burnedfingers said:
As I recall, a 26 is a directly-heated version of the 27, a 2.5v triode, with mu of about 9.
5687's mu is said to be 15, although this does depend to a certain extent on the amount of current passed. c And of course it is a double triode
There would be a considerable difference.
Personally I could not imagine driving a line with a 26 as I think that like its successors, 27 and 37 that it would be a little weedy for this service.
Much depends on how much gain you need.
My preference in this sort of area would be for a 6BL7 (octal double triode, mu = 15).
In fact I am using a couple of these in my own line stage at present and 6BL7 is quite happy driving 15 feet of balanced line.
7N7
Joel and 7N7
Actually I plan to have a collection of lineamps all of which exhibit severe hum problems. JUST KIDDING!!!! Problem solved by poking around with a piece of dowel rod.
Actually the #26 tube is supposed to be really sweet sounding from what I hear.
I found that with the 6SN7 lineamp I barely have the volume control cracked open at all. No, I really don't need that much gain with speakers that are in excess of 102 db 1w 1m.
I plan to build both the 5687 and the #26 lineamp as I have tubes for both. Running for cover now and hiding my #26 tubes from the Antique radio rebuilders.
Joe
Actually I plan to have a collection of lineamps all of which exhibit severe hum problems. JUST KIDDING!!!! Problem solved by poking around with a piece of dowel rod.
Actually the #26 tube is supposed to be really sweet sounding from what I hear.
I found that with the 6SN7 lineamp I barely have the volume control cracked open at all. No, I really don't need that much gain with speakers that are in excess of 102 db 1w 1m.
I plan to build both the 5687 and the #26 lineamp as I have tubes for both. Running for cover now and hiding my #26 tubes from the Antique radio rebuilders.
Joe
Actually the #26 tube is supposed to be really sweet sounding from what I hear.
I found that with the 6SN7 lineamp I barely have the volume control cracked open at all. No, I really don't need that much gain with speakers that are in excess of 102 db 1w 1m.
Sweet-sounding or not, you still have to drive a cable I presume? I cannot imagine 26 driving anything except a cathode follower - your best option in a line stage.
Run your 26s into your 6SN7 configured as a self biased cathode follower - or DC coupled if you have the HT available; that should sound good - and will have very good distortion performance.
If you are getting that much gain with 6SN7 (typical gain about 15), then perhaps your power amplifiers are too sensitive?
If you do not wish to use the cathode followers, this sounds like a job for 12B4 (mu=6), 6BX7, or the beefy half of a dissimilar triode: 6EW7 would be a good choice.
7N7
I found that with the 6SN7 lineamp I barely have the volume control cracked open at all. No, I really don't need that much gain with speakers that are in excess of 102 db 1w 1m.
Sweet-sounding or not, you still have to drive a cable I presume? I cannot imagine 26 driving anything except a cathode follower - your best option in a line stage.
Run your 26s into your 6SN7 configured as a self biased cathode follower - or DC coupled if you have the HT available; that should sound good - and will have very good distortion performance.
If you are getting that much gain with 6SN7 (typical gain about 15), then perhaps your power amplifiers are too sensitive?
If you do not wish to use the cathode followers, this sounds like a job for 12B4 (mu=6), 6BX7, or the beefy half of a dissimilar triode: 6EW7 would be a good choice.
7N7
DISSIMILAR TRIODES.
Hi,
There's a host of dissimilar triodes such as the 6EM7,6DR7,6EW7 and so on out there that lend themselves nicely for preamp+headphone amp.
Most of them contain a low power medium mu triode + a high power (~ 10W) low mu triode.
Use one as an anode follower,the other as a CF and bingo,you're done.
Cheers,
Hi,
There's a host of dissimilar triodes such as the 6EM7,6DR7,6EW7 and so on out there that lend themselves nicely for preamp+headphone amp.
