Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, Nov 24, 2019.
I remind everyone that politics is not allowed in the general forums.
They are actually only $219 each.
If one factors in the average lifespan of these tubes, the yearly cost is chump change. Less than one night out with the XYL at a nice restaurant.
Far greater would be the electricity cost consumed by the tubes over their lifespan.
The 3-500's are about the absolute best bang for the buck tubes on the market. Go price a new Eimac 8877/3CX1500A7's or even the Emiac 3CX800A7's.
Low cost high output ceramic metal tubes like the GU-74 are another great choice as NOS tubes are around $200.
Price I quoted is with shipping cost or true cost to receive the tube. I should have mentioned that.
The Chinese tubes are reported to produce full power after 10 years use. Based upon that, cost per year is a paltry $21.90. No doubt the best deal in high power tubes. That is exactly why I bought a 3-500z amplifier.
I use a SB200 that was rode hard, and put away wet. It was picked up for the cost of shipping.
Since then I refurbished the innards, installed a few Harbach mods and picked up a set of NOS Cetron 572b' @ $140 each. I chose them as the Chinese 572b's are garbage and even RF Parts stopped selling them. The amp does 700w on 80-15 And closer to 600-650 on 10-12. Yes it tunes the WARC bands no problem since I adjusted the input slugs for a 1.3:1 on 10/12 And 15/17. It will even do 550w on 30m (into my cantenna dummy load). That is off 110V.
Not bad for an amp older than I am.
My other amp is a Alpha 374A with 15-80 having the "no tune" bandpass or manual tune capabilities. 10 And 160 are manual.
It was also cheap and came with 6 8874/3CX400A7 tubes that still put out over 600w each. With a pair i get almost 1300w without pushing it but only run it at 1KW CW/SSB.
Treated good, these tubes will surpass my life.
I used three Cetron 572B in an AL-811 as I concur the Chinese 572B are not great tubes and the original 811A are very weak in plate dissipation. I paid about $80 each for NOS Cetron two years ago, but higher price now. I sold the AL-811 amp for $830 and for $800 bought the Amp Supply LK-500zb with new Taylor 3-500z tubes. I had an offer on an Alpha 78 for $750, but the tubes were bad and only produced 600 watts out. Bad news with 'unobtainium' 8874 tubes.
Right now there are 2 guys selling 8874/3CX400A7's on a different Radio website. 3 NOS still in the sealed boxes for $500 each or 3 used in great shape for $175 each or 3 for $475 full refund if not happy.
EBay has both Eimac and Svetlana NOS and used.
I picked up a pair from a US Ham for $200 each and shipped them to a friend in the UK. He is quite happy with the total price and they perform as new.
They are still out there at reasonable prices if one keeps an eye out.
I bought extra sockets and plan on making mine a 3 hole, basically like the Alpha 78.
That would give me over legal limit loafing along, several bands no tune, and still have an extra set of tubes.
Also I picked up an extremely quiet 4" 110v muffin fan that will be wired to the 95V tap. It will keep everything else cool in the amp and force feed the tube fan. Is should be a true "brick on the key" walk away and forget it amp, even on the high duty cycle modes.
QSK Jennings relays are also on the list as my 40 wpm is rough on the TX/RX relay.
I find it more enjoyable to purchase old cheap equipment then rebuild it better and a lot less expensive than the new amplifiers.
According to KM1H on the Amps email reflecctor (link):
FWIW, the Eimac date code looks like this:
The pair that came in my new-to-me SB-220 (ca 1975) lasted 'til cockpit error caused a failure around 2005. The replacement Chinese pair lasted 6 years.
Good to know for the Eimac guys.
Funnily enough, I bought a pair of 572Bs for ny FL2100 about ten years ago direct from China (for less than half the cost of buying them in the USA) . . . they lasted just as long as the Cetron valves in my experience.
I now have a TL-922 . . . and by all accounts they are the original pair of 3-500Zs . . . at present still working fine !
But it's good to know that the Chinese 3-500Zs are pretty good (and not too expensive) - it's one of the reasons I chose this Linear Amplifier !
Cetron 572B are noted to last 25K hours. I doubt the Chinese will last that long, but the Chinese 572B has improved thru the years. You have no choice anyways as NOS Cetron 572B are hard to find and costs $100+ each.