ET 250S hybrid amp question please - re tube input circuit

[golfnutintib]

I recently acquired a nice condition ET250S hybrid amp with 6dj8 tube input stage - quite enjoying the sound.

I do have a question about the tube input stage employed in this unit ... what is the topology of this stage and is it much easier on the tubes as far as tube wear over time and revealing microphonics?

I assume it is different and much more conservative than how the ET5 or ET7-2 linestages use their single 6dj8 (sounds great but infamous for burning through tubes fast) .... of course I can see that the ET250S uses one tube per channel, so the twin triodes in each tube is doubled up driving voltage gain for 1 channel in the 250S, as opposed to the single tube using each triode half to run full-out for each channel in the case of the ET5 or ET7.

Curious to hear folks describe their knowledge and experience of tube sensitivity (to noise, aging in use) in the case of the ET250S in use, and any comments on how the circuitry works in the case of this amp, driving the voltage gain which in turn slaves the MOSFETS downstream for current drive.

Thanks in advance.

[bgiliberti]

You might just want to call CJ directly on this. They definitely pick up the phone and are as nice as can be in answering technical questions such as yours. At least, that's been my experience.

This isn't a direct reply to your question, but my ET250 came with Electroharmonix 6922 tubes (same as the 66dj8 if I'm not mistaken). While they didn't fail per se, they started to sound dull after 250 hours, which is pretty fast, given that the ET250S is a pretty mellow amp to begin with. Maybe no big deal to change early, as the 6922 is not an expensive tube unless one insists on exotica.

[golfnutintib]

Thanks for the reply. Recently, CJ is not answering the phone. They have a recording on the machine referring all inquiries to their website contact page, which I filled out, but there has been no reply to my inquiry asking to speak to someone about the input stage. Oh well.

[roberto]

Hola,
This is what I found about the ET-250S power amplifier. There is a small explanation about the circuit used on it...
https://www.dagogo.com/conrad-johnson-e ... er-review/