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33mA-43mA for EL34's but WHAT type of 12ax7???

SLOhand

Member
Messages
12
Hey guys,

Any help would be greatly appreciated here!!!

...............I read somewhere that the plate voltage on a T-verb can be between 460 - 475 and my EL34 power tubes should be around
33Ma - 43Ma.

SO my question is what should the "pre-amp" tubes be rated at? :jo

I want to get some NOS tubes but don't have any idea of what ma to get


Thanks
 

ked

Member
Messages
911
You won't need to do any adjusting on the preamp tubes. Just get whatever NOS tubes you want and stick them in, they will work fine.


Ken
 

rockon1

Platinum Supporting Member
Messages
12,774
Yep,like ked said, the 12AX7's are "plug and play". FWIW - I wouldnt go over 37 ma on the EL34's if the plate voltage is 470. 37 is actually pushing it at 70% dissapation. 35ma is a safer bet. 43ma would be way hot. Bob
 

SLOhand

Member
Messages
12
Thank You very much guys..........I was sure someone could help me out here. This is great, now I don't have to worry :munch
 

SLOhand

Member
Messages
12
Next question,

is 33mA on the cold side or is 43mA?

if that doesn't make sense - let me rephrase the question
If I had a 33 mA power tube would that be considered a warm tube in a Trem-O-Verb which has a plate voltage of around 470




Thanks for any help guys



:horse
 

rockon1

Platinum Supporting Member
Messages
12,774
The formula for calculating idle dissipation is

max tube dissipation / plate voltage X .7(70%) or .6 for a somewhat cooler 60% or anyhere in between...



25 / 470 = .053 X .7 = .037 or 37ma Thats as hot as you want to set it. Personally I dont see any advantages to running at 70% idling. If it sounds good slightly cooler all the better. The tubes will last longer.At 33 ma your idling at a more conservative 62% idle dissipation. Bob
 

Blue Strat

Member
Messages
30,077
Next question,

is 33mA on the cold side or is 43mA?

if that doesn't make sense - let me rephrase the question
If I had a 33 mA power tube would that be considered a warm tube in a Trem-O-Verb which has a plate voltage of around 470




Thanks for any help guys



:horse
If you're talking about the tube RATING as supplied by the tube dealer, that doesn't tell you much. You actually have to measure and adjust the bias of the amp for any new pair of tubes to get things in line.

Since Mesa's don't have bias adjustments order from a dealer who knows what ratings are correct for Mesas and just plug and play.

We can do that for you.
 

rockon1

Platinum Supporting Member
Messages
12,774
If you're talking about the tube RATING as supplied by the tube dealer, that doesn't tell you much. You actually have to measure and adjust the bias of the amp for any new pair of tubes to get things in line.

Since Mesa's don't have bias adjustments order from a dealer who knows what ratings are correct for Mesas and just plug and play.

We can do that for you.

Oops I didnt even catch that! Thought he was talking about the setting he was at with it.
OP- My post above is meaningless. Bob
 

SLOhand

Member
Messages
12
Thank you gentlemen for responding to all my noob questions......


First off - Mike K you are first on my list to order tubes from, i've been drooling all over your website......lol

back to my question

If I understand you correctly 33mA is good, 37mA is warm, and 43 is over the top HOT/too hot.

Much appreciated guys thanks so much


Lance
 

rockon1

Platinum Supporting Member
Messages
12,774
Thank you gentlemen for responding to all my noob questions......


First off - Mike K you are first on my list to order tubes from, i've been drooling all over your website......lol

back to my question

If I understand you correctly 33mA is good, 37mA is warm, and 43 is over the top HOT/too hot.

Much appreciated guys thanks so much


Lance
If when actually measuring the bias in the amp you got those readings,basically,yes. I would consider a setting of 37 ma warmer than necessary though. Bob
 




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