Tube Rolling w/Crack

[oguinn]

The stock tubes are generally perfectly fine. Many people roll in new combos but I honestly think 80% of people will be fine with what they receive from Bottlehead.

[kill_surf_city]

Finally decided to try out some other tubes than the stock. For the power tube I got the RCA 6AS7G (grey plate). I tried this out first with the stock driver tube. Not much difference, but it did seem to resolve my slight balance issue. Then I bought the RCA 12BH7A. Best info I can find is that it's the early 70's tube, grey plate. Much more forward sound. Very detailed and dynamic. Then I tried out the RCA 12AU7 (black plate). Kind of disappointing considering it was more expensive than the 12BH7A. It's not a bad tube, just more warm and less dynamic. I like clear, forward dynamics and this just didn't do it for me. But I bought a pair of the 12AU7's so I think I'll just throw those in my Jolida JD9 cos I just have the stock tubes in it.

[Paul Birkeland]

I've thought about making an OTL amp with those.  I thought I could probably power it with two Kaiju power transformers.  I'd run it at about 100V P-K and half an amp of current.  Output impedance might be something like 7 ohms.  The cathode load would need to be a resistor capable of dissipating 50W, so something on a big heatsink or a 150+ watt rated part.  That's per channel, a room heater indeed!

I don't even see the internal capacitances listed, but I bet they are HUGE.  You'd probably want a big linear triode of some sort with very low Rp to drive the thing. 

It would make a fun super high dollar OTL amp.  With a little messing around, you could also drive speakers with it.  It wouldn't surprise me if a Mainline sounded a lot better though!

[Mr. Electric Wizard]

So that I'd have some extras, I bought a couple of tubes:
1963 Mullard 12AU7 ECC82
RCA JAN 6AS7G
Tube rolling is totally new to me, so Hopefully I didn't buy crap.  Ha!

[rbond]

My Crack came with a GE 6AS7 output tube, which has always worked well.  I've done the Speedball upgrade and use HD600 headphones.  Based on reviews - and to provide spares for both of the Cracks I have - I bought two Thompson CSF 6080WA output tubes.  When I tested the first tube I can just barely hear the sound when the volume control is turned all the way up.  When I tested the second tube there's no sound regardless of where the volume control is set.  Is there something I'm missing, or are these just bad tubes?  Both were in the original manufacturer's packaging and were purchased from what appeared to be an established business.  Any guidance would be greatly appreciated.

[Doc B.]

Put the original tube back in and see if it still works. If it does, the other tubes are not working. If the original tube also does not work now something has been disturbed in the amp that needs to be fixed, like a bad connection.

[rbond]

Thanks.  Still works perfectly with the original tube in it.  Looks like I just got sold junk.  Thanks again for your quick response.

[2wo]

Before you give up, give the pins a good cleaning and try them again...John

[Tom-s]

My Crack came with a GE 6AS7 output tube, which has always worked well.  I've done the Speedball upgrade and use HD600 headphones.  Based on reviews - and to provide spares for both of the Cracks I have - I bought two Thompson CSF 6080WA output tubes.  When I tested the first tube I can just barely hear the sound when the volume control is turned all the way up.  When I tested the second tube there's no sound regardless of where the volume control is set.  Is there something I'm missing, or are these just bad tubes?  Both were in the original manufacturer's packaging and were purchased from what appeared to be an established business.  Any guidance would be greatly appreciated.

There's some sources from eastern Europe that appear to be selling bad Thomson csf 6080wa tubes. Recently a local guy got 6, all tested bad, some shorted out. Be careful when buying these via Ebay, use a tester before putting them in Crack with fancy headphones.. Clean the pins after you've made sure they'r all safe.

[rbond]

Thanks for the additional responses.  I tried cleaning the pins, but no luck.  These came from a UK retailer, and he has agreed to replace them.  I'll certainly be careful with the replacements as recommended.

[watonwak]

Has COVID effected the price of some tubes? In November I purchased a NOS Tungsram E80CC for about £15 on eBay, but now prices for E80CC's seem to have shot up a lot since then, or did I just get a good deal at the time?

[larcenasb]

It's of course reasonable some sellers would be increasing their prices amid this economic hardship, but old stock E80CC tubes have generally been pretty pricey in recent years--especially those made in Holland. It seems you got a good deal if it's one of those desirable makes and tests at least good. Enjoy it!

[David Joiner]

Quick question on tube rolling. I just finished my crack about 2 months ago. Thought I'd give tube rolling a try and purchased a RU-6H13C from "thetubestore.com". Got it in today, and "rolled" it in. Powered my crack up and the tube crackled and I could see some arcing going on inside for a second. I thought Oh, SH$T, I mean, SHOOT, there goes $25 bucks.

Fed it some audio, and, well, good to go. Sounds great.

So, is that normal for a new tube to do that? Any concerns about tube life or reliability?

I've got a 5998 on order too, so want to make sure if I see that again, it's normal.

Thx.

[Doc B.]

It's not normal. But, it could be that something was lodged in between a couple of parts that vaporized the first time it was fired up. My suggestion would be to fire it up without headphones for a few cycles, letting it cool down completely in between. If it doesn't arc again the tube is probably OK. But if it continues to arc it's not going to get better.

[David Joiner]

Hey Thanks Doc. Well, good advice, I'll try that in the future. Unfortunately, I already cycled the tube off and on since my post, um, with the headphones plugged in. Good news is no new arcing, headphones are all good....

Definitely for any new tubes, will fire up my crack with headphones removed, just as a precaution.

David