assume) compared to vintage Aussie guitar amps, some of which were pretty rough & ready.

Sears Silvertone 005

Sears Silvertone 005

The Silvertone was purchased off Ebay & shipped over from the USA. Unfortunately the amp was not safe to use, with no earth and no fuse, just a 2-prong vintage USA power cord. The power transformer naturally was wired for domestic USA power only, so after some calculations & some assistance from Mercury Magnetics we were able to select a suitable replacement transformer wired for the 240V AC mains supply. The layout on this chassis is very tight indeed, and required some juggling of space to install the new transformer.

Sears Silvertone 006

Sears Silvertone 006

The 8-pin socket for the 6X5 rectifier valve had to be relocated slightly. The inclusion of a 240V primary winding unfortunately necessitates a physically larger transformer. The captive mains lead was replaced with a 3-core 240V rated lead & plug. A chassis earth point was installed, plus an internal fuse. The power supply filter capacitor was years past its use-by-date and was replaced also. This unit comprised 3 x 40uF/350V DC capacitors in a single chassis mounting metal can. Fortunately, these are being manufactured once again for the vintage amp/vintage radio market.

Sears Silvertone 007

Sears Silvertone 007

The valves (tubes) were still the original Sears labelled but actually by Tung Sol and still working fine. That’s quality for you, and we’ll never see valves manufactured to that standard again. Believe it or not, there is no input jack on this amp, but rather a short captive lead with a standard 1/4″ jack plug on the end, to insert into your guitar’s output jack. This lead was seriously crap, so we installed a decent quality captive lead. An electrical safety test, power output test and final play test and the job is complete.

Sears Silvertone 008

Sears Silvertone 008

Many thanks to Jimmy James for continuing to submit his varied & challenging projects. We still have a pair of Jim’s small WEM (UK) amps to bring back up to standard in the not too distant future. Regards, I.R.

Our 1×10 Tone Cabinet

November 3, 2013
Our 1x10 Tone Cabinet

Our 1×10 Tone Cabinet

Welcome back to the blog after a long break. We have actually been very busy designing, building, modding & repairing valve (tube) amplifiers & other rock’n’roll gadgetry, and we thank our loyal customers very much for their continued support. In this blog we showcase the latest offering in our custom range of tone cabinets, the single 10-inch speaker, semi-open-back cab. This model is obviously intended for home recording enthusiasts, and/or the guitarist who primarily plays at home.

the 1x10

the 1×10

However, depending on the choice of speaker unit, this cab will perform more than adequately at those lounge gigs. For example, the Celestion “G10 Vintage” 60W model, ie this is basically the 10-inch version of the well known G12 “Vintage 30″, produces a surprising amount of lows & low-mids loaded into this cab, and is a good choice for creating “British” type tones on a budget.

Our 1x10 Tone Cabinet

Our 1×10 Tone Cabinet

Why choose a 10-inch speaker rather than for example a 12-inch model for your home recording project ?? Consulting with guitarists who have been on the recording scene for decades reveals some interesting facts. The 10-inch speaker in fact has a more focused sound dispersion characteristic. The same comment obviously applies to 8-inch speakers.

the 1x10

the 1×10

This is all very subjective, but there is a strong body of opinion that the recorded guitar sits in the “mix” or the “track” better with the 1×10 or 1×8. But obviously to anyone standing in the room, a 1×10 cab doesn’t sound as big or impressive as a 1×12 cab, but it’s all a question of what the mic “hears” !!

the Weber loaded 1x10

the Weber loaded 1×10

Our good customer ‘Bill’, ordered this particular 1×10 cab loaded with a Weber 30W alnico magnet model, to match up with his 18W 6V6 model Blue Mood series amp, by the Richards Amplifier Company – Australia. Bill is looking to recreate the great late 50′s/early 60′s sounds from the West Coast USA, so this amp & cab are a great match.

Nothing ultimately affects electric guitar tone more than the speaker does. A speaker swap can completely transform the volume, tone & responsiveness of an amp. This is especially true in the case of a valve (tube) amp, where valves (tubes) & speakers share a unique symbiotic relationship.

Never has there been a wider choice of 10-inch speakers available, several “British” voiced models from Celestion, two great “American” voiced tens from WGS, and a bewildering number of options from Weber & Eminence. The biggest problem is – when used for their intended application, each & every one of them sounds great !

Which one to choose ??    IR.

Bondi Intermusic closes its doors !

