6L6s TO EL34s STRANGE OCCURRENCE...ANY SUGGESTIONS??

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mansin_mind

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so. at first i though i was having baising trouble or a faulty tube but thats not the case. im on my second quad of ruby el34s and still... i get a very low pitch hum coming from my speakers and the amp has to be cranked to even hear the guitar. i place back the 6l6s, rebias and everything is normal. the low volume and hum is only with el34s. any thoughts guys? and yes the switch is on el34 not 6l6. :confused:
 
mansin_mind":2sw0g38q said:
so. at first i though i was having baising trouble or a faulty tube but thats not the case. im on my second quad of ruby el34s and still... i get a very low pitch hum coming from my speakers and the amp has to be cranked to even hear the guitar. i place back the 6l6s, rebias and everything is normal. the low volume and hum is only with el34s. any thoughts guys? and yes the switch is on el34 not 6l6. :confused:
Click to expand...

And they're biased to about 70mA per pair? WITH A LOAD when biasing? Full power not standby?

Please let me know.

V.
 
hi there, yes full power on. yes with a load, connected to the 1x8 ohm for my 2x12 cab. well, i want to put in the el34s so according the the diezel it should be around 60 mA per pair. im just following the bias video tutorial. how do i bias the tube sets seperately?
 
You can only bias all four tubes at the same time on the VH4. The two shunts just show your bias
on the inner and outer pairs.

DZLBIAS.jpg


DZLOT.jpg
 
If you have the bias pot anywhere near 45% or more with strong EL34's it's probably going into cutoff
and the tube is choking on itself because the bias is WAY too high, hence the cranking to hear anything.

A. Make sure your not turning the hum trimmer instead of the bias pot
B. Make sure your reading in mA DC.
C. If all else fails, try the EL34's in the 6L6 position just to be sure the switch or resistor is not bad on the EL34 side.
If you are getting a reading of -40,50,60 mA at the OT the switch is fine.
 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ :thumbsup:

This guy never ceases to amaze and impress.

Awesome post M2C. I always default to 'pairs' due to my 4S

Peace,
V.
 
Thanks for the help and quick replies. I'm a little confused so bare with me... you mention that the tubes are biased at ones but that the shunts only measure outer and inner tubes? Huh? So do I place the black wire in the middle then the red to either left or right shunt, bias then switch the red wire and bias again? I am starting to believe the power tube switch has a fault on the el34 side. Would it be harmful to leave it on 6l6?
 
mansin_mind":2yd1gnvv said:
Thanks for the help and quick replies. I'm a little confused so bare with me... you mention that the tubes are biased at ones but that the shunts only measure outer and inner tubes? Huh? So do I place the black wire in the middle then the red to either left or right shunt, bias then switch the red wire and bias again? I am starting to believe the power tube switch has a fault on the el34 side. Would it be harmful to leave it on 6l6?
Click to expand...

Maybe I should rephrase the captions in the photo of the output transformer. Where is says set #1 and set #2, you can think of it as pair #1 and pair #2.
You read the bias off either pair #1 OR pair #2. If you measure your bias on pair #1 all you are basically doing by connecting to the shunt of pair #2 is seeing
how well the quad is matched from the tube vendor. If your setting is 60mA on pair #1, your reading on pair #2 depends on how well matched your power tubes
are. The reading for pair #2 will either be a few mA higher or lower due to the tube matching. If the reading is 15-20mA higher or lower then you know you do
not have a matched quad.

You first need to put the EL34's back in, set the switch to EL34 and see if you get set to 60mA. If you see 60mA on the OT with the switch set to EL34
then it should work. If you do not see, or cannot adjust to 60-65-70mA in the EL34 mode, lower the bias pot to zero and move the switch to 6L6.
Raise the bias pot and see if you can get it to 40-50mA just to test.

My original reasoning behind the improper bias with the EL34 switch is because EL34's draw a good bit more current than 6L6's.
If you did not adjust the pot properly, or you are getting a bad, or improperly set reading on the multi meter the tube is so ON, like
a gas pedal to the floorboard that the power section has no where to go.
 
I shall try once again this weekend. When I bought the tubes supposedly they are a matched quad. On the boxes the numbers were all the same except the IMG #, whatever that is. A pair has 46 the others 26. The PC and TC numbers were the same. Is that a bad quad? The seller gets them from magic parts. Let me know what you think.
 
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