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EL509 (JJ) or PL519?
EL509 (JJ) or PL519?
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Old 13th December 2010, 04:15 PM   #31
artosalo is offline artosalo  Finland
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Quote:
If this power is ok with your speakers it is an excellent amp.
Do you have any test results ?
I think these most of us have been looking for.
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Old 22nd May 2011, 01:54 PM   #32
lechuck is offline lechuck  Netherlands
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Originally Posted by Miniwatt View Post
I was thinking the same, what if I replace the ecc82 with a ecc99, that would probably be the first experiment after building it according to the schematic.

I have just finished building a single ended amp based on the Synola design. At first I replaced the ECC82 with a 8CG7 (8,5V noval version of the 6SN7). This driver was absolutely not able to drive the PL519 on its screen grid, it started clipping at about 1W output power which gave a very distinct and ugly distorted sound.

I have now replaced the 8CG7 with a EL84 in triode mode. I have left out the 82K anode resistor and replaced the cathode resistor with a 6K8 20W wire wound resistor. The EL84 is able to drive the screen of the PL519 so well that I was able to add a second output tube. Since my output tranny is 2K5 prim. this gives absolutely no problems.

The amplifier sounds really, really, really good. The sound is almost better than real and gain is more than enough! I have biased the output tubes for 40mA each (-30V to -35V BIAS voltage)

The amplifier is still in development. I dont fancy the sound of a ECC83 tube so I am thinking of replacing it with a couple of E80CC's. Also I want to be able to swap the PL519's for EL509's so I have ordered new power trannies that can supply heater voltages for both tubes.

I will post the schematics when I am done building the Amp
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Old 22nd May 2011, 02:14 PM   #33
lechuck is offline lechuck  Netherlands
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Originally Posted by adam2a3 View Post
Hello Tom,
it is the Bob D amp I tried. If this power is ok with your speakers it is an excellent amp. Otherwise, at clipping you will not hear distorted music but distorted noises. The trim pot that affects all biasing must be a 10 turn pot otherwise it is difficult to adjust it.
I have build a amp based on the Synola schematics. The distortion that you are hearing is very distinct and it's origin is in the tube that drives the screen grid on the PL519. When I first build the Amp I used a paralleled 8CG7 (kinda 6SN7 tube). This tube wasn't able to supply the current needed for screen drive and started distorting at aprox. 1W output power.

I have replaced the 8CG7 with a EL84 and now this limitation, and it's ugly distortion, is gone.

You can find the schematics of the amp here: http://109.72.83.33/PL519.png

One side note: This amplifier sounds so incredibly good that one MUST build it. I am using it to drive a pair of Jamo Concert 11's. It has more than enough power for these speakers and the soundstage is unbelievable realalistic! This amp will blow away 30K+ commercial amps!
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Old 22nd May 2011, 04:28 PM   #34
Michael Koster is offline Michael Koster  United States
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Quote:
Originally Posted by tubelab.com View Post
Exactly. Mutual conductance is the ratio of voltage change at the input terminal to the current change at the output terminal. It is rare to find specs for G2 transconductance. ....
True, but G2 transconductance (gm) can be estimated from many data sheets by dividing the G1 gm by the G1/G2 mu factor; sometimes they give a "triode amplification factor". Typical sweep tubes have a G1/G2 mu around 4. By comparison, the EL34 G1/G2 mu is 11. So looking at some datasheets, the G2 gm of a 6DQ6 is about 7300/4.4 or 1600. The EL34 is 12500/11 or about 1100. The EL34 would thus need 1600/1100, about 1.5x the grid drive voltage for a similar plate load and power output.

Another method involves comparing plate current for equal G1 voltage from the curves for different G2 voltages. For example, if there is a 125V G2 curve set and a 150V G2 curve set, find 2 places on the curves with the same G1 voltage and same plate voltage, and just divide the difference in plate current between the 2 charts by the difference in G2 voltage.

