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Sustitute 5842 for EC86

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Hans Olofsson

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Joined 2007
#1
I am planning a Phono Preamp using the 5842 tube. However, these tubes seems quite costly and I am considering replacing them for EC86 that I have available and are less expensive. Is that a good idea, and would that require a major redesign of the schematics?
 

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#2
Hej Hans,
The EC86 is a very good tube in RIAAs if you don´t get problems with microphony. The tubes does not have very much in common.

An option could be to use the EC86 as input tube and parallell the the two halves of a E88CC( or 6N6P=lower gain/lower Zout) at the output. Personally I find the EQ a little nweird but it will anyway work. But almost all component-values has to be changed.
 
#4
(u=68 for ec86 and 43 for 5842)
Click to expand...

Gain difference is only just above 4dB so no big deal😉. If you don´t want more total gain you can go for something like 6N6P in the second stage it´s got 6dB lower gain. With E88CC second, total gain will be almost on par.

But still, whatever tube you go for componentvalues have to be altered. Or let´s say the complete circuit should be redsigned.

There are no easy to find substitutes to find for 5842. 6c45 comes to mind but seems hard to get nowadays.
 
#5
Thanks for your input, I understand that the schematics needs reworking and right now I am not in the position to do that. However- someone who has experience ( and a schematics) for a RIAA phono amplifier that would fit the EC86 tube? As I understand it , the tube would qualify very well as a base for a highquality phonoamp.
Regards/ Hans
 
#6
I have used the 6S3P-EV and 6S3P-DR as a cheap substitute for the 5842. Keep in mind that the max anode voltage is slightly lower than the 5842 and/or the WE417. Also keep in mind that the pinouts are not the same...
 
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#8
The WE417/5842 is MICROPHONIC to a degree that in a mic pre you don't need to bother with a microphone!

A far better tube for phono prte is the Russki 6C45, or 6P45 if you like. Even more gM that the 417, far more consistant and much less microphonoc. In current production, and costs less than most NOS tubes.

But I don't understand the reson for the half passive, half active RIAA eq. Doing the active that way is VERY noisy because of the very high impedances seen at the grid of the second tube.

Regards, Allen
 
#11
Hans,

To what Allen says we can add: The second stage is also lousy as the frequency-dependant NFB makes Zout be higher the lower in frequency you go.

The 6C45(mu=52, Gm=45mA/V and Ri just above 1k) is closer to WE437 and a triodestrapped E810F than to a 5842/WE417. But it is the same school.

Still you have a great input tube in EC86.
 
#12
As you mention, the microfonics is a problem with the raytheon tubes, as the author writes in the article- I have to live with that, since I have no option but using the tubes I have, and I´m not in the mood to bye something else. The design is said to be "hybrid equalization" and possibly there is a noise problem- however, mr Tritschler claims a noise figure of -74db below 4mV input and that´s ok by me- it is inaudible to my ears- personnally I find no sense in pushing noise levels to -90, -100 db, levels that has no practical use in ordinary listening situations.
Regards all /Hans
 
#13
Hey Hans,

If you still want to go by this questionable design, that some of us aren´t impressed of, please note that the the guy who designed it now has switched from 5842 to E88CC.

Zout is a few hundred ohms above 1kHz then gradually rising to ca 2kohm at 20Hz.

Still EC86 is a great tube at the input, but not at the output due to high Ri.
 
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