guitar amp repair Archives - Keld Ampworks Guitar Amplifier Repair

Hughes & Kettner Switchblade Amp Repair

21/11/2024 by rowan

I recently repaired a Hughes & Kettner Switchblade amp that had a shorted mains transformer, causing power failure. Thankfully, I sourced a replacement transformer from a genuine parts supplier, ensuring top quality for the repair.

After installing the new transformer, I performed a full service, which included cleaning key components and checking all connections. I also replaced the old output valves with a new pair of EL34s to restore the amp operation.

Following the Hughes & Kettner Switchblade amp repair, I tested the amp at various volumes, and it delivered as expected. The owner was thrilled to have their amp back, ready for upcoming gigs.

If your amp needs attention, don’t hesitate to get in touch—your gear deserves the best!

AER Compact repair

18/11/2024 by rowan

Recently, I had the pleasure of repairing an AER Compact 60 amp that was experiencing frustrating audio dropouts. The owner had noticed that sound inconsistently faded in and out during performances, which can be a nightmare for any musician.

To diagnose the issue, I conducted a soak test—a method that involves running the amp at gigging volumes for an extended period. This technique helps reveal intermittent faults in the AER Compact that might not be evident during a brief test. During the AER Compact repair I monitored the amp, it became clear that the dropouts were linked to oxidized switches. These switches, often overlooked, can degrade over time, leading to poor connections and sound cut-offs.

After cleaning the affected switches and ensuring all connections were secure, I re-tested the amp. The result of the AER Compact Repair? A solid, consistent output with no further dropouts. The owner was thrilled to have their AER Compact 60 back in perfect working order, ready for the next gig.

If you’re facing similar issues with your gear, don’t hesitate to reach out for a repair!

Blackstar HT100 repair

25/10/2018 by rowan

This Blackstar HT100 repair was completed for the co owner of an exciting new Grantham based venture ‘Melody Music Rooms’ in Grantham.

Melody music rooms are a rehearsal space, recording facility and teaching space located on Westgate in Grantham . It’s the brainchild of a group of Lincolnshire and Nottinghamshire music teachers who wanted to provide better music services in the area. Not just a building, they run jam nights and busking sessions featuring local young (and old!) musicians. It’s great to have these guys raising the profile of live music in the area, so do check them out on https://www.facebook.com/melodymusicrooms/.

I’m told that this amp has played Wembley(!) as the owners of Melody Music played some high profile support gigs with their old band. It had been retired when it started blowing fuses, but the owner wanted it brought back to life for the new Melody venture.

There were a couple of valves to replace and the amp had blown the bridge rectifer diodes. Unfortunately Blackstar don’t provide schematics for their amps so it’s always a bit of a tough job repairing Blackstar gear.

Normally at this point I’d put a clip of my repair video, but here’s the repaired amp being used in the studio at Melody Music Rooms.

If you need a Blackstar HT100 repair, please drop me a line.

Polytone Minibrute Repair (Minibrute III repair)

28/08/2018 by rowan

This Polytone Minibrute Repair came in from a Lincoln customer with an obnoxious hum problem. This unit is probably form the 1980s

The issue was solved by adjusting the output stage bias point and improving the connection between the screw mount power supply capacitors and the power amp stage.

The amp is a bit of an oddball in terms of construction, with the preamp contained in the top of the amp, and the power amp in the base of the unit. The power amp unit is held together by the capacitor screws and two large heatsinks.

If you need a polytone minibrute repair, please get in touch.

Bugera Repair – V55

19/01/2018 by rowan

Turned this Bugera repair around quickly in time for it’s owner’s gig in Skegness. The amp is a vintage 55, or V55.

The amp was brought in for a standard 2 hour service, with a few particular points of attention. The owner had noticed that the clean channel was overdriving much sooner than previously. Also the standby switch was broken.

After testing the valves in my valve tester I discovered that the cause of the clean channel change was a very worn Shuguang preamp valve. I replaced it with a new Tung Sol 12AX7. I also discovered that one of the Bugera branded power valves was also faulty, requiring a change of both power valves to EHX 6L6s and a rebias.

