basstone

I've had good improvements by screening using copper tape. As well as the control cavity and pickup cavities, it might be worth screening the PU covers, fiddly but does help. Also ensuring that the Pickup pole pieces are grounded helps. A strip of copper tape across the back of the pickup should do it but I've found that to get the best connection I used some conductive paint to join the pole pieces to the tape. All a bit fiddly but gets worthwhile results. Having said that, using both pickups usually is hum cancelling, combined with a mute switch between musical numbers works well, but remembering to unmute before the music starts!!

It is held in place with velcro tabs and is fairly tight. Probably the best bet is to remove the preamp from the front (not fully as it will be held by cables to the power amp) which should give you enough room to pull the front fan panel off. Alternatively rather than remove the valves it may be possible to get a stick from the rear to push the panel off?

Happy to be a supporter - what a great forum!

You're welcome Matt.

Sorry I won't be able to make it this year as I'm away that week. Gutted!

On the amp front, I've used a Gallien Krueger MB500 for several years, now. Very light (3Kg) and compact giving 300W into 8 ohms. I use it with a GK 210 neo cab most of the time. The cab is probably still too heavy for you but the MB500 would work well with a BF cab I think!

From the picture, I suspect that this is a dual gang 20K pot(C taper) and a single gang 10K (B taper). That makes some sense as often variable frequency middle controls use a dual gang pot for the sweep and a single gang for the level.

Does anyone out there have a schematic or even a simple wiring diagram showing how the controls connect to the board? The 3 sig and ground is probably fairly straightforward but for the middle frequency with 3 sig plus bias it is not obvious how to add this in. Maybe someone with an SR Ibanez with mid sweep could trace it out. It would be a really good asset for the Ibanez owners on the forum. As for the connectors, they are readily available from multiple sources including: https://www.ebay.co.uk/itm/134781932915?var=434274031445 It pays to get the correct wire size and a good crimping tool to make reliable professional quality pin connections.

The cap in question is the dc blocking capacitor in the power amp feedback ensuring that the power amp has unity gain at dc. If this fails any small dc offset in the circuit will be amplified and presented to the output. It will depend on the particular amp design and is not a common failure but worth checking!

A small DC offset will not significantly affect amp headroom but is not desirable as it will increase the possibility of noise and hum on the output as well as a small increase in heat dissipation and a thump or click when the amp is switched on and off or the speaker connected. Also worrying is the possibility of a leaky capacitor in the feedback circuit which if left will gradually allow the DC offset to increase to the point where the amp and or speaker will be fried through thermal overload - I know from personal experience! Glad to hear it's now fixed and sounding better.

As already noted, it's quite likely that a pot connection has made an unintentional contact with the screening foil. I always put an insulating layer of clear plastic sheet between the foil screen and the pots to avoid the possibility of this happening. Screening foil is far more effective than conductive paint in my experience and well worth another go.