Russ Fletcher's HiFi, audio and beyond...

Monday, 7 November 2011

An ageing Fender amp

A very old Fender Tremolux guitar amp recently entered the workshop. A brief investigation revealed that it was a 1962 6G9-B, a blonde, brown face.

About 30 years ago, the owner had bought a good working Tremolux combo and this "non-runner" came with it as a spares donor. It had been in his loft ever since and now it's time for a total electronics rebuild.

A little bit scruffy.

Pity we're not going to re-do the tolex as well as the internals.

The chassis is looking a bit tired.

The filter caps are in various stages of decay and the cover is missing.

A few valves missing, but we're going to replace them all anyway.

This is where most of the work is going to happen.

And a view from the other side.

Check-out the hand wiring.

The mains transformer turned out to be defective, so we'll have to find a replacement.

This is looking a bit better now.

Some new filter capacitors fitted, those carbon resistors are still good and can stay.

The original amp was 110v ac input, a bit of new labelling applied at the rear end.

The new mains transformer courtesy of Mike at Danbury Electronics. The size is perfect, it drops straight in.

A close-up of some new pots.

This is the replacement for the peculiar 350k/70k tapped pots used in the treble positions. I can supply these if anyone needs them.

When fired up, it turned out that the output tubes were running a bit hot. This is a little mod for adjustable bias, now we can trim it a bit more accurately. Apart from this little bias issue, the amp worked first time.

Topside after completion. Those tube shields cleaned up nicely.

A cleaned up front panel with a matching set of the original design knobs.

The finished amp.

IEC fitted at the rear, instead of the grubby old Powercon that was on there.

Tuesday, 4 October 2011

A bit of a fire in a Marshall DSL50 guitar amp

Here's an interesting little job just done.

It's a Marshall DSL50 valve guitar amp with the report "keeps blowing fuses and there's a funny smell".

Let's open it up. The output tubes checkout at very low emission using my Mullard MkIV valve tester. So whatever else I find, they need replacing anyway.

One of the valve bases is a bit black and sooty, and so is the socket that it came out of. Better take a closer look. Let's get to the PCB.

Valves out and top plate removed. That'll be the trouble then!

A closer view at that valve socket.

Get the socket out of the way so we can see what we're really dealing with.

That's major carbonisation between plate (pin 3) and heater (pin 2).

All that conductive area needs to be milled out and generally cleaned up.

The hole in the board is fine, the high voltage won't track across that! The pad at the anode is burnt away, but there's no connection on this side of the board. The burnt pad at the heater is a bit more of an issue, we'll need to make a repair there - de-solder braid is still useful after it's been used for de-soldering the socket. Don't forget to clean up the socket as well!

Here's the topside view, note preventative medicine at the second valve position.

We've lost the pad at the heater pin, but again it's not used on this side of the board - we don't worry about it.

A decent repair at the PCB heater track using a bit of used de-solder braid.

Now reassemble with a new pair of EL34 outputs, refit the original pre-amp tubes, power-up and set the bias. Working great, no more fire or smoke and no funny smells. Soak test for a couple of hours and sign it off.

Quad Electrostatic Loudspeakers - Replacing Noisy Panels

If you've owned Quad electrostatics for any length of time, you're probably familiar with the odd noises that can occur when there's a problem - fizzing, screeching, whistling and rustling. All normally caused by a leakage of the EHT voltage somewhere within the speaker. The usual is a breakdown of insulation on one or more of the panels. You'll need to try and isolate where the problem is before ordering parts or making a repair.

To ascertain where the problem is, you can usually roughly locate it by running an ear closely over the entire speaker frontal area. Once you think you know where that area is, you will often be able to see a discharge or sparking at the exact spot. This is best done in a darkened room (it can be very faint), and you may need to roll down the "sock" (grill cloth - read on for details).

This is the procedure that I've adopted to repair or replace panels in the Quad electrostatic speakers. This is written for the 988 / 989's, 63's are very similar and it could easily be adapted for them.

Please don't ask me to do this for you, it takes a lot of time and requires a lot of space, two things that I don't seem to have much of lately!

988's (and 63's) have four panels arranged in a vertical stack, 989's have two additional panels, one each at top and bottom. In both cases, the centre two have a "bull's eye" pattern which is the arrangement of delay driven concentric rings which generate the point source imagery.

