the WEM Westminster 10

April 12, 2014
the distinctive WEM badge and grille cloth

the distinctive WEM badge and grille cloth

This week we look at a recent repair for a regular customer, known in these pages as Jimmy James. Jim is an amp collector and his specialty is low-wattage valve (tube) amps, both vintage and contemporary, typically up to about 10 watts in audio output. Jim supplied the Matamp C7 which we discussed in our blog back in April 2012. That particular blog has been read many hundreds of times world wide, so we know there is a strong interest in such amps.

the WEM Westminster 10

the WEM Westminster 10

Jim has acquired a pair of WEM “Westminster 10″ 1×12 combo amplifiers, presumably manufactured in the UK during the late 60’s or early 70’s. We have chosen to look at amp serial # CW46047, as this example is in much better condition cosmetically, and also is loaded with a very good sounding vintage alnico magnet speaker, which appears to be original. In fact, apart from the valves, the whole amp appears to be completely original. There are no labels anywhere on this amp to identify the model name or number, the only way we found out this is the Westminster is by comparing the schematics available on the ‘net to the actual amp. The original Westminster models from the early 60’s used a valve (tube) rectifier, whereas this amp has a solid-state full-wave rectifier.

the WEM board is removed for servicing

the WEM board is removed for servicing

Jim’s amp was actually working, but needed microphonic valves replaced and attention to any electrical safety details, which included a new 240V 3-pin plug. The pots and jacks were due for cleaning, and the amp was unstable at higher settings of the ‘treble’ pot. It turns out the bodies of the three pots were no longer earthed (grounded) – earthing the pots back to the board cured the instability problem. The cathode bias bypass capacitor for the output valves was replaced, having been affected by the heat from the cathode resistor.

amp now reassembled

amp now reassembled

The whole amp is built on a steel plate behind the front control panel, which includes power and output transformers and a printed circuit board (p.c.b.) which supports all components excepting the two input jacks. The controls are volume, bass and treble – with the on/off switch part of the ‘treble’ pot. This assembly is fastened to a number of captive bolts, and the whole thing lifts out fairly easily for servicing, although on an amp of this age brittle wiring sometimes has a tendency to break off.

12-inch alnico magnet speaker

12-inch alnico magnet speaker

The amp design is based on a pair of 6BM8 (ECL82 in Europe & UK) valves (tubes), which comprise a triode and a power pentode in the same envelope. The performance of the triode is similar to that of a single triode within a 12AX7, and the power pentode has a maximum anode dissipation of 7 watts, with a maximum anode voltage of 300V for either section. So, the 6BM8 is similar to the 6GW8 discussed in previous blogs (beware: with different pin connections), but with a slightly lower rating for the pentode section, allowing for a maximum audio output power of around 10 watts in Class A/B push-pull (cathode bias), as compared to around 14 watts for the 6GW8. Untold thousands of 6BM8 valves were manufactured back in the day for consumer electronics applications, and unlike the 6GW8 they are still in production. The triode sections are typically used for phase-inverter applications, etc.

the reassembled amp

the reassembled amp

The preamp utilises a single 12AX7, is voiced somewhat like an early 60’s Fender amp, and could be described as low gain. Jim’s pair of Westminster 10’s are the very first WEM amps we’ve seen after decades of amp work, so obviously they were never imported into Australia in commercial quantities. The WEM amps have their own unique cosmetic appeal, including a very distinctive woven speaker grille cloth.

WEM are probably best known globally for their Copicat tape echo units, and David Gilmour famously used WEM 4×12 cabs with his Hiwatt amps in Pink Floyd.

WEM serial # CW46047

WEM serial # CW46047

Although WEM produced a range of UK built all-valve guitar amplifiers for many years, it would appear they achieved their greatest successes with sound systems for large concerts, virtually inventing British concert PA systems. The story of WEM and British concert PA has been related in a number of books and publications. IR.

the mighty HIWATT DR103

March 30, 2014
Hiwatt DR103 serial 12465 April 1978

Hiwatt DR103 serial 12465 April 1978

Hello & welcome back to our blog. We recently carried out service & repairs to a 1978 Hiwatt [UK] DR103 amplifier which obviously has had a long & hard working career in rock & roll bands. This DR103 is the 2-input model with active mixing of the normal & brilliant channels, as distinct from the late 1960’s/early 1970’s 4-input model with passive mixing of the two channels. We suspect that both versions of this model have their fair share of admirers.

