FAQ

How much do you charge?
How long will it take to repair my amp?
What does a service involve?
Do you repair transistor amplifiers?
Do you repair bass and keyboard amplifiers?
Do you modify amps?
Should I modify my amp?
Will modification affect the value of my amp?
How much do JPF amplifiers cost?
Do you repair/modify pedals and other FX units?
Do you sell valves?
Can I supply my own valves?
Do you sell speakers?
Do you buy old non-functioning amps/pedals?
What is a “cap job”?
What are filter capacitors?
What is Blackface conversion of a Silverface Fender amp?
How will Blackface conversion affect the sound of my amp?
What are NOS valves?
Are NOS valves better than new valves?
Why are valve rectifiers getting so popular?

How much do you charge?

A brief look and advice is FREE, otherwise our minimum charge is £48 (1 hours labour) for amps and £22 for pedals, plus the cost of parts. There after we then charge £24 per half hour and £48 per hour plus the cost of any parts required.

Is is very rare for a repair to take more than 3 hours.

We always try to give an accurate estimate for any work after we have made an initial assessment. If a repair is not economical, i.e. it would be cheaper to buy a new amp or pedal, we will always tell you.
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How long will it take to repair my amp?

We carry spares for most popular makes of amplifier, so we can usually turn your amp around in a few days. However, if your amp needs a new transformer or some unusual parts then there may be a delay as we will have to source these.

If you need your amp fixed/serviced in a hurry, get in contact with us and we will see what we can do.
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What does a service involve?

When we service an amp we do the following: we clean all the pots, jack sockets, and valve sockets; we check that all the valve sockets are correctly tensioned; we check the valves for microphony; we check the integrity of the safety earth connection; we check that the output valves are correctly biased; we check the state of the electrolytic capacitors and we give the amp a general check for other potential faults such as dry joints.

We will also play the amp! We and our colleagues have extensive experience of most classic amplifiers, so we can tell if your amp is not sounding right.
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Do you repair transistor amplifiers?

Yes, we are happy to work on all types of guitar amplifier including transistor amplifiers.
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Do you repair bass and keyboard amplifiers?

Yes, we are happy to work on most types of instrument amplifiers.
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Do you modify amps?

Yes. We have a number of modifications that we can perform on a wide variety of amps to help you achieve the sound you are looking for. Popular mods include Blackface conversion of Silverface Fender amps and smoothing out the distortion on high gain amps.
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Should I modify my amp?

There are many small modifications that will improve the tone of your amp. So, if you are nearly, but not quite there with your tone then a mod could be the answer. However, the need for radical surgery normally indicates that you own the wrong amp: buying a different amp may well be the best (and cheapest) option.

If you are on a budget, and who isn’t (!!), there are many good amps on the second-hand market that can be tuned up to give excellent results: for example the Fender Blues Deluxe and the Laney GH100L. Get in touch with us and we can advise you on both buying an amp and what we can do to improve your current amp.

We love vintage amps! We are genuinely excited by the prospect of nursing a sick amp back to health. We would never do anything to damage a vintage amp – so we really can’t put an effects loop and channel switching into your Tweed Deluxe!
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Will modification affect the value of my amp?

Modifications might give you the tone you always wanted, but unfortunately they rarely add value to your amp.

The main determinants of “vintage” amp value are the desirability of the amp and the condition. Regarding the condition of the amp, other than the obvious cosmetics, collectors look for original transformers and speakers.

We will not perform mods on vintage amps that we think will irreversibly reduce their value.Back to the top

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How much do JPF amplifiers cost?

See our products page for our production models, the Sir Charles 15 (£750), and the King Charles 30 (£825).

Our bespoke amplifiers range from around £750 upwards depending on your requirements: the solid gold knobs are expensive!
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Do you repair/modify pedals and other FX units?

Yes. About a quarter of our workload is pedal and FX related. However, our turnaround time on pedals is slower than amps in order to keep the repair economic.
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Do you sell valves?

