Tube Rolling w/Crack

[Paul Joppa]

The hope is to have a prototype running for the March 5 HeadFi meeting at BHQ. At this point I don't know if it will happen that fast, or even if it does, whether the amp will be broken in. It certainly won't be refined yet - we usually screw around with the design and parts a bit before releasing a product.

[hasafraker]

well that's awesome... my birthday is in march   I look forward to hearing more as it develops, who knows maybe I'll have something to compare to the Crack soon

[tdogzthmn]

Sadly, my 5998 went out on me today.  I lost the right channel after I powered the amp on after switching the 12AU7 to a 5814.  I was scared at first but I pulled out the 5998 and put in an a 6AS7G and got both channels back.  Sounds good now but I find there to be a noticeable difference in quality with the 5998 being very dark and detailed.

[hasafraker]

that's too bad at least it was the tube and not some other component but those 5998's are hard to come by unless you can afford what people are asking. I've been trying to get one off ebay but they're never cheap and always people wanting them... someday!

[hasafraker]

question, I saw in another thread PJ mentioned a tube I hadn't seen listed before 7802 as a sub for the 6080/6AS7, I happened a cross a NOS Tung-Sol 7802 pretty cheap so I picked it up, should this just drop in or will it need any changes, I've been looking for a 5998 to try and still haven't seen anything that didn't qualify as "stupid expensive" and I'm not going to spend the kind of money those tubes are going for, I figure if this guy is a drop in and I don't like the sound I won't have any trouble getting my money out of it, assuming it's fully serviceable.

[hasafraker]

well according to the data sheet I couldn't see a reason the 7802 isn't a drop in sub so I plugged it in and it's got about 28hrs on it now and sounds great.

[deltaunit]

You can add the CV2984 to the output tube alternative lists, it's a drop in replacement. I just picked a GEC one up to have as a spare. It seems good nothing really between it and my Mullard 6080 anyway.

[jrihs]

Thanks! Isn't CV2984 just the euro designation for 6080 though? Or am I misunderstanding something?

[deltaunit]

It's the uk military spec version of the 6080 which as far as I know is known as a 6080 here.

[MxT]

Hi guys.

Im not jacked on tube's at all. So if I had to get a suggestion of a drop in tube to try what should I look at??

thanks!!

[dubiousmike]

Can anyone advise as to whether a Shuguang cv181-z is a safe 6sn7 alternative in the crack? 

I've read conflicting comments on the net - one site claiming the cv181-z is a safe 6sn7 replacement "in any circuit" (http://thetubestore.com/sh-cv181-z.html), while another gives it rave reviews while also emphasizing the heightened current draw from the heaters of the cv181-z (http://www.tnt-audio.com/accessories/shuguang_treasures_cv181_e.html).  Has anyone tried this tube in their crack, and is it okay to do so?

Thanks in advance for any comments any of your can offer!

[Paul Joppa]

Neither of the suggested web sites has much actual data, and I'm afraid the tnt-audio one has a fair amount of misinformation. (I am not questioning his listening report, just some of the technical aspects.) Do read his follow-up article. But Grant Fidelity has a spec sheet for the tube:

http://grantfidelity.com/site/files/shuguang%20treasure%20tube%20spec%20cv-181_0.pdf

From these specs, it is equivalent to a 6SN7-GTA, including the same 600mA heater current, the same mu of 20 and transconductance of 2.6mA/volt, and the same 450v maximum plate voltage. In fact the specs are so identical that it is clear they are copies of the 6SN7 specs. A couple of them are mis-labeled but the intention is clear. Not surprisingly, no information is available that I could find reporting how close to these specs the average tube might actually be.

A real CV181 (no -Z, not from Shuguang) is said to be equivalent to an ECC32, but the available information is small and inconsistent - I found one report of 600mA and another of 950mA heater current, for example. Why they would mark a tube with the designation of another is beyond me - unless they mean to indicate the size and shape of the envelope rather than the operating parameters. Kind of like a $20 "Rolex" watch, I guess.  :^)

[dubiousmike]

Much appreciated Paul!  Setting aside the needlessly confusing naming scheme, it sounds like they should at least be safe to try in the crack - at least based on the paper specs.  I've heard generally good things about the "treasures" on head-fi - although I believe most of the chatter was about their 300b variant.  

I just might give one a try.  If I do, I'll make sure to chime back in and let you all know how it worked out.

Thanks again for breaking this all down for me!  

[dubiousmike]

To follow up on my last post, upon further reading, it looks like the verdict on head-fi is that Shuguang Treasures are just "alright" but nothing to write home about. 

If anyone else is interested in reading all or part of a 60 page thread devoted to 6sn7 tubes, here's the link: https://www.head-fi.org/forum/thread/479031/6sn7-tube-addicts/735

[Jim R.]

Yes, after my initial enthusiasm for the 2a3z Treasures, they didn't live up to the hype for me -- very smooth sound, but not very good on the top end.

I really like the Russian military 6h8c 6sn7 equivalents (well, almost equivalents) -- the military version with the metal base -- the regular run of the mill ones are again, nothing to write home about.  Of course the real ones are hard to get and expensive.

-- Jim