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Hi Penguin The reason the 3.9K resistor is OK is because it is in parallel with the pot. If the pot goes open circuit then the 3.9K resistor is there as a back up. In the event that the bias pot fails the 3.9K resistor will allow through a high bias current that will make the amps bias very...

The amp bias does get hotter as you raise the resistance, hence if the pot goes open circuit, (infinite resistance) you will blow the output tubes. That is why putting a resistor in parallel is advantageous as you can put a lower value resistor in parallel, (which is why the Mansfield kit used a...

Just a word of caution. I am no expert and haven't tried this kind of mod but I was under the distinct impression that the fixed resistor is placed in parallel with the variable resistor, and is there as a safety precaution in case the variable resistor, (aka pot), should fail, so I think the...

I wouldn't call that 'picky detail' at all. It's a very important distinction. The LSS is cathode biased however. There has been some debate about this on this forum. In a previous thread someone posted a link to an interview with Randall Smith which quotes him saying that the LSS is cathode...

I would retube if it was me. LSS is cathode biased so you should be OK. If in doubt buy Mesa El84s, or tell your supplier you want Mesa compatible tubes. I would also consider getting a couple of pre amp tubes and try swapping out to see if the crackle goes away. Another thing to try tube wise...

Interesting. I realise the effect of the bright caps diminish as you turn the pot up. I like to use lowish gain and push the amp with drive pedals. The 250pf caps make the amp pretty bright in my experience. It also makes the amp work very well with humbuckers which it didn't really do well...

Yes, most likely the rectifier tube has failed. Seems to happen a lot. There is a mod (use the search function here) to help prevent this happening. The mod should have been applied to later models (serial numbers over 4000 I think). Having said all that my LSS is old, Sn <1000 does not have the...

Thanks Chris. Much appreciated. I have actually, just two weeks ago, soldered bright caps (250pf Silver Mica) across the drive pot and both channel gains. Probably a bit OTT, (may substitute the 250pf for 150pf) but its great having to tame the highs rather than to try to coax them from nowhere...

Actually that is a very good suggestion. The button is probably getting stuck in the 'dent'. Try gluing a thin bit of tin can metal or similar over the 'dent'.

To the OP, my castors slide on and off quite easily, no force required. tle4, to post pics you need to upload them to a photo sharing site. I use photobucket. When you have them uploaded you simply click on the share image link, and paste the link into your post. My castors do look a bit...

Hope these pics help. A bit blurry as I don't have my 'good' camera to hand at the moment. The 'plates' on the castors are 2mm thick btw.

I use a Wampler Superplex with my LSS. I find I need to have the treble quite high and the mids and bass low, (I am talking about the pedal controls here, though the same could be said about the amp controls) but it i sounds very good fo higher gain tones. For more restrained tones the Wampler...

My LSS came castorless. I eventually found someone selling sets on ebay. They only had a limited amount and pretty sure they all got sold. I ended up with a set with 3" diameter wheels. Judging by photos I have seen this is larger than would normally be supplied and I think that is no bad thing...

Chris (or anyone else!), do you know what the circuit reference is of the 220K resistor, or could you help point out where it is? I would quite like to try this mod but don't know which resistor it is. I am actually pretty happy with my LSS but still curious to try it anyway. Thanks Tom

My LSS is quite an old one having a serial number in the 900s. The rectifier tube is a Jan Phillips, (stamped with Mesa on the glass) which I believe to be an older tube made to military standards, and of better quality than new production tubes. I have had the amp for about 3 years with no...

My advice would be to consider the weight of the 2 x 12 combo. Seriously. There is a chart showing the weights of all the amps on Mesas website. The LSC 2 x 12 weighs 79 pounds........They are not called the Big Blue Pig for nothin'. Just a thought......

Thanks for the reply. Apparently, after some more research, silver mica caps are a good option and these are generally rated for 500 volts which is ample. I am actually pretty happy with my LSS at the moment but may give this a go. Probably on the gain pots though not the drive pot.

Hi Thanks for the info. I may try this out. Can you advise on what voltage rating the cap needs to be and if it should be a ceramic cap or whatever. Thanks again. Tom

I'm leaning towards setting channel 2 as a grittier version of channel 1, therefore giving myself two base tones two work with - one being as clean as possible, and one having just a hair of distortion for that touch-sensitive blues vibe. I really get my rock and roll overdrive sounds from my...

Hi Although the LSS is cathode biased I would still exercise some caution when changing tubes. The guy I go to for JJs, (my favourite new production EL84), supplies tubes to Mesa specs. I once bought a set of military grade Sovteks from elsewhere and these were slightly red plating when I put...