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   Home   Help Search  
Pages: Prev 1 ... 5 6 7 8 9 [10]
 91 
 on: Today at 03:14:54 AM 
Started by AB1OC - Last post by AB1OC
Hello Everyone,

I have been considering building a "portable" EME station for 432 MHz for some time. I am trying to understand what level of activity might be found on this band. If anyone has some good information on 432 MHz EME activity and what would be required to build a 75 percentile station or better, please post it here.

Thank you and 73,

- Fred, AB1OC

https://stationproject.wordpress.com/2013/04/12/bouncein-off-the-moon/

 92 
 on: Today at 03:06:18 AM 
Started by N0SQ - Last post by W1QJ
I do not believe so.  Some of the modifications there are not generally accepted as necessary amongst the engineering community.

I had plenty of arcs playing with NOS tubes, and the worst I had to do was replace D16 afterward.

I have to agree with BL.  It seems as though every single ham that comes up with some crazy modification for an amplifier can justify it with some sort of mumbo jumbo talk.  This particular wanna be engineer has his little "pet" modifications he does to all amps.  Mainly his single point ground for the whole grid/cathode circuit path.  He does the same thing to every amplifier.  There may be some good ideas he has but he throws everything out there and sees what sticks.  You have to be able to separate the wheat from the chaff.  It is amazing how a handful of these kinds of people can brainwash the mass.  I have seen several hundred SB-220 amplifiers that I have worked on in some form or another and I have to say I have never seen another brand of amplifier that has had so much written about it in the way of modifications. And the ones I have seen, more often than not have either one modification or any number in between of all of the mods out there.  Sometimes I get the unit with the "full blown works".  It's like that chilly dog with "the works" on it and comes with a free roll of toilet paper.  Well that just added a whole extra amount of time to my job to remove all that garbage  Don't get me started.  One particular person has been brainwashing the newbies for the last 40 years that I know of and possibly longer than that.  It is almost like a cult following.  Think about this, If you have to come here and ask others that may or may not know as much as you about amp modifications, ask yourself if you believe the person who designed the amp in question, whatever brand it might be, if they were qualified to make the judgement to build the amp the way it was.  In the case of the Al-811 series of amps, they have gotten a bad wrap over the years due to the poor quality of tubes that have come down the pike.  Personally, if I was you I would leave well enough alone.  Just my 2 cents.

 93 
 on: Today at 03:05:15 AM 
Started by WZ3T - Last post by W9IQ
Jarrad,

The notion of a phase change from the coax does not have much merit. While there is a very small phase change from the exciter end of the coax to the linear end, the linear has no reference to the original phase to somehow benefit from the slight phase shift.

I would speculate that the more likely effect of the coax length had to do with the exciter. Since the amp is not providing a 50 ohm load, the length of coax is transforming the input impedance of the linear that the exciter sees on its output. This in turn is detuning the output circuit of the exciter and nominally lowering or raising its output power to the amplifier.

- Glenn W9IQ

 94 
 on: Today at 02:52:29 AM 
Started by N9CM - Last post by KA4NMA
Switchboard.com reverse phone number
Lookup or google the number

Randy Ka4nma

 95 
 on: Today at 02:32:57 AM 
Started by W5RBB - Last post by KQ4YA
I've been extremely impressed with the 7300. I bought it for what is really a silly reason - so many people were talking about it and I wanted to see what they were talking about. It surprised me in a good way. Going into things I didn't like the idea of the touchscreen, wondered about the tiny size of the scope and also figured that - at the low price - it wouldn't deliver impressive performance. Basically it seemed like a fun toy.

Instead it's been a lot of fun. I can't compare it to the FTDX3000 but I do have the FTDX5000MP. I think the receiver on the 5000 is better and, for sure (at least based on how I have both radios configured) the 5000 is quieter.

But the difference in performance isn't so great that it would disqualify the 7300. here's the thing I wanted to add. I could easily use the 7300 as my main rig. Sure, I'd miss having a second receiver and, yes, the 5000 is a better radio (to my ears). But the 7300 is closer than I'd have ever guessed. I don't know how a person can rate the fun factor but the 7300 wins there. Also it's given me a chance to at least taste the way radios are headed in the future.

