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6BX8 curves, help !

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kevinkr

kevinkr

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The ECC180 best I can figure crosses to the 6BQ7A/6BZ7/6BS8 which have a mu of 36 - 38 as opposed to the 6BX8 with a mu of 25.

The 6BX8 seems to be extraordinarily obscure. I have not found any so far as my curiosity has been piqued. :D

The 6BX8 also seems to have been designed for cascode operation on relatively low voltages (125V) which is where my interest arises.
 
S

Stefkorn

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Joined 2012
I don' know where I got this info from, I noted it in a spread sheet I made a while ago, it lists substitudes and equivalents. I hope I was not misleading, my apologies. Trouble is when ever I read something which might be relevant I note it, whether it is true or not.
There is too much rubbish on the net.

Thanks anyway.
 
7N7

7N7

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Joined 2003
kevinkr said:
The ECC180 best I can figure crosses to the 6BQ7A/6BZ7/6BS8 which have a mu of 36 - 38 as opposed to the 6BX8 with a mu of 25.

The 6BX8 seems to be extraordinarily obscure. I have not found any so far as my curiosity has been piqued. :D

The 6BX8 also seems to have been designed for cascode operation on relatively low voltages (125V) which is where my interest arises.
Click to expand...

Yes, I was interested for a time in medium-mu (25-40) double triodes; I found Raytheon (I think) boxes labelled 6BQ7A/6BS8/6BZ7 - with one valve inside of course! Obviously they are so close that one wonders why on earth they were developed separately. In the end I settled for 13D3/6158.

Sorry this is a bit off-topic, but I am always fascinated by valve history and curiosities.

7N7
 
Triodethom

Triodethom

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Joined 2009
The reason for multi tube number for the same kind of tube is best I understand was brand rights . Each made a little different tube to go in different set to keep the price up . The common tubes like 12a... 6s.. were common in audio and less so . Later in the 70s multi tube listing on a box where the result of the downsizing of the industry . Most multi tube listing is really the first tube listed that will work in place of the other two but may not be an exact match but close enough for most all uses. Not what most people on the this board want a good starting point to test and tune .
 
kevinkr

kevinkr

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jerluwoo said:
This website lists all 3 of these crosses and a few more to the 6bx8 as well. Tube Cross Reference 6
Click to expand...

These tables were generally created to suggest potential substitutes that may or may not work in any given circuit, and the large difference in mu indicates that they may not always be interchangeable. In a cascode the transconductance is more important than the mu so it may not matter much, in an rc or transformer coupled (audio) circuit it may matter.

Long ago I had a B&W Zenith set that used an unusual dual triode in the cascode amplifier in the VHF tuner, it might even have been one of these, and in fact the only tube that worked correctly was the hard to obtain original type.

I tend to prefer a data sheet to these sorts of tables as useful as they are sometimes. (And I have several of them)
 
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