Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1] 2 3 4 5 Next   Go Down
  Print  
Author Topic: Solid State vs. Tube. Still deciding, but have a question.  (Read 5769 times)
KD7HNN
Member

Posts: 96




Ignore
« on: May 27, 2019, 09:03:16 PM »

Hi all,

My original plan was to go solid state amp like one of the Expert amps. I'm still open to going SS, but recently I've seen a few Alpha 78's for sale at a reasonable price so I could go that way as well. If I decide to go the Alpha 78 route to save some money, are there any performance mods I should be looking for the amp to have or is an unmodified Alpha 78 still a good get?

Thank you
Logged
AD4U
Member

Posts: 2538




Ignore
« Reply #1 on: May 28, 2019, 04:40:05 AM »

I have a Alpha 78. IMO it is a great amp. Tubes are not available so make sure the one you buy has good tubes. If you watch grid current and not try to get more than 1500 watts, the tubes should last a very long time. Some 78's have a high drive board (150 watts in for 1500 watts out) and some 78's have a low drive board (70 watts in for 1500 watts out). A low drive board can be made for several dollars so don't buy the one on the internet for $50.

Dick AD4U
Logged
N8FVJ
Member

Posts: 867




Ignore
« Reply #2 on: May 28, 2019, 06:03:25 AM »

My antenna has 2 to 1 SWR on 75 meters and 1.7 or less on other ham bands. I can tune the SWR lower due to the variable capacitance on the tube amp, thus do not need an antenna tuner. SS amps would not tolerate 2 to 1 SWR and I only have two knobs to tune.

Problem with the Alpha amp is the tubes. NOS are very expensive and used are a crap shoot IMO. There are two Tompson 3CX800 pre-order tubes on ebay for $600 each and not sure of the quality. Only well made tube left are Chinese 3-500z that is known to produce full power after 10 years use. Chinese 3-500Z are only $200 new. For 800 watts PEP out the Heathkit SB-1000, Ameritron AL-80A or AL-80B and Amp Supply LK-450 are great amps. Do not get a AL-80 as it is a poor design with problems.

If you want more power at 1200-1400 PEP out buy a rebuilt Heathkit SB-220. Old Heathkits need a complete rebuild and rebuilt do not cost more than $800 with careful shopping. A Drake L4B is great when rebuilt. A newer amp that does not need rebuilding is a AMP Supply LK-500 series and it has 160 meters. The Heathkit and Drake need a keying replay interface if not already installed. About $30 cost.

The suggested amps are not as pretty as an Alpha, but are much more reasonable regarding costs and especially so over the long run.
« Last Edit: May 28, 2019, 06:20:33 AM by N8FVJ » Logged
W9IQ
Member

Posts: 3241




Ignore
« Reply #3 on: May 28, 2019, 06:47:25 AM »

I can tune the SWR lower due to the variable capacitance on the tube amp...

Perhaps that is just a figure of speech but the output circuit of the linear does not change the SWR. It simply adjusts the output impedance of the amplifier to be a conjugate impedance match for the input impedance of the antenna feedline. The SWR stays the same after the tuning is done.

- Glenn W9IQ
Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
G3RZP
Member

Posts: 1225




Ignore
« Reply #4 on: May 28, 2019, 07:45:30 AM »

Whichever you go for, get some spare final devices. If tubes, swap them around every couple of years to keep the getters active - and some glass tubes need the plate  to get red to absorb gas.

The number of SS devices (and manufacturers for  that matter!)that come and gone over the years is  very large.....

If it uses through hole mounted ICs any where, get spares of those while you can....
Logged
K6AER
Member

Posts: 5694




Ignore
« Reply #5 on: May 28, 2019, 08:38:00 AM »

The metering on a tube amplifiers are calibrated into a 50 ohm load. You can adjust the Pi network for output impedances other than 50 ohms but the power metering will not be accurate. Most Pi networks will tune a 3:1 miss match but in the case of higher impedances the tank RF voltage can get much higher. This might cause a problem with voltage ratings on capacitors especially the tune cap. You could experience tube or tune cap arcing.

It is best to use a separate antenna tuner and keep the amplifier output impedance at 50 ohms. This hold true for solid state amplifiers as well.  Amplifier with built in tuners have a very limited range they can tune.

As Dick had mentioned the tube on the Alpha 78 are rare. I am surprised all the spares in the radio kingdom have not come on the market with SK sales.
Logged
KD7HNN
Member

Posts: 96




Ignore
« Reply #6 on: May 28, 2019, 09:18:28 AM »

Thanks for the comments, guys. My initial attraction to SS amps was quick band changing. My antennas are pretty resonant, and I have an Palstar HF-Auto tuner if it's needed. The cost of a used Alpha 78 is a significant savings, and I could live with tuning 10/160m. However i'm more than a little concerned about the lack of availability of the tubes.
Logged
AD4U
Member

Posts: 2538




Ignore
« Reply #7 on: May 28, 2019, 01:43:21 PM »

The Alpha 78 has manual tuning on 160-10 meters AND band pass tuning on 80-15 meters. Your choice-  manual tune or change bands and operate. On antennas with low SWR the band pass tuning on my 78 is as good as manual tuning. The 78 will operate on WARC bands EXCEPT 12 meters. Do not operate it there without mods. The 78 will operate on QSK in CW.

