tube upgrade benefits, worth the money? 6R3S-1, EF86

[crazymechanic]

Hi folks , I would appreciate some advice , especially maybe someone has had experience with these tubes I am about to mention.
So I have this old tube amp Priboi, and it uses 6R3S-1 (6P3C-1) in the output and 6J32P in the input, the middle tube as much as I read is actually ok and can be left there in an upgrade.

So the analog for the output 6R3S-1 double beam tetrodes is said to be the russian military GU19 (гу19) and for the input tube the western EF86 made by either telefunken or others.

So tube experts is it worth it in terms of sound improvement will there be actual benefits there ?

thanks.

 

[crazymechanic]

anyone ?

 

[Wavebourn]

6R3S-1 is a civil version that is kind of combination of GU-19 and GU-29 military tubes. It is much worse than GU-19 that was manufactured for military, and was quite expensive. Simplified construction, worse technology, as the result - worse reliability. Go for it. Yes, 6J32P is EF86, direct replacement. But when you install GU-19 don't forget about bias adjustment.

 

[crazymechanic]

it's kind of weird that due to my minimal Russian language skills I have to get info about their tubes from across the ocean but so life goes.

have you had any hands on experience with the gu19 and 29 tubes?
the bias for gu 19 is more or less than for the 6r3s-1?

Oh also I think im gonna ask this in another thread but I can also mention it here , what about the 6J32P tube that sands in the input , would ef86 be better or can I just leave the tube as it is, because the ef86 costs some money.

also there are the phase splitter/driver tube 6N6P which is said to be a good tube , but there is the analog 6N1P is that better ?

 

[crazymechanic]

oh and also I find it strange that for the original 6R3S-1 the filament voltage is written as 6.3v with series and 12.6v at parallel. if the filament cant work with 12.6v on filament why would it then work at half that ?

with the gu 19 the filament voltages are vice versa for series they show 12.6 and parallel 6.3, Ii'm confused .

the priboi has parallel heater connections to the output lamps at 12.6v now does that mean it would fry the gu 19 tubes heater or what?

 

[crazymechanic]

P.S. There must be a mistake in the 6P3C-1 tube datasheets because they say that quote
" Filament voltage in case of series connection, Volt 6.3
Filament voltage with filament placed in parallel, Volt 12.6"

the priboi circuit is wired such that each output tubes heaters are placed in series ( each tube having two filaments) each tube has 12.6v coming into its series placed filaments which means that each filament is rated for 6.3v ,
the GU19 lamp states that series connection of it's filaments is for 12.6 while parallel for 6.3v which sounds correct since with series each filament gets roughly 6.3v.

 

[kevinkr]

You may be misinterpreting the data sheet as both tubes filaments are 12.6V in series and 6.3V in parallel.

I believe Wavebourne has a lot of experience with the GU-19 and recommends it highly. I should think it is the right choice for your Priboi. Remember to check the bias.

 

[Wavebourn]

also there are the phase splitter/driver tube 6N6P which is said to be a good tube , but there is the analog 6N1P is that better ?

No. With 6N6P you can get higher linear swing. You may try 6N30P as well, but I would not expect a big difference.

 

[elektroj]

Depends.. but most probably not.
Good western EF86 will have twisted filaments, which, in turn might result in lower hum when AC heated. 6J32P filements are of folded design.
IIRC, closest western equivalent for 6R3S-1 is QQE 06/40, but I'm not 100% sure.
BUT, this all doesn't matter much, because this Priboj amp in its original form is a dog! It's inherently unstable and sooner or later it will destroy itself.
(West Berlin was literally flooded with Priboj amps for a little money in the early '90s (after the wall came down) and many of them found their way to my bench. I've seen many burnt PCBs and even one melted 6R3S-1 )
That doesn't mean the amp can't be enjoyed, it just need to be re-designed.
The output transformer design, HV and output tube filament voltage puts some restrictions on output tube choice, so its better to stick to original tubes. They are OK-ish, but watch for g1 leakage current. The rest is up to the 'cook'

Best,

...
So I have this old tube amp Priboi, and it uses 6R3S-1 (6P3C-1) in the output and 6J32P in the input, the middle tube as much as I read is actually ok and can be left there in an upgrade.

