--- In ham_amplifiers@..., "zerobeat40" <zerobeat40@...>
wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
On Oct 29, 2006, at 5:54 AM, pentalab wrote:
---
### well maybe not too stupid. 3 x YC-156's can be had for
$1100.00 vs huge bux for a 4 x 15.[plus socket]
RICH SEZ... What is Svetlana's price for an 8281?
##### They are now $1995.00 socket is $395.00... both svetlana
brand. The Eimac version of both will make u gag.
Last 8281 I bought brand new set me back about $1050, and I think I
had to add a socket. And, the tube's pushing good and hard at 20k,
while a trio of YC-156's is loafing at 30K. Remember, a YC-156 is
actually a 3CX15,000B7 with a smaller cooler.
### agreed. YC-156/YC-179's are everywhere.. and no [failure
prone} socket to mess with. Note to Tony King here. A buddy of
mine asked Eimac if they could take a YC-156... and put the
3CX15,000B7's cooler on it [7.5"]. Eimac said "no way". BTW...
a broadcast engineer school buddy of mine said they had several
problems with the SK-300A socket burning up on the local 100 kw
ERP FM tx here in town.[abt 18 yrs old now] No wonder Eimac
makes "emergency repair" kits for those sockets. The socket
had burned up twice.... b4 1994 [it was only 10 yrs old at that
point]
You CAN push more air (put the amp in another room, please) and run
them quite harder. I have a push-pull broadband pair of YC-156s
here, runs 2MHz to 40MHz braodband, for EMC measurements, driving a
TEM cell. 30kW CW not a problem. Not pushing ANY of the tube's I
or V limits, and with enough air, I keep the seals below 250C.
### These YC-156/YC-179's.. with their almost 19db of gain..
Eimac says the gain is 14.2db at 6kV.
You have to read all the conditions of that gain spec. 14.2dB is
correct with a 600 ohm load-line. That will give you 24kW PER
TUBE. If you're getting 30-35kW from three tubes, you're running
more like a 1500 ohm load line per tube. At a higher RL, the tube
exhibits more gain.
### agreed.
Also, that 14.2dB is conservative - it's into compression at
that point. Cleanly, it's another dB, then add a few more for the
higher RL.
### agreed. Most builder's appear to be getting 17 to 17.8 db
with a single tube.. running 6500 V - 7200 V ..under load. With
higher ratio's of plate load Z to input Z... gain goes UP.. as u
noted.
### 12 k out with 200 w of drive is quite common. IMO... a
lot simpler than mucking about with a 4x10, regulated screen +
bias supplies, roller's across the input globar..+ step up 9:1
trifilars, neutralizing the entire amp, megabuck sockets, etc.
A good used YC-156[$300-$400] beats a new 4x10 + socket any day.
Something to be said for simplicity. Just whack one hole in the
chassis... done. Round up a 10 kva-120 lb 4800 V hypersil pole
pig for very little.. and there's ur 6800 V no load HV supply.
Besides, nobody who's actually designing an amp depends on the
"typical application" data to predict performance.
### agreed.
You calculate gain from the characteristic curves.
### agreed.
At 20kW output and 6.5kV anode, I see YC-156s typically running
at 17dB gain.
### see my previous notes. Depending on used tube condx, ops are
reporting anywhere between 17 to almost 19db of gain.
Most of my experience in broadcasting with them was with the
3CX15,000B7 version, but they work the same...the YC-156 just needs
to be blasted with lots more air.
are
the 4-1000 for the new milenium... quick, where's that pole
pig ?
### I'm serious....
Serious people look at the mfg's spec sheet instead of
speculating.
Exactamundo. The grounded-grid curves for the YC-156 will predict
all the figures he gave. You just have to know how to use them, and
that's happily explained in "Care and Feeding."
### agreed... like zsac for a given plate V, grid current, plate
current, etc. Heck, I still have the origional Eimac... "tube
performance computer" ! [clear plastic overlay device, when
doing load lines] ... still works, still use it.
Later.... Jim VE7RF
cheers, Jim
R L Measures, AG6K, 805.386.3734
r@..., , rlm@, www.somis.org
