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You got 6CA7s that are too hot (hot = higher current under a given set of operating conditions). Your amp does not have sufficient bias adjustment range to bring the current down to spec. There is nothing wrong with the tubes per se - they are just a misfit for the amp.
You need a set of 6CA7s that are mid range to cool biasing (cool = lower current under a given set of operating conditions). Then you'll be able to adjust the bias to the specified range.
Yes it IS a problem that the 2 tubes are at .416! That is roughly 30% over the spec for the amp.
And finally the .416 is NOT current (ma.) It is VOLTAGE!! It's the voltage developed across a 10 Ohm resistor in the circuit between the tube cathode and ground by the current flowing through the tube and on through the resistor. Using Ohm's Law you can compute the current. The current equals the voltage (.416 volts) divided by the resistance (10 Ohms) which equals .0416 or 41.6 milliamps (abbreviated ma.)
If you own a tube amp it behooves you to learn about bias and biasing so you don't get confused by it.
BTW - what brand 6CA7s are you using?
Sent a couple to grant fidelity because I was interested in the Treasures and they were willing to test the ones I had. And they said they tested over 125% strong....25% more than the max..I tried to contact Tube Depot they would not respond.
Thanks again for your reply.
Your a knollegable person. That's why I posted. Yes I mixed up ma and mv stupid mistake but I do know the difference. I replaced the old tubes that were used for repair and they were low but able to bias correctly at 300mv. I'll order new tubes with that in mind (cool) I was using the EH 6ca7s
Thanks again for your advice
The EH tubes out there these days tend to be hotter biasing. In fact it is difficult to get cool biasing EHs from the factory right now. So be careful that the tube vendor knows what he's selling!
That's probably why Manley wont sell the 6CA7 replacement tube set up any more. They used to offer both the EL34 or 6CA7 replacement tube packages for these amps, but no more and its probably because of this issue....
Thanks again. regards
fin, this is what I was told by Manley staff.
The Snappers were designed with EL34s and initial production shipped with those. That is why you'll see EL34 identified on the top plate. Then they began seeing problems with quality from their supplier so switched production to 6CA7s. After some period of time they found acceptable quality in EL34s again so changed back again. That is how they are produced today and what they recommend for re-tubing. Sorry, I can't identify timeframe for the changes.
Mine had 6CA7s when I bought them and since they were strong I didn't want the expense of changing back to EL34s.
"The piano ain't got no wrong notes." Thelonious Monk
They test very strong. Marshall's bias pot seems to have enough range to handle this. This tube lasts forever in road-bound amps. Really tough cookies!
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