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Old 30th October 2013, 06:53 PM   #121
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Those russian tubes look very well made. The anode material is much thicker than whit western tubes(good against red spots). The glass is thicker and higher temperature? So they ought to be able to be driven harder.


I'm in the process of trying o kill a trioded PL504. Its a hard one. The Philips specimen on my bench has been eating 200 volts at around 400mA for quite some time now. 15 minutes.

What strikes me is that the current hardly changes. The supply indicates 380-420 mA.

I initially had some trouble whit oscillations. I put grid stoppers and ferrite beads in place.


I know that its not oscillating now (I'm watching the anode/G2 supply whit a scope). I put around 10 ferrite beads in series whit the anode. And 1K carbon+ 10 beads in series whit the wire feeding G1 whit a negative voltage.


Edit.

Impressive. I held the anode dissipation constant at 120 watts for 3 minutes. then proceeded to 160 watts which caused the glass to melt and bulge inwards. After observing the phenomenon I went back to 100 watts dissipation, to make sure the glass wouldn't shatter due to a temp shock.

Last edited by v4lve lover; 30th October 2013 at 07:04 PM.
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Old 1st November 2013, 03:46 PM   #122
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The PL504 seem to be pretty consistent if you have philips manufactured examples. Onset of internal glow is at about 40 watts. So 25-30 watts seems like a reasonable operating point.

One observation I made that if you massively overload the tube briefly, it will tolerate this. However under prolonged overload conditions, the beam forming plates will heat up the cathode material and degrade the emissive layer.

Disection of a tube that was killed at a peak dissipation of 180 watts showed a blackened cathode. Under these conditions the screen grid finally gave way and shorted to g1, this caused my Switchmode power supply to dump a lot of current into the little tube. Vaporizing the cathode lead

At 60% efficiency 2*30/40 *100 =150 watts output. This seems to coincide whit George's observations quite nicely.
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Old 2nd November 2013, 05:26 PM   #123
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Wrenchone wrote :
Quote:
Note - there are two Russian tubes touted as EL500 equivalents - the 6P36S and the 6P44s. I think I have the 6P44s.
I have build a SE amplifier using the 6P36S tube...sounds pretty good.

Click the image to open in full size.
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Old 2nd November 2013, 11:14 PM   #124
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That's a nice amp you got there.

Would you mind elaborating on the used topology? I take that is has a 6SL7gt input stage and a 6SN7gt cathode follower ?
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Old 3rd November 2013, 11:04 PM   #125
tomlang is offline tomlang  United States
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Originally Posted by roline View Post
latest amp design running set of 17jt6 outputs, will also run 13gb5 outputs with a couple jumpers
Have you run the 13gb5's yet? What impedance are your OPT's?
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Old 5th November 2013, 06:01 AM   #126
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v4lve lover wrote:
Quote:
Would you mind elaborating on the used topology? I take that is has a 6SL7gt input stage and a 6SN7gt cathode follower ?
Click the image to open in full size.

This is the schematic of the 6P36S SE amp...it's a straightforward circuit and it sounds pretty good. If you have any suggestions to improve it, I would like to hear them.
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Old 6th November 2013, 02:00 PM   #127
tomlang is offline tomlang  United States
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Pete's Red Board using 13GB5's mounted directly on the board. I drilled new holes right into the board to install the chassis mount 13GB5 sockets.

Getting 45 wpc with 320 plate volts and 170 screen volts with a 2k4 output transformer.

--edited to add pics but can't seem to load them right now...

Last edited by tomlang; 6th November 2013 at 02:04 PM.
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Old 6th November 2013, 02:15 PM   #128
roline is offline roline  United States
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Quote:
Originally Posted by tomlang View Post
Have you run the 13gb5's yet? What impedance are your OPT's?
I was going to etch a new PCB, the first one is built up and running with the 17JT6 output tubes, in pentode mode. I have 60 of them, perhaps a life's supply. Also is dependend on the heater tap on the PT.

I'm using 6.6KRaa outputs for a larger class A operation, with minimal feedback. I'm running 89db speakers. @ 4 ohms, using 4ohm tap.
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SO many tubes, SO little time!!!
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Old 7th November 2013, 07:11 PM   #129
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Quote:
Originally Posted by v4lve lover View Post
The PL504 seem to be pretty consistent if you have philips manufactured examples. Onset of internal glow is at about 40 watts. So 25-30 watts seems like a reasonable operating point.

One observation I made that if you massively overload the tube briefly, it will tolerate this. However under prolonged overload conditions, the beam forming plates will heat up the cathode material and degrade the emissive layer.

Disection of a tube that was killed at a peak dissipation of 180 watts showed a blackened cathode. Under these conditions the screen grid finally gave way and shorted to g1, this caused my Switchmode power supply to dump a lot of current into the little tube. Vaporizing the cathode lead

At 60% efficiency 2*30/40 *100 =150 watts output. This seems to coincide whit George's observations quite nicely.
hello , it's possible up power to EL/PL 504 to me build SE ?

because , me use to me build , EL / PL 504 to possible upgrad to EL / PL 502 / 511 for up power to 20 W !

so me no up power max 17 W , i possible use curent to up power EL 504 to EL 502 ?

many thank
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Old 14th November 2013, 08:07 PM   #130
tomlang is offline tomlang  United States
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Now running 1k9 output transformers for an honest 60wpc rms both channels driven using 50 cent 13GB5 aka PL504 tubes.

Can you say D-Y-N-A-M-I-C-S this amp's got it! The transformers, Hammond 1650T's, are idling along, but they sure seem a good impedance match for the 13gb5's.

310 volts on the plates, 170 on the screens. 70 mA idle bias current.

These things have no right to sound as good as they do! Thanks to Pete for a great board!

I need to add a touch of global feedback and mount this stuff on a decent chassis.
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