September 9, 2013
Bondi Intermusic Oxford Street

Bondi Intermusic Oxford Street

Unfortunately folks, it is with great sadness and regret that we have to confirm that Bondi Intermusic of 362 Oxford Street Bondi Junction (Sydney/Australia) has closed its doors and ceased trading. For many years Intermusic served the needs of local eastern suburbs musicians specialising in guitars/amps/pedals and home recording, and also was a magnet for international touring bands, particularly from the UK, that often stayed in the Bondi area.

Yet another victim of the downturn in the music scene generally, plus the longer term after effects of the GFC, and the changing circumstances of musical instrument retailing. Intermusic always had a very friendly ’boutique’ vibe happening, and a sense of fun, so all the best for the future to Brent Williams, Bruce Thomas, Jono Clarke, Jimmi Ivanyi and all the other personnel who played a part in the Intermusic story.

inside Bondi Intermusic back in happier times

inside Bondi Intermusic back in happier times

Our own relationship with Bondi Intermusic extends back to at least 2003, at a time when we were establishing our custom amp service workshop as a full-time entity. Bondi put our FX pedals and amp services well and truly on the map by connecting us with Sydney’s musicians, both the weekend warriors and the top recording and touring professionals. Prior to this we were very much a regional service centre, virtually unknown outside of the NSW Central Coast. Thanks guys !!

Guitar Acoustics 1 Railway Road Meadowbank NSW

Guitar Acoustics 1 Railway Road Meadowbank NSW

But wait – there’s more !   Bruce Thomas, former guitar/amp/pedals sales manager at Bondi Intermusic recently opened his own shop in Meadowbank (Sydney), called Guitar Acoustics. Located in the corner shop position at 1 Railway Road, with ample parking in the street, Bruce’s shop is directly opposite the Meadowbank train station and also the TAFE. Only just established upstairs in the same block of shops is a guitar and music tuition studio.

Guitar Acoustics now open for business !

Guitar Acoustics now open for business !

Bruce Thomas is a well known identity from the eastern suburbs retailing and rehearsal studio scene, and we wish him all the best for this new venture. The location of the shop close to TAFE & music school at least guarantees some passing trade. Bruce has adopted a different approach from past retail experiences for this venture, offering primarily a range of acoustic guitars, ukuleles and accessories chosen for a specific price range.

inside Guitar Acoustics 001

Bruce will also be making available our custom amp and pedal workshop services available to customers as before, and in fact is already shipping amps to us in Wyoming for electronic repair work.

the guitar wall 002

guitar acoustics 007

another wah pedal blog: the Cry Baby Super by JEN of Italy

July 24, 2013
JEN 001

JEN 001

Welcome back to the blog. We haven’t discussed wah pedals since our blog ‘wah wah mods & repairs’ published 21/5/2011. We still regularly receive recent production wahs for basic repairs & setups. In this case a Cry Baby Super by JEN of Italy arrived for a complete overhaul from a customer in Canberra. This wah has been owned by the same customer for well over 30 years & could be considered a ‘classic’. Compared to some modern production wahs it has the most basic no-frills circuitry, and yet it is capable of a more ‘vocal’ sweep that is so musical & engaging that you just don’t want to stop playing !

JEN 002

JEN 002

We identified that the following components were faulty and should be replaced: the ‘pot’, the footswitch, the 9V battery clip & the input jack. The board itself (which included the famous ‘Fasel’ inductor, see JEN 004) was still OK. This was the perfect opportunity to offer the customer a ‘true bypass’ MOD, as we were going to install a DPDT Carlingswitch anyway. This is literally the only modification we would recommend for this wah. This wah already has a 9V DC IN jack installed, but there were no additional components provided for filtering the power or protection against reverse-polarity &/or over-voltage. The customer’s intention is to power the wah using 9V battery only (which some people still feel gives the best results in a traditional wah), so we took no further action in this regard, beyond a fresh battery & a new battery clip.

JEN 003 - replacement of rubber pads

JEN 003 – replacement of rubber pads

Before we could attempt to setup the newly installed pot & footswitch, we replaced the 2 x missing rubber pads on the underside of the pedal as shown in the photo JEN 003. These pads are critical to the ‘feel’ of the wah as you reach the end of the sweep and also dampen the mechanical action of engaging the footswitch. Most important. It is necessary to glue these pads in place and allow the recommended time for the contact glue to set.

