Installing 6l6s in a VH4

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edgemeister

edgemeister

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hey guys,

I want to try and install 6L6CG tubes in my VH4 an would like some information.

Is there a VH4 biasing guide like the herbert one on the Diezel website?

I don't really want to buy a biasrite and would rather do it with my multimeter, I'm tchnically minded and build PCs and guitar effects regularly so this shouldn't be so hard.

Thanks guys...

John
 
Here we go (keep in mind that there are 500 Volts on the OT, be careful, make sure the crocos are tight on the OT, use an insulated screwdriver for the trimmer . . . ):

1 ) take the chassis out of the headshell (and have a look if the bias selector-switch fits your tubes - it is labelled "EL34 and 6L6") and place the amp - pots facing you - onto two books, watch out for powertubes !

2 ) on the right you can see the output-transformer (OT). Its right side (red wires) is the secondary - you need to hook the crocos to the primary, so the left side





3 ) Set DMM to 200mA DC current (many DMMs need another slot for the red for current for voltage !)





4)Hook crocos to DMM leads and the black to the middle of the three primary OT wires, red to either left or right of it







Switch amp on, standby run-position, hooked to load - be careful !

5 ) read current and adjust desired value with the bias-trimmer on the left side of the mainboard, close to the midi board . . .





6 ) this way you are reading the current for one side of the quartet (so 2 tubes), which means that should read 60mA for EL34.

7 ) Switch amp off, you may want to repeat the whole procedure for the other side - in the case of this amp using the blue wire . . .

8 ) Put amp back into headshell after you've unhooked from mains

9 ) Enjoy your fresh biased VH4 !

Recommended current settings for pairs in a VH4:

5881: 50 mA
6L6: 60 to 70 mA
EL34 60 to 70 mA
6550, KT66, KT88: 80 mA


will post pics later . .
 
left
 

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OT with crocos
 

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Thanks for that, pretty straightforward stuff...

Out of curiosity you mentioned 6L6: 60 to 70 mA

Whats the benefits/drawbacks of setting this to 60 or higher to 70?

Would you reccomend a sweet spot?

Seeing as I'm biasing a pair at a time, do I just need to buy 2 matched pairs or should I buy a full mached quartet?

Thanks

John
 
You've got just one bias trimmer ---> quartet.

60 - 70mAs depends on your taste/ears. If the amp stands safely on two books (or whatever) just try a bit around. Keep in mind that if the tubes are brandnew they need some time (1h-2h) to burn in and drift in bias a bit. Thats you §chance" to adjust it to your needs.

Get some Svetlanas btw ;)
 
So ideally I should bias them, then play around for an hour or two to let them break in, then rebias to perfect it?

What sorts of changes in sound will I expect to hear when adjusting the bias higher or lower?

Svetlanas eh? :cool: I was looking at the watford valves harmas as they seem to be a good buy.

I'll look into the svetlanas though...

thanks for the help

John
 
So will this method work with any amplifier that does not have bias test points, especially if I do not have a bias probe, but only a DMM?
 
You guys rock. :thumbsup: Taking my first adventure into biasing an amp tomorrow...no test points and no bias probe. Rock n' roll.

P.S.-Peter....send me a VH4, I wont tell anyone, i swear! Hahaha.
 
So, If i were installing KT88's where would the flip switch reside? EL34 or 6L6? Also, what is the other trim pot on the far side away from the midiboard for? just curious.
 
Yesterday I've got VH4, amazing and very sexy amp :-). This topic / forum helped me to switch to 6L6, it came with old EL34's, like a charm ! Many thanks, I hope this amp will last for ever, it doesn't play, it kills :thumbsup:
 
I'm gonna have to try this method and see if it works on my marshall EL34 100/100. After waiting for info from marshalls for AGES they then told me they can't tell me how to bias my own amp unless I'm a registered marshall tech, for "health and safety" reasons! :jerkit: :doh:

Not in any rush though really, since my herbie's running just fine! :yes:
 
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