I recently paid $40 for 4 NIB 813's from a local and those will eventually replace the 4 well abused ones in one of the AM amps here. I see them often at $20-30 each.
They're cheap for a reason.
Of course; they were in production for about 50 years in the US, tens of thousand NOS were surplused after WW2 and Korea and the tube manufacturers hyped the bigger stuff real cheap and then kept jacking the price. Now its time to retaliate.
The only new 3-500's are Chinese of questionable quality and now pushing $200 a pop including shipping....probably cost $10 to build.
Used or NOS Eimacs and Amperex are a gamble since gas is a very prevalent problem.
IMO, this is an overstated reliability issue. So far, my Chinese 3-500ZGs have been working fine for more than 5 years (and I'm not easy on them). And, on the many email reflectors I've been reading for the past several years, I haven't seen any significant trend of these tubes failing. I will agree about unused tubes tending to be gassy.
You must be on different forums plus you dont get the repair volume that comes thru here. If I believed my own experience there would never be a need for a replacement....my 1986 LK-500ZC still has the original tubes and thats included many DX and WPX contest records, 9BDXCC with several over 300, 8BWAZ and more.
Russian tubes have a reputation of poor IMD and Ive yet to see anybody say different with proof, they are fine for CB
If you want a tube that will last forever go with a 3CX3000A7 or YC-156 known good pull. An easy 1500W at under 3000V and 100W drive.
Or wait for LDMOS to mature.
I've read the opposite about Russian triodes & IMD3. I've also read that running any tube significantly below maximum POUT
results in increased IMD3.
All talk, no proof, as Ive yet to see any Russian tube plots. The ones Ive heard ID'd on the air sound like CBers and that includes several owners from various forums always bragging about their cheap and wunnerful Ruskie crap.
Point.....even MFJ doesnt use them
At $600 to $700, they don't give away 3CX3000A7s (YC-156s go for about half that), and a 7.5V/50A filament xfmr is huge and not cheap.
You can buy brand new Chinese for that and good pulls are $100-200. The $90 transformer can be prorated over a lifetime of use, you wont hurt it with a 100W rig no matter how you try. An unskilled creative person can rewind a suitable size core in a few hours. Yes, YC-156 pulls at full output are $300 and no socket required.
LDMOS has been around a few decades, and many ham equipment manufacturers (including the big names) have been using them for many years. Most people would call that mature. My former employer has been using them to drive CO2
Lasers well into the kilowatt output range (Lasers are awful loads). They didn't experience a big failure rate.
By mature I dont mean industrial service.
Im referring to 1000-1500W capability per device with IMd 3 in the -40's at HF and without having to run them at half power. Most of the linear effort is UHF and microwave.