I’m not a big fan of Bugera’s bias control – a phono output that makes the bias voltage externally accessible and a little finger trim pot. The trim pot is a nightmare to adjust – screwdriver turned pots are much more accurate. And the phono socket exposes a relatively large voltage of between -40 and -80VDC. Also, the bias voltage isn’t a very good way of measuring bias (see this post by Aiken amps). Behringer use it as a way of encouraging you to buy their pre-graded valves. I use the most accurate cathode current method of biasing with a multimeter and a set of custom probes. I set the bias to 38mA, which is 70%.

A specific request on this Bugera repair was to replace the damaged standby switch. It was a quick and easy job – as seen in the image. I often hold generic parts like this in stockin order to fit a variety of amps, or I can always order specific pieces in to suit an amp’s aesthetic.

Upon inspecting the board I noticed a number of areas that were corroded – in the picture you can clearly see the Verdigris (copper carbonate) on component pins and PCB pads. I desoldered these pads and freshly resoldered them. I also spotted a couple of dry joints on valve bases and fixed these up. After this stage I refitted the PCB.The original screws were secured with thread lock, so instead I added a toothed washer and a plain washer – many manufacturers and repairers omit the plain washer, but this is very important in order to not damage the PCB surface and thus loosen the screw.

I was interested to note that the amp uses a ‘Turbosound designed’ speaker. This is because Bugera and Turbosound are both owned by Music Group (Behringer). The amp also uses a V1000 cool audio (I think this is anothewr behringer brand) multifx chip and a V4220M codec on a mezanine board to create the digital reverb.

If you have a bugera repair job for me, please get in touch.

Fender Blues Junior Repair – Urgent Repair

02/10/201730/09/2017 by rowan

This Fender Blues Junior Repair was an urgent repair job for a London based guitarist. I got the amp at 23:30 on the Saturday after a gig in Southwell near Newark and had it diagnosed by 11:15 the next morning before he returned to the ‘big smoke’.

Actually, big smoke was obviously a problem that this amp had experienced in the past as can be seen in the image. A power valve had blown and seriously damaged the PCB. Unfortunately the amp had been taken to a Nottingham music shop for repair and I’m afraid they didn’t know what they were doing!

Whoever fixed it has did something weird and wired up a valve pin that doesn’t connect to anything – it should have been going to the cathode, although they have then wired up the cathode separately. There’s no actual harm with this, it just suggests they didn’t know what they were doing!
They also not secured the valve base very well, so it rocks and lifts the pins when you remove or move a valve. This has started to pull up a PCB track on one of the power valves. This will almost certainly cause problems in the future.

I’ve performed a temporary fix on the problem pin 7 by shaving the solder mask off the copper and adding more solder to give the pin an extra connection.

I recommended rewiring the whole power stage at some point in the not too distant future because the amp is a bit of an accident waiting to happen. Unfortunately there wasn’t time to perform the full repair before the customer left for London.

However all this was a chance discovery. I was actually asked to look at a faulty spring reverb on this blues Junior repair. The problem turned out to be with the tank itself. I checked continuity and ground on the cables and observed signal getting to the tank and nothing coming out.

I’ve got a short Accutronics reverb tank kicking around from an amp I gutted so I thought I’d try it, The impedances didn’t match and it sounded terrible with the Blues Junior! But it proved that this was the only problem with the reverb.

The good news is that the customer could buy a spring reverb unit and fit it himself – you only need a screwdriver.

The customer was kind enough to leave a review on my Facebook page.

If you have a Fender blues junior repair, please get in touch.

Hughes and Kettner Tubemeister repair

03/11/202008/09/2017 by rowan

I’ve wanted to do a tubemeister repair since they first came out a few years back. I guess it’s a testament to general quality that this is the first to appear on the bench. I’m a big fan of the design aesthetic. 3 channels and a midi switching amp for £550ish is a lot of bang for your buck.

However, the owner was more worried about a different kind of bang – and a flash behind V1 when he flicked the standby switch. Afterwards the amp wasn’t making any sound at all.

Hughes and Kettner service manuals are easily the most detailed of any of the modern manufacturers I’ve seen (honourable mention goes to Roland/Boss) but this wasn’t needed to disassemble the chassis and get back to the PCB. The chassis is all metal which reduces weight and size. There’s a bent metal lid, removable end pieces and a separate metal base.

