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    Building, troubleshooting and testing of these amplifiers should only be
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Yet another Priboi thread...

Hello all,

My friend got a pile of Priboi, russian made 2x50W Amplifiers... Now I paired them with a set of Telefunken TLX2 (3 ways).

One of them is black with led power meter in the slots used for attenuators. It is made in Estonia and the built quality seems better, it also came with 2 RCA jacks instead of the DIN.

7 of them are Grey boxes made in Russia with DIN inputs and attenuators.

All of them are using the same power supply and amp boards, I swapped a couple of them and made a test bench to fix a couple of broken boards...

Things I found so far,

-Don't run 6R3S tube sideways :( I was trying to measure the signal in a couple of places...

-Don't run them without load...

-Best running tubes are from October 1979, I don't have newer ones, and none of these died so far (knock on wood)

-The October 1974 pairs are also good warriors but when I ran them sideways 2 of them died... So these might be my fault.

- All of the 1971 and 1977 so far don't last very long, they die one at the time so I now have odd pairs :/ and don't know how matched should they be...


My plan...

Find some Telefunken speakers 8xTLX2 or 6xTLX2 and 2xTLX3
Refurbish all of them and reglue all the seems, take all the old vinil away, resand and paint.

Make 4 Priboi in good shape, I already have 2 in very good working order.
7.1 Home theater ~400W total ouput

Some questions...

If I get this right these are Class B ? By looking at the PCB and their connection I tought they might be Class A ... but the power output make me think otherwise... Or schematic on this forums is not matching what I have...

Yours,
Philippe
 
Got most of them working...

I am suprised to see so many of them working, 6 out of 7 are repaired, only 1 of the 6 is missing a tube to be complete. Considering that the output lamps are supposed to fry like I can eat cookies...

The 7th is missing all output tubes, bottom cover, top cover, front plate and a shield on one of the the input lamps. I also swaped a mute amplifier channel so it really need some help. I don't think it is worth saving it, but the irons are maybe worth using for another project.

I changed my mind on using those for my Turn table, I found a nice Marantz 2235B so I'll use that for it, matched Telefunken TLX3, full German 60's, 70's Hi Fi. That should be less of a suspicious setup to be used by anyone and it doesn't matter as much if they leave it on by mistake.

I have another house where I will use the Audus(Estonian Priboi) until I can find myself a Kenwood KA91x0 in Europe, my dad had one of that series and I loved it, still don't know what I'll match it with.

This will leave the Priboi only for the movies, maybe some games, I am kind of psyched of the idea of having a surround lamp system.

Next week I get the scope, 8 ohm dummy, and signal generator, new caps for all and it is tune up time.
 
Interesting development here ...

I got one of the amps running a pair of TLX1, and for some reasons I had about 6dB loss on one channel, recapped the amp board then PSU, readjusted all pots -50V -35V etc etc... I was about to change the transformers when I realised that the 8ohm and 4ohm taps were interchanged !!!

So if I am right the 8ohm tap should have more turns, so a bigger resistance than the 4ohm ?

So my loud channel was in fact wrongly wired while the channel I tried to fix was actually correct ...

Yeah, got it
 
I got pile of 20 6R3S-1 so I'll wait for that stock to be running low before doing any upgrages on those 5 amps.

I have 2 extra toy Priboi to play and I do have 5 EL34 in a box ...

Now as for the reliability, one lamp died because I ran it sideway before I knew where to get my test points.... I know I was dumb to run a lamp on the side.
2 lamps died before I knew why, probably dead before I got them.

All the other lamps have many hours of service and run 12 to 16 hours / day... 50W is enough for my needs and the sound is OK for now. And I am really trying to kill those and see how long they really last !

So the survival rate is about 3 dead for 28 tubes, 25 / 28.

Since I rebuilt and readjusted in September 0 tube died , knock on wood.
 
6R3S-1 is the result of attempt to get cheap civil hybrid of military Gu-19 and Gu-29 tubes. The result is horrible: people who did that seems to me did not have a clue about what they were doing. "A Camel is a collectively designed Horse" (C) Russian Folklore.

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Modernization, "Priboi" long held in Russia.Iz all options no matter how strange the best were on 6R3s and GU29.
GU-19 is not working properly and the sounds of little use for audio.
EL34 absolutely not suitable for use in this amplifier, as suggested some.

Any recommended voltages for the grid ? Or changes to go with the GU-29 ?

I now have both GU-19 and GU-29 on their way home. I know the GU-29 ask for forced air cooling, but I doubt I'll run them to their maximum ;) I don't know what to expect on the power output with the GU-29, these are monsters.
 

artosalo

Member
2010-02-16 9:00 am
I try to "remotely" locate a problem with one Priboi where the output tubes have been changed to 6550.
The owner has measured only some 20 W output power before clipping occurs.
The screen grid voltage is only 250 V and control grid bias - 24 V. The cathode current is some 65 mA.

Does anybody know what is the nominal impedance or turns ration (to 8 ohms output) of the original output transformer of Priboi ?

Is this conversion (6R3S to 6550) anyhow typical ?
Does it require some modifications to the circuitry ?
 
I try to "remotely" locate a problem with one Priboi where the output tubes have been changed to 6550.
The owner has measured only some 20 W output power before clipping occurs.
The screen grid voltage is only 250 V and control grid bias - 24 V. The cathode current is some 65 mA.

Does anybody know what is the nominal impedance or turns ration (to 8 ohms output) of the original output transformer of Priboi ?

Is this conversion (6R3S to 6550) anyhow typical ?
Does it require some modifications to the circuitry ?


I don't know what are they but I found one priboi transformer drawing with
Primary (A1) 1200 ( +480V ) 1200 ( A2 )
Sec (GND) 105 ( 4ohm ) 25 ( 8ohm )

So I guess it is the number of turns, and this would be 130 turns for 8 ohm on the secondary. I am going to pick up my sig generator some of these days and try to calculate the impedence of the input unless someone else can tell me what it is...

I found out that at least on mine the Anode voltage is +480V ! and not +420V like the schematics seem to indicate.