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  #1  
Old 15th February 2017, 11:04 AM
bob orbell bob orbell is offline
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Default Valve Data confusion.

HI all, a short time ago I changed my modified Pre III, from self biased cathode follower, to CF with active load and followed the CD in Morgan Jones book using two Mullard E88CC tubes, the top valve is feed by 285volt's as in the book, I now read from many Valve Data pages that that particular valve's Va max is 220volt's, it works very well, but I need to make sure that I am not going to over volt the valve. I have in my valve box, two 6N1P tubes, the Data for these is also confusing, some pages say Va max 300, others 250, heater current appears to be + 100% so that will be 1.2 amps as apposed to 0.6, this is not a problem, as I use two power supply's. Can the more advanced members please comment. Thank's. BOB
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Old 15th February 2017, 11:31 AM
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pre65 pre65 is offline
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Default Re: Valve Data confusion.

Bob, what is the page number in the book for that circuit please ?

I believe plate (anode ) voltage is actual anode volts minus cathode volts.
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Old 15th February 2017, 11:32 AM
bikerhifinut bikerhifinut is offline
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Default Re: Valve Data confusion.

Bob:
What's the cathode Voltage on the top Valve? Subtract that from the anode voltage and thats what it effectively is. The V(a) max rating should really be V(a-k).

To put this in perspective for you, the humble EL84 has a Va max of 300V, yet how many times do we see it running at 310 to 330V on the anode?

A
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Old 15th February 2017, 11:34 AM
bob orbell bob orbell is offline
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Default Re: Valve Data confusion.

Hi Philip, I hope you have the same book as me, Third Edition, page 109-110.
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Old 15th February 2017, 11:39 AM
bob orbell bob orbell is offline
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Default Re: Valve Data confusion.

Hi Andy, the Cathode voltage is 206.5, so 285 - 206.5 = 78.5, I think I am understanding. BOB
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Old 15th February 2017, 11:40 AM
bikerhifinut bikerhifinut is offline
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Default Re: Valve Data confusion.

Quote:
Originally Posted by pre65 View Post
Bob, what is the page number in the book for that circuit please ?

I believe plate (anode ) voltage is actual anode volts minus cathode volts.
Bang on Philip.

Bob the other point to remember is that the *CC88/6922 etc etc is designed to work as a cascode valve, so the voltages that matter are V (a-k), and also a little point to pick up on is the V (h-k) ratings are different for each triode. V(h-k1) is 180V with a maximum DC component of 130V, and V(h-k2) is 50V. So in a cascode or other similar arrangement like the active load or mu follower you should really use the a1 g1 k1 triode as the top valve along with your lifted heater reference volts for peace of mind.

My data comes from a proper mullard data book.

Andy
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Old 15th February 2017, 11:40 AM
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pre65 pre65 is offline
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Default Re: Valve Data confusion.

Quote:
Originally Posted by bob orbell View Post
Hi Philip, I hope you have the same book as me, Third Edition, page 109-110.
Yes Bob, got edition 3 in English, and edition 4 in Chinese (present from Morgan himself)

Yes, as Mr Nut agrees with me and the v is 285 -204 = 81v, so within 90v which data sheets say is a good norm.
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Old 15th February 2017, 11:44 AM
bob orbell bob orbell is offline
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Default Re: Valve Data confusion.

Thank's a lot both, that is all making sense now. BOB
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Old 15th February 2017, 11:45 AM
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Default Re: Valve Data confusion.

The MJ article does not mention raised heater potential.

Are your heaters raised potential Bob ?
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Old 15th February 2017, 12:03 PM
bikerhifinut bikerhifinut is offline
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Default Re: Valve Data confusion.

I think that's because by that stage in the book MJ would expect you to know about the pitfalls of heater to cathode insulation. Covered in the power supplies section of the book. I think the sample circuits in that bit of the book are mainly for explanation purposes and the calculations are explained so that you can work your own circuit values out to suit your own Ht voltages and choice of valve.

A.
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