Category Archives: Amp repair

Fender Pro Junior Hum Investigation

By Frank | Published: July 7, 2021

The Fender Pro Junior amplifier is popular amplifier; it sounds good, is portable and loud enough for smallish gigs (the sort I play for example!) if you don’t want ultra-clean. It does have an Achilles heal which is that it prone to be noisy, often to the point that players find their amps unusable, so […]

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Gallien Krueger MB 150 Transformer Replacement

By Frank | Published: June 30, 2021

The Gallien Krueger MB 150 is a popular bass amp, especially with double bass players. We recently had an MB150 in for repair with a blown mains transformer, GK part No. TTO-10879-02 (equivalent to TTO-10879-01) Unfortunatley trying to source a replacement was tiresome. The UK distributor quoted 6 months lead time, and the only other […]

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MESA M-Pulse 360 Bass Amp Repair

By Frank | Published: May 31, 2021

We recently had a MESA Pulse 360 bass amp in our new workshop for repair, with a fault description that it was powering up but not passing any signal. I’d repaired an M-Pulse 360 last year with a identical fault condition, so we wondered whether the fault in both amps was being caused by the […]

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Upgrade PCB for Fender Blues Junior

By Frank | Published: June 3, 2019

The Fender Blues Junior (BJ) is probably Fender’s best-selling valve amplifier. However, it does have a number of poor design features, not least the layout of the PCB on which the EL84 power valves are mounted. The EL84 is a well-designed valve as the high voltages on the anode (pin 7) and screen grid (pin 9) are […]

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WEM / Watkins Copicat tape echo repair extravaganza

By Frank | Published: October 22, 2016

We had a bit of a WEM / Watkins Copicat repair extravaganza at JPF amps. Here’s a nice photo of three of the 8 (yes eight!!!) we had in for repair.   Great sound that can only really be done by a genuine tape echo.

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Leslie 122 Relay Repair

By Frank | Published: October 3, 2015

Here’s an emergency repair I did for a Leslie 122 cabinet. The fast / slow relay had died, and I needed to find a solution with parts from Maplins! The fast / slow replay relay switching is quite interesting in the 122. The cabinet is connected to the organ by a 6 pin connector, however […]

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Fender Tonemaster (Tone-Master) Guitar Amp Repair

By Frank | Published: August 27, 2015

Although much credence is given to the notion that hand-wired amps are inherently superior to other methods of construction, this is certainly not always the case. Here’s the inside of a Fender Tonemaster amp, which as you can see is a total rat’s nest of wires. I dread to think what Harry Joyce would have thought […]

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Gallien Krueger 2001rb Bass Amp Repair

By Frank | Published: June 19, 2015

Gallien Krueger make amps that are both well engineered and good sounding. I recently had a GK 2001rb bass amp in for repair. This is a complex machine (for a bass amp: see photo of innards); it has two 500W class G amps to provide do the heavy lifting in the low end (one each […]

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MESA Carbine M9 Bass Amp Repair

By Frank | Published: June 15, 2015

Here’s some photos from an emergency repair I did for the band Swans. I got phone call from their tech saying that one of their amps. a MESA Carbine M9, had died with smoke emanating from the innards. Swans needed the amp turned around quickly as they were on tour. I said that this didn’t look […]

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Hughes & Kettner TubeMeister 18 Repair

By Frank | Published: June 4, 2015

I’ve had a few Hughes & Kettner TubeMeister 18 amps in for repair. This is an 18W fixed bias amp that uses 2 x EL84s in the output stage. These amps have a quite sophisticated biasing system that automatically adjusts the output valve grid voltage for optimum bias, and also shuts the amp down in the […]

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