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Sv Mkii 100wt Head Mod

yellow jacket tubes

Best Answer amenity421 , 21 January 2015 - 12:48 PM

Sorry man. I should have actually answered your question.

Watch this if you haven't yet:

It explains it. Just ground to amp if it's missing the center pin (you'll know what I mean after you watch the video).

Also, don't die. Go to the full post


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#1 Apologist

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Posted 07 April 2014 - 04:51 PM

I want to swap out the 4X6L6 tubes  that come with the amp and replace them with 2xYellow Jacket (short tubes).

 

It's my understanding that since I am only using 2 of the YJS(s for short 4.5')  I would need to place them in the 2 center sockets and leave the outer sockets empty.

 

Has anyone ever done this mod and if so is this correct?


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#2 Apologist

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Posted 11 October 2014 - 12:00 PM

So after doing some research I decided this mod would be too unsafe and could possibly damage the amp. So I decided to get some JJ 6L6GC'sx4 to go ahead and replace all my power tubes since they are such a good price and great tubes.

 

I really do not have the time to take to service tech and have seen and read info about replacing on my own. I am very aware of the lethality of the ampage even when unplugged and off.

 

Let me run this buy some of you that know more than I do to ensure I am doing this right"

 

First I remove, with the amp unplugged and off) the retainers from old tubes and gently remove them.

 

I then (after using cleaner or ensuring pins are clean) place the new tubes and then replace retainers

 

Then set meter to DC and place black connector to center pin and red connector to the corresponding tube over the blue squares that adjust the bias to the corresponding tube. Turn the amp on and wait for standby warmup..then take it out of standby to adjust by making sure meter reads as close to 35mv as you can get.

 

 

 

This is a SVMKII HD100 head so I do not know if the process is the same in this regard to adjusting blue sqrs and placement of connectors as one would in the SVMKII1X12. 

 

And I guess that is my question before I crack open my head to get to the tubes ... with it being 4 power tubes how will I know which to connect and adjust?

 


I have my plastic screwdriver awaiting a response. :P


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#3 amenity421

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Posted 21 January 2015 - 12:04 PM

Hey there,

I just did my hd100 the other night. It's missing the center pin for ground so I just grounded to the amp. Make sure you have a speaker load connected.

I biased mine at 40mv. Sounds nice and warm now. It had some tung sol 6L6s in it prior and I didn't much like the tone.
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#4 amenity421

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Posted 21 January 2015 - 12:48 PM   Best Answer

Sorry man. I should have actually answered your question.

Watch this if you haven't yet:

It explains it. Just ground to amp if it's missing the center pin (you'll know what I mean after you watch the video).

Also, don't die.
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#5 Apologist

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Posted 25 January 2015 - 07:00 PM

Thanks amigo figured it out the JJ's sound great


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#6 frac82

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Posted 29 January 2015 - 12:51 AM

how should I set the tester? is this procedure the same as for combos as for head? thanx


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#7 frac82

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Posted 18 May 2015 - 12:42 AM

how should I set the tester? is this procedure the same as for combos as for head? thanx

 

UP!  anybody out-there?!?


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#8 Apologist

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Posted 18 May 2015 - 05:00 AM

Frac82:

 

The above youtube video actually is somebody working on the combo. He has simply removed the chasey from the amp to work on it ... if you look closely there are only two power tubes showing.

So the procedure shown here is actually for the combo amp not the SVMKII 100W head.

 

The setting for the tester will depend on what tester you are using but he explains what type of connectors and what he set his at around 6 minutes into the video.

 

Note: Even though this video is the first generation SV the procedure is the same and the board and test pins are the same.


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#9 frac82

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Posted 19 March 2016 - 03:59 AM

Frac82:

 

The above youtube video actually is somebody working on the combo. He has simply removed the chasey from the amp to work on it ... if you look closely there are only two power tubes showing.

So the procedure shown here is actually for the combo amp not the SVMKII 100W head.

 

The setting for the tester will depend on what tester you are using but he explains what type of connectors and what he set his at around 6 minutes into the video.

 

Note: Even though this video is the first generation SV the procedure is the same and the board and test pins are the same.

 

thanx. sorry for late rply


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#10 psarkissian

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Posted 06 April 2016 - 09:03 AM

1) Use tools with insulated handles.

2) Do not bias JJ's to the usual SV bias voltage. Don't use JJ's.

 

Aside from that, the video is okay.

 

These are not like analog tube amps from the 1960's. Can't go swapping tubes out willy-nilly

and go biasing to the usual voltages. There are minor variations in the characteristic curve or

transfer function of the tubes between manufacturers.

 

One bias does not fit all.

 

Love JJ's, love Groove Tubes,... don't use them (or Mesa's) in these amps. I see way too many

of these come across my repair bench for no other reason than the wrong tubes with the wrong

bias. Use the specified matched sets for power tubes, and have them properly biased.


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