DR103 front view of chassis

DR103 front view of chassis

This amplifier was working but had issues with microphony and very scratchy pots – some pots had dead areas on their sweep, so were barely useable. The amp had been modded by persons unknown further back in its history. The high frequency response of the brilliant channel had been boosted to ear-drum shredding levels, and was to all intents & purposes unuseable. Apparently the previous owner had only ever played on the neck position humbucking pickup of his 335 style guitar, hence the need for extreme high frequency pre-emphasis.

1978 Custom Hiwatt 100

1978 Custom Hiwatt 100

In addition to this problem, the amplifier had high levels of hum & noise. We started out by giving the chassis a quick clean up and tightened up a loose transformer. We checked the fuses, and as is so often the case in older amps, they were not offering any protection at all as they were the wrong values ! We installed new fuses, carried out an electrical safety check [PAT test], then moved on with the main part of the service.

DR103 chassis rear view

DR103 chassis rear view

All pots [excepting bass & treble] were in very poor or damaged condition, so we replaced them with those excellent CTS pots. One source of unwanted noise came from the input jacks – they weren’t shorting to earth [ground] when the guitar lead jack plug was removed. We cleaned all input & output jacks, plus the 9-pin valve sockets with DeOxit, which corrected the remainder of the intermittent problems.

DR103 interior view of chassis after replacement of 5 x pots

DR103 interior view of chassis after replacement of 5 x pots

Two only of the preamp valves were tested as being faulty and/or microphonic, so we replaced those accordingly. All other valves, including the quartet of EL34’s tested OK. This amp has obviously been in regular use since manufacture in 1978, and the various electrolytic capacitors in the power supply still appeared to be serviceable. As the customer’s budget did not allow for complete replacement of electrolytics, we left them alone.

the DR103 nameplate tarnished by years of rock&roll

the DR103 nameplate tarnished by years of rock’n’roll

There was still a remaining source of hum within the amp, and this turned out to be a lack of earth [ground] reference for the 6.3V AC heater filament supply. The pair of 100 ohm resistors that provided a virtual centre-tap for the 6.3V AC looked perfect but measured O/C. We fixed this problem with the installation of a pair of 100 ohm 1 watt resistors. The final issue to be resolved was removing the MODs to the front end of the amp.

the mighty 1978 Hiwatt DR103

the mighty 1978 Hiwatt DR103

This DR103 already possesses a very bright voice, especially when plugged into the brilliant channel. The amp had been modded with a double layer of additional brightness, so the brilliant channel was unbearable with a Strat or a Tele. We restored the front-end circuitry to original spec, removing both MODs. How does this amp sound now ? Just fantastic, actually, although at 100 watts I would get thrown out of every gig we do these days, not to mention making my existing tinnitus problem even worse ! It’s just so British, with a warm & fat midrange, sweet & crisp top-end, and a tight but powerful bottom end. I love the balance of tone across the 6 strings of the guitar, but unfortunately for this amp to sound at its best, you have to play bloody loud.

So, we heartily recommend vintage Hiwatt amps as an investment for all you amp collectors out there – they were so well made in the first place, and are a pleasure to work on from the techo’s perspective. We are currently building several custom amps from 15 watts to 60 watts [to a customer order], that while not a carbon copy of the Hiwatt, are very strongly inspired by the Hiwatt and will deliver the classic British tonality at more sensible volumes. These amps are offered with a choice of EL34, KT66 or KT88 output valves. We also offer a single-ended KT88 model at 15 watts output.

Thanks for checking in again, and there’s plenty more amp talk to come. IR.

Farewell Jack Richards

March 9, 2014
Jack Richards 1983 Pedal Steel Interview

Jack Richards 1983 Pedal Steel Interview

Jack Richards, without question the Godfather of Australian pedal steel guitar, passed away age 93 during the night Thursday 6th March 2014. Born 1921 in Sydney Australia, Jack also established himself as one of Sydney’s leading guitar professionals in the 1940’s & 1950’s, a contemporary of the top players of the time, including such names as Don Andrews, George Golla and Jan Gold.

