5881 max dissipation

[Andy Le Blanc]

Sovtek 5881/6L6WGC perform very nicely as a pair cathode bias

420v at the plate..... 52 w total plate dissipation for the pair.

[Firestorm]

Are you running them in Class A? Or did Sovtek up the dissipation spec? I thought they were 25 watt tubes.l

[Andy Le Blanc]

Haven't checked the conduction angle to know where in AB land they're at.
Just biased them to meet the RCA published spec for the type.
It's cathode bias, it is the safest way to operate the device even at max dissipation.
It's got 5881 on the envelope, so I'm gonna treat it like a 5881.

23 w plate, 3 w grid-no. 2 ...

[Gaz]

The Sovtek is is a military grade Russian tube called a 6N3C-E, which you may or may not know.

Here is a thread from Ampage for anyone interested about these ubiquitous Rusky tubes with the nebulous specs. I think it was one of my first posts about tubes:

http://music-electronics-forum.com/t12151/

[Andy Le Blanc]

There really does seem to be a lot of conflicting accounts of how the device
is applied. They're sold as a 5881 equivalent, so..... treat them like a 5881.
If not then sovtek would have screwed them selves, pretty sure they're well aware.

[Ace Carson]

Its the 6P3S-E analogue (6П3С-Е). Seems to be a 25W tube, but I believe the specs to be lowered deliberately to insure long life and reliability.

[dynaman]

Those Russian tubes are dirt cheap and I've heard horror stories about them BUT...a few years ago I gutted a buddy's Carvin X-100 and whipped up a new circuit for him using the original transformers and tubes. It was loaded with a quad of 6N3C-E. He'd owned that amp over ten years and never changed tubes (they were prolly original). They still tested good and were reasonably matched so we ran with them. Fixed bias, 450VDC on the plates, 440VDC on the screens. That was three years ago and they're still running strong and sound good.

Incidentally, I made a 100W amp with those cheapo $35/quad Chinese 6L6 tubes from AES a few years ago. I screwed up wiring the bias supply so that the tubes never received B- until the standby was turned on. With 475VDC on the plates, these things would creak and groan until the bias voltage built up. Dissipation would shoot up to something crazy like 2 or 3X recommended for a few seconds every time the amp was turned on. This clown played this amp like that for about 6 months. He gigged and practiced with just the bare chassis, as he was too cheap to buy a head cab. The only time he had a problem was when he dropped it and mashed some stuff. Two of the tubes' glass envelopes came separated from their bases, so he just ran the other two. Even the beat up tubes still tested good and I use them for testers to this day. Can't beat the price!

[FYL]

They're sold as a 5881 equivalent, so..... treat them like a 5881.
If not then sovtek would have screwed them selves, pretty sure they're well aware.

The Sovtek 5881 is a 6Π3C-E, a 6L6G Rusian derivative but *not* a 5881 equivalent.

Specs at Vp = 250 V, Vg= -14 V, plus max ratings for plate and screen dissipation.

6Π3C-E = 6P3S-E (from the Russian datasheet)

Ip = 72 mA ±18 mA
Is= < 9 mA
s = 5.2 to 6.8 mA/V

Vp = 375 V
Pd = 20 W
Sd = 2.75 W

5881 (from the original Tung Sol datasheet)

Ip = 75 mA
Is= 4.3 mA <==
s = 6.1 mA/V

Vp = 400 V <==
Pd = 23 W <==
Sd = 3 W <==

15% more plate dissipation, higher plate voltage and lower screen current for real 5881's.

You may use 6&#928;3C-E's provided that you bias them colder than real 5881's and keep the screens quite tight. High plate voltages aren't a problem up to 500 V or so.

[Andy Le Blanc]

There's some web statements that are really out there for dissipation and voltage.
Its one thing to make assumptions, but I'm not. If they're gonna market a device,
it had better perform. There are several ratings, design center, design max,
and absolute maximum. A 250 v rating sounds like a design center figure.
Add language translation to it and it's easy to see confusion.
Russian and Soviet industries parallel American industries very well.
I would actually expect a better product, with a very strong mil. rating, even if it was not
reflected in available information. The RCA data set for the type is design center. 400v, 23w plate, 3w G2.....

[FYL]

A 250 v rating sounds like a design center figure.

The 250 V mentioned isn't a rating but a test voltage: apply 250 V to the plate of a 5881, - 14 V to the grid and you should get a plate current of 75 mA and a slope of 6.1 mA/V (transconductance = Gm = 6100 micromhos if you prefer).

And, yes, Tung Sol ratings use the design center system.

[dynaman]

Ooh, design "center" system. You guys sure make it easy for me to rationalize running tubes WAY past published specs!

[Firestorm]

If they're gonna market a device,
it had better perform.

For decades now, some tube manufacturers/vendors/relabellers (Russian, Slovakian, American/etc.) have found it easier to pick up the last guy's datasheet and republish it, rather than doing comprehensive new testing. If I were sure they had designed to tube to meet the original specs, fine, but more often it was just "close enough." Sometimes "Typical Operation" specs get misquoted as "maximum" specs (especially true with the less common rectifier tubes).

I wonder how much the Russian 5881 variants have been redesigned from their Russian military progenitors.

[FYL]

Ooh, design "center" system. You guys sure make it easy for me to rationalize running tubes WAY past published specs!

Three rating systems have been used:

Design center suggested max values for optimum lifetime

Design maximum not to be exceeded, could lead to reduced lifetime if exceeded

Absolute maximum *never* to be exceeded, leads to failure if exceeded.

Plus two contexts, mainly for transmitting tubes and big bottles:

ICAS Intermittent Commercial and Amateur Service. Max performance, reduced life.

CCS Continuous Commercial Service. Long life and reliability.

For instance a 807W used in a PP class AB amplifier is rated at 600V / 25 W plate CCS and 750V / 30 W plate ICAS. Max screen dissipation is the same at 3.5 W.

My experience is that all power tubes can be run above design center/design maximum ratings provided that they are properly ventilated and that screen dissipation is never exceeded.

For instance you may run quality 6V6GT's - rated at 350 V design max - at more than 500 V plate, provided that screen voltage is below 350 V and screen dissipation never exceeds 2.2 W. If plate dissipation doesn't exceed 14 W, the tubes will last thousands of hours.

[Andy Le Blanc]

Here's more.....

[Phil_S]

I couldn't resist and bought a box of a dozen 6&#928;3C just because they were so cheap. These are 6&#928;3C, not 6&#928;3C-E. Searching the net, the information I found suggests the 6&#928;3C is not robust like the 6&#928;3C-E, but that it works very well and sounds good, too, at Va=250. Is there anyone out there who has actual experience with this particular variant of the tube and who can comment?