The 8930 also has the larger heatsink.
Gary WE9Y
--------------------------------------------
On Wed, 8/31/16, Rick Muller <rick.muller(a)asml.com> wrote:
Subject: Re: [Moon-Net] Fair price for NOS 4CX250R?
To: "Bob Atkins" <ka1gt(a)hotmail.com>, "moon-net(a)mailman.pe1itr.com" <moon-net(a)mailman.pe1itr.com>
Date: Wednesday, August 31, 2016, 4:18 AM
#yiv0765484178
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Maybe a 4CX400 can be used for
70 cm ??
Anode is bigger than 4cx250 but
pin-out is the same
http://www.g8wrb.org/data/Svetlana/pdf/4CX400A.pdfhttp://www.ur4ll.net/gs-36b.html
From:
moon-net-bounces(a)mailman.pe1itr.com
[mailto:moon-net-bounces@mailman.pe1itr.com]
On Behalf Of Bob Atkins
Sent: Tuesday, August 30, 2016 7:56 PM
To: moon-net(a)mailman.pe1itr.com
Subject: [Moon-Net] Fair price for NOS
4CX250R?
Still having
efficiency issues with my K2RIW amplifier. I can get 500W
out in Class C, but I seem to be stock at about 45%
efficiency, which would be OK for AB1 but is
low for C. I've tried cleaning and polishing the output
stripline, the fingerstock connectors, double checked the RF
chokes and tuning and loading flaps, but no significant
improvement. One thing I do notice is that the output
coupling flap is just about at
the end of it's range (minimum capacitance - maximum
distance from the stripline) using the original dimensions.
I tried making it slightly smaller, but that didn't
improve things either.
So I'm
thinking of maybe going for fresh tubes to replace the
current ones which were used and pulled from service
sometime back in the 1970s. I'm wondering what a fair
price these days would be for a pair of 4XC250R tubes,
"new old stock", made 20+ years ago. They are hard
to find, so I'd like to get a ballpark figure of what
they typically sell for in case I find some and need to make
a quick decision. I resume they sell
at a premium over the 4CX250B, which seem to go for
anything from $50-$200 each on ebay depending whether they
were made in the USA, Russia or China!
Maybe new tubes
won't improve the efficiency, but it might be worth a
shot. 500W out is OK, but at only 45% efficiency I'm
pushing my Variac and power supply quite hard
and I'm getting close to tripping the 15A braker on my
120v line...
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are at http://www.nlsa.com/nets/moon-net-help.html
It certainly does sound like you got everything covered. I would just like to stress that on more than one occasion I had assumed I was working with a known good component or item only to find out after a lot of pain & agony that I messed up and did not check everything like I should have. When I worked in a RF lab and was faced with a weird problem I liked to tear everything down to absolute basics and make the setup as simple as possible....if you can, replace the bird meter, the slug, and use different & short jumper cables to that load. Also, see if you can (at least as a quick test) find a load good for 70 cm with more power capacity.
To share a quick weird story, I once traced an SWR issue I had on 70cm to the clone 9913 cable I was using. The stuff I got was made by Carol and must have been experimental and tossed into the dumpster and someone grabbed it all and sold many, many 500' rolls of the stuff. Upon careful testing I found that the cable simply could not propagate RF above about 300 MHz ! Perfectly good at 2m etc but not at 432 MHz. Anyway, it just helped teach me not to assume anything when trouble shooting hi-hi......good luck I hope you get this nailed down ! 73
Gedas, W8BYA
----- Original Message -----
From: "Bob Atkins" <ka1gt(a)hotmail.com>
To: "Gedas" <w8bya(a)mchsi.com>
Sent: Tuesday, August 30, 2016 6:57:22 PM
Subject: Re: Fair price for NOS 4CX250R?
Gedas
Your point is well taken. It is a Bird 43 with a 500W 200-500MHz element. Should be good and I've previously compared it with other meters and it was with about 5% of them. I'm working into a long length of 50 ohm coax coupled to a 100W 50 ohm load good to 2GHz, so I think I'm OK there. The coax gets warm and the load gets warm, but I don't see any "hot spots" at the connectors.
The one thing I haven't done is to measure the exit air temperature and compare it with the amp biased to draw standing current that corresponds to what I think my efficiency numbers give me for plate dissipation.
It would be nice if my meter was reading 25% low, but unfortunately I don't think it is! Worth double checking though.