If you want a bit of history, or to get really technical about how ESLs work, here's a few interesting links:-

http://www.quadesl.org/Hard_Core/ESLTheory/esltheory.html
http://www.quadesl.org/Hard_Core/hard_core.html
http://en.wikipedia.org/wiki/Electrostatic_loudspeaker
http://www.f2s61092.f2s.com/review57/review57.html
http://www.onethingaudio.net/FOR/QUA/63/9512-QUA-63-REV-NK-A2.htm

Quad will undertake this work at very reasonable cost, so unless you really want to have a go yourself, it's worth checking with them first. However, shipping is expensive and you'll need the original packing cases. You can arrange to drop off your faulty speakers in person. I believe they no longer offer support for the ESL57s.

One Thing Audio will repair your 57s or 63s. They will even refurbish your original panels or offer a service exchange.

ESL 989, Black

If you are to attempt this procedure, take some time to familiarise yourself with this information before starting and get all the parts in first.

As well as the replacement panel(s), make sure you have replacement dust cover kits (available from Quad’s service department) to hand before commencing – you will need them! One for each side of the loudspeaker, I've found that there's enough to allow for a mistake. You will also need some black cloth tape – duct tape or gaffer tape is ideal.

Be sure that the speaker has had adequate time disconnected from the mains to allow discharge of the high voltages within the assembly.

Remove the top plate – a sharp tap with the heel of your hand (left side, looking from the front) will unclip it from the top moulding.

Release the “sock” from the grip on top of the speaker and pull it down away from the top of the speaker (it will later be removed altogether).

Remove the black cloth tape from around the end of the panel which is holding the grill and moulding together and preventing rattles.

Remove the top moulding by removing the 4 self tapping screws (15mm) to the top corners and releasing 3 self tapping screws (9mm) per side at the top of the grills. The top moulding will also be attached with double sided tape against the grill – break this as necessary by gently prying with a screwdriver, the top moulding will now come away.

Turn the speaker up-side-down (rest it against your work bench or a table) and remove the base plate (held by 17 self-tapping screws (9mm) with toothed washers. Watch out for the ground wire inside the base and disconnect it as the plate is removed.

Disconnect (by de-soldering) the two red HT wires from the vertical PCBs attached to the lower moulding.

Disconnect (by de-soldering) the yellow signal wire from the drive PCB attached to the base of the speaker (along with the transformers).

Withdraw and release the red drain wire which is held in position by the vertical PCBs and stops short of the side of the base moulding.

Remove the base moulding complete with its electronics by releasing the 8 silver M4 hex nuts and flat washers. Note the black grounding wires attached by these.

Now the sock can be completely removed out of the way. Keep the speaker assembly up-side-down.

ESL988, Vintage

Remove the black cloth tape from around the end of the panel which is holding the grill and moulding together and preventing rattles.

Remove the front and rear grills of the speaker by releasing 3 self tapping screws (9mm) per side then gently pry the bottom of each grill (presently at the top!) away from the base moulding, breaking the double sided tape. Continue in such a manner that the grill can be slipped out of the side mouldings and away from the frame.

Clean off the old double sided tape from the mouldings and the grills.

Very carefully cut away the film dust covers from both sides of the ESL (cut as close as possible to the double sided tape which is holding them in place). If you find the old tape is stuck very firm and will not come away easily, leave it in place, otherwise it may be removed.

De-solder the wiring to the top and bottom edges of the panel to be removed (both sides).

If the grey wires from the delay circuitry are in the way of the panel you wish to remove, carefully break the glue bond holding them to the panel lattice and dress them away from the panel.

Remove the 4 self tapping screws (25mm) to the sides of the panel to be removed - these are holding it to the speaker’s frame.

The panel can now be removed from the speaker.

You will notice a central wire from top to bottom on the rear of the faulty panel - remove this and the clips holding it to the plastic lattice, fit it in place on the new panel.

Fit the replacement panel in reverse order, screw in place and then re-attach the wiring.

Reposition any grey wires that were dressed out of the way earlier and put a small spot of adhesive at each slot in the panels such that they will not vibrate and cause unwanted noise when the ESL is operating.

Refit the top moulding with the 4 self tapping screws (15mm) to the corners.

Stick new double sided tape (from the dust cover repair kits) around the edge of the loudspeaker frame, front and back, over the old tape.

The dust cover film can now be stuck in place (do one side of the speaker at a time and refit the mesh grill afterwards to avoid damage during further handling). Try rehearsing this procedure in your mind before attempting it

This procedure is best done by two people. Place the ESL face-down on a flat surface and remove the backing from all four strips of double sided tape.

Carefully stretch out the film above the ESL, pulling it as flat as possible (be careful not to pull too hard as to tear the film). Lower it down on to the tape whilst keeping it as wrinkle free as possible. This is best achieved by sticking down either the top or bottom end first, whilst holding the film just above the speaker (3cm or so). Do not let the film droop and stick to the tape. Move down the sides, keeping the film taught and sticking down about 30cm at a time. Finally stick down the opposite end to where you started from. There will be some wrinkling which can be removed afterwards as described below.

