Dsl50 Bias 50mv+

[PeteTheAussie]

Hi all. Just replaced the tubes in my DSL50 and the bias reading at it lowest is 50mV and above on one side.
I replaced my original tubes with EH EL34’s. Any ideas? First time attempting this sort of thing.

 

[Goldmember]

Did this problem exist with the old, original power tubes? I suggest reinstalling the old tubes and checking bias,
to see if the problem is originating in the tube, rather than a bias resistor.

 

[PeteTheAussie]

Did this problem exist with the old, original power tubes? I suggest reinstalling the old tubes and checking bias,
to see if the problem is originating in the tube, rather than a bias resistor.

Thanks Goldmember. Put the old winged Cs in and it’s nice and low at 25 26 on either side. I took them out and put the EHs tubes back in and they’re back up to just under 50mV... guess it must be a the tubes. :/ My next question is this typical for the EH EL34s or do they sound like they’re a bad set?

 

[m1989jmp]

Thanks Goldmember. Put the old winged Cs in and it’s nice and low at 25 26 on either side. I took them out and put the EHs tubes back in and they’re back up to just under 50mV... guess it must be a the tubes. :/ My next question is this typical for the EH EL34s or do they sound like they’re a bad set?

Some sets are like that; if they're both within 5mA and new, they're working as they should. 25mA sounds like a really cold bias, btw.

You'll have to adjust the value of the bias dropping resistor if you want to use those EH tubes.

 

[mickeydg5]

That tube set runs hot, too hot for the bias setup. See if the retailer will exchange them.

You should be able to adust the bias down to the 20mV area. That is normal for bias adjustment range but you want the tubes to actually bias in the 35mv to under 45mV area.

 

[Goldmember]

I'm using a matched set of JJ EL34 valves in my DSL50, with great results and bias set around 37.

 

[SG~GUY]

-hey Pete-
-Im a fan of cp EH Power & Pre Amp tubes, second only to GOLD LION GOLD PIN PRE's & there Power Tube offerings, i have a couple questions if you don't mind me asking,
-are you sure that you have EL34's-(pentode)- & not 6CA7's-(tetrode)-(but works as a triode or my favorite pentode)-
-how are you measuring your bias?
-I always bias my tubes hot,... Always have, always will,. 70% diss. is a theoretical "safe setting". I use 90% or more & use the -Tube DATA SHEET- for my target for min & max settings,... First & Foremost paying very close attention to the -CATHODE CURRENT-------(plate + screen current = cathode current)---& secondly I use -PLATE VOLTAGE- with
-cathode voltage- being the ignored, red headed step child in the -(WATT'S)- dissapation equation.
-your bias will drop from your initial readings after taking them out of idle and pounding the playing & pounding piss out of them, so keep an eye on them in the beginning by taking readings every 20 minutes at first, then you'll notice they will burn/settle in, but the will continue to drop but the pace depends on the pounding, the tone & the time
-50 is the max for ELECTRO HARMONIX EL34's & 70 for 6CA7's in self bias, according to there DATA SHEET'S-

-I've used the EH 6CA7's @ 90+ with great tone, exceptional performance & endless longevity, at the same point in time there were people reporting repeated failures & they were using 70% and lower dissipation,
this was years ago & haven't heard about it since, go figure, the USA 6CA7 is a HEAVY DUTY MILITARY DESIGNED TUBE,.. maybe she likes it a little rough?

 

[Goldmember]

Did someone say...gold?

 

[Ken]

50 mv is WAY too high. The sweet spot is 32-36 on these amps. I would exchange the tubes for another pair.

Ken