Aletheian, the 5965 is not specced as a remote cutoff device. It's a computer tube, and so the specs are pretty loose. Some are very nonlinear, having a sort-of remote cutoff characteristic, and some are better. I used it at the time because it was the only (or only available) duotriode that had a high enough gm and low enough rp to do the job here, the constraint being the rather low grid circuit resistance rating of the 6V6 when negative-supply biased. Andy Evans in Blighty did some taste tests on various types; he ended up liking the pinch-waist Mullards best, I never found any. Best I found was RCA three-mica 5965, followed by RCA two-mica and orange-label Amperex 7062, then white-label Mullard / Amperex / Philips E180CC.
A lot of the nonlinearity of this tube type is 2nd order, and it's being used here in a diff-amp, which nulls most of this out. They can actually sound very good, but they got 'discovered', they're getting harder to find, and getting good pairs and quads is a bear because they test so scattery.
I think this may be a problem in adapting all sorts of oscillators (6T4), VHF amps (6GK5), sweep and pass tubes, all of that stuff, for audio. It isn't that they're categorically bad, but a lot of things like microphonicity, noise, linearity, tight specs, just weren't cared about, so you takes your chances. For me so far, the 6GK is a definite winner, the jury is still out on the 6T4.
Aloha,
Poinz
A lot of the nonlinearity of this tube type is 2nd order, and it's being used here in a diff-amp, which nulls most of this out. They can actually sound very good, but they got 'discovered', they're getting harder to find, and getting good pairs and quads is a bear because they test so scattery.
I think this may be a problem in adapting all sorts of oscillators (6T4), VHF amps (6GK5), sweep and pass tubes, all of that stuff, for audio. It isn't that they're categorically bad, but a lot of things like microphonicity, noise, linearity, tight specs, just weren't cared about, so you takes your chances. For me so far, the 6GK is a definite winner, the jury is still out on the 6T4.
Aloha,
Poinz
That works to advantage in a PP amp, where even order distortion products from the "finals" are cancelled. Look at the NET distortion spectrum. Jim McShane correctly points out that a "waterfall" net HD spectrum is desireable. The 12AT7/ECC81 is skewed even more towards 2nd order HD than the 5965 and it sounds damned good as a differential splitter. Don't put a 'T7 in a SE amp. YUCK!
Poindexter said:
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Just because there are all too many yutzes out there doing poor open loop designs and hiding their mistakes behind enormous amounts of gNFB does not mean that it's "poison", just misused and abused.
NFB (local and global) is essential to get good performance from any SS amp, and from pentodes. I've done both, and NFB certainly helps improve the sound considerably, but only if you don't overdo it. The judicious use of NFB will make a good sounding SET sound even better. Furthermore NFB also helps in making performance less dependent on each component.
I just did.
The question is: will you learn from it?
Miles Prower said:
My suggestion to anyone (everyone) is to build an amp that you know will perform well without NFB, then go ahead and experiment by adding a little at a time to see if it improves the sound to your ears.
I think it really is a subjective thing, depends a lot on the rest of your system and you're listening habits. You might find a little helps tighten things up a bit. You might find more brings fun and dynamics. Then go back and try none at all again to see what it cost you ...
-- Dave
w5jag, where you come up with this obscure toob stoof? For me, plate caps put me in liability land, but that's a great data point.
jerluwoo, thanx for the 6J6 reference. I'm talking to my vendor right now about a C of them ($1.50/ea at that buy). It's a dedicated diff-amp device, but that's me!
Aloha,
Poinz
jerluwoo, thanx for the 6J6 reference. I'm talking to my vendor right now about a C of them ($1.50/ea at that buy). It's a dedicated diff-amp device, but that's me!
Aloha,
Poinz
6J6s;
jerluwoo, what kind of 6J6s you like? My guy has RCA, GE, Sylvania in inventories big enough to get good matching. Usually I would just try RCA first, since they're almost always good, but I wonder if you (or anybody else around here) has a read on which ones are the luxe.
Cool device, by the way; just the sort of thing I was hoping to find in this thread. The single cathode limits possible applications, of course, but I want to make a diff-amp out of them anyway. so hey!
Mahalo,
Poinz
jerluwoo, what kind of 6J6s you like? My guy has RCA, GE, Sylvania in inventories big enough to get good matching. Usually I would just try RCA first, since they're almost always good, but I wonder if you (or anybody else around here) has a read on which ones are the luxe.
Cool device, by the way; just the sort of thing I was hoping to find in this thread. The single cathode limits possible applications, of course, but I want to make a diff-amp out of them anyway. so hey!
Mahalo,
Poinz
Aittle late but anyway ...
Throw in a few pics of a 6AQ5-PP amp I finished today. The tubes look peculiar - slim and very high.
Throw in a few pics of a 6AQ5-PP amp I finished today. The tubes look peculiar - slim and very high.
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The 6j6s i have are rebadged to eico meant as replacements for oscilliscopes. Had about ten of them so i havnt tried any other brands. I posted a scematic of a very good sounding little hybrid amp here in the tubes section using them. Good little tubes i think. I found only 1 out of the ten that was microphonic.
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Hi,
Just found this thread! I built this 6AU6==>6AQ5 SE amp a couple years ago using OPTs and other parts from an old Sony R2R. I use it at work with eMac IPOD
Very nice sounding.Regards,
dg
Hey; sho-n-tell!
Here's the P O C breadboard of the Machine, with the 5965s replaced by 6GK5s
There's no goin' back; the 6GK5 has 60% more gain, 30% more drive (lower rp), no section-matching predicament, and sounds noticeably better than the 5965. More spacious, more juicy, more see-through.
Hau'oli i Maui,
Poinz
Here's the P O C breadboard of the Machine, with the 5965s replaced by 6GK5s
There's no goin' back; the 6GK5 has 60% more gain, 30% more drive (lower rp), no section-matching predicament, and sounds noticeably better than the 5965. More spacious, more juicy, more see-through.
Hau'oli i Maui,
Poinz