Audio Pentode Data

[DaveP]

I thought I'd share this with the forum as it may be useful to some.

I did some comparisons from the data of various audio pentodes and there are some differences as this chart shows.

The 6AU6 makes the best replacement for an EF86, all other parameters being equal.

All the figures are with both Anode/Plate and Vg2 at 100V.

Best
DaveP

 

[buildafriend]

Thanks!

 

[abbey road d enfer]

The 6AU6 makes the best replacement for an EF86, all other parameters being equal.

It really depends what you're looking for. Although the cut-off characteristics are indeed similar, the slope is much higher on the 6AU6. The internal resistance is also much lower, which results in a similar Mu, but as in most cases, the plate load will be much lower than the internal plate resistance, for a given stage, the gain with 6AU6 will be about twice that of the EF86. A very noticeable difference is the anode-to-grid capacitance, that is about 20 times less on the 6AU6; that would be significant on a mic preamp in terms of HF response.

 

[PRR]

I see the 6AU6 as the "outlier". Plot transconductance: 6AU6 has much more than the others.

6AU6 is a fine tube, but not always a drop-in for any other.

I also have doubts about the difference 6J7 and 6SJ7. These should be the same. They are different by about the amount of manufacturing tolerance. Which may reflect improved production in the 6SJ7 era. Or may be lost in the haze.

 

[DaveP]

I also have doubts about the difference 6J7 and 6SJ7. These should be the same. They are different by about the amount of manufacturing tolerance. Which may reflect improved production in the 6SJ7 era. Or may be lost in the haze.

RDH4
Page  508, chapt12.3
The table shows they are totally different tubes.
Page 510, shows a table comparing Inter-modulation distortion, the 6J7 has about a third of the 6SJ7's.

I think a triode connected 6J7 will be a 6C5, whereas a triode connected 6SJ7 will be a 6J5.

Best
DaveP

 

[emrr]

Good stuff Dave.

I also have doubts about the difference 6J7 and 6SJ7. These should be the same.

In a few circuits I've seen with triode 6J7 sockets rewired for 6SJ7, I find higher current draw.