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Finally got working on a project I've been thinking about for a while... a micro amp made with Russian submini tubes.



This is just the output stage. The tubes shown are 6J5B-V. There appear to be two types of these tubes - one with all the pins in a row, and one with the pins in a circle; the circle ones have a different pin order, and are not mentioned in any datasheet I can find... guess which ones I have? Thus the tape marking which pin is which on the left tube.

The output stage is PP, with an 8k a-a load (provided by the 70V line transformer shown) and 120V of B+. Output power on the order of 0.75W. I'm looking into an SMPS to run everything from a 12V 1A power supply (for now the B+ is from the power supply visible in the background). Right now they've got individual cathode bias resistors. The bias sits at about 2V - these are high Gm tubes (~10k umhos), so this is all they need for full drive! As a test, I hooked up a music source to one of the grids and attached a 45 ohm paging speaker across the load resistor (heh, a 160W resistor dissipating ~0.2W). Sounded decent enough, given the low quality speaker!

The preamp will use 6N16Bs, as the low voltage precludes the use of 6N17Bs (the only other suitable preamp tube I have). It's not like I need much gain, anyway! Phase inverter will probably be floating paraphase of some variety (again, low voltage rules out many of the usual suspects).

More to come as I build.

Really cool!

Actually, 3/4W is pretty significant from a pair of those, isn't it?

Cheers!

I'm running them fairly conservatively at 3/4W out (that is at about 5% distortion, this is a guitar amp after all). They're rated 2.4W plate dissipation and 0.8W screen, and I'm idling them at about 14ma cathode current (at 120V, that's 1.7W total)... bumping the B+ to 140 would net over a watt of power, even more with a 10k load, and still be within specs. I'm trying to use parts on hand though, and I'm concerned about tube life - they get nice and toasty as they are, and I don't want to have to replace them too often...

How many UA's out are they

I am trying to stuff something similar into a suitable (small) chassis, but US 5903 (I think??) running on 150V. Also 3/4W.

I did build a phase inverter and gain stages on the board, but the layout and the long leads lead to 1/2W of RF generation... I did attach an mp3 player directly to the input of the phase inverter, and that produced 1/2W of music instead. Less than the 3/4W my calculations seemed to indicate (probably the curves don't match the datasheet), but enough for me (and I could increase the B+ if I wanted more power). The layout issues have temporarily shelved the amp until I have a few hours and a clear head to fix it...

I looked up the 5903; that's a double diode, so I assume you mean the 5902, which looks quite nice for an output tube. Higher perveance but lower gm, so it behaves more like a traditional output pentode.

Short leads and grid stoppers should solve the RF generation problems (been there, done that more than once).

Old tuber's adage: Amplifiers Oscillate, and Oscillators don't.

Silly joke heard on the radio a few years ago:

How does one titillate an ocelot?

Oscillate a titalot.

I have some assorted US submini tubes in the stash, but no Russians (yet).

/ed B

This is great!
can you draw what you did up until now?
(got the same tubes laying around..

A pair of CK534AX might make an interesting little amp too.

http://www.tubebbs.com/tubedata/sheets/ ... K534AX.pdf

Only needs 30V on plate/screen. A couple of 9V batteries would do it.

John C.

Looking for my schematic... if I don't find it, I'll just redraw it (the board is still together)

Very much appreciated
I wanted to start a project with the 6J5B-V (6Ж5Б-В),
so it's nice to have a starting point.
As we say in Holland "why invent the wheel twice"

Here's the output stage as I built it:



Ok, I kinda lied there - I used separate 150R cathode resistors, for layout reasons. Cathode voltage is between 1.6 and 2V on the samples I have. One thing I did think of was that it would be possible (at this B+) to replace the cathode resistors with LEDs (use one LED per tube, the idle current is about 11-13mA).

With the B+ at 120V, and an 8K:8 transformer (the one I used is a cheap 10W 70V line transformer) power out is roughly 0.5W. It is possible to increase the B+ and get more power out (don't try this with LED bias, though) although I have not tried this to see where the limit is.

Watch the pinout! My tubes did not match the datasheet.

As for a preamp, I'm not going to show you what I had, as it didn't work very well. I used a 6N16B as a "floating paraphase" phase inverter, as the B+ is very low and the common guitar phase inverters need a lot more space to work well, but I wasn't very happy with it when a guitar was plugged in - it worked ok with music input, though (what do you mean my guitar playing isn't music?!?). When I get around to experimenting, I'll try other configurations and report back. One thing to note is that the output stage doesn't need a lot of drive for full output (about 2V pk, 1.4VRMS).

6Ж5Б-В (Russian 6J5B-V) not to be confused with the USA 6J5s (which are triodes, equivalent to half a 6SN7) Sometimes these internationalized tube designators can be confusing

The Russian letter Ж is pronounced like "Zh" and is the closest to a letter J in their alphabet and language. Not a "hard" J as in English.

I was leafing through "Tube Lore", there are a lot iof intersting Sub-mini tubes out there, and TL only covers the US, and some European ones, and nothing from Russia except for a few of the better-known Svetlanas.


/ed B

where is a good source for decent clip leads? the ones i have found seem like they are about 26 gauge at best, and i apply them to everything...yikes. i bet their insulation is rated at about 50v too

Yeah, I'm using the standard Russian transliteration (standard defined as what the ebay sellers use). I have a few RCA 6J5s but I'm having a hard time plugging them into my breadboard

As for clip leads, I really can't help - I got mine at the local Princess Auto. They're 16ga 600V rated wire, but I can't recommend them too highly because the clips are lousy. Some have skewed jaws, and the wires are only crimped in so a couple have pulled out.