Cheap Tubes? Yep, at least before Russia invaded Ukraine.

eBay has loads of cheap Soviet era tubes from the late 70's to the late 80's. The quality in my experience has been solid, and this is due to most of the surplus tubes being military grade, as well as soviet countries using tubes long after the west stopped due to a lack of home grown silicon manufacturing capabilities (An example being the Mig-25 fighter jet of the 1970's was designed to use vacuum tubes instead of transistors as western equivalents were already using. What this all means is Soviets made decent quality tubes even into the 1980's.

Pre-amp Tubes

Pre-amp tubes, specifically the ubiquitous 12AX7 has a soviet equivalent, the 6N2P-EV / 6Н2П (Cyrillic). It is not pin for pin compatible though if your amplifier has a 6.3V heater (Most do) then you are probably in luck. Depending on the exact implementation most likely 1 pin needs to be wired differently. The change is trivial if you have a point to point wired amp or a two layer PCB you can easily cut a trace. These tubes I have found are excellent quality, and usually 1/10 to 1/5 the price of an actual 12AX7. I assume this is due to very few existing radios etc. are wired for the soviet tubes anymore...

One item of note is the Soviets only have an equivalent for the 12AX7, there is no concept of the AT or AY tubes, I guess less was more during that time...

My prototype boards, I ended up adding a switch that changes one of the pins between 6.3V (Western) and Ground (Soviet), this allows me to use any tube with minimal work.

I have pin 9 wired to ground, and pin 5 wired to 6.3V, the toggle switch allows me to toggle pin 4 between ground and 6.3v to work for either a US or Soviet style tube.

There are a lot of diagrams of varying clarity online about doing this, here is one.

Power Tubes

You can find power tube drop in replacements, they are pin for pin compatible and typically nearly specification identical. The unfortunate thing is this makes them worth a bit more, so a set of Soviet power tubes may cost you still 1/2 the price of a western equivalent. I have found the bias points vary more then modern tubes, but maybe I have been unlucky, as long as you bias correctly everything will sound fine.

• 6L6 <=> 6N3C / 6P3S
• 6V6 <=> 6N6C / 6P6S
• EL84 <=> 6P14P-EV  Note: "-EV" designates military spec.