Jack purchased his first steel guitar in 1937 for $3. In 1939 he purchased a new Rickenbacker steel and amp for about $115. At this time (like many in the Richards family) Jack was employed in the newspaper business, working for the Sydney Sun initially as a copy boy straight from school, then as a press photographer, having completed an apprenticeship.

The first pedal steel in Australia (built in a Sydney garage)

The first pedal steel in Australia (built in a Sydney garage)

Jack had a flair for photography, but had greater ambitions in the world of music, well beyond playing lap steel. With the engineering skills of another steel guitar enthusiast, Ivan Ive, the first pedal steel guitar in Australia was built in a suburban garage in Sydney (pictured at left). The steel and amplifier were combined in a single very impressive cabinet, with the initials JR part of the speaker grille. Jack evolved a new style of playing steel within a jazz and big band context together with a (then) young sax player, David Rutlege. Jack became the first person to play pedal steel guitar in Australia at a professional gig, in 1943 at the ‘Roosevelt Club’, a club for American Officers in Sydney during WW2.

In 1944, Jack was hired as pedal steel guitarist by bandleader Leo White for his 15 piece orchestra. In 1945, the same band landed a 6 nights per week 2 year residency at the very swank ‘Princes’ restaurant, at that time literally Sydney’s top nightclub/restaurant. During the WW2 years, Sydney’s nightlife and live music scene had ramped up considerably from the previous decade. In the Leo White bands, Jack also played conventional orchestral/big band style (archtop) guitar, becoming a proficient reader on both instruments.

After the ‘Princes’ gig finished, there was a slow downturn in the live music scene after WW2, as might be expected. Jack stayed busy doing most of the studio sessions in Sydney on pedal steel, also including programmes on both ABC radio & TV. An example is the hawaiian music sessions with Sydney crooner Johnny Wade, who had his own weekly shows on the ABC. Jack also developed his arranging skills during this period. Radio & TV shows were generally broadcast “live” to air with all musicians required to read charts. Definitely no miming back in those days !

The Kord King

The Kord King

During 1947 – 1948 production of the ‘Kord King’ pedal steel guitar took place in a small factory in Cremorne (Sydney). This was arguably the first production run of a pedal steel guitar in the world. The three main partners involved in this were Jack Richards, Ray Olson and Alec Iverson – all photographers and all steel players. My apologies for any errors and omissions in this story, there may have been others who contributed to this project. This time the pedal steel was not a huge console, but rather a portable instrument with a separate amplifier unit. The amplifier was built in another factory in Cremorne, details not known. The initial production run was 100 units plus some lap steels. The boys thought they had it made – that they would conquer the world, but it was not to be. The widespread use of pedal steel guitar in country music was still a long way off. There were only a handful of guitarists with the sophistication to use Jack’s jazz approach to the steel, and interest in Hawaiian music would ultimately wane. In retrospect they were about 20 years too early.

The Cremorne factory eventually moved to Ben Boyd Road, Neutral Bay, on a corner opposite The Oaks Hotel (then the watering hole for the large tram and bus depot right next door), producing cases for jewellery and cutlery, etc. At the time, we lived close by in Grosvenor Street. I don’t think this was a happy period in Jack’s life. After the business was wound up, Jack started ‘Guitar City’ with partner Roy Royston (plus a silent partner), primarily as a teaching studio, but was developed over time as a guitar and amplifier retailer as well. This was arguably Sydney’s first ‘specialist’ guitar shop. I can remember ‘Guitar City’ at three different locations in the Sydney CBD: Railway Square, Telford House and the Gibb & Beeman Building – the latter two both prime George Street locations. I believe that the original teaching studio was in Kirribilli/North Sydney, but have no personal memory of that. The business prospered during the 60’s explosion of guitar ‘groups’, with Jack & Roy selling out to younger owners in the early 70’s.

From this time onwards until his retirement from the music business at age 65, Jack continued teaching in the Manly area of Sydney, and held down numerous club and theatre/restaurant gigs around town. Jack is survived by three sons: Ivan, Trevor and Mark, one daughter: Karen, plus eight grandchildren and five great-grandchildren. Thank you Jack for passing on the gift of music to me !!

