Hi Larry, you wrote:>>
> >Hi John. I hope N1RWY's page comes back - I still would like some of the
information he had there.
*** I don't know what happened to Jay's page. Perhaps he has an alias with
the ARRL and you can email him. A quick Google came up with _n1rwy_
(mailto:n1rwy@amsat.org) @amsat.org
, you may try that. Also Google AM6155 as there are other sites of interest.
>>I got the amp back in October & performed the mods myself to get it on 2
Meters. Do I need those cathode resistors since your amp doesn't have them?
What would be the effect of taking them out, since your amp doesn't have them?
***The resistors add negative feedback to the amplifier. Whether you remove
them or not depends upon how you modified the input, and what tube you plan to
use. The downside of the resistors is the need for a bit more drive (and
imperceptible IMD due to varying cathode bias).
***My input compartment is virtually gutted and matched using link coupling.
>>As far as I know, the 6155's difference was the plunger setting inside the
cavity.
*** The 6155 grid section is different. The grid coaxial cavity is shorter
(as it was meant for UHF), the VHF version uses a swamping resistor on the
grid, plenty of additional capacitance, and the screen is heavily by-passed -
all
not found on the UHF version.
*** It is my belief, the output cavities are the same (less the bolt-on
input compartments).
>> I think that's why the problem started in the first place - the 4X150's
just aren't right for this amplifier.
*** I don't know. The 8930 and the 150 (other than plate dissipation) have
same interelectrode capacitances. Eimac did rate the 150 for 150 MHz and the
8930 for 500 MHz, so perhaps the tube decided to take off.
*** Did you run the heaters for a while? Like hours to a day to outgas the
tube? Did you check the various electrodes for dc shorts? And, as I said
off-reflector; it is always best to bring up the screen and HV slowly.
>>Guess it's back to the drawing board for a replacement tube. Well, not
back too far. I'll have to find the 8930, or set the amp up for the GS-36B
tube.
Either way, I need a backup tube - I don't know what type of abuse my
original tube has been through. I get around 400 watts output with 10 - 15
watts
drive.
*** If you have an original 8930, and it is putting out 400 watts reliably,
that is good. The best I got was 500 watts with a fresh tube. What do you run
the screen voltage at? A small boost in the screen will have a dramatic
effect on output. Just don't raise it so far that you draw excessive screen
current.
**** There was a fellow in Hawaii selling NOS 8930's still in the unsealed
can for about $90. If you can't find him, maybe I can. You can get the
GS-36B/4CX400 on eBay from the QRO-Stuff store. Personally, I wouldn't do
business
with him (I'll gladly detail this tidbit off the reflector). This tube will
give you another 100 watts of plate dissipation. As the plate diameter is a
bit
smaller that the 8930, you will have to bend the fingerstock for good
contact. And, while it may be up for SSB, I am not sure the power supply is up
for
FM service with this tube. Personally, I would stick with the 8930.
>>Do you operate any meteor scatter? I didn't look up your location, but if
we're in range of each other, maybe we can give it a try sometime?
***I am in North Central Illinois and a 2 meter and ATV freak. It will have
to be Scatter or one hell of an opening!
>>> 73's for now, & thanks for your information. You really sound like you
know allot about these amplifiers (insert firm handshake here). ...Larry
N1MIW FN41
*** No, I know just enough to be dangerous (firm handshake back at 'ya).
-John, N9RF
**************Ideas to please picky eaters. Watch video on AOL Living.
(http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/
2050827?NCID=aolcmp00300000002598)
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|