So the analog for the output 6R3S-1 double beam tetrodes is said to be the russian military GU19 (гу19) and for the input tube the western EF86 made by either telefunken or others.

So tube experts is it worth it in terms of sound improvement will there be actual benefits there ?

thanks.

 

[Wavebourn]

Gu-29 picture

6R3S-1 picture:

[IMGDEAD]https://pics.simhost.org/images/97275715034cdfeb494a.jpg[/IMGDEAD]

As you may see, the tube was squeezed into Gu-19 bulb, and simplified. Cooling is worse, anode does not have ribs so being heated it deforms, and the tube change properties. Add here worse vacuum, and the tube runs away melting down. The amps with GU-19 tubes were first designed for Soviet Supreme Council PA system, then new "civil" (read much cheaper) tubes were designed, called 6R3S, then even cheaper tubes were designed and called 6R3S-1.

 

[crazymechanic]

yeah that's what I read too that the GU19 was somehow made for the new system installed in the palace of congress which is a rather interesting looking building built into the Kremlin.Not sure whether that is ultimately the truth or not but.

Well my GU19 are on the way will be here next week.
the GU29 needs a different socket since it has 7 pins instead of 8 so those who modified the priboi with gu29 changed the socket.

as to what you said elektroj, interesting I wonder why they were many of them in Germany because theres almost none here in eastern Europe.
Well I doubt there is much that can go wrong with the amp even if the output tube goes bad, quite frankly there are only a few resistors that can burn out and the tubes themselves and taht's about it.
also I suppose many people who operated the amp payed no respect to the idle current which probably caused half the overheats in the lamps.
I ran my working priboi for many hours every day now just to see how it behaves in the original tube condition and so far I haven't got anything close to overheaing ,

there is a very small background hum that is only audible if you put your ear right next to the speakers when no music is played I wonder could it be from the AC heating filaments or maybe from the mains transformer itself.
tha's also one of the reasons why I asked about the ef86 input tube whether there is any real argument in swapping he 6J32p original Russian tube for that or whether nothing would change.
I understand it's also a matter of which company produced the ef86 and which series from which year.

 

[Wavebourn]

yeah that's what I read too that the GU19 was somehow made for the new system installed in the palace of congress which is a rather interesting looking building built into the Kremlin.Not sure whether that is ultimately the truth or not but.

No, it was about 6R3S-1 that was designed for Верховный Совет. GU-19 was made long before, for military applications. 6R3S-1 uses a bulb from GU-19, but internals simplified from GU-29 which is American RCA 829.

The problem was not in bias current. The problem was, gassy tubes decrease bias current and run away. GU-19 bulb is pretty small for such power dissipation, so it runs pretty hot, and requires forced air cooling. In Priboy tubes are placed in pretty tight place, and no adequate cooling.

 

[crazymechanic]

in the first priboi's they were really tight together but then I guess they scratched their heads and developed the more spacious next priboi's , well I dunno about gu19 but the original tubes in it at least from my personal observations don't run that hot at all , well let's see how this goes.

anyway im planning to replace the caps since their old , i will leave the main filter caps in for one of the two amps for now since they differ , one had the much better quality ones the other had all the Armenian G factory produced ones , the electricians here call them (GAVNO) for the first leter G and gavno in Russian means (crap) i measured them with a capacitance meter and two out of 8 total had none at all , their leads were probably lost contact somewhere or maybe they just dried to an extreme level.

but what caps would you suggest for the lower capacitance film ones that are on the board , having values of 1uF and 100nF , what would be better , polypropylene or polyester film or what ? there is quite a catalog to choose from these days.

 

[elektroj]

as to what you said elektroj, interesting I wonder why they were many of them in Germany because theres almost none here in eastern Europe.

