Real World 6P3S-EV/Sovtek "5881" test

[steve]

I just posted this over at the 18watt.com & AX84.com sites:

I've seen claims that the 6P3S-EV/Sovtek "5881" can dissipate 40W on the net, made by Ken Gilbert, I believe.

I decided to test this out using a 5F2-A tweed Princeton circuit that I built a while back. This amp has Hammond 270EX and 125ESE transformers. I have a 2.7k/.68uF combination on the first cathode of the 12AX7 for more of a Marshall vibe. The second cathode has 1.5k/10uF.

I used a 201ohm/7w cathode bias resistor. This biased the tube at 39w, close enough for RnR. Cathode to ground voltage was 21.88v, plate to cathode voltage was 362v. Actual bias current was about 109mA.

I tried two different "5881" tubes from my tube stash. Both have the "coin" base. Sovtek sells one with a full base called the "5881WXT". The first tube started to get a hint of red on the plate after about 5 minutes. Not good.

I put in the other "5881" and no red plating. My guess is the quality control of the Russian tubes is pretty spotty. I can't really recommend biasing the tubes this hot, but really only two tubes isn't really that big of a sample. The actual data sheet for the Russian 6P3S-EV gives the maximum plate voltage as 250v, which is way under what it can really take. I had a pair in a Soldano designed Yamaha amp which had 500v on the plate in fixed bias.

I tried both 2.5K and 5K for the primary on the OT. I couldn't hear a difference one way or the other.

The tone was less distorted when cranked than a 6V6. It really responded to picking dynamics, though. Dig in and the amp distorts, play softer and the amp cleans up. It didn't seem that much louder than a single 6V6 or Groove Tubes KT66HP tube in the amp.

Neither the OT or PT got even slightly warm after about 20 minutes of playing with the amp cranked. I believe the 125ESE is more robust than the official Hammond specs say and can handle a single 6550 or KT88. Try this at your own risk, though. YMMV.

tung

[Satamax]

Hi Steve! Cool to hear this!

I've had some of the wafer base sovtek biassed at 32 watts at idle. Suposedely the reflector and "radio" brand are tough, and replacement for 6L6 not 6V6, the 6V6 one is the 6P3S, not the S-E!

[steve]

Hi Steve! Cool to hear this!

I've had some of the wafer base sovtek biassed at 32 watts at idle. Suposedely the reflector and "radio" brand are tough, and replacement for 6L6 not 6V6, the 6V6 one is the 6P3S, not the S-E!

IIRC, the Groove Tubes 6V6HD as sold in the 1990s was the 6P3S without the EV suffix. Without the suffix, the 6P3S is a closer to the lower rated 6L6 or 6L6G in specs. Good 6V6s were getting hard to find, especially ones to put into Fender Deluxe Reverb amps. The 6P3S-EV which Sovtek calls the "5881" is the mechanically ruggedized version and has a longer lifespan of 3,000 to 10,000 hours.

The Russian 6V6 is 6P6S. I don't know if they make an -EV version.

steve

[Satamax]

Yep, sorry! That's it, 6P6s for 6V6! I have some nice 6V6 which are italian, but i suspect that they might be of russian origin! They seem to cope in silverface deluxes, tho, i haven't heard of the owners back yet. Fitted few of them with thoses.



The russian valves i like are thoses 6P3S-E

http://cgi.ebay.fr/RARE-5881-6L6GT-6...QQcmdZViewItem That's the reflector/radio brand. And i think that's the type of valves Ken used. Dunno how long you've been here but ken used to be a poster on the old ampage. Basicaly what he was saying, is, better buy theses dead cheap in big lots and match them, than buying matched EI KT90 for his baga!

Actualy you can find bot waffer base 6P3S-E
http://cgi.ebay.fr/6P3S-E-6L6GC-5881...QQcmdZViewItem

And the 6P3S under the radio brand.

http://cgi.ebay.fr/HIGH-QUALITY-6l6G...QQcmdZViewItem

Sorry if it smells, i'm talking out of my ass!