Yes. We stock examples of all the popular guitar amp valves, which are fully tested/matched and reasonably priced (click here for our price list).

However, as we are not a specialist valve retailer, we don’t stock a wide variety of valve brands– just those we think sound good and are reliable. If you are interested in trying different types of valves in your amplifier then we can advise you where and what to buy. You can find the web-sites of valve vendors in the links section.
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Can I supply my own valves?

Yes, this will be no problem.
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Do you sell speakers?

Yes. We are the London distributor of the Tayden brand of speakers.

Tayden offer excellent Alnico and ceramic British-style guitar speakers, and seriously heavy duty bass speakers, and we aim to have all their most popular models in stock.

We are also working with Tayden to develop some decent Fender-style replacement speakers at sensible prices which will be exclusive to JPF Amplification.

We always have a selection of vintage, as new, reconed and secondhand speakers (click here for our price list).

If the speakers in your amp/cab have died we can either get them re-coned — probably the best option for vintage speakers — or order new speakers. We have extensive experience with many types of speaker and are happy to advise you on which speakers would suit your needs.
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Do you buy old non-functioning amps/pedals?

Yes. We’re always on the look out for defunct valve equipment and old dead pedals to play with.
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What is a “cap job”?

A “cap job” is the jargon used to describe the replacement of all or most of the electrolytic capacitors in a piece of equipment.

Electrolytic capacitors are components that have a lifespan dependent, not only on the length of time they are used, but also the conditions in which they are used: temperature and voltage being the main factors.

They contain a gel that dries out over time: a process accelerated by the heat produced in an amp.

Electrolytics usually deteriorate slowly and imperceptibly over years until they become noticeable, producing audible hum, crackles and pops. If left they become prone to catastrophic failure that often damages other components, and in the worst cases they can explode. It is wise to replace them well before you reach this point!

On replacing ageing electrolytic capacitors you will notice your amp sounds punchier and runs with less hum and noise. The maintenance schedules of pro-audio equipment normally require the replacement of electrolytic capacitors on a regular basis depending on usage. As part of a service we test all electrolytic capacitors with an ESR meter to let us know which have reached the end of their useful life.
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What are filter caps?

Filter caps are electrolytic capacitors (see above) found in most power supplies.

They smooth, or filter out, the ripples left after rectification of the alternating mains voltage, producing the clean, steady DC voltage that most equipment requires: hence they are called filter or smoothing caps. Valve amps require a very high DC voltage (typically 300 to 700 V) to operate, so the filter caps used in these amps have to be capable of tolerating these high voltages.

All capacitors store energy within them, and filter caps are designed to store a lot of energy which they use to maintain the high voltages found in valve amps. They are easily capable of storing enough energy to maintain lethal voltages even after the equipment is switched off. If they are not safely discharged they can deliver fatal shocks. If in any doubt do not touch them!
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What is Blackface conversion of a Silverface Fender amp?

After CBS bought Fender in 1965 they initially changed the cosmetics of Fender amps from “Blackface” (having a black front panel) to “Silverface” (silver front panel).

Early Silverface amps from around 1968 are electrically identical to Blackface amps, and can be recognized by the aluminium trim around the grille cloth. Unfortunately, CBS soon started to introduce a number of “improvements” to most of the Fender amp range, usually with the aim of making the amps distort less: perfectly timed to coincide with the advent of heavy rock!

We can rectify these “improvements” by converting the circuit in your Silverface amp back to the Blackface circuit. As Silverface Fenders are still relatively inexpensive, even with the cost of the conversion and a re-valve, you will end up spending less than the price of a re-issue Blackface, if Fender make one that is.
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How will Blackface conversion affect the sound of my amp?

It is difficult to describe the benefits of Blackface conversion without it sounding like audiophile flapdoodle, however here goes. Essentially the sound becomes more dynamic and fuller without the high-end sharpness associated with Silverface amps.

