noise reduction mod for 400+ ??

I've never really had any hum issues with my 400+.

I've also never heard of this mod so I googled it:http://www.google.com/search?source...S222&q=Mesa+boogie+400+++noise+reduction+mod+ and found a guy in the UK selling a 400+, stating he had this mod preformed by a tech named Dennis Marshall at a authorized Mesa repair facility called Emerson Williams.

I've emailed the UK amp tech asking for info about this mod and I'm awaiting his reply.

I did find 1 other reference to this 400+ mod on a current USA ebay auction, but this reference seems to simply have a few (copy and pasted) nearly word for word quotes from same UK sale amp mentioned above...

 

Here's his reply. Sounds like he's probably a good tech but he isn't mentioning any mods...
I'm thinking the "mod" term was simply added by the UK amp for sale guy to make his 400+ seem more desirable.

_______________________
Hi anderbass,



Thanks for the enquiry. There are a few things I can do to the 400+.

The main thing is to make sure the outputs tubes are correctly biased and balanced. I sometimes change the bias components to achieve this.

The preamp stage can benefit from trying out different tubes depending on the required tone.

A clean-out and service is always a good idea

I would need to see the amp to be more specific.



Regards



Dennis Marshall

6 Main Street, Newmills, Fife, KY12 8SR

Tel: +44(0)1383 881761


--------------------------------------------------------------------------------

From: anderbass
Sent: 09 January 2009 04:03
To: [email protected]
Subject: Mesa 400+ Question



Dennis,



I heard you perform a Noise reduction mod on the Mesa 400+ model and I'd be very interested in hearing a bit of info about this procedure.



Thank you - anderbass

 

The only time I ever had any noise issues at all with my 400+ was when one of the power tubes crapped out on me. Other than that it was always dead quiet.

 

Lots of guys wrongly assume they're 400+, 400 or D-180 series model is a 1982 cause thats the trademark date printed on many of the diferent years, rear panels. Ask your amp tech to look for some large handwritten dates he'll probably find on serveral of the large blue capacitors inside for a date of assembly on yours.

I'm still not a 100% sure If Mesa can always date from its serial numbers or not...

I went with a JJ/Eurotubes power tube set he sells for the 400+ in mine. Quite a few other 400+ guys on this forum seemed to really like the JJ set too. They've held up well and sound great in mine. I have a feeling the JJ's are probably one of the cleaner sounding powertube choices and for that reason alone, I'll probably try something else next time. I"m not sure what I'd try next but I've had an adjustable bias instaled in mine now and I'd like to get a bit more daring next time and see if some other quality powertubes might have a bit of diferent flavor.

 

I've just been researching this too, I picked one up a week or so ago and it needs a few tubes, - some Mesa labeled tubes that are pretty widely ranging in mA draw at idle (20 to 45, most around 30). I think the Eurotubes guy knows Mesa and can supply a set that is pretty ideal for that amp, there's also a guy on ebay I've emailed that sells matching sets (up to 12) matched Sovtek 5881s for about $150, and from his email I'm satisfied that he knows what sort of current draw to match for in the 400+. You wouldn't want to get a set that's too 'cold', or too 'hot' for that amp. I've heard from a very reliable source that the Mesa labeled tubes are often poorly matched, so I'd go with Eurotubes or the ebay guy. I've got 6 that are within 2.5 mA (my tech tells me this is ideal), and I've got some more power tubes on the way that I hope to get a good match out of, if not, I'll end up going with the ebay guy for $150. My tech tells me that much more range of idle current than 2.5 mA (a poor bias match) will usually result in some noise.
In case you're also wondering, the Sovtek 5881s are not a true 5881 (like the old small bottle TungSols that go in '50s amps), but a military 6L6GC equivalent, capable of handling high plate voltages just like the best 6L6s.

 

I just wanted to let you guys know I've replied to the UK amp tech asking more specifically if he simply does a very throughal service or actually installs some sort of true mod in these amps. (I'm thinking he might use Psychos 12AU7 driver tube swap... although I was thinking an authorised Mesa repair dealer might not admit to any mods from the origanal design)