To the nay-sayers, this is where TUBE amps are going. And with a life expectancy of 30K hours of continuous operation, if the new owner is 30 years old he will never need to replace the tube in his lifetime. The only down side to doing this is the high current draw of the filament and the related electric bill.
As stated, that tube costs LESS than an 8877 and is a common transmitting tube for broadcast which means there will be availability for some time. Where we may see the 8877 disappear in the next few years.
While I prefer the 4CX3000 tube for HF, 6 and VHF, this design is still viable. And we have no idea where this is going. While we in the states are limited to 1500 watts, some countries do not limit their ham operators to that power level.
And another consideration is that power supply.
The end user may have plans as they have the money to build other RF decks for other frequency bands that could also use that power supply.
That would require tubes with similar plate and filament voltages. So this may be the start of a number of RF decks with a shared supply.
Tubes for ham power levels are going away. And the prices for them are an indication that it's already happening. And dumping the thousands of dollars into a legal limit HF amp, which is the only band readily available at legal limit (which Ameritron TUBE amp does 1500 on 6 or VHF??) Broadcast level stuff is going to be the only option. And just because it's able to FAR exceed the 'legal' limit doesn't mean it has to. How many 'performance ' cars are out there that have never seen 100 plus MPH that are able to do twice that? Those are commonly available, and in truth your wifes minivan will probably do 100 anyway. Far more than the legal limit in the states. This is the reality of things now. Just like no code licenses. And I doubt that it's going to be the downfall of ham radio. Contrary to the claims we had when the code requirement was sunset back in the day.
I went through all of this with Ted Henry and his brother, back in 1990. Back then, a brand new Eimac 3CX-3000A7 was a mere $50.00 more than a brand new Eimac (throwaway) 8877. The 3x3 tube has superb IMD..off the charts at -59 db pep for IMD3 (5 kw pep out). The 3x3 with 50 watts of drive does 1.5 kw out. The joke is, you can use the 225 watt
CCS grid as a dummy load for your FT-1000D. It's virtually bomb proof. And the 3x3 can be rebuilt till hell freezes over (for aprx 1/2 the price of a new tube). Dead easy to cool . 50 ohm input Z. Fil sucks 50 amps @ 7.5 vac...and less with reduced fil V. Any residual heat is just free heat. In hot wx, the hot air exhaust is routed to the outside.
Typ the fil V is reduced by 10% (after being run at 200 hrs at rated vac). Emission increases by a bunch during the 1st 200 hrs, then levels off...at which point the fil V is reduced, either till PO just drops off, or fil V is reduced by 15%. Those 3x6 amps I designed back in 2005 are still running..and still have 6.3 vac on their 7.0 vac rated cathode cathode. (an hr meter was installed on the input of the variac). It's got something like 8700 hrs on it. We will all be dead and gone by the time it requires a rebuild. The secret is controlling the fil V. Some will use a combo of step starting the cathode + the pre-set variac. I use the variac only..and slowly bring the tube up to desired vac..( and current goes 0-1-2-3-4-5...50 amps... no surge). If you just slam on the fil V, the typ fil xfmr is fully capable of supply 2-3-4 times the rated current. I'm 99% convinced that is the cause of most grid to cathode shorts...since thoriated tungsten cathodes typ have a cold resistance of 1/10 to 1/12 the hot resistance.
Plenty of vac tune + load caps on the surplus / used market. Copper tubing is still cheap in the plumbing section of any home-depot / lowes. Simple to silver plate too. Pi tuned input- tube - Pi output. Simple bias. Simple metering. Add the B+ supply, and some vac TR relays..and a box / small rack..done. No rocket science. FT-8, RTTY, who cares. Put a brick on the key and go on holidays if you want. Now we can get digital turns counters in various colors (green /red / blue) . Ditto with air variables + built in 6:1 vernier reduction drives. You can complicate it some more with stepir motors and a myriad of pre-sets. Some will remote the amp next door in the shop / garage / basement.... then control it from the shack via a control console...complete with metering.
There is nothing to repair, cuz there is nothing to blow up. Lately, I have been using small 3M filters on the intake. Then zero dust, nothing to clean. (and they are N97 rated). No myriad of relay switched 2 kw LP filters required either. Nor an automatic 2 kw rated ant tuner..with loads of pre-sets. Flip side is, you have to build it..and that requires some tools. Amplifier building is 90% metal work. I bought a 10 ton hydraulic punch kit from HF (which also accepts my green lee punches). Making holes is fast. Small, modified drill press, metal cutting vert / horz bandsaw, various hand tools..and a roper whitney hand punch kit ( + a bigger bench punch). Green lee makes a combo drill + tap..so you can now drill and tap, all in one motion...for normal screw sizes, like 2-56, 4-40, 6-32, 8-32, 10-24, 10-32, 12-24, 1/4-20..and 1/4-28. With the right tools, it speeds things up very fast. Want 4 x identical meter holes across the front panel...bam done.
Dr Alex still has mountains of surplus gear on his site..and he's shipping every day. Some of the hb amps on his FB page are beyond ingenious. Many are using surplus vac relays, instead of a bandswitch to change bands...fast like. I have taps galore on both the primary + secondary on my dahl xfmr..so can obtain any B+ voltage I want....on the fly. Tube type doesn't enter into the equation anymore.
