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Does anyone really familiar with RCA 5691 tube? I have bought a pair of RCA 5691 (listed as new) recently, adding to the 3 pieces I already have.
On the top of the new pair, there are dark emission or burned marks, which the seller has advised that it is the process of getter flashing that made these marks and not becos of heavy usage. Please advise if you are familiar with this tube. Thank you!!!
You can see my 3 pieces on the left and this new pair on the right.
Follow Ups:
It is quite possible that the discoloration is from the manufacturing process.
The tubes are dual triodes, so a heavy use pattern would most likely show signs of 2 spots instead of one.
Look at the bottom edge of the flashing as it would likely also show signs of heavy discoloration or fading.
Assuming they test to spec (and are triode balanced), I would not be concerned.
Thank you for your input. Yes, I believe it is from the getter flashing process.
I'm not sufficiently familiar with these tubes to answer specifically. However, every dual-triode octal tube I've ever seen that had heavy use has exhibited two brown spots on the bare glass directly above the filament windings. I have never seen such spotting with tubes that were top-gettered like these. That might be an indication that the spots on your tubes were not caused by use.
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Buy Chinese. Bury freedom.
Thank you for your thought. After hearing from other users and some researches, I begin to believe it is really caused by the getter flashing process during the manufacturing of these tubes. Nevertheless, these tubes are working fine, I will run them for sometime and will report back if any abnormalities occur.
Take care.
I don't know the answer to your question. I got out my three RCA NOS 5691s in military boxes and none of them show the discoloration of the getter flashing.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Mine are as Tre described.
The 5691 and 5692 are RCA military tubes-- 5691 is a
6SL7 AND 5692 is a 6SN7.
While these are a solid lasting tube, they
don't perform in audio very well.
The later RCA and G.E. models that are all
glass, with only a thin wafer as the base,
greatly outperform the Mil-Spec variety.
-Dennis-
I find the "coin" base tubes to be some of the worse sounding tubes I own.
BTW Telling people that a 5691 is a 6sl7 without informing them that it draws twice the heater current is somewhat irresponsible. Maybe you didn't know that and maybe that's why they didn't perform well for you?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Gosh! Heater is .3 amps in one, and
.6 amps in the other. Both need 6.3 volts.Now, if the filament supply is robust,
it will provide the 6.3 volts at either
load, so in a device that can (should)
provide 6.3 volts for either tube, then
no problem.When I compared the tubes to each other
(sonically), the 6SL7 filament voltage
was 6.4 V.A.C., the 5691 filament setup
was at 6.35 V.A.C., so I deduced that difference
not to be a problem. In any case, I was discussing the
sonic characteristics. If one is using an inferior filament
supply, it might not like a different load as you point out.Von Gaylord had also used those coin-base tubes in his amps.
The RCA 5691 was better than other brands of it.
This robust industrial tube had plenty of drive,
really good bass, and a clean mid-range, but it just
couldn't convey a musician's artistic intentions
like the designed-for-audio tube can.The large bases of the non-coin base tubes sonically
(mechanically) shunt-out the really good highs.The coin-based models do not have this DEFECTIVE BASE.
The coin-basers reproduce far more of the high
frequencies. Equipment that exhibits some distortion
in the highs will benefit from a tube-base that knocks-out
some of the H.F. musical information.-Dennis-
Edits: 08/12/21 08/12/21
Whoa!!! I didnt know that, really good to know. Thank you for the info, greatly appreciated.
You're welcome.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/27/21
Others might disagree but I agree that they are not really as magical as others have exaggerated on the sound. They somehow give me an impression of "short breath" on the vocals, especially with Jazz, Blues, Ballad, etc... Same as the Tung-Sol 6SU7GTY, which I dont realy like either, I think these tubes are more suitable for rock, metal, pop, etc...more aggressive music. I have tried these tubes on rock, metal, pop...and they do sounded more lively and fast compared to tubes like Mullard ECC35.
The 5691 draws twice the heater current as a 6sl7 and in some heater power supply designs this will cause major problems.
Were you taking that into account?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Thank you for the advise, appreciated.
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