JMI  AC30 Conversion to AC30/4

The original JMI AC30/4 is regarded by many as the benchmark AC30. The EF86 front end in combination with the EL84 outputs provides an elusive brilliance and tone hard to match. In purest description, it is a classic AC15 with doubled output power. There is truely something magical about the tone of the AC30/4. Original AC15's of any description are increasingly rare these days, and it's proper big brother, the AC30/4 is all but extinct. Out of production since 1960, it is almost impossible to find, and if you do, it will be out of the price range of most. My offer is to convert any JMI non topboost chassis to one of these elusive AC30/4's.

An original AC30/4 Control Panel

As part of a personal restoration project of a very early AC30 I had to produce a reproduction 4 input Black and Gold AC30 panel. I went to painstaking lengths to get it as close as possible to the original, consulting many photos and getting numerous measurements from other AC30/4 owners to confirm dimensions. The result was well worth the trouble. A very high quality panel with virtually identical artwork and produced using the same photo anodising process as used by JMI back in the early 60's It was un-economical to get just one made, so I went ahead and made a small quantity. I am now in a position to offer, for a very limited time, conversion any AC30/6 non topboost chassis to an AC30/4. This is not an attempt to create forgery amps, but to provide access to an amp that is all but unobtainable to most persons. Every effort will be made on my part to make them true to JMI building specs, but I will not build forgeries. I have a wide variety of used and NOS 60's switches, 60's carbon composition resistors, and 60's Philips 'mustard' Polyestor Foil caps. These will be used if desired, at extra cost. All that is required for modifcation is the aluminium section of your chassis. It is a fairly simple thing to seperate it from the power amp section, and will keep postage costs very low. It requires 7 screws removed and approx 9 wires unsoldered. No transformers or tubes need be sent , and the chassis will be shipped back as such, ready for you to fit your preferred EF86 and your other original preamps. It will have the circuit modified to 4 inputs, and all other relevant wiring and component mods performed. Voltage selector and power switch will remain as supplied unless early types are specifically ordered, at an extra charge. One resistor change is required in the power amp section. This resistor and a diagram will be returned with the upper chassis to enable the user to do this simple change, as well as information to ensure the two sections are re-united correctly Examples of AC30 Chassis that are suitable for conversion to AC30/4

Non Topboost Grey Panel Missing Panel Non Topboost Chassis Standard Copper Non Topboost Chassis EarlyTransitional Black Panel Non Topboost Chassis

An example of an AC30/4 Conversion

Step one - the AC30/6 was seperated from the power section of the chassis  by the owner and packed up for shipping. It was sent by Airmail from the UK and arrived in only 4 days. Here it is just opened and ready to begin work on. The Aluminium section is surprisingly light, and travels very easily.

Click on the images to see them fullsize

Step two - the AC30/6 is inspected. In this case it is in working order but has a variety of replacement parts from servicing through the years. It has a very recent rotary switch for the Vib/Trem selector, which I was able to replace with a more correct one after discussion with the owner. The tagstrips had assorted replacment caps and resistors which were all checked for correctness. It ended up with more vintage components after the conversion than it arrived with, which was very satisfying to see.

Step three - The actual conversion. Easy to type, not so easy to do. I enjoy the work and love AC30's so it's not such an unpleasant chore though. It also means I take pride in what I work on. In the case of this amp I was able to fit quite a few NOS Philips mustard caps which were more correct for the amp, and certainly made it look the part. Here is what the owner had to say when he unwrapped it back in England. "...Glen, This is a work of art! I just stood and looked at it for an hour or so. Not sure whether to re-assemble it or hang it on the wall...." Michael Grabham, UK

Here's what everyone really wants to see though! - pics of the repro AC30/4 control panels. A lot of time and effort went into these, and I'm really pleased with the result. Here you see the panel fitted to the chassis. The protective plastic is still in place. Click on the images to see them full size.

