maal1605 said:
Here is the example from Soviet "Radio" magazine, 1958
An externally hosted image should be here but it was not working when we last tested it.
From the same magazine, with better speaker damping using positive feedback by current.
An externally hosted image should be here but it was not working when we last tested it.
St-35 with 6P15P tubes
Hey All,
I found some 6P15P tubes online from a Russian retailer and bought 17 of them. I was under the impression that they were identical to an EL84 but now find that to be untrue.
I plan on using them in a Dynaco SCA-35 I'm building. I'm substituting ST-35 boards to swap the 7199 for the 12DW7 preamp/phase splitter. And removing everything but the volume control from the circuit.
Obviously, on the EL84 the suppressor (?) grid is internally connected to the cathode on pin 3. The 6P15P does not have this connection. If my tired old eyes aren't failing me the suppressor grid on 6P15P is connected to pins 1&6. The ST-35 manual voltage chart lists 13.5 volts on pin 3 and 0 volts on pins 1&6. This is important because of the 150 volt limit on the suppressor grid for the 6P15P.
I also found the "Hazen" mod for Decware amps where the EL-84 cathode and suppressor grid are connected by a non-polarized film cap. Since there is an internal connection for these I'm assuming the cap is a bypass cap?
So these are my questions. Is the 150 volt limit on the grid for a pentode amp where the grid is driven? This not the case in the ST-35 as it is an ultra-linear amp. Second, should I connect the cathode to the suppressor grid? Third, Does anyone know the value of that cap? And lastly, could I damage my new amp by experimenting with this connection either by cap or by a wire?
Since the ST-35 boards use a chassis mount socket for the EL-84 rewiring the output tube sockets is easy.
As always, thanks for any help you could provide!
Hey All,
I found some 6P15P tubes online from a Russian retailer and bought 17 of them. I was under the impression that they were identical to an EL84 but now find that to be untrue.
I plan on using them in a Dynaco SCA-35 I'm building. I'm substituting ST-35 boards to swap the 7199 for the 12DW7 preamp/phase splitter. And removing everything but the volume control from the circuit.
Obviously, on the EL84 the suppressor (?) grid is internally connected to the cathode on pin 3. The 6P15P does not have this connection. If my tired old eyes aren't failing me the suppressor grid on 6P15P is connected to pins 1&6. The ST-35 manual voltage chart lists 13.5 volts on pin 3 and 0 volts on pins 1&6. This is important because of the 150 volt limit on the suppressor grid for the 6P15P.
I also found the "Hazen" mod for Decware amps where the EL-84 cathode and suppressor grid are connected by a non-polarized film cap. Since there is an internal connection for these I'm assuming the cap is a bypass cap?
So these are my questions. Is the 150 volt limit on the grid for a pentode amp where the grid is driven? This not the case in the ST-35 as it is an ultra-linear amp. Second, should I connect the cathode to the suppressor grid? Third, Does anyone know the value of that cap? And lastly, could I damage my new amp by experimenting with this connection either by cap or by a wire?
Since the ST-35 boards use a chassis mount socket for the EL-84 rewiring the output tube sockets is easy.
As always, thanks for any help you could provide!
You can't use 6P15P in ultra-linear amp designed for EL84 tubes. Screen grid is denser, and if to apply the same voltage as to the EL84's screen grid, it's current will be too high. 6P15P was designed for more linear mode in video amps with higher voltage swing on anode, that's why the difference. When I did not know what exactly was different, I thought that it is the same tube specified for more linear operations, but surgical experiments confirmed that screen grids are different, so in pentode mode voltage on the 2'nd (screen) grid must be lower than for EL84 tube.
So you have to run them like the TV tubes on Pete Millets PP Distortion Cancelling Amp (Big Red Board) ? I think it runs 150V screens and about 360V on the screens.