I am not attempting to make an argument either way here as far as which would offer the best performance - just to say that if I had to pick between it and the 3000, I'd get the 7300. My guess is that either radio would do everything a person needs. It's just that - for people like me - part of my hobby is the fun factor. The radio as a toy. And the 7300 has proven to be a terrific toy.

 96 
 on: Today at 02:21:32 AM 
Started by AD5IW - Last post by VK3BL

... would you do me the curteousy of finding out what the price for a newly made 2017 tube is, and the minimum order quantity?
Svetlana prices are really high and I see no why a ham would like to give an arm and a leg for a factory new tube, since there are plenty of reasonably priced NOS tubes that are no worse at all.

What really matters for us is that the production continues and the currently produced tubes will be available as NOS after 5-10 years.

Anyway, having a spare tube on hand is a must for every tube amplifier owner. No matter of the amplifier brand model.

I agree, continued production is the single most important factor.

I was of the belief that this was not the case, as I have never seen a new or even recent GU-74B offered for sale.  The most recent example I can find is the Svetlana US "4CX800A", stocks of which are now depleted.

Out of interest why did Acom discontinue Acom 1011 the 2x 4CX250B amplifier?  I thought that was a really neat product, given the continued US production of 4CX250Bs, the Chinese production of FU-251Fs, and the huge stock of surplus tubes.

The shelf life of 4CX250Bs is fantastic so long as they are stored well.

 97 
 on: Today at 02:15:40 AM 
Started by KF5NAJ - Last post by VK3BL
I put a swr meter between the radio and amp and this is what the readings are, does this indicate a input problem
common to all bands
  80m  3.1
  40m  2.3
  20m  2.1
  15m  4.5
  10m  2.1
I have a swr less than 1.2  between the amp and dummy load

Two weeks ago I was getting 500  plus watts from all bands
What would cause this be a common problem to all bands

I plan to test the tubes in another amp to try and eliminate them as the problem

I did not think tuning at 100w for 10sec or less would be a problem

Thank you

The input SWR is not ideal, so you may need to adjust the input network.  Someone more experienced with SB-200s could confirm this and help you do it.

Tuning at 100w is not ideal, mainly because it can really stress the tubes the output circuit is off resonance.  The grids in 572Bs are very rugged, so they won't get damaged, but the extra heat can cause 'outgassing' of the metal in the tube, which can lead to cathode poisoning and reduced output.  Probably no harm done if you do it by accident, but don't make it a practice.

Sort the input SWR problem out first, and see how you go.

 98 
 on: Today at 12:32:52 AM 
Started by KF5NAJ - Last post by KF5NAJ
I put a swr meter between the radio and amp and this is what the readings are, does this indicate a input problem
common to all bands
  80m  3.1
  40m  2.3
  20m  2.1
  15m  4.5
  10m  2.1
I have a swr less than 1.2  between the amp and dummy load

Two weeks ago I was getting 500  plus watts from all bands
What would cause this be a common problem to all bands

I plan to test the tubes in another amp to try and eliminate them as the problem

I did not think tuning at 100w for 10sec or less would be a problem

Thank you



 99 
 on: Today at 12:10:56 AM 
Started by DU7DVE - Last post by K5TEN
I am about to put up an end fed 73 foot antenna (sloping) and 3 very long radials   one 75', 250' and one 125.    I'll post how it goes when I get it up and can test.

 100 
 on: Yesterday at 11:56:35 PM 
Started by AD5IW - Last post by LZ1VB

... would you do me the curteousy of finding out what the price for a newly made 2017 tube is, and the minimum order quantity?
Svetlana prices are really high and I see no why a ham would like to give an arm and a leg for a factory new tube, since there are plenty of reasonably priced NOS tubes that are no worse at all.

What really matters for us is that the production continues and the currently produced tubes will be available as NOS after 5-10 years.

Anyway, having a spare tube on hand is a must for every tube amplifier owner. No matter of the amplifier brand model.

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