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Tube Rolling in Little Dot Mk II Pre-amp

haisaikat

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Starting a new thread to provide updates on tube rolling for my newly acquired Little Dot Mk II pre-amp. The previous thread of acquiring this can be referenced at https://www.hifivision.com/threads/pre-amp-suggestions-needed.72243/page-3

I have mainly followed the following BIBLE https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/ posted elsewhere for getting the comprehensive idea of various tubes and their possible effect on sound signature.

The LD I acquired came with 6H6PI power tubes and Mullard M8100 driver tubes instead of the default 6J1 tubes which the previous owner had upgraded.

From the above tube rolling guide I came to understand that Mullard M8161 is another great option for the LD and hence ordered the same from ebay, the link to the item was https://www.ebay.com/itm/310391381072 . As its evident from last post of my previous preamp thread that I received in turn a pair of tubes that had CV4015 kqdd/k written on it with nowhere the name Mullard. After several message exchanges with the ebay seller it was concluded these are a separate category of Military Spec Mullards and this is the way they manufactured the M8161 for military. Unfortunately since these were internationally shipped I decided to keep them and go ahead with the rolling.



I will provide subsequent pics and steps of the rolling shortly.
 
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haisaikat

Well-Known Member
Joined
Dec 12, 2010
Messages
2,810
Points
113
Location
Kolkata
There is a online version of the Little Dot MK II user manual available at https://www.dropbox.com/s/5pmrnv1twu42y9i/Little Dot MK II Reference Guide.pdf?dl=0 which is the main guide for the tube rolling steps. Except from the manual is given below

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So per above post the jumper pins have to be altered in connection to allow from 8100 to 8161.

So I opened the bottom set of 4 screws on front and rear faces ( 2 screws each side) of course after taking out the 4 tubes from top
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This allows taking out the bottom cover easily and after that belown circuit is exposed.
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Ideally this is upside down. Note the ones circled are the red gain switches presently set at 3db only by default and is apt for most high impedance amplifiers. No changes there. But it's the other jumpers that we need to alter position, as per manual by default the jumper is set towards the EF 95 label and we need to set it towards the EF92 label in order to use M8161. Quite easy job as it seems.

This is the final state after setting the jumpers to EF92 option.
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Now I am going to screw it all together. And here is the final state with new tubes placed in, listening impressions to come later. For a Chinese one seems well documented and organised.
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For reference here are old/existing tubes, tucking away for now, the black bottom guards came with the new ones.

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