JEN 004

JEN 004

24 hours later we returned to set the height of the footswitch, ie its point of engagement, plus the sweep of the pot. The original pot we removed measured 250K ohms, which is not a standard value for wah pots these days, but we successfully installed a 150K pot which when adjusted resulted in a very nice sweep. We discovered that there are significant physical differences between the original pot, rack & gear compared to current production (not for the first time). Therefore the nylon clamp that holds the rack nicely in place up against the pot gear was actually exerting way too much tension for this wah pedal to be of any practical use. Much trial & error later we finally had it just right.

JEN 005

JEN 005

You can see the original nylon clamp with the new pot in photo JEN 005, plus the ‘true-bypass’ MOD has been implemented. A resistor has been added to minimise pops & clicks (ie, a ‘pull-down’ resistor). We added some foam (JEN 004) to enable the battery & clip to be padded down firmly when the bottom plate is re-attached.

The sweep of a wah & the ‘feel’ of the bypass switching are so much a matter of individual preference, in most cases we can only adjust to what we think is appropriate, based on practical experience. We returned the completed wah via parcel post to our valued customer, Mr John Milton, and some days later received this very positive feedback & testimonial:

HI Ivan…………….and I must say how great it sounds. Certainly feels different under foot, but the sweep & the clarity of the wah is most notable and it didn’t take long for my memory of the pedal to return. Also noticed there was hardly any change (when using the Jen) of tone apart from the wah effect, of course, and the subtle transition of OFF to ON & vice versa. Very clean signal, and the low tones of the sweep don’t go muddy & gurgly (!?!). The newish ones seem to do that and it is horrible (the Zac Wylde version in particular). All in all, I’m really happy and it is great to get that ‘sound in my head’ back, which I didn’t realise was gone for a few years. Thanks again for a fantastic job and I certainly do appreciate it. I wouldn’t want to make any further changes, it is perfect for what I try to do. JM.

Sounds Like Sunset & the RICH FUZZ pedal

June 26, 2013
the boys from Sounds Like Sunset

the boys from Sounds Like Sunset

Sounds Like Sunset are back in the spotlight with their new single ‘Open Up My Eyes’ – equal parts shimmering noise pop, infectious hooks and bursts of the swirling, fuzz-pedal-friendly noise that’s defined their sound for over a decade – plus a chorus you won’t shake for days.

Recorded by Wayne Connolly in the big room at Alberts Studios (Neutral Bay/Sydney) in about 2010 – and then lots of DIY overdubs & vocals later (much, much later) at home in Wyoming (NSW) by David Challinor.

Mixed by Wayne Connolly in 2013 at Alberts (Neutral Bay) in Doug Mulray’s old broadcast studio on a crazy old refurbished (vintage) Neve desk.

an early Rich Fuzz pedal with traffolyte label & LED

an early Rich Fuzz pedal with traffolyte label & LED

Dave wrote to us this week with this update:

Here’s a single we’ve just released called Open Up My Eyes – we’re fortunate enough to be getting airplay on community radio such as 2SER & FBi, and also Triple J on & off (see Soundcloud link below).

The main reason I’m sending you this link is because the main drunken-swerving melody lead-guitar line in the song was recorded using my Rich Fuzz pedal. It was perfect for slithering & snarling around underneath the frequencies of all the other guitar tracks – just above bass range but below normal guitar range. I’ve had the pedal for years & years (it’s so old it’s from your pre-LEDs era – you previously had to retrofit an LED in it for me), and of course it’s still a great pedal !

We’re launching the single this Friday night (28th June 2013) at The Square in Haymarket (Sydney).

Another innovative indie band to use the Rich Fuzz extensively in their recordings is Sydney’s Circle (formerly Opanoni). We have been hand-building the Rich Fuzz since 1997, and although the cosmetics have changed from time to time, plus an LED status indicator was added when the 3-pole footswitch became available, the circuitry and component selection has stayed exactly the same, so you can be confident that a Rich Fuzz purchased in 2013 will sound exactly the same as the pedals built in 1997. Currently available from Bondi Intermusic (Sydney) or direct from Ivan Richards Audio.

(*) Wayne Connolly is an Aria Award winning producer, engineer, musician & composer with over two decade’s experience in the music industry.

major overhaul 40 y.o. Orange “Graphic” 100W head

June 10, 2013
Orange Graphic 100

Orange Graphic 100

Welcome back to the blog ! This week we look at a major overhaul to a battle-damaged classic from around 1971 – the Orange ORS100 “pics-only” head. Our very good customer David Challinor, guitar & vocals from the band Sounds Like Sunset, had recently acquired this vintage masterpiece, but in its existing condition the amp was quite unstable and of dubious electrical safety.