Make sure the film is stuck down all the way around the speaker frame and trim to size close to the tape outer edge.

The wrinkles in the dust cover must be removed, since these will produce audible rattles. This is achieved by means of heat which thermosets the plastic film and may be applied by a warm air blower, such as a domestic hair dryer. You will find this easier with the speaker standing on end.

The nozzle should be held close to the dust cover and moved from side to side across the unit slowly and steadily in regular lines to cover the whole area.

To achieve sufficient heat to thermoset the plastic, it may be necessary to restrict the supply of air to the dryer by placing a hand over the intake. This can be dangerous so ensure that is equipped with a thermal cut-off.

Repeat the process until all wrinkles have disappeared, but always treat the whole area and do not tackle individual wrinkles separately.

A certain amount of skill is required in the operation. Obviously, if the nozzle is not close enough and/or the speed of travel too great, there will not be enough heat to affect the cover. On the other hand, too much heat at one point can quickly burn a hole. When carrying out this process for the firs time, progressively reduce the distance and speed until the desired results are obtained.

An “industrial” hot air gun, such as those used for heat-shrink tubing, is a lot more powerful so proceed with caution if you intend to use one of these – you will need to move it faster to avoid holes appearing in the film!

Take your time with this process and persevere if you damage the film. It will be frustrating to start over, but, as mentioned, there is usually sufficient tape and film in the repair kits to allow for a disaster or two!

Don’t forget to re-fit the grill to the side you have completed, this will protect the work you have achieved so far. Some new double sided tape is required along the top and bottom edges of the end mouldings to prevent the grill rattling. Once the tape is in place, remove the backing in preparation for the grill. Slot the grill into the rebate one of the side mouldings. Bow the grill across the front of the speaker and slot it into the other side moulding. Be careful not to slip and damage the film you have just finished.

Repeat the procedure for the other side of the ESL.

988 and 989, Nouveau

With the speaker standing on end (bottom upward), put some new black cloth tape (approximately 2cm wide) around the bottom end of the speaker in order to bond the grill and moulding together and prevent rattles.

You can now replace the sock over the speaker. The seam in the material should be positioned to a rear corner and thus be less visible. Carefully feed the sock over the end of the speaker, being sure not to ladder the material on the way. Pull it down the speaker as you go in order to get the bottom (presently facing upwards) tidy. Leave about 3cm surplus material for fixing in place. When you are happy with the positioning of the sock, press the surplus material at the end into the grips on the end moulding.

Next re-position the base moulding and electronics over the 8 M4 studs at the bottom of the panel.

Place the 8 silver M4 clear flat washers over the 8 studs.

Replace the black grounding wires onto the M5 studs - 2 to each side.

Tighten down with the 8 silver M4 hex nuts.

Reposition the red drain wire through the holes in the vertical PCBs and pull through towards the side of the base moulding stopping short of the side at approximately 3mm.

Re-connect (by soldering) the yellow signal wire to the drive PCB attached to the base of the speaker (along with the transformers).

Re-connect (by soldering) the two red HT wires to the vertical PCBs attached to the lower moulding.

At this point, apply mains power to the loudspeaker and switch on, allow a few minutes for the elements to become properly charged. BE AWARE OF HIGH VOLTAGES AT THE ELECTRONICS WITHIN THE BASE – DO NOT TOUCH THE INTERNALS WHILST MAINS POWER IS APPLIED, ALLOW SUFFICIENT TIME FOR THE EHT TO DISCHARGE BEFORE HANDLING.

Check over the loudspeaker for spurious noises indicating other panel defects.

Note the neon lamp (N1) on the control PCB - this should be flashing at around 10/second.

Refit the base plate (held by 17 self-tapping screws (9mm) with toothed washers. Don’t forget to re-connect the black ground wire inside the plate.

Turn the speaker over and stand it upright on its base.

Put some new black cloth tape (approximately 2cm wide) around the top end of the speaker in order to bond the grill and moulding together and prevent rattles.

Pull the “sock” up the speaker, stretching out any wrinkles, and press the surplus end into the grip on top of the speaker.

Refit the top plate – align the two pegs into the brackets in the top moulding, a sharp tap with the heel of your hand (right side, looking from the front) will clip it into place.

Reassembly is now complete.

Apply mains power and connect to an amplifier output. Switch on and allow the elements a few minutes to charge up. Play some music and check for correct operation, enjoy!

