Optimal settings for 6P3S-E (6П3С-Е) output tubes

[kasperbergholt]

Hello clever people,

I'm not a builder, but hope it's okay to ask a question about the optimal settings for Russian 6P3S-E (Russian: '6П3С'-Е) output tubes in a Leben CS-600 amplifier.

The Leben CS-600 can be configured to use a variety of output tubes through two switches:

1) 'Plate voltage,' which can be set to either 350V/DC or 410V/DC.
2) 'Cathode resistor' can be adjusted to 680 ohms or 460 ohms.

Both switches can be set either up or down. According an overview of settings for different types of output tubes - of which 6L6, KT77, 6L6GB, 350B, KT66, KT88 and 6550A tubes can be used - switches can either both be up or left one up and right one in the down position for the 6P3S-E variant.



Overall, I'm interested in the best sound quality, but I'm also concerned about the longevity of the 6P3S-E/6П3С-Е tubes.

The quad I got are military-grade from Reflector from the 80s.

I'm thinking there might be a trade-off between the two?

Huge thanks in advance!

[pdf64]

Optimum longevity will mean putting least stress on the valve, ie lowest voltage and lowest dissipation.
So 350V and 680 ohms.
Optimum sound quality can’t be derived without knowing the screen grid voltage and output transformer primary impedance.
My guess is that it’s a tough valve and will cope with any combination of those settings, so failing more info, maybe use your ears to assess that 

[kasperbergholt]

Optimum longevity will mean putting least stress on the valve, ie lowest voltage and lowest dissipation.
So 350V and 680 ohms.
Optimum sound quality can’t be derived without knowing the screen grid voltage and output transformer primary impedance.
My guess is that it’s a tough valve and will cope with any combination of those settings, so failing more info, maybe use your ears to assess that 

Thank you for the swift reply - this was exactly what I was looking for :)

I'll try and see if I can find more information about the voltage & impedance.

[acheld]

My own experience with those tubes is that they are incredibly rugged.  Personally, I don't worry about their longevity at all.  My builds routinely run these tubes between 420-450 VDC.

I'd suggest tuning for the best sound (within your presets).   If you can't tell the difference between two settings, use the lower stress setting.

These tubes generally sound very good, but I confess I've fallen in love with the Tung-Sol 6L6GC-STR.  I have no idea why these tubes sound good to me, but they do. Maybe they EQ around my oldguy hearing loss . . .

[tubeswell]

The 6P3Se datasheet says it’s a 20.5W tube. Its namesake cousin the 6P3S is a 20W tube, but the ‘e’ is a completely different envelope and electrode cage and is much tougher. It’s designed for use in jet aircraft and military equipment etc (it has a mechanical ‘G’ (Gravity’s) rating and its coin base is designed to fit into a special type of secure retaining clamp.). I’ve used these in a lot of guitar amps and I’ve found them to be reliable and rugged. They can run happily at 460V in fixed bias PP idling at 70%Pmax, or even at 400V in cathode bias class A idling at 20.5W. Some people claim these can run happily as a 25W or 30W tube, but I prefer to follow the datasheet.

[kasperbergholt]

My own experience with those tubes is that they are incredibly rugged.  Personally, I don't worry about their longevity at all.  My builds routinely run these tubes between 420-450 VDC.

I'd suggest tuning for the best sound (within your presets).   If you can't tell the difference between two settings, use the lower stress setting.

These tubes generally sound very good, but I confess I've fallen in love with the Tung-Sol 6L6GC-STR.  I have no idea why these tubes sound good to me, but they do. Maybe they EQ around my oldguy hearing loss . . .

Thank you for your feedback, it's appreciated :) I'll do some comparative listening sessions - the Tung-Sol you mention are they new productions or old/NOS?

And which brand are your 6P3S-Es? I'm considering investing in a couple of more quads. NOS 6L6s have become way too expensive.

[tubeswell]

Reflektor

[acheld]

Tung-Sol you mention are they new productions or old/NOS?

New ones.   

I've used Reflector, OTK and "unidentified" 6P3S-e tubes with equal success.

[HotBluePlates]

I've used Reflector, OTK ... 6P3S-e ...

"OTK" is not a brand.  It is a quality-control stamp placed on items that passed inspection (mainly during the Soviet era).

You would identify the factory by noting the logo stamped on the tube (sometimes surrounding the type number).  Some examples can be seen here and here.

[acheld]

"OTK" is not a brand.  It is a quality-control stamp

Well, thank you for the clarification.       Now you know why I don't read, speak, bet, speculate or think in Russian!

As to the brand of 6P3S-e tubes I've used, that reduces it to Reflektor and "Unidentified."   Regardless of that, they have all seemed to be very rugged tubes that sound pretty good.

[PRR]

...that reduces it to Reflektor and "Unidentified."...

In a non-competitive centrally-planned economy, it may make sense to not have two factories making the same part. Even in the nominally highly competitive US tube market, tubes of multiple brands were often all from the same factory. Military planning may like Second Sources, but they can't always get what they want.