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Author Topic: Interest in kit (QRO) amps?  (Read 14064 times)
KI6SZ
Member

Posts: 21




Ignore
« Reply #45 on: July 09, 2010, 05:31:26 PM »

OK -- I've been struggling with the liability aspects of the kit amp, and I think the associated risks could be addressed.  Several folks have highlighted probably the other greatest single motivator -- price.  Don't get me wrong, I'm pretty darn frugal with my money -- I'm currently in a 12-step program for recovering cheapskates...

The amplifier that I am contemplating will have features that most QRO+ tube amplifers do not have such as automatic tuning, etc.  It is difficult to compete with the manual tune amps like Ameritron, etc., on price, even if the labor costs are reduced due to it being a kit.  I'm not bashing Ameritron or any other amplifier manufacturer -- I'm just using them as an example since others have used them as a cost comparison.  They do in-fact provide good value per dollar.

My preference would be to stick with American made tubes.  However, in this day and age, that pretty much limits the choice to Eimac (CPI).  In doing so, I end up paying a premium for tube(s), probably making the amplifier unattractive when looking at it purely on the basis of price.

The question that I'm build up to in a long-winded fashion is this:  Would the perceived value of the kit amplifier diminish it if used a foreign tube?  Some sources have dried up or have also become quite expensive, and I worry about future availability.
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K0WA
Member

Posts: 95




Ignore
« Reply #46 on: July 09, 2010, 07:18:25 PM »

Foreign Tubes:  I would be OK with a foreign made tube.  I think you would have to make your amp kit...tube universal.  Now, I might be barking up a wrong tree here, but make the amp kit so different tubes can be selected depending on what is available at the time.  So, what happens in the future...some 40 years later?  Well, I for one will be 90 and won't care, but it would be nice for the amp to be flexible that a tube change out (to a totally different kind) would be fairly easy to do.  Now, how do you warranty foreign tubes.  Dunno!  Maybe buy enough to warranty yourself for 5 years.  The other thing about some of the (older) tubes being offered on the market is how to condition them before using.  That also would have to be addressed.

ACOM is selling well and they use a foreign tube or non American tube.

Then on a wild note...make your own tube.  Wow!  That would be fun.

I think I need that 12 step program myself....

Lee = K0WA
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K6AER
Member

Posts: 3529




Ignore
« Reply #47 on: July 09, 2010, 08:41:46 PM »

Don,

Almost everyone is using Chinese tubes. CPI (Eimac) has priced them selves almost out of the business. The most common tubes are listed below.

CPI 8877 $1300
CPI 3CX12200A7 $1360
CPI 4CX1500B $1325
CPI 3CX800A7 $750

The Chinese 3CX1500A7 is about $490 from Penta or Taylor tubes. The larger problem is the MRI market has gone solid state and the market for these small tubes is almost HAM only. As a result the demand is no longer there. Given the universal popularity of the 8877, that would be my tube of choice. The Chinese are doing a good job of making the 8877 and in many aspects have built a better product than CPI.

The larger problem with a legal limit amplifier is the tank circuit will require more skill than the average ham is capable of. To build a proper high efficiency Pi "L" circuit is beyond the soldering capability of the average ham.

I still don't know how you are going to get around part 97.313 and TIA 603C for harmonic regulation and case emissions.
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KI6SZ
Member

Posts: 21




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« Reply #48 on: July 16, 2010, 05:20:20 PM »

Mike,

Thanks for the info.  I know that Greenstone is marketing an 8877 clone but just not sure how attractive the tube would be -- I thought they were being built in Vietnam.  Also I believe that the pentalabs tube structures are made somewhere in Asia, but the tube itself is then assembled in the US, using the asian-made components.  I might be wrong on that however.

Back to the kit amp...
I think this is a very interesting issue.  Part 97.313, etc., are standards that affect everyone -- hams as well as manufacturers.  But I think I'm missing your point.  If the other manufacturers are able to meet these specifications, then why wouldn't the kit amp also be able to meet these same specs if properly engineered and manufactured?

97.313 specifies maximum permissable power, etc.  There are amps sold now that can exceed these limitations but are still legal for sale in the US.  It is the responsibility of the operator to adhere to the power level rules, etc.  As far as harmonic regulation, etc., that is up to the designer (me in this case) to come up with a design and implementation that adheres to and achieves the mandated emission specifications.  I agree that the kit would certainly need to meet all such requirements for spectral purity, etc., but clearly this has been achieveable by the other manufacturers.  Why would a well designed & engineered "kit" not be able to similarly & consistantly meet such performance specifications?  I would be very interested in speaking with you directly about this -- You've got plenty of expertise and I value your inputs.