Most of them contain a low power medium mu triode + a high power (~ 10W) low mu triode.
Use one as an anode follower,the other as a CF and bingo,you're done.
Cheers,
burnedfingers said:
Hey Joe,
That's exactly what I found to be the case. The extra gain from the 12AY7 really only came into play when using 63 ohm headphones. Then I regularly had the volume set to one o'clock.
RE: 26
That's a DHT, so there's no easy way to do a cathode follower output... you're going to have a high output impedance. Keep the cables very short, and make sure the power amp has an input of at least 100k.
I went through this whole phase a while back, and I realized that in order to give the preamp a reason for living, all or some of my DIY power amps would need to be weak on gain - ie. very low input sensitivities on the order of 8 volts.
It just doesn't seem like it's worth the extra wire and possible degradation.
If I were you, I'd take your beloved 26 and make it the front end of a new poweramp. And, if you've got 102db speakers, your possiblities are wide open. You could even build a 71 SE!
burnedfingers said:
Joe, just as a philosophical note - shouldn't you strive for transparency from your gear, not "sweetness" or any other kind of coloration?
Anyway, there's nothing wrong with building a project around a #26, but I wouldn't waste my time with preamps.
Why not pick your favorite directly-heated power tube and make an all DH power amp with two #26's as the first gain stage + driver?
RCA 26
Hi,
here's an application note from the RCA Radiotron:
As an audio-frequency amplifier,the 26 should used wuth transformer coupling in order to secure the greatest amplification per stage.
Keep in mind this was published in 1933 though.(RC11)
This is a low mu tube with a factor of 8.3 at best so I feel it is best suited as a driver stage not as an input tube,unless you don't need the gain and don't intend to use global feedback.
Which is not recommended for transformer coupled stages anyway.
Typical operating point in this case:
Va 135 V
Vg -10
Rp 7K6
Ra 5.5 mA
Heater can be AC or DC at 1.5 V/1.05A.
Cheers,
Hi,
here's an application note from the RCA Radiotron:
As an audio-frequency amplifier,the 26 should used wuth transformer coupling in order to secure the greatest amplification per stage.
Keep in mind this was published in 1933 though.(RC11)
This is a low mu tube with a factor of 8.3 at best so I feel it is best suited as a driver stage not as an input tube,unless you don't need the gain and don't intend to use global feedback.
Which is not recommended for transformer coupled stages anyway.
Typical operating point in this case:
Va 135 V
Vg -10
Rp 7K6
Ra 5.5 mA
Heater can be AC or DC at 1.5 V/1.05A.
Cheers,
Re: RCA 26
Frank, I just built an amp using two '01A's as gain and driver, and I can swing 40 volts with them on the grid of a 71A. With choke loading, the gain of each is 7.7 (at 1kHz) out a possible 8.
Joe, I don't think you'll find a commercial amp using that driver, and certainly an old amp design from the 1930's would need need to be reworked to be a hi-fi.
The key is finding an output tube that can be driven successfully by a 26. What would be nice is using just a single 26 to drive a more sensitive output tube. How about a 26 --> 6L6 ultralinear?
If you want to go more old-school, two 26's cascaded can swing a max of 60 or so volts, with transformer or choke loads. Probably 48V or less with RC coupling.
fdegrove said:
Frank, I just built an amp using two '01A's as gain and driver, and I can swing 40 volts with them on the grid of a 71A. With choke loading, the gain of each is 7.7 (at 1kHz) out a possible 8.
Joe, I don't think you'll find a commercial amp using that driver, and certainly an old amp design from the 1930's would need need to be reworked to be a hi-fi.
The key is finding an output tube that can be driven successfully by a 26. What would be nice is using just a single 26 to drive a more sensitive output tube. How about a 26 --> 6L6 ultralinear?
If you want to go more old-school, two 26's cascaded can swing a max of 60 or so volts, with transformer or choke loads. Probably 48V or less with RC coupling.
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