| Author | Message | ||
     bradleyny |
I just purchased a 212 Sixty-Five that I dated as a '79 (No 12AX7). Everything about the amp is original including the tubes. I've been thinking about changing them. Can anyone tell me if I get new tubes, will I have to have the amp biased? Also, what tubes (6CA7) do you guys recommend? | ||
| Warren Peace |
JJ EL34L $34/pair (tubestore.com) SED "Winged C" (not Svetlana) $40/pair (tubestore) GrooveTubes EL34LS list $60/pair, Take a look at the reviews at watfordvalves.com, take note that they are old and any reference to Svetlana relly means SED - "Winged C" today. If you want a headache, look at guitaramplifierblueprinting.com BTW, I like the JJ's. I've seen a few amps with the original tubes still installed. In a couple of cases I've found that one of the filter caps has gone 'DC'. That left the output section with much less voltage. This let the tubes run cooler and this kept them alive longer. Unfortunately, the amp's sound wasn't up to par. But then again, putting the voltage back where it should be increases the likelyhood that some older components might fizz out... Old amps=fun And yes, a qualified tech must bias. The voltages in your amp can kill. | ||
| bradleyny |
Any difference between the JJ El34s and the KT77s? | ||
| Ed Goforth (ed_goforth) Username: ed_goforth Registered: 06-2006 |
I hear a lot of good about the JJ's sounding very good in the HD-65/130 amps. I have a pair of Svetlana Winged "C" EL-34's now and it sounds very good as well, maybe a bit brighter. So if you want more of a slightly darker, like the old Sylvania, the JJ's might be the ticket from what I have read, though the Svet- "C"'s are good too, just maybe a matter of tonal taste? Yes! definately get them biased if you don't know how, they could either run too hot and blow the amp or not hot enough and sound weak. You could get a bias King or take the amp apart and measure the current across the 10 ohm 1 watt resistor on pin 8 and 1, set to ma. on a digital voltage meter. If you have not been in an amp you may want to have a qualified person do it, since there are some high leathal voltages in there, about 725 or so depending on the power setting, which is also important to make sure the readings are done with the amps power in the HI position. I believe the reading should be about .500 or so. I would not go higher. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Ed. I hate to correct you but don't measure the CURRENT ACROSS THE 10 OHM RESISTOR. You set the meter to VOLTAGE, measure the voltage and it converts on a factor of ten to current. I don't usually suggest that because it give you a total cathode current for TWO tubes but if that's all you have, go for it. It would be .5 VOLTS and THAT'S to hot. Drop it just a little. |