Thanks,
Don
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K2QPN
Member

Posts: 70




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« Reply #49 on: July 19, 2010, 09:29:44 AM »

I would be interested in a kit amp. I have built an SB-200 back in the day - it still works. I build QRP kits so soldering is OK.
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KI6SZ
Member

Posts: 21




Ignore
« Reply #50 on: August 29, 2010, 07:36:40 AM »

Would anyone be interested in a liquid cooling option?  This would be more complicated, but would make it much quieter.

Thanks,
Don
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K6AER
Member

Posts: 3529




Ignore
« Reply #51 on: August 29, 2010, 09:15:41 AM »

Don,

Sorry it has taken me so much time to get back to you question of certification. I have been covered up with developing the new 6 meter amp at Alpha and the FCC type acceptance of the new amplifier. Also I have been putting up towers in the Denver area and 70 hour work weeks is the norm. Gosh how I long for the good old days when I was young and only had a 40 hour work week.

Getting back to the certification process. As of about 2-3 years ago the FCC regulations changed and HF amplifiers that can be used above 25 MHz also must meet commercial specifications TIA-603C and D for harmonic emissions. Basically it is 43+10Log of the power for any amplifier capable of use above 25 MHz. Harmonics are tested in conducted (coax spigot) and case radiation out to the tenth harmonic. At 1500 watts out that means the radiation from the case must be down -74 dBc. Ouch. This is a bear.

When you look at the FCC web page and go out to the technical section and look up every ones certification you find most of the amplifiers are certificated to 21.45 MHz as the highest frequency of certification. You are no longer allowed to cut the green wire for ten/twelve meter operation. Many amplifiers are being imported but the FCC and ARRL has not paid attention to what is being sold and what they are actually certified for. This is a can of worms waiting to be tipped over.

I addition the amplifier must have negative gain from 26-28 MHz. This is at any power level. You are no longer allowed to have a burning HV choke resonate at 27 MHz like the old days. Basically most use a pic micro as a frequency counter and faults the amplifier if RF is detected in the 26-28 MHz spectrum.

The last 20 dB of the specification for operation above 25 MHz is a ball crusher. The keying line and power cable must radiate less than -13 dBm using the antenna substitution method on a test range. Both polarizations at 0-40 degrees elevation angel. Every ten degrees azimuth, Test takes about 4 hours to complete.

Another item surfaces when testing is the amplifier operates at the full output for up to 4 hours. This is a real brick on the key test. I have found many transceivers cannot provide 50 watts out for four hours.

One last item. The amplifier must require more than 50 watts drive for 1500 watts out on all bands. Some of the tubes out their can be pretty frisky when it comes to gain. Even the ARRL is testing for this now.

When you have time give ma a call at 303 246-3518. I can fill you in on more detail.

73, Mike






« Last Edit: August 29, 2010, 09:18:36 AM by Michael S. Higgins » Logged
K9FV
Member

Posts: 480




Ignore
« Reply #52 on: August 30, 2010, 10:39:02 AM »

WOW Mike those are TOUGHT!! certs to meet. 

This has been a very good thread with LOTS Of good knowledge shared.  I do hope this is a success - While I've been drooling over tube amps for many years, I sorta expect MOSFETs are the way of the future...  "larger problem is the MRI market has gone solid state" - there must be a reason the MRI market has moved away from tubes.

Again, good luck and I do hope to see a kit on the market soon.

To the poster who compared the cost of this kit at $1100 to the MFJ's 811 at $800 - you are comparing a 600 watt amp to a legal limit amp - BIG!! difference.

73 de Ken H>
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NK2F
Member

Posts: 33




Ignore
« Reply #53 on: September 08, 2010, 12:08:57 PM »

Does the text below mean that if a ham were to sell the kit to hams only, for use at that ham's station, the amp does not need to meet any FCC certification requirements?

Part 97 : Sec. 97.315 Certification of external RF power amplifiers

(a) Any external RF power amplifier manufactured or imported for use at an amateur radio station must be certificated for use in the amateur service in accordance with subpart J of part 2 of the FCC Rules. No amplifier capable of operation below 144 MHz may be constructed or modified by a non-amateur service licensee without a grant of certification from the FCC.

