Marshall JCM 2000 Repair – TSL 100

17/06/202604/06/2014 by rowan

Marshall JCM2000 repair

Update 2026: I get quite a lot of the JCM2000 series in for repair – both DSL and TSL. The most common issue is with the amplifiers bias circuit. We’ve made a fix for this problem, and it’s available for sale from ROS-2000 PCB for JCM2000 Amplifiers – Valve Tube Guitar Amps.

If you’d like to read more about how our fix was designed, then visit the ROS-2000 board design page.

I’m writing the blog post quite a while after the repair now, so I’m looking at my notes to remember the issue. The amp needed new valves and the owner had made a mistake with the biasing of the amp. 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. 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.

Fender Repair – Blues Deville

30/04/201509/10/2013 by lois

Fender repair time!

This is a lovely Blues Deville fender amp that’s seen some serious loving! The owner has been gigging it for 15 years. Unfortunately, first the Low gain input died, then the high gain became intermittent. The owner asked for a full valve amp service and I promised to repair the jacks as part of the service.

Repeated insertion and removal of the jack had moved the jack socket and over time pulled the PCB pads from the PCB. This led to the intermittent crackling that was heard and would have eventually torn the thin copper trace off.

Quality chassis mount switchcraft models were used in the repair to replace the two input jacks. These were wired into the PCB using flexible wires to remove the mechanical coupling to the PCB. Now if the jack socket moves then the wires will move and the PCB will not, and the integrity of the connection will be maintained.

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

Post by Keld Ampworks Guitar Amp Repair.

Myth Avoidance: Amp geeks often debate PCB vs turret or tag mounted components. I have to say that unlike many independent amp builders I’m a believer in PCB technology, but for mechanically and thermally stressed parts it is wise separate the component from the PCB to avoid causing stress. This fender repair is a good example of that principle.

Vox Repair – AC30CC2

14/12/201501/05/2013 by lois

Much as its nice to be taxed by a complicated repair, I love a simple job too! Despite a number of problems, this Vox repair was an easy fix for the customer, in fact, thanks to a dodgy screw the hardest part was getting into it! The customer complained of a crackle and intermittent volume dropout – I was able to sort both problems out for just £30!

These amps with the Alnico Blue speakers do sound great. I’d recommend checking them out.

If you have a Vox repair that needs some attention, please get in touch.

Dr Z Repair – Mini Z

11/12/201516/03/2013 by lois

Dr Z Repair – Mini Z

This Dr Z Repair was a simple job. This DR Z amp is a 2 valve class A amp with one ECC83/12AX7 and one EL84. In this case, the output EL84 valve was faulty, the heater.

The customer asked me to replace the amp with one the fancy ‘cryo’ frozen valves from Harma. I’m not entirely sure if this changes the amp’s tone or just makes Princess Leia fancy it. Maybe if you’ve tried one, you could let me know!

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.

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

Marshall Repair – JCM2000 DSL100

11/04/201804/03/2013 by rowan

Marshall Repair

This Marshall Repair was brought to me with one of those sneaky ‘hard to find’ problems. The amp was blowing fuses when the customer was playing it. He’d taken the amp to another repairer who hadn’t found any problems. Unfortunately the amp continued to blow fuses.

Guitar amplifier repairs of this kind often have to be treated in a different way. After an initial examination, opening up the amp and checking for any burnt components or loose joints I placed the amplifier on soak test. This involves playing a representative signal through the amp into a dummy load in the conditions that the amp was in when it was blowing fuses. During this soak test I observed that under certain conditions one of the power valves was sparking internally. I swapped the set of valves, re-biased and then placed the amp back on soak test. Since the amp wasn’t blowing fuses or sparking any longer, I decided that it was ready to go.

If you have a Marshall repair job that needs doing, please get in touch via the contact page.

Laney Repair – VC50

25/02/201527/02/2013 by rowan

Laney Repair

This Laney Repair was a mixed bag of several issues! The amp is a VC50 – 5 12AX7 valves and 2 6L6s in the output. This particular specimen has a strange an whine present whenever channel A’s spring reverb was used, also a faulty gain control on channel A, an intermittently working footswitch and a rather noisy pre-amp stage.

Since the amp is old and worth under £300 in used condition I advised the customer that an in depth repair might not be in his best financial interests. We agreed a price limit, within which I was able to fix the faulty gain knob, the reverb oscillation and the intermittent switch. This then allowed the customer to sell the amp in working condition and he put the money towards a new amp that suited his purposes more closely. Everyone was happy!

Forgot to photograph this one – apologies for the stock image!

If you have a Laney repair job that needs doing, please get in touch via the contact page.