D-Moll Plate Voltage?

Crunchtime

Crunchtime

Member
Does anyone know what the plate voltage should be for a D-Moll?

I just got a D-Moll and plan to check the bias with my Bias Rite this weekend. I would like to know the pv in advance because I am curious just how accurate my Weber Bias Rite actually is.

Thanks in advance. :rock:
 
Peter Diezel":34e6vjb0 said:
Depending on your wall power the plate
voltage should be between 470 and 490 volt DC.

Best,
Peter
Click to expand...

Thank you, Peter. Should the KT77 be biased as if it were a EL34? I've seen one bias calculator suggesting a KT77 would be biased a bit higher. I've also heard to bias new production KT77 tubes as if they were EL34's.
 
Crunchtime":1e1jbxgl said:
Peter Diezel":1e1jbxgl said:
Depending on your wall power the plate
voltage should be between 470 and 490 volt DC.

Best,
Peter
Click to expand...

Thank you, Peter. Should the KT77 be biased as if it were a EL34? I've seen one bias calculator suggesting a KT77 would be biased a bit higher. I've also heard to bias new production KT77 tubes as if they were EL34's.
Click to expand...

I believe they have a MPD of 25W, so they should bias like an EL-34.
 
Crunchtime":1ifcnwxj said:
Peter Diezel":1ifcnwxj said:
Depending on your wall power the plate
voltage should be between 470 and 490 volt DC.

Best,
Peter
Click to expand...

Thank you, Peter. Should the KT77 be biased as if it were a EL34? I've seen one bias calculator suggesting a KT77 would be biased a bit higher. I've also heard to bias new production KT77 tubes as if they were EL34's.
Click to expand...

Yep, biased the same as EL34. Both Gold Lion and JJ KT77s bias up pretty nicely around 30-35ma in my Einstein, same in my Hydra (plate voltage of 470).
 
If an amp is designed around an EL34 you should treat any other tube as an EL34 when biasing. I know you are using KT77 so this really doesn't apply. A lot of people think because they install 6550 in their Marshall they should bias the 6550 as you would in a 6550 amp. Not the case. The OT has the primary impedance for EL34, so biasing a 6550 as you would normally will not mean the tube is operating as it should. You will not get more output either with KT88, 6550, or 6l6 in an amp with an EL34 transformer.
 
glip22":11p0ecbo said:
If an amp is designed around an EL34 you should treat any other tube as an EL34 when biasing. I know you are using KT77 so this really doesn't apply. A lot of people think because they install 6550 in their Marshall they should bias the 6550 as you would in a 6550 amp. Not the case. The OT has the impedance for EL34, so biasing a 6550 as you would normally will not mean the tube is operating as it should. You will not get more output either with KT88, 6550, or 6l6 in an amp with an EL34 transformer.
Click to expand...

Never heard this before. Especially since as I understand it (Mr. Diezel can elaborate if he wants), amps like Diezels that are designed to accept any tube type you should bias a tube according to its specific design specs and plate dissipation. It's not like the transformer was designed to operate for one tube type. But I do know that some amps—like my Peters Hydra—if you use 6L6 tubes, it is recommended you bias to how the tube should be biased but then half the speaker output impedance. For example if you're running a 16ohm cab, use the 8ohm output. But this isn't for reliability or anything it's just that the sound/feel of the amp will change slightly.

But 6550s should be biased much higher than an EL34. They would sound pretty awful if you biased them at 30mA per tube... Super cold.
 
FourT6and2":1fosjldt said:
glip22":1fosjldt said:
If an amp is designed around an EL34 you should treat any other tube as an EL34 when biasing. I know you are using KT77 so this really doesn't apply. A lot of people think because they install 6550 in their Marshall they should bias the 6550 as you would in a 6550 amp. Not the case. The OT has the impedance for EL34, so biasing a 6550 as you would normally will not mean the tube is operating as it should. You will not get more output either with KT88, 6550, or 6l6 in an amp with an EL34 transformer.
Click to expand...

Never heard this before. Especially since as I understand it (Mr. Diezel can elaborate if he wants), amps like Diezels that are designed to accept any tube type you should bias a tube according to its specific design specs and plate dissipation. It's not like the transformer was designed to operate for one tube type. But I do know that some amps—like my Peters Hydra—if you use 6L6 tubes, it is recommended you bias to how the tube should be biased but then half the speaker output impedance. For example if you're running a 16ohm cab, use the 8ohm output. But this isn't for reliability or anything it's just that the sound/feel of the amp will change slightly.

But 6550s should be biased much higher than an EL34. They would sound pretty awful if you biased them at 30mA per tube... Super cold.
Click to expand...
This is what Chris Merren told me years ago. That is why they make different output transformers for different tubes. Maybe if an amp can accept different tube types the transformer is made with a different impedance range. Also to operate certain tubes efficiently more is needed than just having the bias range to do it. For example to run 6L6's efficiently two pins on the power tube sockets should be jumpered that are not jumpered to run el34's efficiently. If you run 6550 in a Marshall you will hit diminishing returns by biasing within spec of what the 6550 calls for as this tube will never run efficiently with an EL34 transformer.
 
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