[steve]

Yep, sorry! That's it, 6P6s for 6V6! I have some nice 6V6 which are italian, but i suspect that they might be of russian origin! They seem to cope in silverface deluxes, tho, i haven't heard of the owners back yet. Fitted few of them with thoses.

Those look Russian to me. Here is a 6P6S that was sold by Sovtek in the US as a 6V6GT:




I had a quad of Sovteks in my Jim Kelley FACS amp. They survived, even at the insane plate voltage of 470v. I still can't explain why they didn't burn out.

The russian valves i like are thoses 6P3S-E

http://cgi.ebay.fr/RARE-5881-6L6GT-6...QQcmdZViewItem That's the reflector/radio brand. And i think that's the type of valves Ken used. Dunno how long you've been here but ken used to be a poster on the old ampage. Basicaly what he was saying, is, better buy theses dead cheap in big lots and match them, than buying matched EI KT90 for his baga!

I've been posting on Ampage since it started

Here is a shot of the test amp and actual tube I tested (the one that didn't red plated):



Looks identical to me, except for the silk screening.

Actualy you can find bot waffer base 6P3S-E
http://cgi.ebay.fr/6P3S-E-6L6GC-5881...QQcmdZViewItem

And the 6P3S under the radio brand.

http://cgi.ebay.fr/HIGH-QUALITY-6l6G...QQcmdZViewItem

The Cyrillic characters on those boxes when transliterated into Latin charcters say "radio lampa." The Sovtek 6P6S boxes have "elektronnaya lampa" written on them.

Radio could be a brand, but I think it is more of a description of the contents.

steve

[soundmasterg]

I wonder whats happened to Ken? I don't see him posting anywhere anymore. Lots of guys have dropped out that used to post though so its no surprise. I've been on Ampage since it started too....traditionally its been the best amp site around!

[Satamax]

Soundmasterg, Ken is a dad now and might not have as much time as he wanted, i'm pretty sure he's an ocasional lurker over here and has posted once or twice on the new ampage. P¨lus he became intrested in subaru raly car tuning, so that might take up some of his free time too.

[Satamax]

Hi everybody!

Steve, would you ming taking two pics of your 6P6/6V6 thing from the top like theses ones? So we can tell if they're from the same origin.

Thanks a lot.

Max.

[steve]

Max,

I took a picture of the top of the two Russian 6V6s I have. The one on the left is a Sovtek tube labled 6V6GT. The one on the right is a National tube labled 6V6GTA "Made in USSR."

http://www.diycustomamps.com/images/6p6stop.jpg

They look pretty close to yours to me.

HTH,

steve

Hi everybody!

Steve, would you ming taking two pics of your 6P6/6V6 thing from the top like theses ones? So we can tell if they're from the same origin.

Thanks a lot.

Max.

[Satamax]

Look pretty close to me too Well, looking at the relations between Italy and USSR till the seventies, i'm pretty sure they're sovtek/reflector and not "made in Italy" as advertised!

[Steve Conner]

Hi Max,

I have a pair of 6V6s that look just like that too. I seem to remember one was badged Brimar and the other Zaerix, though the print came off them. They both were labelled "Made in U.S.S.R".

I tried them in my Toaster amp at 475V plate and 360V screen once when I was feeling bored and destructive. They actually survived fine, though to be fair I biased them pretty cold.

The 6P3S-E is a tough tube, and while it may be able to dissipate 40W, it's no replacement for a 6550. I was testing tubes a while back, and I tried a pair of them against a pair of 6550s and a pair of KT88s. I found that they couldn't deliver the current that the larger tubes can. As I loaded the 6550s heavier, the power output increased, but the power output of the 6P3S-Es fell again and they started to redplate. They worked best with the same sort of load impedances recommended for 6L6GCs.

If you're wondering what happened to Ken, yea, I think he's just too busy. I saw him post here a couple of months ago, so I doubt he's gone altogether. He has a website at http://ken-gilbert.com/

I remember seeing his BAGA years ago, thinking it was awesome and wanting an amp like it. I just recently managed to get parts to make a 3/4 size replica ;-) and I need to decide whether to power it with 6 6550s or 12 6P3S-Es....