EBS Amp repair – HD360 Bass amp repair

EBS amp repair

Today I repaired an EBS amp repair on a 2 hour turnaround! The customer brought the unit to my Newark workshop from Nottingham.

EBS are a swedish brand. It’s the first time I’d worked on an EBS unit, though I’ve played alongside bassists who’ve used EBS gear and been quite impressed.  I contacted their technical support team for schematics and they were great – after I’d signed my life away they provided me with schematics very quickly.

The amp had an intermittent fault on the filter (EQ). When engaging the filter active switch there was an intermittent buzz sometimes, sometimes a very tinny treble sound, sometimes too much bass and sometimes normal operation!

The problem turned out to be with the bass control, which had an intermittent resistive short to ground at all times. Fortunately I was able to repair the bass amp with parts that I hold in stock. It arrived at 10am and was back after repair and PAT testing with the customer by 12:00.

If you need an EBS amp repair, please get in touch.

Ashdown 550 Touring Repair

Ashdown 550 Touring Repair

The first task for last week was an Ashdown 550 Touring Repair, brought in from a Newark customer bec because the amp wasn’t making any sound – actually it was making a very weak tinny sound. I like ‘no output’ or low output repairs – they’re often easy to fix. Fortunately this was the case here.

The problem turned out to be a faulty speaker connection. The touring 550 has two 10″ LF drivers and a little HF driver. There was a loose connection in one of the LF drivers – I suspect from the way that wire broke that it had been badly wired in the factory. The weak, tinny sound was the tweeter operating on its own. I re-soldered this connection and added some heatshrink to support the connection. And the amp was working!
Ashdown 550 Touring Repair
It was obvious from the external state of the amp that it had been kept in a damp environment – the tolex and top wood layers had swollen around the screw joints and the fixings were horribly rusted. The owner had bought this amp in the faulty state, so I then proceeded to give the amp a 1 hour service to check for any further sonic gremlins.

The amp uses two preamp valves – 12AX7s. These were unbranded valves but tested fine on my valve tester.

I discovered that the master volume pot was quite badly oxidised, but cleaned up nicely with a bit of Caig DeOxit D5. The gain pot had similar problems. I also cleaned the sockets and the valve bases as a precaution.

Checking the output level into 6.8 ohms the amp produced >288W. This is about right for a 550W amp rated into 4 ohms, which would produce a proportionately larger signal, allowing for transformer sag.
 Ashdown 550 Touring Repair
If you have an Ashdown 550 Touring Repair, please get in touch.

Trace Elliot GP12 Repair – Keld Ampworks, Newark

Trace Elliot GP12 Repair

The symptoms exhibited by this Trace Elliot GP12 repair were a loud hum and distortion evident during note decay. Unfortunately I wasn’t able to replicate the customer’s problem which makes repair difficult, so I took a number of steps.

I left the amp on soak test for 2 hours, which involves heavily driving the output stage – this normally shows up faults that are temperature or power supply related.

What I did find was that one of the internal IDCs was causing audible noises when manipulated. I’ve seen this before with another Trace Elliot GP12 repair Mostly crackles, although there was a slight increase in hum sometimes which matched the symptoms described. Cleaning the IDC fixed this and that connection is now stable. I also cleaned the FX loop sockets because unused FX loops are a prime candidate for noises such as those described.

As part of a general service I also cleaned the Graphic sliders as there were a few little crackles – nothing to do with the described fault.

The next step in hum busting would have been to replace the reservoir caps. I avoided this because it adds significant cost and I had no concrete reason to suspect them. The description of the distortion on the note tail does sound a bit like caps, but the soak test didn’t reveal any problems with them.

The amp was returned to the customer. When I contacted him again the next month, the amp was still working well, another successful repair!

Note that the image is an old image, not the amp in question, it’s actually

If you are in need of a Trace Elliot GP12 repair, please get in touch via the contact page

Mesa Boogie Bass amp Repair

Mesa Boogie Bass 400+ Repair

This mesa boogie bass amp repair had the highest power valve count I’ve seen. The amp uses no less than twelve 5881 6L6 valves!

Like the recent fender amp repair this valve amp was blowing fuses. Also like the fender repair, the failure was down to a damaged power tube. Two in fact.

Much is made of Mesa Boogie’s insistence upon the use of mesa branded valves on guitar forums and these guys come in for quite a lot of stick. You can read Randall Smith’s defence of the idea here. My opinion is that the principle is reasonable for the majority of non technical users.

In this case, the amp had been fitted with Sovtek valves. Aside from the two failures many of the valves no longer matched well.

By testing mesa boogie valves in my valve tester I know what non mesa valves are within mesa parameters for use in their amps. I could tell that 4 of the sovteks were out of spec, meaning that 6 of the 12 needed replacing. After completing this simple task the amp was fixed.

If you have a mesa boogie bass amp repair please contact me via the contact page.