Before returning a converted AC30/4 chassis I attach it to this power section that I keep specifically for testing. So it is powered up and fully tested before leaving. Here's a final shot of a chassis with new  control panel, fully modified and ready to be repacked and returned overseas to the owner. Sad to see them go sometimes......

Testimonial - From the owner immediately after he re-assembled his AC30/4. "Glen, I finally completed reconnections and powered her up.... no smoke, no weird noises.... so went ahead and plugged in.... It's the middle of the night here at the moment so I thought I'd just plug in and try it at 1/4 volume for a coupla minutes to make sure it's working right. WHAT A MONSTER! I LOVE IT! An hour later later and I'm still honking away and up to 1/2 volume. Can't wait to give it an uninhibited work out tomorrow. The tone is just how I like it, fat and rich with a nice raw edge, and never thin. Trem channel sounds supurb too. What with that and the bright switch there are 3 usable flavours of great tone PLUS the Trem. S#@t hot, I'm more than well pleased. I'll speak to you tommorrow when I've tried different guitars and more volume....God Bless Australia, Mick." Day two- "Glen, This amp sounds just bloody marvellous. I've given her full throttle with plenty of axes/pickups....every one sounds great. Les Paul screams, Strat sounds just like you want it to (bridge pickup usable at last!), got an early Ephiphone Coronet with single P90 that really loves this amp too. Everything I've tried just sounds HUGE!.... Beautiful rich vibrant clean sounds with the guitar turned down too..... lovely..... and never ever thin or clanky. It may be a cliche but I can't find a duff sound anywhere on this thing. Looks like this is going to be my #1 amp from now on. Youve done a fantastic job in every way, just like to let you know that it's genuinely appreciated. Truly great stuff!" 2003 - Michael Grabham, UK

What's Possible? - Anything from a fully operational, to a wrecked chassis is a viable prospect. An indicative price guide is found below but there will be variations depending on the level of work required, the desired authenticity of components, and the current state of your chassis. The conversion requires no drilling or mechanical modification to the original chassis. You are free to keep your original panel. Rear panel topboost modules are not required for an AC30/4. They can be retained if desired, or traded in as part of the conversion. The conversion will be very neatly done in such a way that it resembles an original. It will have the appearance of factory work - no untidy rat's nest. There will be as little interference to the original tagstrips as possible. The process would also be reversable if you desired later. I have a feeling that this is unlikely though. All chassis will be fully tested before being returned. What you will get back is an AC30/4, with the performance and appearance of the real thing. It is not a 'mod' it is a conversion, both electronically, and cosmetically. Special orders - I am also able to rebuild to an original AC30/6. This would be suitable for persons having a wrecked non topboost chassis desiring this later style AC30. I have the tagstrip material and information to reproduce them. I will not be able to convert an In-panel Topboost AC30/6TB to a 4 input chassis, as the panel holes will not line up, but would be available to rebuild a wrecked AC30/6TB upper chassis if desired. I have the materials and all the neccessary information to do so. For replacment Output or Mains transfomers in the Americas I recommend Heyboer Transformers of Michigan,USA. & Bluebell Audio for Britain and Europe. Please contact me for Transfomers in the Australasia region.

Indicative Price Guide Convert working AC30/6 non Topboost AC30 to AC30/4 -                                                        US$400 Convert non-working AC30/6 non Topboost chassis to AC30/4, no major parts required -            US$475 Rebuild wrecked AC30/6 non Topboost chassis to AC30/4 - (not incl. transformers)                    US$600 Fit old style linking voltage selector - $ By arrangement Fit old style metal toggle switch - $ By arrangement Shipping of just the aluminium chassis section means a smaller managable package weighing a little over 1kg. As an example of pricing, postage would take 4-6 days from the USA and cost approx US$25. From the UK approx 20GBP. All prices include work on the Preamp (Aluminium section)Chassis only Turn around time is estimated at 2 weeks, but will vary depending on shipping, workload, parts availablility and work required.

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New Information Copywrite by Glen Lambert 2007