I bought my 78 in 1985. It still operates the original tubes. It will easily give 1500 watts on all bands with 75 watts drive - 90 watts drive on 10 meters for 1500 watts. Full output into a dummy load on SSB is 1900-2100 watts with 100 watts drive with still low grid current.

Granted I have many amps and my 78 is not used often, but when I use it with my TS-930S they are still a good combination.

Dick AD4U
Logged
KD8MJR
Member

Posts: 5536




Ignore
« Reply #8 on: May 28, 2019, 06:05:46 PM »

No way would I go with a Tube amplifier.  If you want to sell a SS amp it is a lot easier to do.  If you just want the more power and not something that requires extra work to tune up or wait to use then SS is the way to go.  Since you say your antennas are fairly resonant then I would certainly go SS.   I love having a 1500+W Radio that just follows me around the bands without a second though.   If you had asked me this question ten years ago I might have hesitated but tubes are going extinct.  And no matter what people tell you about SS finals becoming hard to get when they are discontinued, any amplifier you buy now you can buy extra finals for cheap and put them down now.  Even the SD2933 that everyone thought had evaporated now seem to have an endless supply on eBay thanks to some guy getting a truck load of OEM units. At $10 a piece I bought 10 of them, that will last me through any foreseeable problems.


73s
Rob
Logged

“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
K6AER
Member

Posts: 5694




Ignore
« Reply #9 on: May 28, 2019, 07:57:30 PM »

So where would one go to buy a 1500 watt SS amp with a couple of dB head room for $1500?
Logged
G4AON
Member

Posts: 1383




Ignore
« Reply #10 on: May 29, 2019, 01:36:39 AM »

Whichever way you go, there are a couple of issues to be aware of...

Solid state amps will not tolerate overdrive spikes and many transceivers have very poor control of the output power when running less than full power. The same overdrive issue applies to tube/valve amps such as the Acom 1000. Several hams moan that their amps are defective, when in fact it's their lousy transceiver that can't control the output power. Don't use the ALC connection to try and avoid spikes from poor ALC.

Sadly, the ARRL reviews of transceivers do not show the transmit envelope at reduced power, yet it's an easy test to send a few "dits" on a keyer at 20 Watts output and see how well (or how poorly) the transceiver behaves... All it takes is an oscilloscope to check.

Until you have used diode change over you won't appreciate how nice and fast it is. The Elecraft amps use diode c/o and are a delight to use. The poorest amps use open frame relays for a slow and noisy change over. If you are a CW op, forget those old clunky relay amps.

73 Dave
Logged
K4QXX
Member

Posts: 50




Ignore
« Reply #11 on: May 29, 2019, 05:27:28 AM »

My opinion, if you have the money, get a solid state amp.  I have been using a Ten Tec Titian amp for over 15 years and it has served me very well.  I just got a Flex PGXL amp last week and I will never go back to a tube amp again.  Instant on, don't have to tune every time I change bands, etc.  I also use my radio remotely quite a bit and it would be almost impossible to do remote with a tube amp.  I believe these newer LDMOS transistors are much more robust than the older transistors.  Only negative is the price of the amps but my guess is when more SS amps become available on the market, the prices will start coming down.

K4QXX
Logged
W1VT
Member

Posts: 3310




Ignore
« Reply #12 on: May 29, 2019, 06:16:50 AM »

Those old amplifiers using 3cx400s are over 30 years old.  It is quite likely that they are on their spare set of tubes by now.

I've made 30k contacts using a solid state amp I bought five years ago.  I've gotten a lot of value for my money already!
Logged
N9AOP
Member

Posts: 1154




Ignore
« Reply #13 on: May 29, 2019, 08:37:08 AM »

New tube amps the likes of OM Power and ACOM are usually 2/3 the price of the same wattage solid state amps.  I don't see the price of the solid states ones coming down.  Elecraft sells their KPA 1500 for approx $6,000 and they are selling many.  Why would they want to go cheaper.  If FLEX ever gets theirs into mass production, I would expect to see similar pricing. 
Art
Logged
KD8MJR
Member

Posts: 5536




Ignore
« Reply #14 on: May 29, 2019, 10:42:17 AM »

So where would one go to buy a 1500 watt SS amp with a couple of dB head room for $1500?

Where did the OP mention a $1500 spending limit?
Logged

“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
Pages: [1] 2 3 4 5 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!