6V6 to EL-84 adapter question

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Are these adapters generally considered sound/safe for lower wattage tube amps? Will I need adjust the bias? :icon_scratch:
 
Generally, I would not call them safe.  There are several issues, the main one being that the maximum rated plate voltage for the el84 is 300V.  Many 6V6 amps, even the low power ones, run at 400 to 450 volts.  Some (like the Princeton reverb) don't even have screen resistors. 

Now, it is possible to run high plate voltages on an el84, but you really need to use sane voltages on the screen (like one-half b+) and hefty screen resistors (like 1k; not the tiny 470R that Fender used to use).  That is, you need to design the output circuit with the plate dissipation and voltage ratings of that particular tube in mind.  Traynor used to do this with some very clever designs (super custom special anyone?) but they were the exception.  Well, ok music man did this kind of thing as well.

So, in general, no.  Not safe.  Which is annoying because you can't find 6V6 tubes right now
 
Mayfly said:
Generally, I would not call them safe.  There are several issues, the main one being that the maximum rated plate voltage for the el84 is 300V.  Many 6V6 amps, even the low power ones, run at 400 to 450 volts.  Some (like the Princeton reverb) don't even have screen resistors. 

Now, it is possible to run high plate voltages on an el84, but you really need to use sane voltages on the screen (like one-half b+) and hefty screen resistors (like 1k; not the tiny 470R that Fender used to use).  That is, you need to design the output circuit with the plate dissipation and voltage ratings of that particular tube in mind.  Traynor used to do this with some very clever designs (super custom special anyone?) but they were the exception.  Well, ok music man did this kind of thing as well.

So, in general, no.  Not safe.  Which is annoying because you can't find 6V6 tubes right now

So in essence what I am hearing is they are perfect if I wanna roll the proverbial dice and damage my amp or even blow the output transformer. :icon_thumright:
 
Spud said:
Mayfly said:
Generally, I would not call them safe.  There are several issues, the main one being that the maximum rated plate voltage for the el84 is 300V.  Many 6V6 amps, even the low power ones, run at 400 to 450 volts.  Some (like the Princeton reverb) don't even have screen resistors. 

Now, it is possible to run high plate voltages on an el84, but you really need to use sane voltages on the screen (like one-half b+) and hefty screen resistors (like 1k; not the tiny 470R that Fender used to use).  That is, you need to design the output circuit with the plate dissipation and voltage ratings of that particular tube in mind.  Traynor used to do this with some very clever designs (super custom special anyone?) but they were the exception.  Well, ok music man did this kind of thing as well.

So, in general, no.  Not safe.  Which is annoying because you can't find 6V6 tubes right now

So in essence what I am hearing is they are perfect if I wanna roll the proverbial dice and damage my amp or even blow the output transformer. :icon_thumright:

This is the kinda thing that keeps me doing amp repairs!  :icon_thumright:
 
Mr. MayFly, not to keep beating this subject into the ground. (get it ground!?)  :laughing7: however, are THD Yellowjackets an EL-84 "adapter" an exception in your opinion? I ask as I have one more new set of 6v6's but 4 unused sets of EL-84's (and no longer have an EL-84 amp). Are these safe? I am guessing probably as they were designed by Andy Marshall. Or have they proved temperamental also?
 
I have not had any experience with that particular brand.  I would wonder, if it's not a direct connection, what kind of circuitry is in there and how it manages to achieve the ~150V drop on the plate voltage and required screen dissipation.
 
Thank you sir. I will dig a bit further.  :icon_thumright: I did find some info and posted it but then deleted it as I have seen too much conflicting info regarding these things to be completely comfortable using them. I am gonna be safe and trust MayFly here.

Some say perfectly fine, others disagree.
 
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