Ivan Richards.

for more information ref the development of Aussie pedal-steel, please see the ‘history’ archive at my website:  http://www.ivanrichards.com

emergency repairs for the Steve Edmonds Band

February 25, 2014
Steve Edmonds (official) promo photo

Steve Edmonds (official) promo

Steve Edmonds is a well established and much admired guitar player on the Australian music scene, based in the Sydney area. Steve has put a lot of hard work into carving out his own niche as a blues guitarist, a straight ahead rock guitarist, ie the Steve Edmonds Band, and is also well known for his Jimi Hendrix Tribute shows, eg Hendrix and Heroes.

'57 Tweed Twin replica blowing fuses

’57 Tweed Twin replica blowing fuses

More recently, Steve has come up with a fresh concept and a new band by the name of Mescalero. With Esteban (Steve) on guitar/vocals, Antonio on drums and Alejandro on double-bass, Mescalero are described as a Roots Rock band, which incorporates Rockabilly, Surf, Western Swing, Bop, Big Band, Ska, Mambo and Country influences ! The new band is already gigging and recording.

'57 Tweed Twin replica (with a couple of vintage amps in the background)

’57 Tweed Twin replica (with a couple of vintage amps in the background)

Which brings us to the subject matter of this blog – both Steve and Alex had amp mishaps last week which required immediate attention as there were gigs booked from Thursday night onwards. Firstly, there was Steve’s amp. This is a replica of the ’57 Tweed Twin Amp, made in China, and distributed locally by Lawrie Minson in Tamworth, New South Wales. These are the models that famously (in the Fender line-up) introduced separate Treble and Bass controls, rather than a single Tone control (the addition of a Midrange control was still a year or two away), along with the Bandmaster, Super and Pro amp models (apologies to Fender enthusiasts if we’ve left out any details).

the culprit !

the culprit !

Steve’s amp was repeatedly blowing the mains fuse – if this happens more than once clearly something is seriously wrong ! At first we all assumed that one or both of the 5U4 rectifier valves had developed a short-circuit (S/C). This is quite a reasonable assumption, but it was not to be that simple.

'57 Tweed Twin replica amp chassis

’57 Tweed Twin replica amp chassis

We first plugged the amp into the mains via a ballast light, so that we didn’t have to keep replacing blown fuses while troubleshooting the problem. We removed all valves (tubes) from their sockets but the S/C was still there. Obviously the problem was in the power supply, and potentially the power transformer was the culprit. One by one we removed the transformer secondaries, so that each secondary was unloaded, and retested. Please don’t try this at home !!

under the chassis of the '57 Tweed Twin (China)

under the chassis of the ’57 Tweed Twin (China)

Finally, we had the primary connected directly the the active and neutral wires and we still apparently had a S/C in the power transformer. So, we emailed Lawrie Minson who sent us down a replacement transformer which we installed, along with a bit of tidying up of the 240V primary wiring. With all valves reinstalled and tidying up of the disturbed wiring with nylon cable ties, we could successfully test Steve’s amp for electrical safety and power output. Back in the day, even with a pair of 5U4 rectifiers, these amps only delivered around 30 watts rms, and this replica of course delivers similar performance.

Installing a pair of Celestion 'Greenbacks' into Steve's amp

Installing a pair of Celestion ‘Greenbacks’ into Steve’s amp

Steve actually requested slightly earlier break-up, so we installed a single 5U4 by Electro-Harmonix, our favourite sounding current production 5U4, which also has a good reputation for reliability. The factory loaded speakers with this amp were a pair of the budget model Celestion G12-65 (not the ‘Heritage’ model), which were letting the amp down quite noticeably. At Steve’s request we upgraded these to a pair of Celestion G12M25 ‘Greenbackspeakers, at 8 ohms each, wired for the system impedance of 4 ohms.

still one of the sweetest sounding guitar speakers !

still one of the sweetest sounding guitar speakers !

This upgrade improved the tone and response of the amp 100 %. The woody, somewhat midrange-scooped tone of the Greenbacks balanced better with the flat midrange response (at most settings) of the ’57 Tweed Twin amp, and introduced a warmth and sweetness that wasn’t really there before. When Steve came to pick up the completed repair/upgrade he gave the amp a good workout with our Fender ’52 Tele Reissue loaded with the Pete Biltoft Vintage Vibe pickups (see blog NOV 24, 2013).