You will also find that your amp will have more punch, and distort more musically and at slightly lower volume than before. We always offer to convert your amplifier back to Silverface spec for free if you are not happy with results of the conversion. No one has yet taken this offer up.
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What are NOS valves?

NOS stands for New Old Stock. These are valves that are unused, hence “new”, but are no longer currently in production, hence “old stock”.

Interest in NOS valves started in the 1980s when most Western countries were winding down their valve production. Some valves such as the KT66 and GZ34 went out of production completely, and the general consensus was that the valves being produced in the old Eastern block, or China were of poor quality.

There is much truth in this view; however this is not always completely fair as some companies were often branding “equivalent” current production valves as something they weren’t, and using them inappropriately. An example of this is the Russian 6P3S, which we have seen labelled as 6L6-GC, 6V6-HD or KT66, when in fact it is none of these.

Due to dwindling supply, the price of many NOS valves has risen dramatically, with the price of a quad of matched NOS GEC KT66s, if you can find one, now in the eye-watering category.

Fortunately, there are an ever-increasing number of new production valves to choose from. For example, there are currently at least 4 types of KT66 in production, up from none in 1997, and at least 5 types of 6V6-GTs in production, up from 1 in the mid nineties.

Thus, for nearly all guitar amplifiers there are several current production valve options, making chasing down of potentially very expensive NOS valves unnecessary.
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Are NOS valves better than new valves?

It is pointless to make generalizations about NOS valves, and it would certainly be incorrect to state that all NOS valves are better than all current production valves.

We have had very good results with for example NOS RCA 6L6-GC black plates, Sylvania 6L6-GC STR387, and Sylvania 12AT7s, and there is no doubt that these deserve their reputation as some of the best ever made, although we would be hard pushed to definitively state that these are better than equivalent current production valves.

On the other hand we have been disappointed with some (but not all) NOS Mullard ECC83s, which command a very high price, and we know of one very well-respected amplifier manufacturer in the US who prefers JJ-Tesla E34Ls to NOS Mullards.

One thing to bear in mind is that NOS valves have been in storage for many years, and may have deteriorated e.g. gas leakage into the envelope etc. Thus if you want to try out NOS valves, unless they are very cheap, buy them from a vendor who will test them extensively, and preferably one that gives a guarantee.

As NOS seems now to be an indication of quality, and hence premium price, it is noticeable that a number of vendors have been labelling recent production Eastern block valves as NOS. These are often the very “poor quality” valves that promoted the NOS phenomenon in the first place!
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Why are valve rectifiers getting so popular?

With the advent of very cheap silicon diodes valve rectifiers were considered obsolete technology and by the late 1980s no major guitar amp manufacturer was using them.

Four 1N4001 silicon diodes for use in the bridge rectifier cost less than £0.10, whereas the popular GZ34 valve rectifier typically costs at least £10.

Besides cost, valve rectifiers have several other disadvantages when compared to silicon diodes: they are relatively fragile; have a finite life; they require a separate tap on the power transformer to power their filaments adding further cost; and their filaments generate heat which has to be dissipated, for example a GZ34 generates 10 W of heat just to power the filament!

They also have relatively high internal impedance, which can be seen as either an advantage or a disadvantage.

If you want maximum power from your amplifier, and this seems to be an obsession in the sales departments of many manufacturers, then you want a low impedance power supply, ie silicon diodes.

However, if you want to experience a phenomenon often referred to as “sag” then a higher impedance power supply is better.

Despite what many manufacturers claim nearly every push-pull guitar amplifier runs in a mode of operation called class AB. A consequence of this is that when the amp is played at higher levels more current is drawn from the power supply. If the power supply has a relatively high impedance valve rectifier, the increased current draw will cause a greater voltage drop across the rectifier, lowering the supply voltage to the amp. The sonic effect of all this is to compress the guitar sound when the amp is played at higher levels, and many players like this effect.
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