Thursday, 13 January 2011

Fender Vibroverb

Here's a few pictures of a Fender Vibroverb (re-issue) that I've recently done some work on for a client. Apart from the obvious aesthetic refurbishment, it also had some minor electronic issues which were also sorted (some noisy pots, vibrato not working, footswitch needing re-termination).

This is how the amp arrived

Close-up of the deteriorated grill cloth

Baffle board removed

Reverse side showing the original 10" speakers

Chassis and reverb tank

Internals

Cleaned-up cabinet

The finished article

Back to the beginning for comparison

Sounds awesome!

Sunday, 2 January 2011

Rob's Guitars

I've been out into the countryside this afternoon, went out for the trip with my good friend and guitarist Tony Farmer, also to return a repaired amp to a new customer and meet the man properly.

This was Rob (Barry) at Rob's Guitars out at Constantine, between Helston and Falmouth.

If you're looking for something new or to do a trade on your existing instrument, I'd highly recommend that you give Rob a call.

Saturday, 1 January 2011

How things are progressing.

A number of things have been pre-occupying my mind of recent times and combined, they have prevented me from "getting it together" and I apologise for not posting anything up here for a while. Therefore, my New Years resolution is to be more active on the Blog scene.

We're now just a little over six months from the official start date of the new business. It's been a little slow getting off the ground and much time has been spent researching my market and "networking". This has invariably meant spending quite a bit of time in the local pubs, that's where much of my clientèle tend to appear reliably! I've also done a fair bit of leaflet dropping, especially around the local churches.

But we're gaining momentum and things are improving. I'm now getting recommendations and regular customers. Here's a bit about what I've been up to:

The Pub Scene

Pubs tend to need sound systems these days and if they already have one, it tends to need servicing from time to time. Whatever the situation, it's good to meet the landlords and talk about what I do. The punters also like to gripe over their latest electronic failures or enthuse about their latest desires. A little eavesdropping and a comment at the appropriate moment can generate a little extra income! The pub is also the place where local musicians tend to appear, especially if they have a gig there! Guitar amps and PA gear need repairs and service, I'm doing a lot of this, so it pays to "bump" into these guys as often as possible. I like the music scene too, not to mention the beer, so it has a positive enjoyment factor as well!

Installation and Maintenance of Equipment on Site

I have now been involved with a number of on-site maintenance issues. These include:

PA systems that are not working properly
Induction Loops (for the hard of hearing) that are not working properly
Radio mics that have ceased to function
Radio mics that function improperly (mainly due to inexperienced installers fitting the wrong products)
CD players that have ceased to recognise discs and won't play

I've also installed several Loop systems, Background Music systems, done a major Church installation and sorted out one or two domestic audio systems.

This month I have a 3-zone pub audio system to install and I shortly start work on a new build village community hall. Here I shall be putting in:

A background music system for the bar with:

Speakers zoned to the toilets
Speakers zoned to the foyer
Speakers zoned to the patio

A comprehensive hall audio system capable of being configured for practically any event.
Induction loop for the hard of hearing
A video projection system with DVD/CDG player
A stage/theatre lighting system with LED colour wash units for back drop or other wash effects.

PAT Safety Testing

Every electrical/electronic product that comes my way for repair or service gets safety tested. It is recorded on the repair sheet and a label is attached with the details. I keep a backed-up electronic copy of all repair sheets along with my business accounts.

On a number of occasions, I have also performed PAT safety testing for commercial clients in their premises. A detailed report is provided for their records, a copy of which I also keep electronically. This will bring up a reminder on an annual basis such that I can keep the customer informed.

Sales
I now have a tremendous array of products available to me owing to my requirements for the installation activities. It therefore follows that, on occasion, I have been able to fulfil sales enquiries. I also have a number of contacts in the industry and have a "knack" for finding used product. Someday, I might even get a webshop up and running?

Guitar Amp Repairs

This seems to be my most active duty at the moment. This is possibly because it's something I'm good at and the musical community is spreading the word.

A selection of guitar amps that I've recently had in for service:

Fender FM15G

Marshall Valvestate 80V

Ashdown ABM300 head

Ashdown MAG300

Fender Hot Rod Deluxe

Marshall AVT275

Marshall JCM800 2204

Session Sessionette 75

Fender Vibroverb 6G16

Vox AC30 Coppertop

Marshall Superbass

Hi-Fi Repairs

I've also had a good few items of Hi-Fi in for repair as well, this is something I need more of. There must be hundreds of CD players out there that no longer read or play discs properly. Unlike the musicians, a lot of Hi-Fi customers are finding me via internet search, I'm starting to crop up all over the place!

A selection of Hi-Fi products that I've recently had in for service: