Tube Rolling w/Crack

[cddc]

When is a tube out of range? Tubes have a large number of operating characteristics and parameters, as well as the different physical and mechanical bits. Circuits can have some range, more and less, of operational latitude to operate a tube under.

I bring this up around a specific curiosity of the Crack's output tube. The 6080 and 6AS7G have identical electrical characteristics, and they differ in packaging. I see the 6H13C and 6H5C (using Cyrillic here) typically called, or often treated as, direct substitutes for each other and to the 6080/6AS7G. They all look very close on the datasheets. Calling out the Gm, the 6H5C is quite a bit lower than the others - 5,000 vs. 7,000. What difference might this transconductance difference make in the Crack?

What prompted me to post this is someone mentioning to me recently that they've heard people report the GEC 6AS7G sounds as good or better than the Western Electric 421A/5998. Looking at the data sheet, the WE 421A has a Gm of 20,000. Isn't that a large Gm difference from the 6080? Could the tubes be direct subs in the Crack?

I really like the SED 6H13C and 6H5C. I can't hear a difference between them.

The thing is, even with the same specs tubes can sound significantly different, especially from different brands, due to different technology, materials, ..., designs used. And even a tube from the same manufacturer but from a different period can sound quite different.

GEC 6AS7G is the Holy Grail of 6AS7G/6080 tubes, insanely expensive...haven't heard one yet, so not sure how it compares to my 5998.

I'm quite surprised to hear that 6H13C and 6H5C sound the same, because they have different transconductances, which should affect the sound somehow (my understanding is that higher transconductance means higher gain). I asked the same question pages earlier, and one fellow here said they sound different, and while 6H13C is pretty good 6H5C sounds dull. I own several 6H13C's, they're decent tubes, definitely better than the crappy RCA's.

5998 can be used directly in Crack, I think you should be able to find it on the Crack drop-in replacement tube list on Page 1. But it has higher transconductance and gain than 6AS7G/6080. I read somewhere that to achieve 5998's best performance you'd better change some resistors on the Speedball to achieve its optimal working points.

 

[cddc]

Because it's price is very high compared to NOS probably.
Here a 6N13S / 6H13C that's also out of Russia, looks and sounds good imo and saves you a lot of money.

https://www.ebay.com/itm/6N13S-6-13-6AS7G-RUSSIAN-100-TESTED-TUBE-NOS/283678599033?hash=item420c8fe779:g:4TsAAOSwoG5Z8FWl

Hi Tom, I remember you mentioned earlier that you dismantled some plastic adapters in order to fix the wiring inside. So just curious:  1. how the ceramic socket is attached to the plastic base in an adapter like below (do they use glue?), 2. do they use PCB or wires to rearrange pins, and 3. how to dismantle the adapter? Do you have any photos of inside? Thanks a lot.

[Tom-s]

I regularly repurpose/resolder my valve bases but rarely rewire adapters (although i've also build a few just for use on my tester).

But! Manufacturers (especially Philips/Valvo/TFK) did this all the time, along with relabeling tubes as fit their needs (could be the exact situation with some 6N5S/6N13S ). From personal experience, if you are chasing a fancy tube, it's worth to look at the same internal construction on another base. Especially on rectifiers. AZ4/RGN2004/4004 for example, are pretty expensive. Just buy them with a broken P base (those things are a weak link) and put a new B4/5 (or UX4 for US) base on it. Got a few of those yesterday, just for this type of surgery.

Going back on topic.
So on the adapter you showed. The wiring inside is just good insulated point to point inside from my experience.
There's no glue to be seen in the one on your photo, and that makes it a good one to work on. You can reveal the wiring by loosening the bottom screw, that keeps hold of the top part. (Oh, you can't find the screws on yours? It's below the sticker in the middle ).
The one downside to this kind of adapter is the "long" wires inside. When some wires crossover very closely, this could introduce noise (in theory at least, as i never had issues with this).

The other adapters one can work on themselves are the dual to single tube adapters. Like the 6J5, 76 to 12au7/ecc88. These use a PCB that is very very versatile. You can rewire it from 6 to 12V amps by making a few marked connections on the PCB. Or rewire the top part by switching the PCB tube sockets from 6J5 to 76 par example. Or rewire the bottom from 12AU7 to E88CC yourself by just unscrewing that part and rearrange them. These also come with all the holes and solder points for the cap connections. So if you have a 6J5 adapter like this, it's easy just to put in the top cap connections on the right places with a wire of choice, and voila, your own CV6/7193 to 12au7 adapter.

Small note on buying adapters. Compared to "china" adapters, it's worth looking into Deyan adapters on Head-fi. Friendly guy. Just got 6 adapters in the mail from him last week. Really good quality, well build stuff. (All adapters to B4 base, made to order, as nobody makes adapters for them (who uses B4 tubes anyway?! ) ).

