| Author | Message | ||
     Greg Williams (gwmn) Username: gwmn Registered: 08-2013 |
Well I just got through trying some new JJ 6CA7, double getters, in my 210-65, 12AX7 driver. Tried the bias at 19,22 and 25 and they sounded thin and brittle on all three. I put my old Sylvania, single getter, 6CA7's back in. World of difference. Smooth and musical compared to what I would call, very harsh. I did try different 12AX7's also with the new JJ's with the same results. I don't know what they were after with these tubes, but they are not similar to the old Sylvania's in my opinion. (I know..... that's expecting too much) Had similar results with some early 2000's winged C's. I need to find something close so maybe I'll try the JJ EL34's as I've heard some decent feedback on these. Just had high hopes for these JJ 6CA7's. One of my Sylvania's is weak and works great on the low setting but runs away in bias on the high. New tubes bias fine. Darn!! | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
I know that the JJ tubes are historically tough. You might try warming them up even more. You MIGHT contact Bob at Eurotubes(don't know where you bought them) and ask HIM how hot they can run. I know he likes to torture stuff to death but you have to use his advice with a grain of salt. I would try them at 30 and even higher. they SAY they will 50mA but that is at something like 400V. Warm them up a little and see if it changes the sound. Here's the link to the 6CA7 data sheet. http://www.thetubestore.com/lib/thetubes tore/JJ-6CA7.pdf Mike. | ||
| Greg Williams (gwmn) Username: gwmn Registered: 08-2013 |
Thanks Mike, I'll call him tomorrow. I bought these from them. | ||
| Steve Kennedy (admin) Username: admin Registered: 03-2002 |
You might try the JJ E34L tube. It is sort of like having a tube that is between the 6CA7 and and EL34. I believe this is the JJ tube that Bob at EuroTubes suggests for the Music Man amps because it withstands the higher plate voltage better. Steve | ||
| Greg Williams (gwmn) Username: gwmn Registered: 08-2013 |
I've been eyeing up the L's and if the 6CA7's won't cooperate that's what I'll try. Only other option is to search for Sylvania's, though the stock has been picked over quite a few times already. One thing I forgot to mention that was kind of strange. The tremolo cycle with the JJ 6CA7's would fade completely in and out on 3 or more, as compared to the Sylvania's, which would sound the way it should. | ||
| Lars Verholt (lmv) Username: lmv Registered: 11-2009 |
Winged =C= EL-34 is another great option (albeit somewhat expensive). As I've said on this forum before, the premium 'cryo' version, in my opinion, is like paying extra for whitewalls on your tires. You may feel good about paying extra but it doesn't actually do anything ;o) Cheers, Lars Verholt | ||
| Greg Williams (gwmn) Username: gwmn Registered: 08-2013 |
I tried warming the bias up on the JJ 6CA7's and they won't adjust above 28, after 20 min, bias pot maxed. Maybe they'll work for clay pigeons. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
You CAN get them to go hotter. You just need to REDUCE the amount of - voltage going to the bias adjust pot. This will allow you to INCREASE the amount of current going through the tubes. Maybe put another 5K resistor in front of the bias pot to decrease the available control grid voltage. Mike | ||
| Greg Williams (gwmn) Username: gwmn Registered: 08-2013 |
Thanks Mike, I've got some 1/2w CC 5K's around here somewhere. By the way, I am retaining all of this usable knowledge you are passing along for future reference. By the time we're 90 I won't have to bug you anymore. | ||
| Greg Williams (gwmn) Username: gwmn Registered: 08-2013 |
Just talked to Eurotubes, Bob wasn't there until tomorrow, but the one I did speak with said not to go above 28. Hogwash! Got my helmet on headed for 30 plus!! I guess I better put the resistor in first. Only had a 4.7k | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
I just looked up the actual 6CA7 tables and they work out to around what he said so MAYBE he was right. I figured the 6CA7's would take more than that. Stick with his suggestion. Mike. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
The more i look at that, I think MAYBE you should add the 5k or so AFTER the pot. THAT way it shouldn't muck up the voltage downstream that it needs for the +and- voltage for the IC's. Not that I think that it will make THAT much difference but it will effect the voltage before it dumps into the 100K dropping resistor. I'm just thinkin' here...... Gawd, it's hell to get old! Mike. | ||
| Greg Williams (gwmn) Username: gwmn Registered: 08-2013 |
I'll try that Mike, thanks. But first I need to wait on my probably foolish purchase of a pretty closely matched, (I hope), Sylvania 6CA7 to the one good one I have. Paid $55, it's a single getter like mine that looks good on paper. Wish "my" aging brain would let go of the tone obsession a little with this amp, but ever since I've heard it with these old Sylvania's it's hard to get it out of my head. I go just a little overboard with that sometimes. I just finished up a tweed champ build from scratch, (not a big fan of kits or sticking to the schem.), and I wore out screws,wire and turrets from changing things around so much, but found what I was after........I think. Thanks again Mike. | ||
| Greg Williams (gwmn) Username: gwmn Registered: 08-2013 |
Got my Sylvania 6CA7 and it worked out great. (A little prayer involved) Biased at 22 on both and it sounds wonerful - wonerful. Thanks again for all the help. |