I bought some Winged C EL34's for my Mark V head and ordered them in "Mesa spec". Just to be safe I used my bias rite and measured around 434 plate voltage and the tubes are running at about 67 ma in the middle and 462 plate voltage and 51 ma on the outer tubes. Is this a safe range and is anything going to be damaged running it this hot? It seems high to me but I don't know for sure. :?
Mark V EL34 bias reading help
- Thread starter bradg
- Start date
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What kind of "Bias Rite" model are you using ?
If your readings are indicated for "pair of tubes", that means
33.5mA per tube (67mA for inner pair) and 25.5mA per tube (51mA for outter pair).
You're running Mark V in safety zone but cold, around 50~60% plate dissipation.
Use Weber Bias Calculator as reference.
http://www.webervst.com/tubes1/calcbias.htm
If your readings are indicated for "pair of tubes", that means
33.5mA per tube (67mA for inner pair) and 25.5mA per tube (51mA for outter pair).
You're running Mark V in safety zone but cold, around 50~60% plate dissipation.
Use Weber Bias Calculator as reference.
http://www.webervst.com/tubes1/calcbias.htm
bradg said:
I wouldn't run those tubes. The ones in the outer (AB) pair are running at 94.2% of their maximum plate dissipation (following Ohms Law, 462V * .051A = 23.5W). The 'average' Class AB MPD is generally around 70-75%.
Even though the inner pair is "Class A", that's still really hot as those positions are coming in at 116% MPD (29 Watts).
Maybe someone with Mesa STR-447 EL34's in their MKV can take some readings so we can compare to a baseline?
Dom
A
Anonymous
Guest
some one already took some bias readings with mesa 450 http://forum.grailtone.com/viewtopic.php?f=33&t=38013&start=30
just remember that some vendors do not realize that the markV runs a bit hotter than other mesa amps.......
good luck
just remember that some vendors do not realize that the markV runs a bit hotter than other mesa amps.......
good luck
Yeah I saw that post. It looks like mine are about 10 ma above those readings per tube. I guess I'm just wondering if that's a lot or not that big of a deal. I've had a couple people tell me they wouldn't run them that hot and a couple people say if they aren't red plating and they sound okay, then they are fine. I haven't played anything on them running that hot yet so I don't know what or if anything will happen. :?
It's a brand new head so I don't want to f anything up right off the bat.
It's a brand new head so I don't want to f anything up right off the bat.
A
Anonymous
Guest
bradg said:
brand new amp, i wouldn't risk it.......tell the vendor that you need an exchange for something colder ( no i am not talking about beer...jijiij).....
good luck
>Photi G<
Well-known member
salvatruco said:
He screwed things up a bit. The class A sockets are the OUTER 2. That's where the EL34's should have been, so that their MPD would have been below 100%, when running the hybrid combo, and a higher current draw, mebbe?
JOEY B.
Well-known member
>Photi G< said:
NO I did not. The early Mark V manual was wrong. I spoke with Mike Bendenelli about the tube configuration in the Mark V. He said that he did not know why the Class-A sockets were moved to the inner positions on the Mark V, but he advised me of such. It must have something to do with the 10 watt mode. Take a look at the all 6L6 or all EL-34 readings printed in the post, and you will see that the inner pair has the hotter bias. This was with a matched quad.
