Interesting bit of information

Post new topic   Reply to topic

Go down

Re: Interesting bit of information

Post by Admin on Sun Feb 11, 2018 9:36 pm

@John_1981
That sounds like an interesting idea. If you have any circuits I would be interested. But the only tubes I use are the 6v/12v types, which makes the heater less of a problem.

@Ruud
I have never used any solid-state tubes. I would perhaps like to experiment with one, but I seem to be doing well with conventional tubes.
I like the "instant on" idea, but I saw the spec of a couple of these devices and thought that the HT could be a problem. For example, not enough output swing from my ECC81, no problem, just woof up the HT from 300v to 600v. That works fine and the 600v only tickles it Smile .

After my remarks, they released a service sheet describing how to solve the problem.

That would be interesting to read. Before I play with these tubes I would want to do a lot of reading.
I suppose the glass would keep the smoke in, but the devices may still be a bit critical. I remember when the 1f capacitors (SED's) were introduced. They were rated at 5.1v max. I would be willing to bet that 5.5v would make them smoke, draw current, explode, or a combination of those.

BR Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: Interesting bit of information

Post by Ruud on Fri Feb 09, 2018 7:23 pm

I just found this, from a long time ago:

"Phædrus Audio AC701 is a real triode tube; it is not a solid-state (silicium) replacement"

Well, it isn't a real tube! (Also their VK14 replacement isn't a real tube!)
I have used a couple of them and they are solid state replacements.
You can also notice this, because they are 'instant on'. (No time to heat up.)
There is even a warning not to reverse the "heater" wires!
In the case of the VK14 you can see some of the electronic components inside.
I have had a couple of contacts with the friendly people of Phaedrus, because one of the problems that I encountered was a slightly different behaviour than a real tube.
After my remarks, they released a service sheet  describing how to solve the problem.
avatar
Ruud

Posts : 61
Join date : 2012-11-26
Age : 63
Location : Haule

View user profile http://www.vansteenisaudio.nl

Back to top Go down

Re: Interesting bit of information

Post by John_1981 on Sun Feb 04, 2018 10:08 pm

[apologies for posting this initially under the wrong thread]

Have you thought of using a self oscillating half bridge converter to provide power for heaters and HT? I knocked one together one evening to power the heaters of some PL519 valves. I will dig out the circuit if you are interested. It used a ferrite core from a LOPT, a pair of TV horizontal output transistors, a small ferrite ring to provide the feedback and a handful of other parts. Efficiency is better than a standard Royer oscillator as only the driver transformer saturates, not the power transformer. Circuit is similar to a CCFL driver.

John_1981
Guest


Back to top Go down

Re: Interesting bit of information

Post by Admin on Sat Feb 03, 2018 6:43 pm

Hi Ruud,
The total voltage in the project was 1200, but I found that the transformer I used has poor regulation. When I fire up the triode the total voltage drops to about 950 volts. I already have the case, so I now need to plan the front panel and get suitable rotary switches.

I can't order anything from Chine, or e-bay as the delivery time is too short for me to receive them. The Swedish post office will return to sender if not collected in 14 days, so I have to wait until middle of march, when I return to Sweden.

Your story on the old tubes was very interesting to read. I thin that I will make a traditional GDO with one of them, and an audio oscillator with the other. I need a decent oscillator to complement the oscilloscope. But these days everything takes so much time.

30 years ago I did a LOT more with my time, but these days I seem to be fully occupied with other dull, boring things, and don't have any children to rear, either!! Something feels kinda wrong.

Anyway, thanls for the interesting reading. Will let you know how the scope project goes (eventually).

Best regards from Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: Interesting bit of information

Post by Ruud on Wed Jan 31, 2018 6:46 pm

Hi Harry,

Good to read that there is progress with your scope project!
Let's hope the metal case will arrive soon, because personally I don't like 550 volts on the bench...

Concerning the 5718 tube: that is a very kind offer, but I recently bought a batch of 25 pcs. NOS 6S6B tubes from Russia.
I have tested them all and they are excellent, very low noise, so well suited for tube microphones.
In fact, I recently had a Neumann M269C microphone in for repair.
Almost everything that could have been wrong with it, was wrong!
The owner also had no power supply and (7 wire screened) cable for it, so I had to build him one.
Biggest problem was the expensive(!) AC701 tube that almost was at the end of its life.
I noticed that when I had completely restored the microphone, but it was still making a 'rustling' sound.
So I tried one of the recently aquired 6S6B tubes in that microphone and the result was excellent.
Maybe even better than with the original AC701 tube... The only thing I had to change was the cathode resistor, to set the bias correctly*.
The result was a 'historic' (ca. 1960) condenser microphone that perfoms like a brandnew one.
Those vintage microphones (when in good working condition) are now worth around $4000...
No need to say that the owner was very happy with the result. 