Ampeg Repair – SVT pro ii


What a huge beast this Ampeg repair is! Weighing in at an incredibly heavy 32kg I wasn’t sure that my workbench would take the strain!

It’s an SVT ii powered by 6 KT88 output valves meaning two massive transformers, owner for three mains and one for the output stage. When both must be capable of 300W continuous, that’s a lot of iron!

The owner was finding that the amp would drop in volume after a few minutes of running. It’s a common problem that I was quickly able to trace back to an oxidation issue, meaning a nice low cost repair for the customer.

If you have an Ampeg repair that needs attention, please get in touch , but you’re carrying it in!

Trace Elliot GP7SM Repair


A recent Trace Elliot GP7SM Repair, a amp service actually.

The owner brought the amp in for a check over before sale. This is a really beautiful Trace Elliot!

This particular AH350 (from the early 90s) uses the Trace MOSFET output stage, with Lateral type audio FETs. These are expensive, but worth it – the other Trace Elliot Bipolar output stage has some reliability issues that I’ve seen in the past.

This GP7SM was fine though. No problems.

It’s got a really cool optional UV light at the front. I haven’t seen one like this before. Makes the green front panel glow nicely. Great, if you like it!

Available to buy (as of Nov ’14). If you’re interested I’m obviously not going to publish customer’s details, but I can put you in touch.

Laney Repair – RBX700


This Laney Repair was an RBX700 with an annoying intermittent problem that I was at first unable to replicate. The customer descibed the fault as a volume drop-out after about 10m or so of playing. On the bench at the repair shop it worked for several hours on several occasions without any issues.

When I have an intermittent fault to fix, I first of all inspect all solder joints in the amp with a magnifying glass. Then I run a high RMS signal to heat up the amplifier and attempt to dislodge any power supply or output stage joints that may be affected by heat. I’ll then use insulated tweezers to ‘poke’ likely culprits inside the amp and in PCB amps like this Laney I’ll flex the circuit board by hand. I don’t recommend anybody does any of this to a live amp unless they really know what they’re doing.

Anyway, all to no effect in this amp!

The repair issue turned out to be the FX loop jacks known as the the ‘dreaded switching jack problem’ that I’ve heard about, mostly from non-UK repairers who deal with amps in more humid conditions. The FX loop jacks in most amps are in circuit all the time, they utilise back contact switching to pass signal through when no cables are plugged in. In this Laney, the FX loop jack contacts had oxidised and a layer of insulation built up to cause the described symptoms.

Oxidised jack contacts can be fixed using simple techniques described here.

The customer sensibly said ‘but I don’t use the FX loop!’ but this issue is actually compounded by lack of use – in the other jacks on his amp, eg the input jack, any oxidation would have been rubbed off by constant use.

I like these Laney RBX amps – they make a great sound and don’t cost too much.

If you have a Laney repair, please get in touch.

Carlsbro Repair – Cobra 80

Carlsbro Repair

Carlsbro Repair – Cobra 80

The owner of this Carlsbro repair complained of an intermittent crackling and occasional dropout. The fault was found to be within the power supply – a not uncommon source of trouble in bass amp repairs.

One of the pins on the bridge rectifier had developed a hairline crack through the pin. It was mounted to the rear panel, and when the panel flexed, the power connection arced, creating the described noises.

This repair was easily finished within the diagnostic period. When I find a quick fix for customer’s amps I always perform a routine ‘mini service’ to ensure the customer gets their money’s worth.

They’re not bad little amps these old Carlsbro Cobras – I gigged for many years in a jazz band using a Cobra 45!

If you have a Carlsbro Repair job that needs doing please, get in touch.

Trace Elliot Repair – GP7SM 200W

Trace Elliot Repair

Trace Elliot Repair – GP7SM 200W

This Trace Elliot repair is actually a service. My solid state service procedure involves the following steps:

  • Cleaning of all pots and connectors
  • Re-soldering dry or suspect joints
  • Any preventative maintenance required
  • Replacement of out of tolerance or defective components
  • Output power test.


I’ve seen a couple of Trace Elliot repairs in a pretty sorry state. The main cause of trouble is normally the ‘bipolar bear’ (bad electronics joke by the designer) output stage. This unit uses a lateral MOSFET output stage that is more reliable, so the customer has little to worry about. I’d recommend that owners of a Trace Elliot amp with the original stage have the output stage replaced at some point if the amp gets really heavy use.

Here’s the owner’s feedback, taken from the now extinct review site ‘www.qype.co.uk’ before it merged into ‘Yelp.co.uk’ and deleted all old reviews!
“ Rowan at Ampworks very kindly serviced my Trace Elliot GSM200 solid state head at extremely short notice. He did a thorough job of making sure everything was as it should be inside, re-soldered any suspect connections, checked the electronics and pots. I can’t recommend Rowan and Ampworks enough. John (Leicester) “(pigbobman, 28-03-2013)
Thanks for the kind words John. I’m glad you were happy with your service.

If you have a Trace Elliot Repair job that needs doing please, get in touch.