Bob
From: moon-net-bounces(a)mailman.pe1itr.com <moon-net-bounces(a)mailman.pe1itr.com> on behalf of Gedas <w8bya(a)mchsi.com>
Sent: Tuesday, August 30, 2016 6:40 PM
To: moon-net(a)mailman.pe1itr.com
Subject: Re: [Moon-Net] Fair price for NOS 4CX250R?
Bob, I'm sure you have this covered but I would make absolutely sure your power meter is known to be accurate. I would also test the PA into a known and trusted load, and if need be, change out any jumper cables between the PA and meter & load etc just to eliminate variables.
Gedas, W8BYA
----- Original Message -----
From: "Leif Asbrink" <leif(a)sm5bsz.com>
To: moon-net(a)mailman.pe1itr.com
Sent: Tuesday, August 30, 2016 6:38:07 PM
Subject: Re: [Moon-Net] Fair price for NOS 4CX250R?
Hi Bob,
Unlike transistor amplifiers, tetrode amplifiers are fairly easy to
understand. Capacitances do not change when voltage is changed.
When running in class C you have some grid current. For full
power something like 25 mA in each tube with -90V on the
grids. This is easy to measure.
If g1 is OK, then monitor screen grid current and plate current
as you tune the tank circuit. The screen grid is a voltage probe
for the plate. If your load is not coupling well enough, the AC
voltage on the plate will go very high and the voltage will
periodically be much lower than the screen grid voltage. In such
a case the screen grid current becomes very high at the point
of maximum output power. In such a case you need stronger coupling.
If, on the other hand coupling is too strong, the plate will always
be at a higher potential than the screen grid in which case the
g2 current would be low or negative. In this case you need weaker
coupling.
The nice thing with tube amplifiers is that you can remove all
voltages and run the amplifier cold. Put a suitable resistor
between plate and screen grid. It should have the value of the
output impedance of the tube at the desired operating conditions.
Then send some (low) power into the plate resonator through the
antenna connector. Tune for a good VSWR. Then replace the resistor
with one of half the resistance and verify you can match that
one also and finally verify that you can match a resistance
twice above the desired.
For details, look here: http://www.sm5bsz.com/power.htm
73
Leif
> Still having efficiency issues with my K2RIW amplifier. I can get 500W out in Class C, but I seem to be stock at about 45% efficiency, which would be OK for AB1 but is low for C. I've tried cleaning and polishing the output stripline, the fingerstock connectors, double checked the RF chokes and tuning and loading flaps, but no significant improvement. One thing I do notice is that the output coupling flap is just about at the end of it's range (minimum capacitance - maximum distance from the stripline) using the original dimensions. I tried making it slightly smaller, but that didn't improve things either.
>
>
> So I'm thinking of maybe going for fresh tubes to replace the current ones which were used and pulled from service sometime back in the 1970s. I'm wondering what a fair price these days would be for a pair of 4XC250R tubes, "new old stock", made 20+ years ago. They are hard to find, so I'd like to get a ballpark figure of what they typically sell for in case I find some and need to make a quick decision. I resume they sell at a premium over the 4CX250B, which seem to go for anything from $50-$200 each on ebay depending whether they were made in the USA, Russia or China!
>
>
> Maybe new tubes won't improve the efficiency, but it might be worth a shot. 500W out is OK, but at only 45% efficiency I'm pushing my Variac and power supply quite hard and I'm getting close to tripping the 15A braker on my 120v line...
_______________________________________________
Moon-Net posting and subscription instructions are at http://www.nlsa.com/nets/moon-net-help.html
Bob, I'm sure you have this covered but I would make absolutely sure your power meter is known to be accurate. I would also test the PA into a known and trusted load, and if need be, change out any jumper cables between the PA and meter & load etc just to eliminate variables.
Gedas, W8BYA
----- Original Message -----
From: "Leif Asbrink" <leif(a)sm5bsz.com>
To: moon-net(a)mailman.pe1itr.com
Sent: Tuesday, August 30, 2016 6:38:07 PM
Subject: Re: [Moon-Net] Fair price for NOS 4CX250R?
Hi Bob,
Unlike transistor amplifiers, tetrode amplifiers are fairly easy to
understand. Capacitances do not change when voltage is changed.
