Orange

Orange amps are characterised by their distinctive colour, original sound, great build quality and over engineering that sets them apart and above their rivals.

Orange Bass Terror

The original bass terror in its small tin box with carry bag was an immediate success. Great sound and highly portable. It comes in 500w and 1000w variations and is pretty reliable.

Some issues that I have come across are:

  • Power supply dying, blowing fuses repeatedly usually suddenly. Fortunately repair is achievable and if not replacement modules from Orange are available.
  • Power amplifier burn out caused by overheating, overload or just bad luck.
  • Other faults are typical service things like valves, control pots and jacks.
  • Like all class D amps reliance on good fan airflow is essential so make sure to clean it out every couple of years or so.

 

Repair success is pretty good on these amps thanks to the excellent support from Orange.

Orange Rocker 30

These 30w, 1×12, dual gainy channel amps have very little to go wrong in them.  The only issues I have seen are from typical wear items like damaged pots, jacks and valves.

Amp Restoration

Capacitor Restuffing

This section is about some techniques and ideas for restoring old equipment.

First section is on Cap restuffing.

On vintage amps and radios we often want to retain the amps capacitors since they such a part of the look. Particularly true when they are visible like on Ampeg flip tops.

In the above case of a delightful Park 50 amp several of the caps had dried up and various repair solutions had been tacked on with tape or glue. This conscientious amp enthusiast wanted to restore it properly and asked me for some options.

In this case because the cap cans are quite big 35mm and 25mm it was easy to restuff them. What is restuffing? Well it is what it sounds like. Replace the innards and have new capacitors that the eye cannot see.

It is a time consuming that involves cutting into the aluminium can of the capacitor, heating up its insides so that gunk and glue inside melts and can be removed. Next we need to find suitable replacements such as the excellent miniature range from Rubycon that are between 10 and 12.5mm diameter and similar height so fit into the cans directly.

I like to use two capacitors in series, with equalisation resistors to make the working voltage that each cap must deal well within its range. On This park B+ was over 450 the same rating as the caps but in fact when I checked the spec the caps peak is 450 and working is 450vdc.

Care needs to be taken with adequate insulation material since the series cans will have high voltage on one of the cans. I like to do a PAT insulation test on the the cap to be sure that there is no possible short as well.

Once the caps are in the can then the wires are brought through tiny holes to join on to the old cap terminals. Don’t forget that our original cap can is in two halves now but we can join together using wire diameter heat shrink and optionally some plastic plumbing tube internally is strength is required. This sounds a bit flimsy but don’t forget that the cap is going into a metal holder and that will provide a firm grip on out new but old looking part.

Visually you can only tell that cap has been restuffed if you look very closely. You can see the wires coming through the top but that is all.

And it’s great to know that you are running with brand new caps. In the case of this Park 50 the amp was a little bit hummy beforehand so has benefited from the new caps although it was not so bad to have needed them doing.

Restuffing a capacitor like this typically takes a couple of hours time, great patience but the results are rewarding.

Visually hard to spot

Tube Amp Doctor Kit Amps

Kit Amps like this beauty from TAD offer the best way to get an unaffordable amp into your hands for a reasonable amount of money.

This particular remake of a classic Marshall is pretty much identical to the original and has a few upgrades that make it better.

Things like ceramic valve sockets, noiseless (well compared to marshall) transformers and the cloth wiring adds to the sense of luxury.

Ok you never see this stuff but it is kind of comforting knowing that it is there inside.

Once built you then own a classic sounding amp with an expected lifetime of forever.

JTM45/100w KT66

HiFi

I don’t really work on HiFi, why you ask?  It’s a fair question and the reason is that there are just so many different makes, manufacturers that it is difficult to gather any experience on them all.  So there are a few makes that I like or have success with and I will accept them for repair projects.

Some of these makes  are:

    • Marantz
    • Exposure
    • Cyrus
    • Most valve amps

 

Marantz Hifi

I really love the sound of the old Marantz HiFi amps from the 1970s.   Walnut veneer chip board surrounds, glowing lights what a joy.  I don’t usually work on HiFi but here I make an exception.

These amps are made to the highest standards and feature great transformers and parts top to bottom.

A couple of issues I have come across and are worth sharing to help others.

Crackling no matter volume level

Seen on Marantz 4240 but applies across the range.  In this scenario the amp works as normal but produces a fairly constant rustling / sizzling bacon style crackle. The fault may increase gradually folowing switch on or be permanent.  Even with no input connected the fault is present and not effected by the volume control.

The cause is leaky tone recovery transistors on the PCB driving the amplifier blocks.

Worn Capacitors

Everywhere on the internet people talk about replacing capacitors.  It’s a bit over stated.  Often their are visual signs like rupturing. leaks and yes these should be replaced in pairs but shotgunning the whole amp is wasteful of time and money and unlikely to be worth it.

So concentrate on where it is needed.

    • visibly worn decoupling caps
    • interstage electrolytic coupling caps
    • Tantalum caps

If you have one of these amps that you would like to sell either for restoration or parts donor I would be interested to hear from you.

