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Anyone tried this at home?

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universum

universum

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Joined 2003
Wanna try this nice piece of Russian-art,It's stamped RK-71....but believe it's a GK71,when I am correct.Looks a lot like a 813 too.
Anyone familiar with this tubie?
Sure would help me:))
Thanks in forward!
Arthur.
 

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316a

316a

Member
Joined 2002
universum said:
Wanna try this nice piece of Russian-art,It's stamped RK-71....but believe it's a GK71,when I am correct.Looks a lot like a 813 too.
Anyone familiar with this tubie?
Sure would help me:))
Thanks in forward!
Arthur.
Click to expand...


These valves look super-beefy and are on my 'to do' list ! Lit up with the lights off , very impressive looking . I estimate trioded Ra to be about 1.5k if the mug1g2/transconductance specs are anything to go by . After trying various triode strapped pentodes and tetrodes with anode voltages way over the g2 limit , 700V should be handled easily triode-strapped . I have built sockets already from teflon septars and will plot curves on the tester up to 400V , should give a good idea if my Ra guestimate is correct . One point to note : the heater requirements are a little on the 'nasty' side and will require DC for SE usage (20V heaters) , I doubt a hum pot and AC heating will be quiet enough . I'll post the triode test results once I've completed what's currently on the bench

316a
 
universum

universum

Member
Joined 2003
graphite

fdegrove said:
Hi,



It is a GK71 but that tube isn't a 813.

Like most of those big bottles it's a transmitting tube, in casu a tetrode.

If you have a few spares they're certainly worth building with.
Love those graphite anodes...

Cheers,;)
Click to expand...


Hi Frank,

That's what i thought too:)
Would be a shame to leave them laying around...I have three of them left(gave two away to a friend),sure like the white filements once lit up looks like a bulb(no orange glow here:))what a light!!
What should i put in front of these biggies?
I was thinking of an El-84 followed by an EL-34 and the the GK-71,but maybe I should stick to DHT's?Suggestions?
Thanks in forward!
Cheers:))
 
universum

universum

Member
Joined 2003
Re: Re: Anyone tried this at home?

316a said:



These valves look super-beefy and are on my 'to do' list ! Lit up with the lights off , very impressive looking . I estimate trioded Ra to be about 1.5k if the mug1g2/transconductance specs are anything to go by . After trying various triode strapped pentodes and tetrodes with anode voltages way over the g2 limit , 700V should be handled easily triode-strapped . I have built sockets already from teflon septars and will plot curves on the tester up to 400V , should give a good idea if my Ra guestimate is correct . One point to note : the heater requirements are a little on the 'nasty' side and will require DC for SE usage (20V heaters) , I doubt a hum pot and AC heating will be quiet enough . I'll post the triode test results once I've completed what's currently on the bench

316a
Click to expand...
According to the specs the limit on g2 is 400 volt,so wanna be a bit on the save side,you really think they can handle up to 700 Volts?Was thinking of triode strapping and put an el-84 an EL-34 in front..(triode mode too:)
Wanna try AC on the heaters too,if that doesn't work i can go to DC later:)But I am very curious how your testresults develop:)
Please keep me posted:)
Let there be light!(can read my paper next to it:))orange?...nah white!

Thank you all for your replies!
 
universum

universum

Member
Joined 2003
Re: Re: Re: Re: Anyone tried this at home?

316a said:


YES ;) Here's my prototype teflon socket

WOW looking great!Did you make them yourself?Looks prof to me.

Don't have one:-(or two...do you sell?


Did you use clip leads to light yours up ?

Yes i did..whehehe,on 12 volt dc...only for the picture...

Well it's gonna be a while when i start the project,working on other amps that must be done first,then the nicer things..

What are you planning to make?
Click to expand...
 
316a

316a

Member
Joined 2002
Re: Re: Re: Re: Re: Anyone tried this at home?

universum said:
316a said:


YES ;) Here's my prototype teflon socket

WOW looking great!Did you make them yourself?Looks prof to me.

Don't have one:-(or two...do you sell?


Did you use clip leads to light yours up ?

Yes i did..whehehe,on 12 volt dc...only for the picture...

Well it's gonna be a while when i start the project,working on other amps that must be done first,then the nicer things..

What are you planning to make?
Click to expand...

12V DC ! Thats a bit wimpy . The things look far more impressive with 20V on them . The sockets are adapted from teflon septars . The contacts are removed and the holes opened up . I then insert bullet crimp shells inside the holes and use a slice of teflon with a nut and bolt to retain the contacts . Topcaps can be made from terminal blocks withe the connectors removed . I just drill out a slice of 1" teflon bar and push the teflon on to the connector once its screwed on to the topcap . None are for sale , you have to make them yourself but I do have a fair quantity of the septar sockets in stock in case you are interested in making some yourself . I should really get busy with the triode curves now......

316a
Click to expand...
 
universum

universum

Member
Joined 2003
Re: Re: Re: Re: Re: Re: Anyone tried this at home?

316a said:


12V DC ! Thats a bit wimpy . The things look far more impressive with 20V on them .


I know,tried before,then it's a really lightbulb!



The sockets are adapted from teflon septars . The contacts are removed and the holes opened up . I then insert bullet crimp shells inside the holes and use a slice of teflon with a nut and bolt to retain the contacts .

You have slices of teflon laying around...

Topcaps can be made from terminal blocks withe the connectors removed .

Have made a nice sort of "spring retainer" for that...All clamped nicely,and for high temp..

I just drill out a slice of 1" teflon bar and push the teflon on to the connector once its screwed on to the topcap . None are for sale , you have to make them yourself but I do have a fair quantity of the septar sockets in stock in case you are interested in making some yourself .

Well i sure am:))

Maybe i can make you happy with something else to trade?
What do you really need,maybe i have it:))

I should really get busy with the triode curves now......

OOOoops,yep...didn't want to disturb...:))

Thanks,have a nice evening.

Arthur.

316a
Click to expand...
 
316a

316a

Member
Joined 2002
GK71 as a triode

Ran some tests last week on the AVO using an outboard filament supply . Limited by the AVO CT160 tester limits (400V / 100mA) , mu measured as 4 and gm at 2.6mA/V (approx 1.5k) at 60mA/250V . As I can only test up to 400V at present , 250V is about central for calculating mu which is very constant as was gm at various operating points for the same current . As current increases so will mu and Ra will decrease , I would expect Ra to approach 1k and mu to increase to 5 >100mA . Curves are similar to the 845 but lower Ra . Hopefully will have some 5K SE transformers wound in the next few months to see what the things can really do , unless anyone UK based has a pair of 5k SE outputs going begging ;)

316a
 
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