Blackstar HT100 repair

Blackstar HT100 repair

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

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)

Polytone Minibrute repair

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.
polytone minibrute iii repair
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

Bugera repair V55

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.

Bugera repair V55Bugera repair V55 - replace standby switch

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.

Bugera repair V55 verdigris on PCBBugera repair V55Upon 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.


Bugera repair V55

Bugera repair V55Bugera repair V55

Bugera repair V55

Fender Blues Junior Repair – Urgent Repair

Fender Blues Junior Repair

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

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

Roland Cube Repair

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)!
Roland Cube Repair Jack Socket.jpg

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

Orange AD30R Repair - stockphoto

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


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.

Vintage AC30 repair – 1962 Vox repair

1962 Vintage Ac30 Repair

The guys over at Confetti in Nottingham brought me this vintage AC30 repair. It appears to be a 1962 JMI era Vox model but I’m an amp tech, not an amp historian, so I may be mistaken! It’s definitely an AC30/6 model, only made in smooth black vinyl in 1962. It’s very nice!

The customer brought this to me because they were worried about the amplifier getting very hot. I also noticed that the power cord was damaged and that the amp had a ‘Pin’ style voltage selector common in vintage amp repairs. I always recommend that this is wired out if not already.

The power cord has been replaced and the voltage selector wired to 245 (best match for modern UK), so the switch is now a dummy.

The overheating was caused by leaking reservoir caps which were replaced. Electrolytic caps have a lifetime of about 20 years so leaking caps are common in vintage amps. Faulty capacitors can lead to a much higher current draw through the transformer, overheating it, causing the issues we’re seeing. It also ties in with the internal HT being over 100V too low.
Vintage Ac30 Mains transformer temperature rise
I noticed that the tremelo mode switch had come loose and the resistor wires have sheared at the body of the device. They were replaced using vintage style carbon composition resistors for authenticity’s sake. (Do carbon composition resistors make a difference to tone? According to R.G Keen, The jury is still out!). If you have one of these vintage units, make sure that you keep the switch tight to avoid similar problems.

The amp didn’t run especially hot after the caps had been replaced. The output valves are all matched and measure sensibly, and the amp is cathode biased, so there’s little risk of the output stage being out of spec. I had another vintage AC30 repair in (a cream ’61 model), so I was able to make a proper comparison of the running temperature of the two amps. You can see how close they were in the graph above.

I’m pleased to say that the customer was very happy with the vintage AC30 repair! If you have a Vintage vox, or any guitar amp in need of repair, please get in touch.

Marshall JCM 2000 Repair – TSL 100


Marshall JCM2000 repair

I get quite a lot of the JCM2000 series in for repair – both DSL and TSL. I think it’s because they were so popular, rather than any endemic issues. This particular JCM2000 is a TSL100, the triple super lead model.

I’m writing the blog post quite a while after the repair now, so I’m looking at my notes to remember the issue. IIRC, the amp needed new valves and the owner mistakenly paired valves 1+2, 3+4, instead of the correct 1+4, 2+3. He knew how to bias his own amp and knew about pairing valves, but had always replaced for a matched quad in the past. When he paired the valves wrongly things had become hot and smokey – the valves red-plated For more information on valve amp bias, check my bias FAQ.

The amp had become so hot that a screen grid resistor (R78) – mounted upside down in the amp – had melted its solder connection and fallen out of the amp, melting some cabling where it landed. I replaced this resistor (with a lighter weight, but equally rated component). I also replaced the burned out suppression capacitor that can be seen in the picture.

The lesson to be learned: read my bias FAQ before replacing power valves yourself. If in doubt, ask!

If you have a JCM2000 repair, do get in touch.