Thanks again and all the best from The Netherlands!

Ruud.

*: In those situations I am happy I belong to the generation that grew up with tubes!
avatar
Ruud

Posts : 61
Join date : 2012-11-26
Age : 63
Location : Haule

View user profile http://www.vansteenisaudio.nl

Back to top Go down

Re: Interesting bit of information

Post by Admin on Wed Jan 31, 2018 6:01 pm

Hi Glenn & Ruud,
FYI, the scope project is extremely low as I always seem to have no time. BUT a little bit of interesting information,
I could not get the trace to fill the full width of the tube, used two complimentary triodes and it was better, but still too little.

I increased the heater voltage to 6 Volt and increased the HT to 550 Volts. NOW I have enough grunt to drive the horisontal deflection. Vertical I can drive with just 25 V AC, and I now have a working oscilloscope - as a bird's nest - on the bench. I got a metal case from RS a week ago.

I don't think Nuvistors will take the 550 V but I am happy with the ECC81. I will look into Nuvistors for the future.

@Ruud, I have  pair of miniature wire-ended tubes - They are SYLVANIA type 5718, and I believe they are triodes for up to 500 MHz. I think they are very cheap as I found them for 5 Euros on Ebay. I have two of them if you want them? I have no use for them. If you don't want them then perhaps I may make a genuine Grid Dip Oscillator, or a lightning-safe antenna amplifier, but that will be a long, long time in the future as I have loads of more conventional tubes.

Best regrads from Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: Interesting bit of information

Post by Glenndk on Sat Dec 30, 2017 4:27 pm

How about replacing the glass triodes with nuvistor triodes - even for condenser microphones? I have not checked transconductance nor any other charateristics:

http://en.wikipedia.org/wiki/Nuvistor
Quote: "...
Nuvistors are among the highest performing small signal receiving tubes.
...
It was also later found that, with minor circuit modification, the nuvistor made a sufficient replacement for the obsolete Telefunken VF14 tube, used in the famed Neumann U 47 studio microphone.[1]. Tektronix also used nuvistors in several of its high end oscilloscopes of the 1960s[2], before replacing them later with JFET transistors.
..."

https://en.wikipedia.org/wiki/Neumann_U47
Quote: "...
Custom tubes equivalent to the VF14 have been manufactured specifically for the U 47, by Telefunken[2][3] and others.[4] Beginning in 1962, Neumann offered a fully functional Nuvistor, small signal receiving tube replacement kit for the VF14 and required minor circuit modification.[3]
..."

6CW4 Nuvistor High-Mu Triode Tube:
http://datasheets.hypertriton.com/6CW4.pdf
http://electrontubestore.com/index.php?main_page=product_info&cPath=68_78&products_id=1044

2CW4 Nuvistor Triode Tube
http://electrontubestore.com/index.php?main_page=product_info&cPath=68_78&products_id=2156

8056 Medium-Mu Triode Nuvistor Tube:
max 50V 0,45Wa
http://datasheets.hypertriton.com/8056.pdf
http://electrontubestore.com/index.php?main_page=product_info&cPath=68_78&products_id=1049

Glenndk

Posts : 40
Join date : 2017-01-06
Location : Copenhagen, Denmark

View user profile

Back to top Go down

Re: Interesting bit of information

Post by Glenndk on Sat Dec 30, 2017 4:18 pm

Hi Ruud

Phædrus Audio AC701 is a real triode tube; it is not a solid-state (silicium) replacement:
http://www.phaedrus-audio.com/AC701%20Data%20sheet.pdf

Ruud wrote:
Nowadays there is even a company that produces a solid state replacement for the AC701 microphone tube: 
http://www.phaedrus-audio.com/AC701%20electronic%20tube.htm

Glenndk

Posts : 40
Join date : 2017-01-06
Location : Copenhagen, Denmark

View user profile

Back to top Go down

Re: Interesting bit of information

Post by Glenndk on Sat Dec 30, 2017 3:38 pm

I also wish you a happy new year.

