A reader of ours wrote me to ask about a ferrite ring that broke while he was opening up his Marshall VS 265 amp.  I have no idea how it broke, but he was replacing potentiometers when it happened.  Does anyone know which wires/cable (AC mains?) go through the ferrite ring , and if it's just straight through or wrapped or what? 

In my music schools we use a number of Line 6 Spider III 150 watt amplifiers, and the controls on them have always been a bit screwy.  The controls, such as a six position effects selector, use potentiometers which I assume go to some sort of A/D converter with triggers for when each switch "position" has been reached.  There are small LEDs around the perimeter to indicate which effect is selected.  However sometimes these LEDs will dance around a bit (change on their own, without the knob being touched), and clearly the amp is confused about which effect is selected.  This is at best disconcerting and at worst prevents you from selecting something.  And worst of all, it's intermittent - comes and goes, and we've never been able to correlate it with any other activity or location. 

My assumption further has been that this is due to some sort of power line noise or poor power supply regulation or noise filtering.  We have six of these amps and they all do it from time to time at all locations.  While I haven't asked them in a couple of years since we bought them, the retailer and manufacturer have both answered along the lines of "check your power," ignoring the fact that this happens in all three commercial buildings we lease, as well as in my home, as well as in several different clubs where we've used them to gig.  Their answer might as well be "upgrade the mid-atlantic power grid" as far as I'm concerned, but I digress.

I've got one of these amps on my bench right now to fix an input jack.  I thought I might also try to address the noise problem.  I'm soliciting the forums suggestions for 1) your agreement or alternative theory on what the cause might be and 2) if you think it's a power noise issue, where would you attempt to improve the power conditioning and how?  For example, I might try a ferrite core on the power cord, or something in the filter section, or perhaps something at the potentiometers?  I'm really looking for practical experience here on suppressing transients that might confuse switching logic.

thanks

I'd be interested to hear what methods/procedures other repairers recommend or follow to test an amplifier after its been repaired.  I've generally used a 1kHz tone and run the amp into a dummy load for 8 hours or so to see how it handles getting hot, but someone's probably got a better procedure.  What do you do?

I have an opportunity to buy a non-working Kasino Snake Eyes bass amp for $50.  I've read a little bit of the background of these amps and their connection to Kustom.  Anyone ever worked on one or know anything about them?

I just picked up a Peavey Supreme TransTube head, and unusual for me, it works without my needing to repair it.  I really was just in need of an empty 4x12 cabinet for use in a music school as a room divider, and saw this Peavey half stack advertised for $300.  The cabinet has 4 Eminence G12K85 speakers in it that I'll sell.  Between the head and the individual speakers I think I can get my $300 back and get the cabinet for free.  I'm really impressed with the head though - very nice tube sound, nice features and construction.  This is my first experience with the TransTube technology and I have to say I'm impressed by it.  It also looks like it would be very straightforward to work on if needed.  The opamps are socketed, which is nice, and the rest of the layout is very clean and open. 

Thanks to Teemu for his book and direction to the Peavey Papers on TransTube - an interesting read.  Anyone else have any experience with this amp?  Does anyone want one or more of the speakers - I'll let them go for below the price I see quoted in eBay, as thanks for the assistance I've gotten through this forum.  Let me know.

Regarding Teemu's book - is there any reason I shouldn't link to it from GuitarKitBuilder.com?  I think our readers would want to know about it.

I have an opportunity to buy a Carvin SX-200 amp for $100 with a non-working clean channel (owner reports noise and hum on it).  The distortion channel is reported to work fine, and the effects are fine.  I haven't worked on one of these before but from a look at the schematic I think the clean channel will be fixable.  Carvin sells these new for $299 and I see one one eBay for $269.  If you know this amp, what do you think of it?

I'm replacing a damaged 2SK1058 MOSFET on a Marshall Valvestate 8200 but I'm not sure of what type of heatsink coating they use to keep the MOSFET electrically isolated.  Does anyone know?  It's a yellowish-tan in color but I can't tell for sure if it was a film of some kind, or what.  The area behind the removed MOSFET is damaged a little so I'm leery of reinstalling without also fixing the surface of the heatsink.