Steve's amp reassembled !

Steve’s amp reassembled !

Part-II of the story: Mescalero bass player Alex Campbell brought his amp to the workshop – a Hartke 500 watt bass amp head. A mishap when moving the bass rig caused a jack plug to break off inside a speaker jack on the back of the amp, and worse still the master volume control was smashed and unuseable. Aside from those two issues the amp appeared to be unharmed.

Alex's Hartke 500W bass amp head

Alex’s Hartke 500W bass amp head

We removed the broken speaker plug from inside the amp, wired Alex a new heavy-duty jack-jack speaker cable, and stripped out the preamp/power supply PCB to replace the 10K Lin 16mm master volume pot. This involves unscrewing many, many screws and removing the front panel – the complete job takes about an hour. While we had the amp apart we cleaned up accumulated dust from the power amp’s forced air cooling system – an important little task to keep the amp running reliably.

inside the Hartke bass amp

inside the Hartke bass amp

The design and assembly of the Hartke amp is completely conventional – there is no digital circuitry, no switching power supply. The amp is isolated from the 240V mains by a huge toroidal transformer. From the point of view of the service tech, this is a positive thing – the whole amp is accessible for ease of servicing. The only problems we’ve had with the Hartke amps over the years (with one or two exceptions) have been ‘dry’ solder joints and poor quality input jacks. The Hartke does not have a ‘signature’ sound, but this is a matter of personal taste.

Many thanks to Steve and Alex for their continued custom ! We wish Steve all the best for his new band – please check out Mescalero soon.

http://www.mescalero.com.au

http://www.hendrixandheroes.com

http://steveedmondsband.com

Service Centre for Jackson Ampworks in Australia

February 22, 2014
Jackson Ampworks 'Britain'

Jackson Ampworks ‘Britain’

Hello, welcome back to the blog. We are now offering world-class (non-warranty) service & repairs to the range of valve (tube) amplifiers from Jackson Ampworks of Keller, Texas USA. We should point out that we have no official relationship with Jackson Ampworks, so we cannot accept any warranty repair claims without the endorsement of their Australian distributor.

Jackson Ampworks 'Britain' amp head

Jackson Ampworks ‘Britain’ amp head

We recently serviced the Jackson ‘Britain’ amp for one of our customers, who is a guitar tutor and professional player – the amp is featured in the accompanying photos. The Jackson amps are built in Texas, but are British-voiced. The concept of the Jackson ‘Britain’ is broadly similar to our own Richards ‘Expressionist’ amplifier models – there are two discrete preamp channels, voiced as per vintage VOX amps.

Jackson 'Britain' rear panel removed

Jackson ‘Britain’ rear panel removed

CH-1 is based on the EF86 pentode preamp valve (tube), and CH-2 employs the more familiar 12AX7/ECC83 valves and is effectively the top-boost channel. The EF86 is famously rather prone to microphony in guitar amps, but sounds absolutely wonderful in the right situation. The ‘Britain’ power amp section is switchable between a pair of cathode-bias EL84 valves for low power, and a pair of fixed-bias EL34 valves for full power.

Jackson 'Britain' chassis

Jackson ‘Britain’ chassis

The Jackson amp is very compact – about half the size of most comparable amps, ie amps in the 30 to 50 watt range. This amp depends absolutely on forced-air cooling for its survival, so if the fan ever stops working the amp needs to be serviced a.s.a.p. Some of the amp functions normally carried out by passive components appear to be implemented with the use of solid-state devices, which are mounted to vertical heatsinks, also in the forced-air cooling path.

'Britain' chassis: front view

‘Britain’ chassis: front view

Fortunately, for this service job there was nothing more serious than some noisy valves, which we replaced accordingly with a full check & test. The only problem we encountered was that the light aluminium chassis was quite resonant, at a frequency that was very close to the resonant ring from certain brands of EL34 power output valve that we tried in the amp. This was so noticeable that we substituted several brands before settling on the least resonant combination.