6P15P has a higher anode dissipation than EL83. (12W against 9W) The Russian datasheet says that the NOMINAL g2 voltage is 150V, with a maximum of 330V. Have a look at the datasheet, and you'll find all you need. http://www.magictubes.ru/sprav/pdf/6p15p.pdf
By the way, 6P15P maximal dissipation for g2 is only 1.5 watt, versus 2 watts for an EL84. So, beware of screen current when using 6P15P instead of EL84
Anatoliy,
If I design a pentode amp with 300 volts on the plate and 150 volts on the grid with an 8k transformer I should be OK? I have some Japanese 6GK5 single triodes. I want to use them as the front end. Any reason that wouldn't make a nice little twenty watt amp? And on the transformer any recommendations? I'm assuming I could use an ultra-linear transformer As long as I don't connect the screen taps?
Kevin
If I design a pentode amp with 300 volts on the plate and 150 volts on the grid with an 8k transformer I should be OK? I have some Japanese 6GK5 single triodes. I want to use them as the front end. Any reason that wouldn't make a nice little twenty watt amp? And on the transformer any recommendations? I'm assuming I could use an ultra-linear transformer As long as I don't connect the screen taps?
Kevin
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There are ways around the screen voltage issue. A long thread took place about it last fall iirc. There were some dangling issues that people were pursuing.
I've used a large dropping resistor between the screen and UL tap, with a 1uF bypass cap and then a small value resistor to the screen (470R) with good results on the 6П41С. I tried a zener bypassed by the 1uF cap and was not pleased.
I've used a large dropping resistor between the screen and UL tap, with a 1uF bypass cap and then a small value resistor to the screen (470R) with good results on the 6П41С. I tried a zener bypassed by the 1uF cap and was not pleased.
^ my 6LU8 pp amps runs in pentode mode with G2 zener regulated using a string of 3 x 47v 5watt zeners.....
sound is crystal clear, bass is tight, i can feel it, the kick drums sound as it should be....i am satisfied....
doing this technic on the 6P15p would bring simmilar results imho....
sound is crystal clear, bass is tight, i can feel it, the kick drums sound as it should be....i am satisfied....
doing this technic on the 6P15p would bring simmilar results imho....
Hey Guys,
I know this kind of an old thread. but if anyone is still listening I have a simple Question. Can a 6P15P be tested as if it were an EL84? I need some tubes matched and I was wondering if putting them in a tube tester would damage them? I'm assuming that American testers made in the 1950's or '60's wouldn't be set up to test a Russian tube.
Kevin
I know this kind of an old thread. but if anyone is still listening I have a simple Question. Can a 6P15P be tested as if it were an EL84? I need some tubes matched and I was wondering if putting them in a tube tester would damage them? I'm assuming that American testers made in the 1950's or '60's wouldn't be set up to test a Russian tube.
Kevin
It was my mistake Kevin when I assumed that they are identical. If to put 6P15P in position for EL84 current will be higher, also it needs connection of the 3'rd grid to cathode. It is closer to EL83, but pinout is a bit different.
Useles idea. How they would work without proper connections?
Better put them in a tube socket with 180 Ohm cathode resistor, 1'st grid grounded, 3'rd grid to cathode, 2'nd grid and anode to +200, and write down voltage drops on 180 Ohm cathode resistor for each tube. Then select best matched pairs.
Better put them in a tube socket with 180 Ohm cathode resistor, 1'st grid grounded, 3'rd grid to cathode, 2'nd grid and anode to +200, and write down voltage drops on 180 Ohm cathode resistor for each tube. Then select best matched pairs.
I have seen 6P15P described elsewhere as close to EL83. In fact it is very close to EL822; I think that 6P15P with its good gm and high anode resistance and very nice curves would make, like EL822 an excellent pentode current sink should one need a sink with 12w Pa.
Paul
Paul
Wavebourn,
I have seventeen or these tubes. I have a plan to build a push pull parallel using eight tubes. I might as well build the amp and test the tubes when I get it done.
But your idea sounds fairly easy too, thanks.
I have seventeen or these tubes. I have a plan to build a push pull parallel using eight tubes. I might as well build the amp and test the tubes when I get it done.
But your idea sounds fairly easy too, thanks.
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