Orange Graphic 100

Orange Graphic 100

Dave contributed the Vadis/Galaxie amp that we blogged back in January 2012, which has been one of our most widely read blogs (for Australian readers). We have previously discussed the servicing of Orange amps back in April 2012, October 2011, & May 2011, but those amps were products of the contemporary Orange company. This is our first ever blog of an original Orange from 40 years ago.

Orange Graphic 100 internal prior to overhaul

Orange Graphic 100 internal prior to overhaul

Any guitar amp this old will have numerous issues to be resolved, including electrical safety, some components (eg electrolytic capacitors) will be well past their use-by-date, and also there will have been repairs carried out on-the-run which may well have to be corrected to produce a stable amp which performs as originally intended.

This amp is designed to run its quad of EL34 power output valves at a very high 525V DC, similar to some very old Marshalls from that era. This places additional stress on modern production EL34′s, as well as being a potential source of problems for printed circuit board designs.

Orange Graphic 100 internal prior to overhaul

Orange Graphic 100 internal prior to overhaul

Sure enough, there had been a melt-down in this amp, probably many years ago, which resulted in permanent damage to the p.c.b., with some tracks & pads having lifted, required the circuit to be completed with wire links. This had been repaired reasonably well previously, and we carried out some additional repair work in this area. You can see from the photo immediately above, the amp had been modded with the addition of zener diodes to lower the EL34 screen grid voltage. Quite amazingly given the high DC volts, there was no bias adjustment available on this amp.

Orange Graphic 100 rear view of chassis prior to overhaul

Orange Graphic 100 rear view of chassis prior to overhaul

Our agreed strategy was to restore the amp where possible to the original design, and update selected components, plus create an adjustable bias supply for the EL34′s. In Dave’s words: if you are able to drag the amp from being a potentially lethal museum piece & back to its former glory, then please proceed ! The trickiest bit was removing the p.c.b. from its position without introducing any more problems. These amps were really well made, built like a proverbial British tank, but employed single core wire, which as it ages becomes rather brittle and prone to breakage.

Orange Graphic 100 chassis front view prior to overhaul

Orange Graphic 100 chassis front view prior to overhaul

We cleaned up the copper side of the board and replaced all 9 x electrolytic capacitors, together with some 2 watt carbon film resistors. We installed a bias trimpot in place of a fixed resistor, which gives  a very broad range of adjustment, permitting the installation of various EL34 alternatives, eg E34L or KT77. We bedded down the high voltage capacitors in a blob of silicone for stability. We replaced the 4 x worn out pots and added an earth wire to the rear of the pots to improve shielding.

Orange Graphic 100 checking electrical safety issues

Orange Graphic 100 checking electrical safety issues

External to the board, the pair of vertical mounting 100uF/500V main power supply caps were replaced. All jacks & 9-pin valve sockets were cleaned with DeOxit. V1 & V2 were replaced with JJ 12AX7-s valves, which would be a reliable choice given the rather high cathode voltage in the V2 phase-splitter stage. The EL34′s tested OK and were retained. We found that the earth connection to the terminal block in the photo to the left had a stripped thread, which meant that the earth connection could not be tightened ! We replaced the terminal block and added a multi-strand earth wire connection direct to the chassis.

 

Orange Graphic 100 HV capacitors replaced & board repaired

Orange Graphic 100 HV capacitors replaced & board repaired

One unusual feature of the ORS100 design, especially compared to the published schematics of vintage Orange amps available on the internet, is that the huge filter choke actually carries the entire HV current draw of the amp, not just the screen grids & preamp valves. This probably has a positive impact on the amp’s performance when driven into clipping. However, the down side is that the voltage on the EL34 screen grids is too high. As a general rule of thumb, the voltage on the screen grids should be lower than that on the anodes, so we increased the value of the 4 x screen grid resistors, and installed those W22 series enamel body resistors which are intended for the harshest conditions.