Edit: IMPORTANT! I go completely bonkers on insulating wiring inside my own bases/adapters to prevent shorts. Can't stress this enough, be safe.

[cddc]

Tom, thank you very much for the detailed suggestions on rebasing tubes and rewiring adapters!

I am pretty bad at soldering, so I don't have the courage to rewire my Crack sockets for new tube types. I normally buy adapters for new tubes.    Just as your fantastic writing on repurpose adapters, I asked for the internal construction of adapters because I realized some adapters can possibly be rewired for other purposes this afternoon, and you just gave out the perfect answer to my questions. I think it is much safer to rewire adapters so that you don't run the risk of ruining your perfectly working Crack. Your maximum loss is an adapter, it's not a big deal at all, compared to loosing your beloved Crack for couple of days or couple of weeks. 

And of course people need to pay great attention to rewiring, any short in adapters would possibly ruin the amp. Not only that. I recently read on HF some tube veteran incorrectly plugged in the power tube (the tube had a missing guide pin, so pins were mispositioned when plugged in), and it caused short and ruined the power supply of a very expensive amp.

Deyan is a nice guy to work with, I've bought several adapters from him. Thanks a lot for the recommendation 

[Tom-s]

Don't get me wrong. My amps keep their designation. I never change sockets or the wiring inside of them (aside from the switch inside my Crack to use 7119's/E182CC's).
I also use adapters when needed or rebase a tube.
But a rebase is only with pre-WW2 socket tubes from Europe (comes with the fact that i don't like P sockets and prefer B4/5). And with such age, a rebase is sometimes needed. Plus some are so incredibly scarce it's a very worthwhile exercise to salvage them IMO.

[cddc]

LOL...obviously I made a mistake. I was thinking about rewiring the amp sockets instead of rebasing the tube. 

Rebasing a tube needs lots of tools and efforts, it is a mission impossible to me 

But if the tubes are rare antique goodies, I am sure it's worth it.

[legion1capone]

Is this a real sed tube?

http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=183557656844&category=64627&pm=1&ds=0&t=1582397799267&cspheader=1&oversion=a394b17f

[cddc]

Is this a real sed tube?

http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=183557656844&category=64627&pm=1&ds=0&t=1582397799267&cspheader=1&oversion=a394b17f

Yes, it is a real sed winged C 6H13C.

Slightly different print than mine, mine has "6H13C" printed inside the Winged C logo, this one is printed outside the logo. But internals seem the same, so should be real.

The price is a little bit on the high side, normally you can find 6H3C around $8-12 apiece, plus $8-12 shipping from Russia or Ukraine for 3-5 weeks. This seller is located within U.S. so shipping will be much faster.

[legion1capone]

What are your favorite power tubes?

[Tom-s]

I'd only recommend "cheap" tubes to try.
20$ range: 6H13C, Thomson CSF 6080, Philips mullard mitcham factory 6080 (found labeled Mullard, Philips, Adzam, Valvo, Telefunken).

I'm now listening to a new setup. 15$ each tube, 30$ adapter.
For those who want a fun experiment with Crack. A pair of A2293's works as output tubes.

[oguinn]

I love the Thomson 6080

[Deluk]

I love the Thomson 6080

Using this in my standard crack. Smooth but detailed, quiet and inexpensive. What's not to like. See no reason to change and I have others. Using it with a CV4003.

[Tom-s]

Rebasing a tube needs lots of tools and efforts, it is a mission impossible to me 

For me there's only one "special" tool involved that i don't use with other amp related construction -> The "special" toilet roll.

Here's how to rebase a tube in a few steps.

1. Get all needed: old tube, "new" base, wire, solder station (set to max heat/power), solder, desolder braid, cutters, glue.
2. Desolder old tube socket carefully or demolish them without breaking the glass (what i do) and "clean up".
3. Solder new wires that are 3x longer than you actually need and add insolation where needed (the extra length is mandatory to route them in the new base).
4. With new base on, solder new wires in place, cut to length and glue the base to the glass.
5. Before every step / when possible, check for shorts / test the tube in a tester.

I pictured one replacement last weekend.

Top picture: "new" base B4.
Middle picture: example of old P base.
Bottom picture: with removed P base, note the amounts of glue used by previous owners.

[cddc]

Wow...bravo....I can't imagine I can do the rebasing with my soldering skills. Need to get a soldering station first, and need to polish my soldering skills if I were to do the job.

[Bullpride]

Just ordered my Crack w/Speedball.  What are your thoughts on the stock tubes?
Also, if you had to pick one other set to pair with The Atticus, which would it be?