Jackson 'Britain' underneath the chassis

Jackson ‘Britain’ underneath the chassis

Finally, we were happy with the end result and our customer was pleased to get his amp back, working correctly again with unwanted noise at a minimum. You can see from the photo to the right that the amp is indeed hand-wired and the chassis layout is very tight indeed. Access to some components is limited or not possible at all without stripping out the electronics from the chassis.

Jackson 'Britain' chassis

Jackson ‘Britain’ chassis

Hardware components are by Carling, Switchcraft, Alpha and others – the standard of electronic components is also good. So there we have it – our very first experience of servicing the Jackson Ampworks product ! These amps look and sound great, but are relatively new to the Aussie music industry so we cannot pass any comments with ref to long term reliability issues. If you are in New South Wales and own a Jackson amp that needs servicing, please contact us @ ivan@ivanrichards.com

another Morgan amp in our workshop

January 27, 2014
Morgan RCA35

Morgan RCA35

Welcome to our first blog for the year 2014 ! Another Morgan amp came to our Wyoming workshop for repairs a while back – this time the RCA35 model. We previously discussed repairs to the Morgan SW50 back in January 2013. The RCA35 is voiced quite differently to the SW50, and is intended to be a ‘clean headroom’ amp, according to the Morgan website. A pair of cathode-biased 5881 output valves delivers 30 watts output @ the onset of clipping.

Morgan RCA35

Morgan RCA35

Our good customer, Josh, had purchased this amp about 6 months previously and advised us he was getting some very strange sounds, almost like an octave-fuzz pedal. At our first attempt to diagnose this, the RCA35 behaved perfectly so we were none the wiser. This situation happens sometimes ! After Josh got the amp back home again, of course it played up immediately, so he recorded the sounds on his ‘phone & sent them to us, and indeed the amp sounded like there was an octave fuzz pedal happening.

Morgan RCA35

Morgan RCA35

Back in the workshop, I strongly suspected that this degree of amp instability must surely be down to a faulty electrolytic capacitor (or capacitors) in the amp’s high voltage power supply. Josh was preparing to head off for a short tour in central western New South Wales with a band, so we couldn’t take the risk of leaving an intermittent fault in the amp. Therefore we took the decision to replace all four HV (high voltage) power supply caps, plus the cathode bypass cap for the output valves, just to be sure.

Morgan RCA35

Morgan RCA35

You can see from the photos that the original capacitors were of standard consumer electronics quality, and of recent production. There were no tell tale signs of leakage or faulty manufacture. We installed a set of those very fine F&T capacitors, bedded down in some silicone (neutral cure) for stability. Sprague ‘Atom’ capacitors would also be an ideal choice although their larger physical size sometimes limits their application in service work. The list of capacitors reads as follows: 2 x 30uF/500V, 2 x 22uF/500V plus 1 x 100uF/100V.

Morgan RCA35

Morgan RCA35

We also tightened a loose fuseholder and changed the fuse size from 2 amp to 1 amp as in Australia our mains power is obviously 240V (sometimes higher), and labelled the rear panel accordingly. The manufacturer and their local distributor really should have taken care of that particular issue. With the high voltage supply reading +430V DC, we measured 15.6V into 8 ohms = 30 watts @ the onset of clipping. We were pleased to hear that Josh got through his tour OK and there were no further problems with this amp !

Morgan RCA35 original HV capacitors

Morgan RCA35 original HV capacitors

Morgan RCA35 upgrade caps installed

Morgan RCA35 upgrade caps installed

Margan RCA35 after completion of repairs

Morgan RCA35 after completion of repairs

Ivan’s new Hame 1×12 cab

December 13, 2013
Hame 1x12 cab

Hame 1×12 cab

Hello & welcome back to our blog. Occasionally our customer amplifier projects require the input & support of a specialised cabinet builder, for work that is beyond our amp building workshop’s resources. For example, we have utilised the unique cabinet building skills of Mr Peter Davies (ex NSW Central Coast, now resident in Melbourne) several times for our exotic hardwood cabs.

Hame 1x12 cab

Hame 1×12 cab

More recently we have enlisted the help of Mr Brandt Horrocks of Hame Speaker Cabinets (Wagga Wagga NSW) to produce a pair of specialised 2×12 cabs for baritone guitar stylist, Mr Chris Earle. As a spin off from that project, Chris also ordered a pair of somewhat more compact 1×12 cabs, one each for Chris & Ivan, for rehearsals & lounge gigs. We will look at the 2×12 cabs in greater detail in a later blog, as part of the broader Chris Earle project.

