Hi,
I have recently ordered some Mullard 12At7s to swap out in my Art VLA Pro mkii and have just received the valves today. Thing is, 1 is an ecc81, and the other is an ecc81WA.
Are they for all intense and purposes the same?
I wasn't really too fussed getting a matched pair, but having 2 different models may be going too far.
I have contacted the company and am awaiting a response, but thought I'd ask you peeps in the meantime.
I tried looking up the differences, but couldn't find anything other than one is military? Possibly?
The Art is a dual mono/stereo compressor which I want to use on stereo mixes so don't really want a difference in the tubes.
Many thanks
Jim.
Mullard Ecc81 and Ecc81WA
Re: Mullard Ecc81 and Ecc81WA
Usually WA on the end of the number denotes special quality version.
Does not always mean better.
But usually has been through a selection process i.e. for military use.
Often WA versions are less microphonic.
Does not always mean better.
But usually has been through a selection process i.e. for military use.
Often WA versions are less microphonic.
Re: Mullard Ecc81 and Ecc81WA
But do you think that this would mean they are significantly different enough for them to be incompatible in a stereo unit?
They should be compatible but will not be identical. As Simon says, WA generally refers to high quality: a high quality envelope. Although it's the first time I have come across a Mullard valve with the WA suffix. The military version of the ECC81 is the CV4024.
I don't have the circuit diagram for the Art VLA Pro MkII, but it is likely that it has one ECC81 in each signal path, so I would prefer to use a matched pair, or at least an identically numbered valve.
If you want a matched pair, Watford valves, for example, can supply them.
Re: Mullard Ecc81 and Ecc81WA
In theory a 12AT7/ECC81 should meet pretty tight specifications, so should be as closely matched as you are likley to get. Differences will be due to slight mechanical positioning variations of components within the valve.
There are plenty of other things within the VLA that are probably less matched than the valves will be. Resistors are generally 5% with some at 1% tolerance.
If there are any significant differences it may well be in noise and microphony levels rather than output levels, but that could still happen even if they were both ECC81 or both ECC81WA versions.
Differences in channel level are what the TLA's balance control is there for (this is the 2nd channel output level when the TLA is in stereo mode), so if you want stereo operation to be fully balanced it's worth running test signals through to get the outputs the same for the same input signal. I would use a scope or a meter for this, not the VU meters.
The valves are run off a 45v supply, so there aren't lethal voltages present inside the unit when it's switched off, but I'd still give it an hour or so to let any residual stored charge on the capacitors dissipate before opening it up.
(I found the schematic for the majority of the unit here https://www.eserviceinfo.com/downloadsm ... ro-2.html )
There are plenty of other things within the VLA that are probably less matched than the valves will be. Resistors are generally 5% with some at 1% tolerance.
If there are any significant differences it may well be in noise and microphony levels rather than output levels, but that could still happen even if they were both ECC81 or both ECC81WA versions.
Differences in channel level are what the TLA's balance control is there for (this is the 2nd channel output level when the TLA is in stereo mode), so if you want stereo operation to be fully balanced it's worth running test signals through to get the outputs the same for the same input signal. I would use a scope or a meter for this, not the VU meters.
The valves are run off a 45v supply, so there aren't lethal voltages present inside the unit when it's switched off, but I'd still give it an hour or so to let any residual stored charge on the capacitors dissipate before opening it up.
(I found the schematic for the majority of the unit here https://www.eserviceinfo.com/downloadsm ... ro-2.html )
Reliably fallible.
Re: Mullard Ecc81 and Ecc81WA
I forgot to ask, what is the reason for replacing the valves? As Wonks kindly states, the HT is a low 45V and probably the heaters have a DC supply, so the valves should last a very long time. (Some of my ECC81s are really quite old but still work fine).