Orange Graphic 100 new capacitors plus bias trimpot installed

Orange Graphic 100 new capacitors plus bias trimpot installed

The customary earth shield between the input jacks & the output transformer connections was missing, presumably lost at an earlier unknown repair job. Given the proximity of the input jacks to high voltage (HV) wiring, this was a contributing factor to the amps instability issues. Luckily we had a suitable shield in stock which we had manufactured for our own Richards amps, and you can see it has been installed in the photo to the left. After hours of work we were finally in a position to carry out a PAT test and a power output test. The result was 30V/8 ohms = 112 watts @ onset of clipping.

Orange Graphic 100 repairs completed

Orange Graphic 100 repairs completed

What did the ORS100 sound like ? This amp is designed to be played loud ! We gave it a blast in the workshop, and the more we turned it up, the better it sounded. The treble, bass & presence controls are very effective, but we really preferred the 6-position FAC switch on maximum anti-clockwise for a maximum full-bodied tone. There may not be too many venues left where you can actually use this amp to its full capability.

This overhaul exceeded the original budget by quite a margin but Dave seemed to be very excited by his new amp acquisition. Here are Dave’s initial reactions to the amp as conveyed by text message:

HI Ivan  – the Orange was wonderful, thanks ! Enormous sound. I love it !!

Once again the Orange was phenomenal at rehearsals. It’s my new favourite amp. I think it’s because it handles pedals so well too. I really, really love this amp & as always your work is top notch.

Thanks Dave, we love that kind of talk. IR.

MODS to the Marshall JTM600/JCM600 series amps

May 19, 2013
JCM600 range from Marshall website

JCM600 range from Marshall website

We are now implementing mods & upgrades to a broad selection of guitar & bass amplification, primarily valve (tube) but occasionally solid-state as well. The most common examples are the Fender Pro-Junior & Blues Junior models, however we have been selectively modding Marshall amps since the 1980′s. In this blog we have a quick look at the Marshall JTM600 & JCM600 series amps – it would appear that the differences between the two are limited to cosmetics & choice of speakers, the electronics remains the same for both series.

JCM600 combo

JCM600 combo

These amps remain among the more obscure of Marshall’s amp offerings of the last 20 years or so, very few guitarists would have played through one of them, let alone owned one. We do have a few Central Coast (NSW) customers that quite enjoy these amps, including “Gazebo”, the man who inspired this blog by commissioning us to mod his JTM60 amp head (we modded the “clean” channel only).

JCM601 model

JCM601 model

These amps don’t have a great reputation for reliability. We have replaced several transformers over the years, for example. The first batch of JTM600′s were blowing the main high voltage filter capacitors during the warranty period, although this problem has obviously been resolved. They are not particularly easy to work on – getting the circuit boards out and re-installing them is quite time consuming. Operating the EL34 power output valves (tubes) in the horizontal plane rather than the more conventional vertical plane is just asking for trouble. You have to choose your EL34′s carefully - with some brands there is the potential for an internal short-circuit to occur, if the heater filament sags for example. Please note, this is not normally a problem with the 12AX7 preamp valves. Regardless of your choice of valves, most of the heat from the power output valves goes straight up into the amp.

the JTM30 combo

the JTM30 combo

Over the years, we have tried to come up with ways to “bullet proof” these amps. Not all EL34′s like high voltages on the screen grids, for example. Installing a small DC powered cooling fan may assist the issue of heat build up within the chassis. The JTM30 model has presented less problems, but has one stupid design mistake – a non adjustable bias supply voltage, which complicates replacing the 5881 output valves unnecessarily.

Stock, the 60 watt amps sound a bit thin and a bit sterile. The “lead” channel develops a type of distortion that sounds like it came from a stompbox, rather than from a valve amp. The main focus of our mods is to convert the “clean” channel to a circuit sounding as close as possible to a Marshall model 1987, ie a blues/crunchy tone with more fat bottom end and crisp high end. This is achieved by substituting selected components (resistors/capacitors) with more traditional “plexi” circuit values. This is what we achieved for “Gazebo” just this week. Once the job was completed, the “clean” channel was suddenly very useable for many styles.

With the “lead” channel you could easily go overboard, spending hours rebuilding the whole circuit. The simplest approach would be to remove the clipping diodes for a more natural valve (tube) medium distorted tone, although having done this it may be necessary to make some changes to balance the circuit for the now much higher signal levels.

Modding the clean channel as described, plus limited mods to the lead channel is a cost effective way to significantly improve the performance of these amps. We need to allow a minimum of 2 hours labour for this work, plus materials. We would have to quote re specific improvements to the power amp, eg adding a cooling fan, etc. Regards – I.R.


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