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ECC85 any good for audio?
- Thread starter OneyedK
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Except for heater wiring (voltage is 6.3v instead of 12.6v), it looks to be very similar to the 12AT7. I'd expect most circuit designs that work well with the 12AT7, would also work well with the ECC85/6AQ8.
BTW: It will sub for the 6BQ7, as a plug-in. Gain is a higher than the 6BQ7, but the loading (bias, etc) is close enough for a drop-in functional replacement. It'd also plug in in place of the 6DJ8, but you'd need to see if the tube biases up in a usable range (the transconductance of the 6DJ8 is about twice as high as the 6AQ8).
Regards,
Gordon.
BTW: It will sub for the 6BQ7, as a plug-in. Gain is a higher than the 6BQ7, but the loading (bias, etc) is close enough for a drop-in functional replacement. It'd also plug in in place of the 6DJ8, but you'd need to see if the tube biases up in a usable range (the transconductance of the 6DJ8 is about twice as high as the 6AQ8).
Regards,
Gordon.
To make it work in place of a 12AT7- as long as the power transformer has 6.3v heater windings- you can just rewire the heater pins on the tube socket, so that heater power is provided to pins 4 and 5 individually, instead of 4 and 5 being in parallel for one heater connection, and pin 9 being used for the other heater connection (as they would be for the 12AT7).
Once you do that, you can plug in the 6AQ8.
In fact, if you wanted to "A-B" compare the "sound" of the 12AT7 to that of the 6AQ8, you could just get a pair of 6DT8, to contrast with the 6AQ8s. The 6DT8 IS the same tube as the 12AT7, just with a 6 volt heater (only) pin-out (same pin-out as the 6AQ8).
Regards,
Gordon.
Once you do that, you can plug in the 6AQ8.
In fact, if you wanted to "A-B" compare the "sound" of the 12AT7 to that of the 6AQ8, you could just get a pair of 6DT8, to contrast with the 6AQ8s. The 6DT8 IS the same tube as the 12AT7, just with a 6 volt heater (only) pin-out (same pin-out as the 6AQ8).
Regards,
Gordon.
OneyedK
Active Member
Great tip! Thanks!
The bigger problem you will likely have is not getting them to sound good in a circuit, but finding quiet ones. With such a large stash, I'm sure you will -- but they will likely be the exception rather than the rule. Like other RF based tubes, it is a frame grid tube, which is always prone to noise in audio circuits.
They were handed to you? Life is so unfair at times!
Dave
They were handed to you? Life is so unfair at times!
Dave
jaymanaa
RIP 1961-2018
Hi DC, can you explain further what a frame grid tube is? Thanks in advance, Jay And yeh, I wish somebody would hand me an old worn out 5u4, but not even that happens.
Yes, and this is the same difficulty that is had, by people using 6DJ8/6922 tubes, for the exact same reason.
It is possible to find quiet ones, but it's not always easy.
Regards,
Gordon.
jaymanaa
RIP 1961-2018
Exactly what I figured, but damn does a 6DJ8 have a beautiful tone. I haven't had too many that couldn't be tamed with dampers really., and the would definitely be worth a suspended sub-chassis mount to me.
jaymanaa
RIP 1961-2018
I recently read that the computer versions of the 6DJ8 (like HP) are even more noisy due to a thinner grid or filament wire, but I can't remember which (grid I'm pretty sure). Apparently the computers (at least in some regards) didn't give a crap about noise?
Kegger
R.I.P. 1/12/1966 - 6/1/2017
If I may chime in,
If actually had much better experience with these than an 12AT7..
They test better, last longer staying fresh, mostly even between sections.
And have not had noise issues, I Much prefer these over 12AT7's in audio.
Also they tend to come in the better "audio" brands as well, good euro tubes.
There also not a frame grid tube, basically there the same as a 12at7, just pins.
If actually had much better experience with these than an 12AT7..
They test better, last longer staying fresh, mostly even between sections.
And have not had noise issues, I Much prefer these over 12AT7's in audio.
Also they tend to come in the better "audio" brands as well, good euro tubes.
There also not a frame grid tube, basically there the same as a 12at7, just pins.
jaymanaa
RIP 1961-2018
If I may chime in,
If actually had much better experience with these than an 12AT7..
They test better, last longer staying fresh, mostly even between sections.
And have not had noise issues, I Much prefer these over 12AT7's in audio.
Also they tend to come in the better "audio" brands as well, good euro tubes.
There also not a frame grid tube, basically there the same as a 12at7, just pins.
Dang it Keg, now you done it. I guess I'm heading to epay before word gets out. :dammit:
Why are these always worn out in old tuners? They are always perched up there with a shield, you know what I mean. I swear, they are always crummy testing when all the other tubes test good. Maybe my tester doesn't like them, it sure doesn't like the 6DJ8. I almost threw away a box full of good ones once (DJ8s).