Matchless

They really are…


Shock absorbing valve sockets
Matchless Clubman 35

Great build quality start to finish.

  • Carpeted capacitor bed. Though red tape is a bit of surprise.
  • Sealed pots
  • Paper wound transformers
  • All screws locked with sealant
  • Anti vibration valve sockets
  • Valve clamps
  • Ventilated pre amp tube shields
  • Neat wiring and point to point layout
  • Very low noise.
  • Anti vibration pad lined chassis

Mesa Boogie MK IV

Too many controls on a Boogie’s front panel for me to be a fan but people seem to love them.

This one below was cursed with a strange fault of bias instability which would lead to humming as the bias drifted off and ultimately to red plating after 30 mins or so.

The cause of the fault was some sort of PCB contamination. I initially thought that this was some sort of chemical residue on the PCB but after much cleaning it didn’t really improve.

In some conditions the amp would actually spark as voltage jumps between worn out circuit pcb paths as in the case of the bias supply or worse when adjacent parts of the pcb are a little too close. Then unrelated HT would jump to say a channel switching circuit. Take a look at the videos for examples of this.

The solution in this case was to remove affected parts from the PCB and mount them off the board following point to point construction methods. The challenge here is the space. Boogies are famous for cramming a lot in so it is a very cramped working environment.

Fender Supersonic Twin 100

Seen a few of these recently and worth sharing some problems and interesting solutions that I have found.

Fender no sound or fading sound

If your amp produces no output and the lights on the back are flashing about then you might have a faulty autobias unit.

The auto bias unit fitted to these amps,  as well as some Fender Bassmans I believe dynamically control each valve’s grid bias thus ensuring that your amp’s valves stay perfectly adjusted no matter what the wear level or matching level is with the tubes. The board does this by measuring the bias current and comparing it with a reference signal and adjusting the grid bias accordingly in fact it does this thousands of time a second thanks to an innovative little chip. You can adjust the control a little as well between cold, medium and hot levels which is nice.

Unfortunately this innovation seems to be a little unreliable. The two issues I have observed are either: 1), unreliable cables connecting the auto bias unit on the amp’s rear panel to the main PCB,  or 2)  a faulty autobias unit which seems to either permanently fail or work for a moment at start on and then fail with flashing lights and no sound. Fortunately the board fails safe and pushes the power valves bias way into cut-off silencing the amp but protecting those precious tubes. So, what is the solution to this annoying issue?

Well you could just replace the auto-bias unit and hope that it works out ok. However the amps that I have seen with this fault are just a few years old and so I wonder if replacing the autobias unit could be a just a temporary short term solution.

What about another approach such as down grading the amp to a simple bias pot and accepting that you need to always use well matched valves. Well that is an option and just what one of clients recently asked for as he was fed up having an unreliable amp.

In theory this should be quite a simple mod but the complication lies in the fact that this amp has two operating levels: club and arena and this means two different bias levels rather like the Famous Fender The Twin (or evil twin) from the late 80s.

With my mod you preserve the club and arena feature by automatically switching between two bias levels as you move between the two modes.

The mod consists of removing the auto-bias PCB completely and replacing it with a tag strip of parts, a bias pot away from the hot power valves.  The bias pot is located on the underside of the amp near the effects loop well out of the way of the power valves and does not add significant noise levels.  The result is an old school amp and one that is much more reliable.

This seems like a downgrade but really it is copying the design of the Fender twin which has been successfully powering amps that belong to some of the world’s most successful musicians. So why not?

Fender Supersonic Crackling Noise

Another problem with these amps is excessive cracking noise. This sounds a bit like crackling of old plate resistors or more descriptively the same as sizzling bacon in a frying pan; just a little louder and really annoying. It certainly does not have any vintage amp charm. None at all. In the case of the most recent amp it was impacted by the reverb control which can be helpful to know when trying to fault find such an issue.

What I have observed is issues with internal layers in the PCB multi layer board. The layers have broken down and make am unreliable connection and that gives you a crackle through your speaker.

If you have been affected by these issues leave a note on this page or get in touch to book yourself in for repair.

 

Vox AC15

Restoration project of a 1962 Vox AC15.  Clearly seen some earlier work clue being the orange drop capacitors fitted around twenty years ago.  Most of the carbon composition resistors were high asnd showing signs of surface cracks so all replaced.  The Mullard valves appear to be original and in fine working order.  What a  great find.

Wurlitzer 750-E

All the way back from 1941 this is got to  be one of the oldest amps that I have worked on.  Pair of 6L6 output power valves red chassis, lots of rust – sounds good as gold.

Bit of history with this amp as it was stationed in Pearl Harbour back in the day and presumably saw some action.  Later on it found its way over to the UK at some point where it has been waiting for restoration for some time.  Virtually all of the old resistors were drifted so much in value that the amp would barely output anything.  That restored and a few worn out valves replaced and the amp is back to full power.  Not surprisingly it sounds great and distincively to a different era.

Wurlitzer 750-E

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