Hame 1x12 cab

Hame 1×12 cab

This 1×12 cab design is a much simplified version of the original 2×12 cab design, which included angled speaker baffles. In both cases, the cab design allows sound to pass through vents on either side of the cab. These vents are not tuned, as in a “bass-reflex” system (ie, the cab is “de-tuned”). Sound emanates from the sides of the cab much as it would from the rear of an open back cab, while providing better dispersion & more consistent tone from venue to venue. In the 2×12 cab design internal angled reflectors push the sound from the rear of the speakers to the side vents.

Hame logo

Hame logo

The end result is a speaker cab that is never “boxy” or “boomy”, with outstanding dispersion, clarity & a solid low-end. The intended companion amp for Chris Earle’s 1×12 cab is a brand new model from the Richards Amplifier Company – Australia: the KT88se, ie a single-ended/class-A KT88 amplifier. This amp will be part of the “British Lead” series, meaning that the front end is voiced as per some of the classic amps from the golden-age of British rock. This amp is the result of months of R&D during 2013, & will be the subject of a future blog.

the pair of 1x12 Hame cabs under construction

the pair of 1×12 Hame cabs under construction

Please take the time to check out these photos of the new cabs. Regards – IR.

under construction

under construction

completed

completed

completed

completed

completed

completed

2x12 cabs completed

2×12 cabs completed

MODs to the HIWATT 20H amplifier

December 10, 2013
HIWATT 20H

HIWATT 20H

Recently we implemented some home-grown MODs to a HIWATT 20H amplifier for Rick Altavilla, now on guitar for home-grown Central Coast band Sparrows – fronted by the one & only Scotte Woods (formerly of One Dollar Short). Rick purchased this amp new, fully expecting that it would sound like a scaled-down version of the great original HIWATT amps. Unfortunately it sounds & performs nothing like an original HIWATT. This is not a cheap amp either – it’s actually a rather expensive one, even allowing for the fact that it is hand-wired from the UK. To say that the guys from Sparrows were disappointed with this amp would be an understatement.

HIWATT 20H

HIWATT 20H

The 20H has some design problems in common with the Marshall C5 discussed in our previous blog. Much of the available gain is thrown away due to some bizarre design choices and the 3-band passive EQ just doesn’t work at the desired guitar frequency ranges. Indeed, the 20H sounds really flat.

Basically, you could consider this amp to be a kind of modern AC15, with a couple of sequential gain stages, a buffer stage driving the EQ, a pre-PI stage master-volume, and a zero negative feedback power amp employing a pair of cathode-bias EL84/6BQ5 output valves. Such an amp design potentially should sound mighty fine.

HIWATT 20H

HIWATT 20H

The power amp & PI (phase-inverter) stage were OK – no apparent problems there, so we concentrated our attention on redesigning the preamp, within the constraints of the existing electronics & layout, to achieve a useable amp. We reconfigured the gain stages to get some drive & balls from the amp, & revoiced the EQ as per the C5 to achieve a useable & effective sweep from all controls. The 20H now sounded like a baby “British” amp from the 60s golden-era, which is not a bad result at all !

Thanks Rick & Sparrows. IR.

MODs to the Marshall Class 5 amplifier

December 5, 2013
the modded C5

the modded C5

Welcome back ! Over the last couple of years, in our blog pages we have presented MODs to the Marshall JTM600/JCM600 amps, Peavey Valveking 100, Fender Pro Junior & Blues Junior, Laney LC30, amps by Rivera, bass amps by David Eden, plus wah wah pedal MODs. We offer all these MODs and more here in our Wyoming workshop.

Marshall Class 5

Marshall Class 5

In the coming weeks we will publish a blog re our home-grown MODs to the HIWATT 20H valve amp head, which is a seriously disappointing amp (sorry about that, HIWATT !). But our latest MOD project to present to you is the Marshall C5 amp. These amps have sold really well in OZ due to a very reasonable price point for a made-in-UK Marshall with an all-valve (tube) signal path.

