S3X change?

[Mucker]

If I want to use a 6DN7 tube in an S3X, is it just rewiring of the tube sockets that is required? I am ready to pull the trigger on this amp but it looks like finding an inexpensive 6FJ7 replacement tube is getting harder. From reading, I understand there won't be much if any performance difference if doing so. Is that safe to assume? Thank you!

Greg

[Thermioniclife]

The 6dn7 and 6fj7 are the same except for the package, 8pin vs compactron.

[Thermioniclife]

It is quite doable, I did this and other changes to a pair of s3x amps. I insralled the octal sochets with the keyway pointing to the left.
YMMV

[Paul Birkeland]

6FJ7s aren't widely available because we bought up all the ones that were advertised.  The supply will recover and you should be able to get replacement for under $10 each in a couple of years. 

These tubes last a long, long time.  I was getting 5 years of 24/7/365 use out of them when I ran an amp with 6FM7s without ever turning it off.

[mcandmar]

lol

If you ask any of the larger tube sellers they may have some in stock, they fall into the "who the hell would want these" category and not worth the effort creating listings for.  I picked up many 6DN7's that way.

[oguinn]

I was buying 6FJ7s when I saw them come up (I think they're kinda cool in addition to using them in the S3X). I think I have a dozen or so if anyone needed a couple.

[Mucker]

Wow, all kinds of great info, thank you all! Sounds like a very robust tube so should be good for quite a while.

I appreciate your thoughtfulness oguinn!

Cool amp Thermioniclife!

Sounds like it's time to take the plunge!

[Mucker]

My amp (edit: plus C4S) is ordered and now waiting out the joys and pains of the gestation period. 

I was able to find some affordable Sylvania spare tubes today on the infamous auction site, so all good now.

I built a Crack/SB back in 2014 or 15 and upgraded the output caps to dayton and changed the pot to an alps. Other than that, it is all stock, and bombastically wonderful.

Are there any "right off the bat" upgrades I should do with S3X or just build it all stock and enjoy?

I will primarily use it with DT 1990 Pro and HE6se headphones (prob Grado RS-2e and AH-D5000 too) and also would like to use Klipsch RP-600M speakers.

They are rated at 8 ohms, but an article I read said they measured as a 4 ohm design:

https://www.hifinews.com/content/klipsch-rp-600m-loudspeaker-lab-report

According to the manual, it sounds like I would want to wire the output transformer's secondaries for 4 ohms ......  Is this correct?

Oh... and ... I see choke bell housings on many S3X kits I look at. Are they included in the kit? Are they necessary? The 1st page of the manual shows the built product without them. I think it looks cool without ...

Probably will have a few more questions as I go ....

Thank you!

Greg

[scblock]

I’d consider the C4S upgrade worthwhile if you didn’t order it with the amp, but in either case I’d start with a stock build and get to know it first before installing.

I use my amp to run headphones as well as Klipsch R-51M speakers at my desk. I believe the current version of the manual recommends building to 4 ohms for headphones or if you’re unsure. Mine is wired at 4 ohms, no issues, and that’s probably the way to go here.

I assume you’re referring to the plate chokes with the bell housings. Unless something has changed they come with the housings installed and are not removable.

[Mucker]

Yes, the housing's for the chokes. Was going to type that in but forgot (edited my post above). Thanks for the info on those.

Yes, I did order the C4S upgrade too.

Thanks for the feedback on 4 ohm. That sounds like the way I will go.

[Paul Joppa]

I also recommend 4 ohms for the RP600M - see the discussion in a nearby thread at https://forum.bottlehead.com/index.php?topic=13629.0

That should do for most of your list, except the hifiman, which is very inefficient. At 4 ohms, it will still go louder than the RP600M but if that were the only thing you used it for, and you like to listen loud, you might prefer to wire the transformer for 16 or even 32 ohms. (Those options exist but are not documented in the manual.)

[Mucker]

That's great information Paul, thank you. One of the main reason's for purchasing the amp was for heavy use with HE6se. I think I'll have to see how I want to utilize it and then will be back with some questions if I need to make a change in my approach. Thanks!