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7788 Triode Curves

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Re: D3A Datasheet question

dsavitsk said:
The D3a datasheets that I can find
http://www.mif.pg.gda.pl/homepages/frank/sheets/009/d/D3a.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/128/d/D3a.pdf
both suggest (when triode strapped) a plate voltage of 160V, Rk of 470R and an anode current of 24mA. Now, 24mA through Rk of 470R is going to bias the grid up over 11V, which is not possible according to the curves ... so what am I missing?


You are missing the fact that in the data given, there is +10V on g1!

I have often seen this technique used in makers' data on high-gm types.

7N7
 
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Re: Re: D3A Datasheet question

7N7 said:



You are missing the fact that in the data given, there is +10V on g1!

I have often seen this technique used in makers' data on high-gm types.

7N7

This technique avoids the need for tiny resistors and huge electrolytic caps when doing the measurement. Large electrolytics were very expensive and not particularly good performers (they still aren't) in these sorts of applications. It also reduces inconsistency in sample to sample operating point for the transconductance measurement.

In my phono stage I needed about 1.0 V of bias on the D3A below a convenient value for led bias, and I ended up with a 60 ohm cathode resistor with a BG 1000uF//BG 22uF//4.7uF film to get it to sound good. Using this approach depending on (unselected) tube quiescent point is 15 - 20mA. (Quite a large variation actually.)

For measurement purposes the variation in bias point becomes a small % of the overall voltage developed across the large cathode resistor resulting in a more consistent operating point for measurement purposes.
 
Thanks Kevin, another mystery resolved.

In fact when using pentodes as constant current sinks, I used put up to +50V on g1. This meant that I could increase radically the value of the (unbypassed of course!) cathode bias resistor and therefore increase the output resistance of the sink.

7N7
 
Yes I have used E810F (7788) as a (pentode) cathode follower; this was a development circuit for a mid-range amplifier I had planned but never completed. The results on test were excellent.

The circuit comprised 7N7 diff pair with active loads and cascode CCS, cap-coupled to a pair of E810Fs with cascode loads and active g2 regulation via emitter followers. There were +ve (300V) and -ve (-280V) rails. The cathode followers were to be DC-coupled to a pair of YL1071s triode strapped. (I had previously used D3As as cathode followers in the "INSTOCK" amplifier that I discussed here about five years ago).

I tested the stage for distortion and at +40dB output (77.5v rms) THD was 0.063%; 3rd harmonic was -87dB but really my test equipment wasn't good enough to be certain since the test gear itself produced this kind of level of THD.

7N7
 
7N7 said:
Yes I have used E810F (7788) as a (pentode) cathode follower; this was a development circuit for a mid-range amplifier I had planned but never completed. The results on test were excellent.
{..}
(I had previously used D3As as cathode followers in the "INSTOCK" amplifier that I discussed here about five years ago).
Did you get to listen to it too at all? How would it's sonics compare to (whatever) the best CF you've heard, be??
 
Ok gentlemen;

I can buy bunch of 6F12P, 6J52P, 6J53P tubes. In case of a group buy they will be relatively cheap, but we have to do that as fast as possible because since somebody already mentioned them here (@#$%@!!!) prices will go up rapidly!!!
They were designed for later tube TVs, very precision grid alignments, good technology, as the result they are very universal: can work as pres, drivers, outputs (I used to swap them with 6P14P in the same TV sets to get color picture back when urgently needed, without audible sound degradation).

I believe I can get them about $1.5 per tube plus shipment.

PM me who are in.
 
Majestic said:
Did you get to listen to it too at all? How would it's sonics compare to (whatever) the best CF you've heard, be??

No, it was never built as an amplifier; life's realities got in the way.

The "Instock" did sound good (13D3/D3A pentode cathode followers/6528A p-p) despite its cheap output transformer.

7N7
 
jlsem said:


I'm in for 16. What is the best way to pay you?

John

It would be right to pay to the seller directly through http://www.moneybookers.com/ so we would share money transfer expenses, but I am afraid it will be a nightmare... Let me collect money then buy the bunch.

A first, you should add 3% that we'll loose on money transfer, and second, calculate shipment from Pleasant Hill, CA 94523 to you, and add. You may mail me a check.
SY may not bother with shipment costs because I'll be there February 23 and can bring you the toobs. However, if you want them as soon as they arrive here you may pay for shipment as well.
If somebody lives nearby we can meet in person.
 
Hi boys,

following you can find some Sofia curves for:

E810F triode connection:
http://www.multitask.it/tubes/3-E810FTR.BMP

E810F pentode connection
http://www.multitask.it/tubes/2-E810FPEN.BMP

Match between 417A and E810F triode (more vertical curves, of course)
http://www.multitask.it/tubes/6-417-EF.BMP

This one is the match between E810F (always more vertical curves)) and EC8010
http://www.multitask.it/tubes/7-EF8-EC80.BMP

I amplaying for years with 417A but non in deep with theother two types; I am trying the soviet tubes similar to that.

Bye

Walter
 
Mullard E810F triode curves

Better very late than never, here are Mullard's triode curves for the E810F
 

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