If I remember correctly, it was German discounter Atzert who got some sort of a direct deal with Taganrog factory. At that time there were only a few High End tube amps available on the market and they all were very expensive. Everything over 2x35W (2xEL34) was twice as expensive. Then suddenly some strange looking 'commie' tube amp appears in the shop claiming to provide 2x50 Watt TUBE power at the price of mere DM300,-. No wonder they sold like hotcakes. Everyone and his brother bought one.
Халява!
As to the 'none here in Eastern Europe' - I don't think so, you're probably just late to the party. They all are in the good hands.

 

[Wavebourn]

Speaking of гавно, there were indeed very bad Soviet caps K50-6, with retort sign on them. K50-3, or K50-12 are usually very long living caps, thought huge if to compare with modern caps.

[IMGDEAD]http://fadedead.org/temp/public/auto-thumb/20cc/4071d52e657bc1b111c0505e67b07fb1-772x600-afo.thumb.jpg[/IMGDEAD]

 

[Wavebourn]

Armenian cap is on the right. Sometimes it was enough to squeeze it by pliers to resurrect back.

 

[crazymechanic]

Well I dunno what you mean exactly by " they are in good hands" but honestly they just aren't that many of them if you compare to other soviet era products of similar categories.
the other one i have is the 75UM version so when i will get the missing output transformer and fill in the blank filter cap spaces I will see how that one performs.
at least one thing the soviets did good was they didn't lie about the power output ratings.

 

[crazymechanic]

Ok so i got the GU19-1 tubes and swapped them into my priboi , at first I was surprised , the signal was so distorted the feeling was like it has no power at all.
I quickly realized the problem , rule of thumb the better a Russian tube is the higher idle current it will demand atleast in many cases.

I adjusted the bias voltage pots on the PSU, and to my surprise even more i had to turn them like almost 90 degrees the other way they were standing , and at the same time measured voltage across each output tube's cathode 10 Ohm resistor until i got about 400 mV across the resistors which according to ohm's law turns out to be about 40mA of idle current.
some sources say that a higher idle current is desired about 60mA.
Also i adjusted each output tube since they had fallen out of symmetry , especially one channel had almost no idle current a one lamp's cathode resistor while having a decent one at the other.
I will have to get another multimeter to do this job more properly otherwise having just one i have to disconnect it all the time and swap places.


the strange thing is that the original 6R3S-1 tubes were running on almoust no idle current at all and while listening to them i couldn't hear any distortion , or maybe they require much less of it than the GU19 I'm not sure.
havent listened much to these new lamps but feels like the music will be more powerful and the bass feels stronger.
although there is one thing I have noticed I'm not sure whether this is similar with all tube amps or with just some specific topology's but I like how they play the mids and high end , in musical terms i like listening beatles or mozart or many more such musicians with it and the sounds feels richer, but when it comes to the low end some club type tracks or techno and much more the bass feels rather weird , at some frequencies the bass is strong and can't feel difference between a transistor amp but then at some others the bass kind of sags or is suddenly very silent or sometimes non existent all you can see is the movement of the speaker cone.

I recently attached the apex high power amp that is also featured here on forums to a smps and it sounded much like a transistor amplifier but in terms of how powerful the bass is the bass feels much stronger there.I would say I would love to biamp my setup and put these tube things for the mids and or high end and have some powerful semiconductors for the low end it intuitively feels better that way.

 

[crazymechanic]

also since im not that experienced with tubes could you folks please comment on whether my adjusting technique is correct.
I have circled out in the schematic with red the two resistors that across which I measured the voltage to then calculate the current going through them to determine the idle current for each lamp,
with green i have circled out the symmetry pot with which i adjusted so that the idle currents are similar through each of the two cathode resistors for each of the two lamps in one channel.

the idle current i adjusted to about 40mA for each lamp.
yet the bass feels kind of weak at higher signal levels I wonder why is that maybe the idle is still too low or maybe something else?

 

[emk2]

I would say I would love to biamp my setup and put these tube things for the mids and or high end and have some powerful semiconductors for the low end it intuitively feels better that way.

Go for it if you can, that's the best option.

A friend who helped me to do this for my Klipsch Cornwall's explained that tube amps are not very good in bass department because of back EMF from the bass driver which disturb a lot the tube amp.

Not a big deal if you listen to chill music at low volume, but not the same story if you start to push the volume..