Tube Rolling w/Crack

[Paul Birkeland]

I've never bought anything from them.  A custom order like that which isn't handled by a website shopping cart will take a little extra time, I would encourage patience. 

[JLDub]

Noted! Will definitely give it a little more time and see what he comes back with. Although if it takes too much longer guess I'll just move on.

Thanks for your take.

[L0rdGwyn]

I think I accidentally deleted my post Re the 6BX7, so here is my recreation:

I am a Crackatwoa owner.  I am in the process of purchasing a custom built OTL headphone amplifier than takes 6BX7/6BL7 output tubes.  I recently read here in the BH forums that a single 6BX7 could be used in the Crack(atwoa) given it has the same pinout and its plate current/dissipation are low enough to not be "dangerous".

I bought some of these tubes in advance of my custom OTL amplifier arriving and threw one in my Crackatwoa thinking I would check them for noise and maybe they would "make music"...

I was shocked to find that they sounded very, very good in the amplifier, listening with my ZMF headphones (Atticus, Auteur).

I know the driver current is much less than ideal for the 6BX7, but regardless, it sounds excellent in the output position.  If there are no negative consequences of using the 6BX7 in a non-optimized circuit, I would recommend giving one a shot.  The GE manufactured can be had for ~$10.

DISCLAIMER: from my readings below, not recommended without the Speedball.

Information from the forums I have found:
https://bottlehead.com/smf/index.php?topic=2604.0
https://bottlehead.com/smf/index.php?topic=663.1335

[cddc]

Very interesting...can 6BX7/6BL7 output tubes be used in Crack (w/ Speedball)?

BTW, I read somewhere on head-fi that only 6080/6AS7G family tubes are suitable for OTL design due to their low output impedance. So now we have new candidates for OTL, i.e. 6BX7/6BL7? How about 300B tubes in OTL, they should also have low output impedance (can't remember where I read 300B's impedance) ?

[Paul Birkeland]

Very interesting...can 6BX7/6BL7 output tubes be used in Crack (w/ Speedball)?

They are close enough that you can plug one in and see.

BTW, I read somewhere on head-fi that only 6080/6AS7G family tubes are suitable for OTL design due to their low output impedance.

That is incorrect.

How about 300B tubes in OTL, they should also have low output impedance (can't remember where I read 300B's impedance) ?

No, a pair of 300Bs would have twice the output impedance (roughly) compared to a 6080 or other similar tube.

[cddc]

Cool....it seems lots of different tubes can be used in OTL. I guess LD3 OTL uses 6SN7 as power tube, although I think 6SN7 is not so powerful as 6080.

I like more power. If possible, I'd really like to stick a 300B into my Crack w/speedball...lol   so that I can try these power hungry bad guys like K1000 or planars. 

[cddc]

BTW, how much watt per channel the Crack (/w speedball) blows into a 300 ohm headphone (like HD650 or HD800)?

[Tom-s]

You'd be better off with a Kaiju.

Thats probably more easy as converting Crack for 300b output tubes.

Crack puts out 0.3w into 300ohms i think.

[Paul Birkeland]

Cool....it seems lots of different tubes can be used in OTL. I guess LD3 OTL uses 6SN7 as power tube, although I think 6SN7 is not so powerful as 6080.

If one puts feedback around a circuit, a tube like a 6SN7 can be made to work properly.

I like more power. If possible, I'd really like to stick a 300B into my Crack w/speedball...lol   so that I can try these power hungry bad guys like K1000 or planars. 

300Bs in the Crack circuit would be a poorer choice to drive power hungry headphones, especially low impedance ones.

[JLDub]

I've never bought anything from them.  A custom order like that which isn't handled by a website shopping cart will take a little extra time, I would encourage patience.

Update on order from DBTubes in CA. The tube finally arrived on Friday and sounds great in the Crack. Tung Sol 6080 had for 15+10 Shipping to US. Tube is in great shape minus some greenish oxidation on the base. It is super quiet, not microphonic at all. David managed to find this one loner laying around in his stock.

I will say, I did not place an order directly from his website so I cannot speak to that experience, but this was one of the lesser experiences I've had in terms of seller communication. I had to reach out by phone every time to follow up and make sure my order was shipped as I didn't get confirmation after payment. I am glad it arrived in good shape the literal day before they went on a month long vacation. Probably wouldn't buy from again in that capacity.

[JLDub]

So I read something on the forums in passing about Chinese fakes. It got me a little paranoid about a Mullard cv4003 I picked up from eBay a couple months back from a seller in Taiwan that has quite a large stock of these claimed NOS Mullard M8136 tubes. I picked one up thinking I got a great deal and noted how remarkable the packaging was for an older tube. Here is the listing: https://www.ebay.com/itm/Mullard-ECC802S-M8136-12AU7WA-ECC82-box-plate-small-shield-UK-made-TUBE-VALVE/173814424654
Can anyone with more experience in these matters offer up their take on this? Do you think I've been had? I can upload more detailed pics of the tube and packaging if anyone asks.
Just seems a little too clean now that I think about it.
Thanks

[oguinn]

Not saying those are genuine because I also don't know, but I've gotten some pretty clean NOS tube boxes. Maybe I've been had, too?

Off topic: I picked up the adapter to use a 6SN7 tube and a NOS Sovtek 6H8C and rolled that in today. Sounds pretty good! Not sure that it sounds appreciably better than the Motorola 12AU7 it replaced, but it's nice to know it works and gives me more rolling options.

[Paul Birkeland]

https://www.ebay.com/itm/Mullard-ECC802S-M8136-12AU7WA-ECC82-box-plate-small-shield-UK-made-TUBE-VALVE/173814424654

Those are the real deal.

[JLDub]

Those are the real deal.

Well that's good to know. Thanks for weighing in PB. I gave it a once over when I got home and it seems legit. My mind is at ease.

Here is the actual website in case anyone is interested
http://tubes.tw/shop/index.php?cPath=22_27&sort=3a&filter_id=14
They have a boat load of different 12AU7 brands and date codes. Not sure how much shipping costs from their web store, but prices seem to be cheaper than their eBay store.
The exact one I purchased from eBay is listed for $48

The picture I attached I found on Google. Apparently it lives somewhere on their site. Shows the differences between the CV4003 through the years. Very interesting.

Note this is the same seller that lists the French Thomson CSF 6080WA that was linked to a couple of pages back. They have a HUGE stock of those.
http://tubes.tw/shop/product_info.php?products_id=1279
Definitely worth checking out at those prices. I will probably grab one myself at some point.

Sorry for the lengthy post. I hope someone finds it useful one day!

[cddc]

If one puts feedback around a circuit, a tube like a 6SN7 can be made to work properly.
300Bs in the Crack circuit would be a poorer choice to drive power hungry headphones, especially low impedance ones.

You'd be better off with a Kaiju.

Thats probably more easy as converting Crack for 300b output tubes.

Crack puts out 0.3w into 300ohms i think.

Thanks a lot, PB and Tom!

I was just kidding for sticking a 300B into Crack. It requires heavy modding...way too much for me.

On the other hand, I would love to see Bottlehead to add a headphone jack to their 300B or 2A3 speaker amps if possible. It will definitely increase the amps' use and hence increase sale volumes. You know, Woo's 300B amp WA5 can be used for both headphone and speaker, and lots of other 300B amps too.