Anyone with 5965 tube experience here?
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diamondsouled
Recycle belly button lint!
Same as a 12AV7 except made for computers.
Here's a handy gain factor chart:
http://thetubestore.com/gainfactor.html
Cheers
Lar
Here's a handy gain factor chart:
http://thetubestore.com/gainfactor.html
Cheers
Lar
Phototone, no, specific need for less gain, just a good deal on a lot of tubes. I went ahead and sprang for 18 of them that have been tested and the results printed on the box. I got them very cheap.
Diamondsouled, Thanks for the chart.
Do any of you think the difference in gain will make any significant audible difference overall?
Diamondsouled, Thanks for the chart.
Do any of you think the difference in gain will make any significant audible difference overall?
Phototone
Super Member
It all depends on the circuit they are used in. Those commercial amps that use negative feedback will compensate.
Yes, mine do use negative feedback. They are VTA boarded st-70's, all upgrades and GL kt66's. Can you explain how this compensation occurs?
I recently had a pretty disgusting experience with JJ 12AT7's, so I'm willing to play around with REAL American tubes, especially if I can find them this cheap again!
BinaryMike
Pelagic EE
In general, feedback circuits take a sample of the output voltage and subtract it from the input signal. If open-loop gain is 100 and you feed back enough signal to reduce closed-loop gain to 10, then all distortions are reduced by a factor of 10. One of these distortions is gain error. If open-loop gain changes by 20% due to a tube with lower gain, for instance, then closed-loop gain changes by just 2%.
Ok, so if I'm understanding this correctly, an amp with a negative feedback cicuit is playing a sort of balancing act within itself between signal and open loop gain? And now i'm guessing slightly higher or lower mu tubes affect this balancing act one way or the other, but only to a certain degree, I imagine? Is this what they call "learning"?
BinaryMike
Pelagic EE
There's more than one way to visualize negative feedback functionality. I often think of it as being centered around the input stage where signal subtraction takes place, and that's often a differential amplifier. The output of this stage is a pre-distorted signal whose shape and amplitude is tailored to nullify errors introduced in all subsequent stages. The accuracy of error cancellation depends primarily on how much excess gain you can devote to this purpose. It's common in SS power amps to have 100 times or more gain than necessary (open-loop). When the loop is closed, distortions reduce to 1% of the open-loop values. The whole proposition hangs on one salient fact: Gain is cheap. Extra gain is about the cheapest thing you can possibly throw at the problem. In tube amps, gain isn't so cheap. You can still use 10x excess gain or a bit more, but phase shift in transformers generally prevents taking the feedback principle to extremes.
vinylkid58
Super Member
Try GE "5-star" 6201's if the 5965's don't work out. They're still relatively affordable.
jeff
seanrr
Well-Known Member
I second the 6201 suggestion - I found those to be quite good in a Bottlehead Stereomour. That said, I have the 5965 in a Darling 1626 amp that I use for headphone listening, and it works best of the different types of 12AT7 I have tried - the guy who made the amp also had noted that the 5965 would work particularly good in that circuit. Anybody have suggestions for good 5965 tube manufacturers? I noticed that Telefunken even made them, but those seem to be outrageously priced on that auction site.
The 12AV7, 12AT7, and 5965 are all different tubes with different MU, plate resistance and transconductance. Check your tube manual! The 6201 is an industrial part number for the 12AT7.
Since each tube type has a different operating point, they will each work slightly differently in any particular circuit and one type may be prefered over another simply as a result of synergy with the circuit operating point. Negative feedback MIGHT NOT need recalibration since a lower gain tube will generate less NFB.
The bottom line is that these tubes are relatively cheap if purchased on epay. My own technique is to find an auction where multiple NIB tubes are presented. Say you find an auction with 5 identical tubes, or the same tube in multiple auctions. Test each tube IN CIRCUIT. Look for equal plate voltages and equal cathode voltages for all four sections on two tubes . That's to say that for a stereo pair you want to find two tubes with relatively equal plate voltages and cathode voltages for both sections. Those tubes are at least matched for quiescent current and will probably be well matched for their plate curves too. To find two well matched tubes you will probably need 4 or 5 tubes to choose from.
In my "El Cheapo" amp I found that I prefer the 5965, but that could be predicted from the plate curves in the tube manual. Plate curves for the 12AT7 show considerable 2nd harmonic distortion and the design engineer must attempt to reduce that 2nd harmonic distortion through differential amps and negative feedback. The GNFB for my "El Cheapo" is just 4.4dB.
Since each tube type has a different operating point, they will each work slightly differently in any particular circuit and one type may be prefered over another simply as a result of synergy with the circuit operating point. Negative feedback MIGHT NOT need recalibration since a lower gain tube will generate less NFB.
The bottom line is that these tubes are relatively cheap if purchased on epay. My own technique is to find an auction where multiple NIB tubes are presented. Say you find an auction with 5 identical tubes, or the same tube in multiple auctions. Test each tube IN CIRCUIT. Look for equal plate voltages and equal cathode voltages for all four sections on two tubes . That's to say that for a stereo pair you want to find two tubes with relatively equal plate voltages and cathode voltages for both sections. Those tubes are at least matched for quiescent current and will probably be well matched for their plate curves too. To find two well matched tubes you will probably need 4 or 5 tubes to choose from.
In my "El Cheapo" amp I found that I prefer the 5965, but that could be predicted from the plate curves in the tube manual. Plate curves for the 12AT7 show considerable 2nd harmonic distortion and the design engineer must attempt to reduce that 2nd harmonic distortion through differential amps and negative feedback. The GNFB for my "El Cheapo" is just 4.4dB.
gogofast
Addicted Member
in my experience, i did hear gain differences, but not much problem with distortion. i have half a dozen diy headphone amps that i use at work almost everyday, and sometimes my co-workers mess with 'em and leave 'em on for days at a time - so i had to swap out many tubes. unless you're going from 12ax7 to 5965 or 5963, 5965 in place of 12at7 should work fine imho.
also, 12at7 tubes are still quite cheap. i'd look into mullards and 'funken's if its place is critical in your amp.
also, 12at7 tubes are still quite cheap. i'd look into mullards and 'funken's if its place is critical in your amp.
primosounds
Powered with pure tube sounds.
The 5965 is a "computer" tube, designed to be operated under "cut off" conditions for long periods. It seems like having large plates helps them to do this. I find that for single ended amps using certain brands of 5965 as a driver tube in place of the 12at7 sounds better.
Also in a pinch you can use them in place of a 12dw7.
Also in a pinch you can use them in place of a 12dw7.
