JT30.com |
Amps:
www.HarpAmps.com Tab: www.HarpTab.com Contact Webmaster |
Links:
www.HarpLinks.com Learn: www.HarpLog.com Rock & Roll Lyrics |
Vacuum Tubes for Amps
6V6 duty cycle
reaike--(at)--x.netcom.com (Randall Aiken ) wrote:
>
(Said Joe, more or less..)
>>abused in all guitar amps.. 415V is no big deal to a 6V6, if you look
at
>>their absolute max ratings, the plate voltage is 1200V max. (or is it
>>1400? been a while since I looked it up..) 425V is, as a MOF what
>>Sylvania reccomends for running class A...
I agree with your comments vis duty cycle, and I believe we are saying
similar things: I'm saying that the plate voltage level alone is not the
big issue (as do you I believe). Max plate voltage, forgetting
dissipation for a moment, is a function of lead spacing in the pinch
primarily from what I understand. If the tube couldn't handle 400V, it
couldn't handle 1200 for any period of time, forget current draw and duty
cycle. We also agree, I believe, that running AB (less than 100%, more
than 50% duty cycle) is cooler for the tubes than is running class A. If
a class A spec has the tube sitting at 425V, then I think it's reasonable
to conclude that 425V at a colder bias and lower duty cycle should be ok.
(all else equal) The thing that caught my eye about the Sylvania design
example is that the spec they use is a 250V spec - I had always assumed
that 250V or 315V (what RCA lists as max for the 6V6GT) were the Vmax..
but in the example they perform at the end of the book, it is clear that
the voltages spec'd in those tables are the center points of the
operating characteristic. So, if 250V sits idle at 425V, where does that
315V (and 350V) spec sit at idle? Above 425 I'd say. Anyhow, that 250V
spec is in every tube book I've seen, give or take a few. It's the one
that goes:
Va 250V
Vg2 250V
Bias -12.5
Rk 250 Ohms
Iplate (zero signal) 45mA
Iplate (max signal) 47mA
Ig2 (zero signal) 4.5mA
Ig2 (max signal) 7.0mA
rp (approx) 50,000 Ohms
Transconductance: 4100 umhos
Load Resistance: 5,000
Max signal pwr output: 4.3W
THD 4.8% 2nd, 5.7% 3rd HD
I also agree 100% that the tubes being sold as "6V6"'s are not up to the
job that our old GE's and RCA's were up to. I guess my only real point
in posting that last note was just that I'm kinda tired of seeing these
unsubstantiated rumors of Princetons and Deluxes being "tube eaters".. It
makes no sense historically (Fender amps are reliable as heartburn at a
chili cook off..) and like I said before, I have not found (not yet
anyhow) here, or in print, any evidence to support those rumors. I just
hate seeing people get all paranoid for nothing. Further, I've been
gigging & rehearsing steadily for 3 years now on the same set of NOS GE
6V6GTA's, in a Deluxe Rvb running at 415V--(at)--dle and current draws of 15mA
& 20mA resp. And the tubes are just starting to show their age a bit.
Some tube killer.
Anyhow, I hope I didn't come off as too hard headed.. Thanks for the
interesting reply.
Joe
micK pages