When running in class C you have some grid current. For full
power something like 25 mA in each tube with -90V on the
grids. This is easy to measure.
If g1 is OK, then monitor screen grid current and plate current
as you tune the tank circuit. The screen grid is a voltage probe
for the plate. If your load is not coupling well enough, the AC
voltage on the plate will go very high and the voltage will
periodically be much lower than the screen grid voltage. In such
a case the screen grid current becomes very high at the point
of maximum output power. In such a case you need stronger coupling.
If, on the other hand coupling is too strong, the plate will always
be at a higher potential than the screen grid in which case the
g2 current would be low or negative. In this case you need weaker
coupling.
The nice thing with tube amplifiers is that you can remove all
voltages and run the amplifier cold. Put a suitable resistor
between plate and screen grid. It should have the value of the
output impedance of the tube at the desired operating conditions.
Then send some (low) power into the plate resonator through the
antenna connector. Tune for a good VSWR. Then replace the resistor
with one of half the resistance and verify you can match that
one also and finally verify that you can match a resistance
twice above the desired.
For details, look here: http://www.sm5bsz.com/power.htm
73
Leif
> Still having efficiency issues with my K2RIW amplifier. I can get 500W out in Class C, but I seem to be stock at about 45% efficiency, which would be OK for AB1 but is low for C. I've tried cleaning and polishing the output stripline, the fingerstock connectors, double checked the RF chokes and tuning and loading flaps, but no significant improvement. One thing I do notice is that the output coupling flap is just about at the end of it's range (minimum capacitance - maximum distance from the stripline) using the original dimensions. I tried making it slightly smaller, but that didn't improve things either.
>
>
> So I'm thinking of maybe going for fresh tubes to replace the current ones which were used and pulled from service sometime back in the 1970s. I'm wondering what a fair price these days would be for a pair of 4XC250R tubes, "new old stock", made 20+ years ago. They are hard to find, so I'd like to get a ballpark figure of what they typically sell for in case I find some and need to make a quick decision. I resume they sell at a premium over the 4CX250B, which seem to go for anything from $50-$200 each on ebay depending whether they were made in the USA, Russia or China!
>
>
> Maybe new tubes won't improve the efficiency, but it might be worth a shot. 500W out is OK, but at only 45% efficiency I'm pushing my Variac and power supply quite hard and I'm getting close to tripping the 15A braker on my 120v line...
_______________________________________________
Moon-Net posting and subscription instructions are at http://www.nlsa.com/nets/moon-net-help.html
Hello all
A question comes to my mind and maybe this could be off interest.
Charly presented in Venice a very interesting study about
Circular and Linear Polarisation on 10ghz.
Now my question.
Will on the lower band (23 to 6cm) the results be the same.
circular to circular -1.4db against Linear to Linear.
Or is this effect only on 10ghz and up!!!
73 de Michel
HB9JAW
Hallo all
The last 2 days iam trying to instal 2 wsjtx programs.
One for H-pole and one for V-pole.
This on one computer under XP.
Can someone tell me how to do this on a XP computer.
It is working fine on my laptop that is running under windows 10
73 GYS PA1GYS
Sorry for BW.
73,
Hervé F5HRY
---
L'absence de virus dans ce courrier électronique a été vérifiée par le logiciel antivirus Avast.
https://www.avast.com/antivirus
The LNA is spoken for.
73
Fred
N1DPM
On 08/29/16, Fred<n1dpm(a)verizon.net> wrote:
I have a WA2ODO 2 meter LNA for sale.
It has a test sticker on it that is dated 3/25/15and the measurements on the sticker are 0.170 dB NF and 26.169 dB Gain.
I just measured it on my HP8970A and 346A noise source and measured 0.24dB NF and 24.92dB Gain.
I would like to sell it for $50 plus postage.
Please contact me directly if interested.
Thanks and 73,
Fred, N1DPM
_______________________________________________
Moon-Net posting and subscription instructions are at http://www.nlsa.com/nets/moon-net-help.html
I have a WA2ODO 2 meter LNA for sale.
It has a test sticker on it that is dated 3/25/15and the measurements on the sticker are 0.170 dB NF and 26.169 dB Gain.
I just measured it on my HP8970A and 346A noise source and measured 0.24dB NF and 24.92dB Gain.
I would like to sell it for $50 plus postage.
Please contact me directly if interested.
Thanks and 73,
Fred, N1DPM