Hughes and Kettner have a power tube management system called TSC. This checks tube balance and bias. Orange amps have a similar system (see orange amp repair). The Hughes and Kettner TSC can occasionally fail and show up an error code on the TSC lights. The parts must then be replaced with these parts. But that wasn’t necessary here.

I discovered that the HT fuse had blown, which accounts for the bang the player heard. The valves all tested good, but since the TSC turns on the power tubes using a FET in the cathode I strongly suspected the power valves. After replacing the valves and the fuse the amp came back to life!

If you have Hughes and Kettner tubemeister repair, please just drop me a message and I’ll get you up and running again.

Roland Cube Repair – Cube 80

21/10/2016 by lois

This Roland Cube Repair was a cube 80 from the ever popular Roland Cube range. These amps have a reputation for indestructibility and I’m not surprised. Despite their popularity and the hundreds of amp repair enquiries I receive, I’ve only ever had 3 Roland repair enquiries! Two were from the Roland Cube range, of which this is one. You’ve probably also seen the Anderton’s videos in which they set a Micro Cube on fire and shoot it at the local archery range! It survives the archery and the electronics survives the inferno (the paper speaker cone burns of course)!

But this one is not even really a faulty amp. The owner had used a cheap balanced jack as a guitar cable. Unfortunately the cable plug had disintegrated inside the amplifier, leaving a jack tip inside the input socket.

It was a relatively simple job to remove the rogue part, but I got an opportunity to admire the rigid construction of the amp whilst doing it.

If you have a Roland Cube repair you’re unusual(!), but please get in touch and I’ll get it sorted for you.

Orange AD30R Repair – Valve amp Service

21/10/2016 by lois

This Orange AD30R Repair came in semi-urgently for a full service. The customer had a gig with his band at the Bodega in Nottingham on the thursday and he brought me the amp on Monday night. I do offer an urgent 24 hour turnaround service but fortunately the customer didn’t need that, just a 48 hour turnaround!

After testing all the valves in my valve tester, I determined that the EL84s in the output stage were mismatched. It’s important to match output stage valves to ensure continued good amp health and reliable tone. Fortunately I hold stock of EL84 valves so it didn’t delay the service.

I confess I’ve had to use an Orange AD30R image from Google because I forgot to take a photo!

If you have a Orange AD30R Repair, please let me know and I’ll take a look!

Egnater Repair – Rebel30

30/11/201517/06/2015 by rowan

This amp is a Rebel 30 by Egnater. At first, I had a bit of trouble with the Egnater repair but I’m pleased to say that I found a solution for the customer. The diagnosis itself didn’t prove a problem, the problem was simply the gain potentiometer itself. This is a dual ganged part (2 pots in one). One half of the pot behaved fine, the other half was open circuit in the first part of the turn. This caused a loud clunk at the point where the track re-appears (see the video).

There was no maker’s mark on the pot so I couldn’t be sure what brand it was: probably a far eastern part sourced by the contract manufacturers. It’s quite easy to find dual ganged 500K pots from guitar gear suppliers but they’re designed to fit inside guitars or in ’boutique’ hand wired amps – none of them will fit in to the space in this tiny Egnater repair.

Of course I tried to contact Egnater, but received no reply. Unfortunately I wasn’t been able to find an alternative panel mount part that will fit into the space constraints inside the case. There are switches and capacitors internally that would prevent the available chassis mount parts from being suitable.

However I came up with a fix that sorts some of the issues with the existing pot. There is still a small bit of silence for the first part of the turn, but the very loud bang is mostly gone, with only a whisper remaining, inaudible unless you’re listening for it. The sound returns whilst the channel is still within the ‘clean’, not yet crunchy part of the drive channel turn, so all the useful elements of the gain channel remain.

Mathematically, the fix I’ve employed affects the potentiometer ratio only very slightly (as in the graph), I’d argue imperceptibly. The truth is it’s probably even closer than the theory suggests, as real pots don’t curve this smoothly! I’ve done a video comparing the tone before and after the mod, to demonstrate that there’s no real difference, but who knows, you may pick up a nuance. As you can hear, the bang is very evident in the video before the mod, but inaudible after.

The video appears here:

I’m pleased to say that the customer was very happy with the Egnater repair! If you have a Rebel 30, or another Egnater in need of repair, please get in touch.