-

In this document on page 28, it is mentioned that a low power fetron is made of cascode consisting of 2N4882 (equiv. 2N5543) and a selected 2N3823:
http://hrsasa.asn.au/docs/Fetron.pdf

I can not find 2N4882 nor 2N5543, but I found these possible upper cascode FETs:

DN2540N5-G 400V 150mA TO-220 15W fast (depletion but lower fet might only have 1Vds) Cgs=200pF:
http://ww1.microchip.com/downloads/en/DeviceDoc/DN2540%20B060313.pdf

450Vds 140mA 2W fast (enhancement - needs a Vgs voltage source) Cgs=70pF:
https://www.diodes.com/assets/Datasheets/ZVN0545G.pdf

LND150 30mA 500Vds but slow 1,3 uS fall time (depletion but lower fet might only have 1Vds) Cgs=7.5pF (best? => fastest cascode?):
TO-243AA (SOT-89) 1.6W:
TO-92 0.74W:
http://ww1.microchip.com/downloads/en/DeviceDoc/LND150%20C041114.pdf

Maybe the fet source should be driven by this low impedance high current output op-amp?: LMH6723 370MHz -3dB:
http://www.ti.com/lit/ds/symlink/lmh6723.pdf
Quote: "...Current Feedback Operational Amplifier..."


Last edited by Glenndk on Sat Dec 30, 2017 5:09 pm; edited 3 times in total

Glenndk

Posts : 40
Join date : 2017-01-06
Location : Copenhagen, Denmark

View user profile

Back to top Go down

Re: Interesting bit of information

Post by Admin on Sat Dec 30, 2017 9:26 am

Fetron, now I am learninf something more :-)
I read years ago that FETs could replace tubes, but I never realised there was a marketable product produced.

I will look into it. Thank you very much.

Happy New Year to you and all from Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: Interesting bit of information

Post by Glenndk on Sat Dec 30, 2017 7:45 am

Admin wrote:
...
Last night I realised that an ECC81 takes 300mA to heat.
Since I am only using an anode current of 0.5mA I thought about lowering the heater current a bit more. I tried both heaters in series (12v) and fed them from the 6v transformer. Current is now less than 100mA and they glow. The valve works very well with the lowered emission and I have about 8v Pk-Pk to drive the tube plates :-)

Just a bit of interesting data.

BR Harry - SM0VPO

How about using Fetrons instead of tubes. No heater current needed. The lifetime are supposed to be 100 years. No microphony. Extremely robust. Semiconductors might replace tubes in the future... No warm up time. Faster "warm-up time" than todays computers. Computers takes minutes to warm-up :-)

https://da.wikipedia.org/wiki/Fetron

https://en.wikipedia.org/wiki/Fetron

https://www.radiomuseum.org/forumdata/upload/Fetron_TS6AK5W.pdf
Quote: "...
TS 12 AT 7 ~ ECC 81 49.-- 41.-- 36.80
..."

http://hrsasa.asn.au/docs/Fetron.pdf

Glenndk

Posts : 40
Join date : 2017-01-06
Location : Copenhagen, Denmark

View user profile

Back to top Go down

Re: Interesting bit of information

Post by Ruud on Fri Dec 29, 2017 9:03 am

Yes, sometimes pentodes are used in a triode configuration in condenser microphones.
I have used the 5840 (pentode) tube with reasonable success in a microphone.
What is very important is the noise generated by the tube itself.
We are dealing here with very small signals (sometimes lower than 1 mV.) and extremely high impedances (1 G.ohm)
From all the tubes I have tested, the 6S6B-V was the best.
Nowadays there is even a company that produces a solid state replacement for the AC701 microphone tube: 
http://www.phaedrus-audio.com/AC701%20electronic%20tube.htm
I have thought about how they could have done this. I suppose it is a source follower combined with a high-voltage NPN transistor stage.
But of course the "phreakz" (they are the worst!) want a real AC701 tube!

(One of the things I do is the repair and restoration of vintage studio microphones. For some reason people think that microphones from 1950-1960 are better than the ones produced nowadays.)
avatar
Ruud

Posts : 61
Join date : 2012-11-26
Age : 63
Location : Haule

View user profile http://www.vansteenisaudio.nl

Back to top Go down

Re: Interesting bit of information

Post by Ivan on Fri Dec 29, 2017 7:33 am

Hi Ruud,
what about Russian pentodes like 1ZH29B? If you connect the 2nd grid with the anode, they should behave like triodes. The filament voltage is smaller and DC.