Marshall C5

Marshall Class 5

Unfortunately, the C5 straight out of the box is not an amazing sounding amp. The 3-band tone controls do not seem to have a particularly effective sweep, and especially not at the frequencies you expect from a Marshall (ie, the “Plexi” or “Super Lead”), plus due to the absence of a master volume control or attenuator – 5 watts is still too loud in some home playing or recording situations.

C5 chassis with original transformers

C5 chassis with original transformers

We agreed to implement the full range of possible MODs to this C5 for our customer, to transform the amp from a just OK unit into a high performance tone machine, with the option of turning down to conversation levels with the addition of an attenuator (controlled from the front panel).

C5 chassis with mercury Magnetics transformer set installed

C5 chassis with mercury Magnetics transformer set installed

Mercury Magnetics have developed a transformer set specifically for upgrading the C5, which comprises power transformer, filter choke & audio output transformer. Our customer requested installation of the full set. The addition of a filter choke will improve the performance of this Class-A/single-ended design significantly.

C5 chassis after mods

C5 chassis after mods

Other C5 MODs that we recommend include (in no particular order): raise input impedance R20 & remove C10, change cathode bypass cap C8 for tighter/plexi lows, add a (subtle) ‘bright’ cap across VR1, change ‘bass’ EQ cap C20 to implement a useable (plexi) sweep, change ‘slope’ resistor R28 for a more balanced (plexi) sound, change signal path caps C2 & C5 for improved lows & low-mids.

C5 p.c.b. connections & installing the VVR module

C5 p.c.b. connections & installing the VVR module

There are several other potential MODs which will have a less significant effect. The law of diminishing returns starts to kick-in. Note that all the above modding requires removal of printed circuit boards (p.c.b.’s), and changes to p.c.b. connections. The final MOD to this amp is the installation of a VVR module, available commercially on-line, to compensate for the lack of a master-volume or attenuator on the C5.

C5 p.c.b. connections- looking to the rear of chassis

C5 p.c.b. connections- looking to the rear of chassis

The VVR (Variable Voltage Regulator) is a relatively simple circuit that when installed in an amp such as the C5, will make the high voltage DC supply (usually referred to as HT, HV or B+) continuously variable from the maximum normally available from the amp’s existing power supply, to a minimum level which is preselected by changing resistor values on the module. In other words, by electronically varying the high voltage supply within the guitar amp, we succeed in reducing the audio power output of the amplifier from its design maximum to a preset minimum.

the VVR module requires 2 x additional chassis holes

the VVR module requires 2 x additional chassis holes

The VVR module employs a high-voltage power Mosfet device such as the NTE2973. In most cases it will need a heatsink, and ref the C5 bolting the Mosfet to the chassis is quite adequate. Thus we will need to accurately drill/punch 2 x additional holes in the C5 chassis – 10mm for the VVR control mounted conveniently to the front panel, plus 3mm for mounting the Mosfet, which must also be insulated from the chassis.

C5 front panel - the VVR control installed

C5 front panel – the VVR control installed

It just happened that a convenient place to install the VVR control is right where the Class 5 logo appears. It doesn’t look too bad actually, and our customer was happy with that, however it is an issue to take into consideration. We didn’t have any suitable Marshall-style control knobs to suit, so we ended up using a small “chicken-head” knob from Cliff.

Any of the power amp attenuation devices such as the VVR or London Power Scaling (for example) will solve the problem of reducing power for playing in the home, as will speaker attenuators such as the THD Hotplate & so on, in the latter case the amp still runs at normal power levels but the output is attenuated before it reaches the speaker. In spite of all the hype about some of these devices, they DO have a quite noticeable effect on tone & performance – it’s inevitable ! By definition, reducing the available voltage to the valves (tubes) will impact on dynamics & tonality – the various types of output valves in common use in guitar amps will sound & behave differently at different B+ voltage levels. Lower voltages particularly impact on the low frequency response of a given amp design.

We are happy to install devices such as the VVR in your amp (where appropriate) – just keep in mind that there is a trade-off.

By the way – our customer just loves his upgraded C5 amp now ! IR.

Warning !

While the VVR described above is a simple circuit it is not a simple MOD to install. It should only be installed by a suitably qualified amplifier service technician.

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

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


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