Thanks for all the feedback guys 
. Very helpful! Yes Disco I have seen that article. I thought it was quite funny actually . I could be waging war with a bunch of EF50's if they prove troublesome for audio. HA!
I guess I could just breadboard one EF50 up in the existing chassis and see how it performs. And I can check for the Microphony that Nafunga mentioned. The bases are all there so just need to add a PSU and throw something together.
I have been studying some old vary-mu tube comp/limiter designs and would love to base a design on one of them. Problem would be sourcing the correct trafos...
But maybe a distortion/overdrive unit would be easier as a bit of noise may not be an issue then...
Any further ideas re the EA50 diode tubes? I see in the old tube comp/limiters such as the RCA Ba-6a they use a 6H6 double diode tube for rectifying the O/P signal in order to control gain, so maybe I could use these EA50's in the same way? But then I would have to question whether using modern diodes would make any difference at all!
. Very helpful! Yes Disco I have seen that article. I thought it was quite funny actually . I could be waging war with a bunch of EF50's if they prove troublesome for audio. HA!I guess I could just breadboard one EF50 up in the existing chassis and see how it performs. And I can check for the Microphony that Nafunga mentioned. The bases are all there so just need to add a PSU and throw something together
.I have been studying some old vary-mu tube comp/limiter designs and would love to base a design on one of them. Problem would be sourcing the correct trafos...
But maybe a distortion/overdrive unit would be easier as a bit of noise may not be an issue then
...Any further ideas re the EA50 diode tubes? I see in the old tube comp/limiters such as the RCA Ba-6a they use a 6H6 double diode tube for rectifying the O/P signal in order to control gain, so maybe I could use these EA50's in the same way? But then I would have to question whether using modern diodes would make any difference at all!
Hi,
I have a bunch of those LM Ericson 6761. It's a noval output pentode. It appears
to be high quality longlife, ruggedised tubes. Wa 10W, quite low anode voltage
and high current (compared with EL84) Transconductance 12 mA/V
I hope that someone with more knowledge could enlighten me and give me some
boost to actually build something with these tubes.
Here's a link where L.M.Ericson gives data and tell about the development of
this tube.
https://www.dropbox.com/s/qaj06cmov7ux2xl/Ericsson1955_3.pdf
Emnitec said:
I have a bunch of those LM Ericson 6761. It's a noval output pentode. It appears
to be high quality longlife, ruggedised tubes. Wa 10W, quite low anode voltage
and high current (compared with EL84) Transconductance 12 mA/V
I hope that someone with more knowledge could enlighten me and give me some
boost to actually build something with these tubes.
Here's a link where L.M.Ericson gives data and tell about the development of
this tube.
https://www.dropbox.com/s/qaj06cmov7ux2xl/Ericsson1955_3.pdf
Finding an suitable OPT is not easy, perhaps it makes a decent driver for a power triode? Or a choke (?!) reading this:
"Among other applications, the tubes are used as serial tubes for stabilized rectifiers. At 100 mA plate current the voltage drop is only about 100 V when the grid voltage is zero. A further use in power units is as a substitute for chokes; the plate resistance, which is about 30,000 ohms, corresponds to a choke of about 50 H at 100 c/s. The weight of the tube and necessary circuit components is considerably less than that of a choke. "
The "low" Ra-a (actually 3.5k in the article) is due to the fact the tube was designed to work with relatively low plate voltages, I don't believe there is any inherent dis-advantage for having a low primary impedance.
Ok, I was thinking that the low impedance also would bring a lower
primary inductance. I know to little about this.
Thank you for your input, jazbo8.
I feel that I have to read up on this subject. I also feel that I'm a bit off topic.
So excuse me for that.
When I have learnt more and have the right questions I may start a new topic.
Rolf
primary inductance. I know to little about this.
Thank you for your input, jazbo8.
I feel that I have to read up on this subject. I also feel that I'm a bit off topic.
So excuse me for that.
When I have learnt more and have the right questions I may start a new topic.
Rolf
Hmmm, my opinion is that one might put this tube in use if there's an advantage to be had. Compared to the EL84 one needs a low rAA output transformer (2K5) which is scarce. Your effort will be rewarded with a meager 10W output power, following the suggested circuit. When using a more common 8K output, the output power will drop further. I guess it is not that interesting to make a 2W single ended penthode amp out of it... right?
The situation differs when you can drive a for instance #50 output tube directly, making use of the unique (?) properties of this penthode. This calls for a relative low impedance source with clean amplification, capable of delivering some power to overcome Cmiller. If this rare penthode is up to the task there will be demand for it in this exceptional application. The datasheet promises low noise because of superior electrode alignment.
The situation differs when you can drive a for instance #50 output tube directly, making use of the unique (?) properties of this penthode. This calls for a relative low impedance source with clean amplification, capable of delivering some power to overcome Cmiller. If this rare penthode is up to the task there will be demand for it in this exceptional application. The datasheet promises low noise because of superior electrode alignment.
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Lower required impedance=GOOD, because it is easier to make a good transformer. You just need to custom order it, thats all
btw, this valve looks close to the EL86 / PL84 / UL84 . Maybe have a look in schematics for these.
Good points. I have a pair of 'Philips 4683' (AD1/350) maybe I could adopt yourdisco said:
ideas and drive the power triodes with the 6761.
My interest in these 6761 is just because I happen to have them.
costis said:
My first project
will probably be a conventional p-p amp. Then later if a dare I will get me a pair
of beefy SE output transformers and blow some life in those 4683:s
Again, Thanks to all you guys for your help.
Regarding the use of EF50's in Audio, I have now found that the EF50 is a remote cut-off pentode, which as Ian stated, only sharp cut-off pentodes can really be used. And since trying to calculate parameters for screen voltage, current etc using the data sheet I have found it impossible for a small signal audio amp stage (maybe someone can clarify as I am new to this detail of tube trickery!). This is due to there not being any details in the data sheet on different screen voltages. Unless someone has a different data sheet than the one at R-type and other sites...
I have however managed to put audio through one with good fidelity, but I don't have the test equipment for detailed measurements. I found some of them to be very microphonic, so I built an EF86 pentode amp as the first stage in my pre-amp. I am now considering just using the EF50s in some form of AGC role as the only examples I have found as audio amps are lacking real conclusions or details on how they perform.
I have however managed to put audio through one with good fidelity, but I don't have the test equipment for detailed measurements. I found some of them to be very microphonic, so I built an EF86 pentode amp as the first stage in my pre-amp. I am now considering just using the EF50s in some form of AGC role as the only examples I have found as audio amps are lacking real conclusions or details on how they perform.
@NAFUNGA, How did you find them when you used EF50s for Audio (other than the microphonics which I also encountered)?
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Here is a very interesting article/post regarding the Ef50 and driving the suppressor grid negative in order to control the gain. Something which was never detailed in the original data sheets but happens to work!
EF50 suppressor action
I wonder could this be an innovative way to build a compressor/limiter using a negative voltage corresponding to the gain reduction needed?
EF50 suppressor action
I wonder could this be an innovative way to build a compressor/limiter using a negative voltage corresponding to the gain reduction needed?
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