Jay -- Unlike a conventional 12AX7 -- where the grid wire is spiral wound around two secure posts, frame grid tubes use grid wire that is many times finer that that of a 12AX7, allowing the grid to get closer to the cathode -- which creates the rather large Gm figure that modern frame grid tubes have. But the wire is so fragile, that it must be built on a ladder frame for stability. The frame is adequate enough for stability with RF work, but the shifting on the ladder from heating, combined with the cathode formulation used that is not quite as stable, causes the tubes to generate more audio noise. From a theory standpoint, frame grid tubes have the capability of being the quietest audio tubes, as normal tube noise is a product of grid noise multiplied by the amplification factor of the tube. With such a small grid, the actual grid noise can theoretically be smaller than with conventional grids. Therefore, it's the practical matters of construction that get in the way of making quiet frame grid tubes.
Frame grid tubes were one of the last tubes to be developed. By the time anyone could get around to making them quiet for audio work, tubes were gone, and development work was abandoned. What a shame.
Dave
Frame grid tubes were one of the last tubes to be developed. By the time anyone could get around to making them quiet for audio work, tubes were gone, and development work was abandoned. What a shame.
Dave
Front end RF tubes operate at high current levels over that which they operate at in audio circuits, which is why they wear out so fast in tuner sections.
Keg -- Everything I've ever read speced the 6AQ8 as a frame grid tube, but of course, putting my hands on any of that information now would take a lot of searching. Do you know for a fact that the tube employs a conventional spiral wound grid?
Dave
Keg -- Everything I've ever read speced the 6AQ8 as a frame grid tube, but of course, putting my hands on any of that information now would take a lot of searching. Do you know for a fact that the tube employs a conventional spiral wound grid?
Dave
jaymanaa
RIP 1961-2018
Great info from you and Keg as usual, i love learning these things and the reason why.
It does seem that advent of the transistor killed the tube right in it's heyday. The compactrons were awesome, and I read that they were getting ready to start adding other passives inside the bottle. Don't know how they would have worked around the heat, but I do have several cold cathode tubes. No telling where tubes would have gotten to if it hadn't been for Roswell, dang aliens and their sand. I bet it was a bugger to reverse engineer that stuff. Oh dang, I haven't plugged in the ground on my tin beenie yet.
Kegger
R.I.P. 1/12/1966 - 6/1/2017
As far as I know Dave, the 6AQ8/ECC85 is not an frame grid tube.
Now could there be some out there, I'd imagine there could though.
(as I've seen Chinese 12at7's with a plate structure like a 6dj8 does)
But I've never seen a spec sheet describe them as an frame grid tube.
Correct me if I am wrong but when a tube has a plate structure like an
12au7/12at7/12ax7 they won't be of the frame grid design where tubes
of the frame grid design there plate does not look like a traditional 12ax7.
In other words you can tell by the plate structure whether an tube would
be a traditional grid or have a chance to be the frame grid type by looking.
A 6AQ8/ECC85 plate looks just like a 12AT7 does, quite different then your 6DJ8.
Not that a plate has to Only look like a 6DJ8 to be frame grid, but not like 12AX7.
Now could there be some out there, I'd imagine there could though.
(as I've seen Chinese 12at7's with a plate structure like a 6dj8 does)
But I've never seen a spec sheet describe them as an frame grid tube.
Correct me if I am wrong but when a tube has a plate structure like an
12au7/12at7/12ax7 they won't be of the frame grid design where tubes
of the frame grid design there plate does not look like a traditional 12ax7.
In other words you can tell by the plate structure whether an tube would
be a traditional grid or have a chance to be the frame grid type by looking.
A 6AQ8/ECC85 plate looks just like a 12AT7 does, quite different then your 6DJ8.
Not that a plate has to Only look like a 6DJ8 to be frame grid, but not like 12AX7.
Keg -- Invariably, the operating portion of the plate structure (that is, minus any additional "area" that simply aids cooling) is smaller on frame grid tubes, because the grid assembly is so much smaller. Therefore, the plate structure can be smaller as well. It doesn't HAVE to be smaller, but virtually always is to gain maximum performance.
Note that the plate structure of the 12AT7 looks nothing like that of traditional AU or AX tubes, as it was an early attempt towards emulating the qualities of modern frame grid tubes (higher transconductance, lower capacitance, etc.)
It is hard to judge the grid construction of a tube by its plate structure. Remember that these tubes ALL have their roots in RF applications, and things at those frequencies can get really weird. Nothing of audio applies at those frequencies, and nothing of RF applies at audio frequencies. Therefore, the plate structures may be more of an indicator of application than construction.
I'll have to research the 6AQ8 some more. Heck this may come down to the goofy 6CA7/EL34 construction where one is a beam power tube, and one is a pentode. Maybe the 6AQ8 is a frame grid while the ECC85 isn't, or visa versa? It's an interesting question!
Dave
Note that the plate structure of the 12AT7 looks nothing like that of traditional AU or AX tubes, as it was an early attempt towards emulating the qualities of modern frame grid tubes (higher transconductance, lower capacitance, etc.)
It is hard to judge the grid construction of a tube by its plate structure. Remember that these tubes ALL have their roots in RF applications, and things at those frequencies can get really weird. Nothing of audio applies at those frequencies, and nothing of RF applies at audio frequencies. Therefore, the plate structures may be more of an indicator of application than construction.
I'll have to research the 6AQ8 some more. Heck this may come down to the goofy 6CA7/EL34 construction where one is a beam power tube, and one is a pentode. Maybe the 6AQ8 is a frame grid while the ECC85 isn't, or visa versa? It's an interesting question!
Dave