(b) The requirement of paragraph (a) does not apply if one or more of the following conditions are met:

(1) The amplifier is constructed or modified by an amateur radio operator for use at an amateur station.
(2) The amplifier was manufactured before April 28, 1978, and has been issued a marketing waiver by the FCC, or the amplifier was purchased before April 28, 1978, by an amateur radio operator for use at that operator's station.
(3) The amplifier is sold to an amateur radio operator or to a dealer, the amplifier is purchased in used condition by a dealer, or the amplifier is sold to an amateur radio operator for use at that operator's station.

(c) Any external RF power amplifier appearing in the Commission's database as certificated for use in the amateur service may be marketed for use in the amateur service.


As of about 2-3 years ago the FCC regulations changed and HF amplifiers that can be used above 25 MHz also must meet commercial specifications TIA-603C and D for harmonic emissions. Basically it is 43+10Log of the power for any amplifier capable of use above 25 MHz. Harmonics are tested in conducted (coax spigot) and case radiation out to the tenth harmonic. At 1500 watts out that means the radiation from the case must be down -74 dBc. Ouch. This is a bear.

When you look at the FCC web page and go out to the technical section and look up every ones certification you find most of the amplifiers are certificated to 21.45 MHz as the highest frequency of certification. You are no longer allowed to cut the green wire for ten/twelve meter operation. Many amplifiers are being imported but the FCC and ARRL has not paid attention to what is being sold and what they are actually certified for. This is a can of worms waiting to be tipped over.

I addition the amplifier must have negative gain from 26-28 MHz. This is at any power level. You are no longer allowed to have a burning HV choke resonate at 27 MHz like the old days. Basically most use a pic micro as a frequency counter and faults the amplifier if RF is detected in the 26-28 MHz spectrum.

The last 20 dB of the specification for operation above 25 MHz is a ball crusher. The keying line and power cable must radiate less than -13 dBm using the antenna substitution method on a test range. Both polarizations at 0-40 degrees elevation angel. Every ten degrees azimuth, Test takes about 4 hours to complete.

Another item surfaces when testing is the amplifier operates at the full output for up to 4 hours. This is a real brick on the key test. I have found many transceivers cannot provide 50 watts out for four hours.

One last item. The amplifier must require more than 50 watts drive for 1500 watts out on all bands. Some of the tubes out their can be pretty frisky when it comes to gain. Even the ARRL is testing for this now.







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KH6DC
Member

Posts: 663




Ignore
« Reply #54 on: September 13, 2010, 10:13:12 PM »

Don,

I would be interested.  I just bought a Tokyo Hy-Power HL1.2KFx to repalce my aging Ameritron AL-811 but would be very much interested in building a QRO linear.  I'll pass on the liquid cooling but would love soldering.

73, Delwyn KH6DC
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73 and Aloha,
de Delwyn, KH6DC
G4ZOW
Member

Posts: 42




Ignore
« Reply #55 on: October 07, 2010, 02:08:46 AM »

Several of you have mentioned the high cost of suitable solid state devices when in fact there are some relatively inexpensive RF fet's  out there that I'm surprised have not been picked up by the ham amp manufacturers. Some of the MRF and 2SC transistors still being used by amp manufacturers are getting rather long in the tooth now and there are some far more efficient and lower price point devices out there. Maybe these companies are afraid of treading on new ground.

I shall quote typical list prices as against quantity trade prices.

For example Ameritron in their 500W mobile are still using the old Toshiba favourite bi-polar 2SC2879 12V 100W pep $30.00

When you now have this : ERF7530 plastic RF mosfet http://www.rfparts.com/pdf_docs/ERF7530%20Datasheet%20-%20Rev2%200.pdf 12V 75W pep $10.00

For a solid state base amplifier look at these beauties: http://www.st.com/stonline/products/literature/ds/15501/stac2942b.pdf  50V 350W in FM service 20dB gain and only $60.00

We use these in our 1Kw continuous duty PA and TX: http://www.fm-transmitter.com/images/tx1000-front-large.jpg

Four of these devices sit there 24/7 at up to 1200W and are up there in the low 80% efficiency department.

We use a very compact Murata switcher supply and have had no trouble in over 700 units used in all environments;

http://www.murata-ps.com/releases/mps277a_d1u4.html?feature=acdc 1600W typically $500.00

I'd like a 1500W HF mobile amp please if anyone's thinking of designing one.

G4ZOW
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