Tube Rolling w/Crack

[jrihs]

Sure that makes sense but funny that they would use both within slavic countries. Извини, пожалуйста!

[Bolivar]

When looking at suitable alternative tubes, what are the main points that I should look for in the datasheet. For instance I have a 12AV7 (5965) tube. Could this work in place of the 12AU7?

[Paul Joppa]

For a good match, you must match gain (mu), plate resistance (rp), and transconductance (gm). They are related, and a match of any two means the third will match as well. However, rp and gm are strong functions of plate current, so make sure the parameters are quoted at similar currents. Here is an example:

12AU7  at 10.5mA  mu=17, rp=7700, gm=2200
6CG7    at  9.0mA  mu=20, rp=7700, gm=2600

These are within less than 20%, indicating a close enough match for most purposes. Note that the 6CG7 needs twice as much heater current, fortunately Crack has enough current available to handle this requirement. You should always check this too, though!

[stereo_eyes]

While wandering through an electronics junk store while visiting my daughter for Thanksgiving I couldn't stop myself from buying a couple of tubes from their piles (literally) of tubes. I got an RCA 6ca7g that was just sitting in the bin (no box) that could be new (or not), and what appears to be a new in box GE 6ca7ga. The place (see below for those of you in the silicon valley area) had a simple pricing scheme: all tubes of a given type cost the same, independent of condition, with no testing and no guarantee!

So here's my real question: I now have two tubes that could be perfect or could have been sitting in that bin since somebody determined they didn't work 40 years ago and never got around to throwing them out.  Having experienced some rather interesting tube failures over the years, I'm a little nervous to just plug them into my shiny new crack and fire it up.  So nothing to worry about, just slam them in and look for fireworks in case I need to pull the plug? Or just write off this small impulse buy and get some tubes from somebody that has actually tested them before I put them in?



*http://www.yelp.com/biz/hsc-electronic-supply-santa-clara-2

[Jim R.]

Well, the 6CA7 is a power pentode (el34 equivalent), so there's no place to use it in the Crack.  Both tubes in the Crack are dual triodes -- one small signal, one power.

HTH,

Jim

[stereo_eyes]

Okay, violated my "don't ever send email after midnight because bad things happen" rule.

The two tubes are, of course, really a 6AS7G and 6AS7GA. I guess I have 6CA7 seared into my brain after too many years of nursing a Dynaco Stereo 70 in my youth (showing my age!).

[Jim R.]

Ah, well I'm sure we've all been there :-).

If it were me I'd probably start with the one in the factory box, do a visual inspection to make sure everyting looks ok internally, then make sure the filament is a low resistance and the other pins are very high -- ruling out any shorts between elements) and then give it a try.

This is assuming that you know the amp is working to begin with.

HTH,

Jim

[stereo_eyes]

Thanks Jim, that sounds like good advice. It's been 25 years since I had tube technology in my system, and I've forgotten even the basics. I'll be home in a couple of days and give the tubes a try.  The recently finished crack is working just fine, but all of the discussion of tube rolling made me feel like I needed to play around as well. Besides, the crack will look a lot cooler if the ST bottle tube works ;-)

[langendorf]

Hi


Do any of you have som link for tubes om ebay?

I would like som tubes that give more lower end/bass

[langendorf]

http://www.ebay.de/itm/6H13C-Svetlana-Rohre-6AS7G-6080-NOS-Rohrenverstarker-Tube-amp-/390366303246?pt=LH_DefaultDomain_77&hash=item5ae3a5140e

http://www.ebay.com/itm/6N5S-6H5C-6AS7G-C-SVETLANA-USSR-TUBE-NIB-60s-/250948155938?pt=Vintage_Electronics_R2&hash=item3a6dacfa22

Would they be any good?

[Bolivar]

I have one of those Svetlana 6N5S tubes, and yes the lower end is somewhat more pronounced than in a 6080.

[Lee Hankins]

langendorf, If I remember correctly the RCA 6080/6AS7 tube usually has more base.

[langendorf]

Hi

I just orderet the 6H13C Svetlana. But i should i order the Svetlana 6N5S to?

If you have any suggestions on input tube. And links to ebay i would apriciate it

Thanks

[Bolivar]

The 6N5S(6H5C) is a military version of the 6H13C. I'd guess sonic differences between the two would be very small.

As for the driver tube, I like a Philips 6189W with my 6N5S. But these are a matter of taste, really. And your choice headphone will make a big difference on tube matching aswell.

[langendorf]

shure it