BR from Ivan

Ivan

Posts : 234
Join date : 2012-11-25
Location : Praha, Czechia

View user profile

Back to top Go down

Re: Interesting bit of information

Post by Ruud on Thu Dec 28, 2017 8:13 am

The reason for the high price is that Telefunken only produced a limited number of them.
The AC701 tubes for condenser microphones have the suffix 'K' (German: 'Klingarm') which stands for 'non microphonic'.
The tube itself is a simple single triode with a 4 V heater.
There are many of those tubes with wires through the glass instead of pins.
Recently I bought a batch of 25 pcs. NOS Russian 6S6B-V tubes.
I have tested them all, and they all can be used for condenser microphones.
The noise of those tubes is very low. (Important for a microphone!)
But the "audiofools" insist on having a real AC701 in their microphone, and apparantly are willing to pay for it!
avatar
Ruud

Posts : 61
Join date : 2012-11-26
Age : 63
Location : Haule

View user profile http://www.vansteenisaudio.nl

Back to top Go down

Re: Interesting bit of information

Post by Admin on Wed Dec 27, 2017 8:46 pm

Ruud wrote:By the way: did you look at the price of a replacement AC701 tube?
https://tubedepot.com/products/ac701
Shocked
Oops, no I missed that.
Good grief, are they expensive? or are they expensive!! I presume the price reflects the demand and availability of them. Are they no-longer made?

I wonder if that particular package is (or was) common? I am not certain but I think I have some similar, wire-ended tubes, of about the same size. Not sure if they are here or in Spain. I will have a look for them. If they are similar, then can you use them? No promisses.

BR Harry

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: Interesting bit of information

Post by Ruud on Tue Dec 26, 2017 9:13 pm

By the way: did you look at the price of a replacement AC701 tube?
https://tubedepot.com/products/ac701
Shocked
avatar
Ruud

Posts : 61
Join date : 2012-11-26
Age : 63
Location : Haule

View user profile http://www.vansteenisaudio.nl

Back to top Go down

Re: Interesting bit of information

Post by Admin on Tue Dec 26, 2017 8:34 pm

Hi Ruud,
Thank you very much. I really appreciate your comments.

My thought was that the tube would last longer, but that was based on supposition and not technical knowledge.

I have already observed that the noise is somewhat lower (or I have a particularly good tube), but now I have learned a lot more from you. I don't have any experience of runing valve cathodes cooler than about 1000°C.

Unfortunately I need an ECC81 for the timebase and another ECC81 for the x-axis amplifier. I only have a 10-Watt transformer so I have to run the anodes at 500µA and a total heater budget of 2-Watts. I already have 300µA bleeders for every 300V stage (0.5-Watts) as well as the current drawn by the CRT.

But I will have it working as soon as I we have finished renovating, decorating, Christmas, tidying, fixing, changing curtains, cleaning, washing, Easter, etc.. Maj-Lis goes back to Spain in 2 weeks so I can maybe steal a few hours when she is not here.

Best regards from Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: Interesting bit of information

Post by Ruud on Tue Dec 26, 2017 4:37 pm

Interesting.
So two tubes in series on 6v, this means 3v for each tube.
It works, I did this once with one of my tube microphones.
Underheating a tube also reduces the self noise of a tube microphone.
But I was warned to be careful with that!
I ran a 6.3V tube on 4V, no problems. 
Some people told me that underheating a tube could exhaust the cathode, in other words: it would reduce the lifetime of the tube.
In my case this would have been interesting, because the old tube microphones used an AC701 tube, with a 4 V filament. I found a good replacement, but with a 6.3V heater. Of course it would be great if you could only replace the tube and NOT change the power supply, but this was seriously discouraged.
I thought it was good to let you know, for what it is worth...

By the way: (link) AC701 ...  (This is exactly the reason for finding a good replacement!)
avatar
Ruud

Posts : 61
Join date : 2012-11-26
Age : 63
Location : Haule

View user profile http://www.vansteenisaudio.nl

Back to top Go down

Interesting bit of information

Post by Admin on Tue Dec 19, 2017 3:05 pm

I am presently striving to get some time to work on the oscilloscope. The problem is that Christmas is in the way.

Last night I realised that an ECC81 takes 300mA to heat.
Since I am only using an anode current of 0.5mA I thought about lowering the heater current a bit more. I tried both heaters in series (12v) and fed them from the 6v transformer. Current is now less than 100mA and they glow. The valve works very well with the lowered emission and I have about 8v Pk-Pk to drive the tube plates :-)

Just a bit of interesting data.

BR Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: Interesting bit of information

Post by Sponsored content


Sponsored content


Back to top Go down

Back to top

- Similar topics

Post new topic   Reply to topic
 
Permissions in this forum:
You can reply to topics in this forum