One can also obtain screen drive plate curves from most sweep tube data sheets, measured with G1=0 volts, from which G2 transconductance may be determined, or G2 drive load lined directly plotted (see attachment).

If you drive both G1 and G2 together, the net gm can be calculated in a manner similar to calculating resistances in parallel, using the G1/G2 drive voltage ratio.
Attached Images
File Type: jpg G2loadline.jpg (67.6 KB, 744 views)
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Old 22nd May 2011, 08:35 PM   #35
Mush is offline Mush  United States
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Hi Lechuck

I want to build it. What are the voltages you are using? Do you have recommendations for the power supply and transformers? Thanks very much.
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Old 25th May 2011, 12:26 AM   #36
EvilMose is offline EvilMose  United States
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Originally Posted by artosalo View Post

I have built prototypes (and tested) with this principle by using the tubes 811A, GU50 and 807.
How did you find the operating points? Limiting factor in trying some of these designs seems to be want of data for those without curve tracing capability.

Thanks!
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Old 25th May 2011, 05:40 AM   #37
artosalo is offline artosalo  Finland
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Quote:
How did you find the operating points? Limiting factor in trying some of these designs seems to be want of data for those without curve tracing capability.
I begun with 811A. Its datas are well available. I searched for optimum bias and anode voltage that suited my Edcor GXSE15-8-10 k and GXSE15-6-10k transformers (10 k to 6 ohms and 8 ohms ).

Then is continued similarly with 807 and GU50 by experimentation.

I use adjustable power supplies and distortion analyser together to find the best operating conditions.
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Old 15th June 2011, 09:11 PM   #38
lechuck is offline lechuck  Netherlands
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Originally Posted by Mush View Post
Hi Lechuck

I want to build it. What are the voltages you are using? Do you have recommendations for the power supply and transformers? Thanks very much.
Very good! I do have some suggestions based upon the orignal Synola schematics.

Firstly I don't like the ECC82 buffer stage. I have tried to replace it with a double 6CG7, however this tube is not able to provide both the current for R5 and for the screen of the power tube. Removing R6, putting an EL84 in place of the 6CG7 and changing R5 to 6.8k - 20W seems to be the solution. This removes all the ugly distortion that you'll get when the screen grid of the end tube is not correctly driven by the buffer stage.

I have tought myself SPICE last weekend to play around with the schematics. I found out that there is no real reason for the buffer stage to be grounded. In my schematics R5 draws almost a wimpy 30mA and consumes 7.5W, the screen grid draws about 8-15 mA. This means that the buffer needs to provide 38mA at zero signal and at least 45mA at max. I realized that R5 can be removed because the screen grid of the power tube consumes enough current to keep the buffer going. The buffer stage now only consumes the current that the screen grid draws, and we save about 20 watts of unused energy.

I think that a single ECC82 triode could be capable to provide the current needed for the screen grid, thus you can use two JJ ECC832 tubes to reduse the amount of tubes. Simulations confirm this, however I still have try this in the real world.

The power supply that I am currently using allows me to parallel the end tubes and gives me a B+ of 360 volts. My OPTs are 2.5k primairy.

So in short, drop R5, R6 and one ECC82. Then connect the cathode of the remaining ECC82 directly to the screen grid of the power tube.

Feel free to drop me a PM.

Last edited by lechuck; 15th June 2011 at 09:18 PM.
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Old 16th June 2011, 06:16 AM   #39
artosalo is offline artosalo  Finland
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I think that it would be useful to test a higer gm driver (ECC88...6N6P, 6J9P (E180F) etc. etc). The problem with ECC82 is its low gm and thus too high output impedance.

Have you notice that the buffer does not need to be grounded by simulation or in practice too ?

When the cathode resistor of the buffer stage is removed, the total current is reduced, but also the transconductance of the buffer, which is fatal to the linearity of the buffer stage.
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Old 16th June 2011, 08:07 AM   #40
lechuck is offline lechuck  Netherlands
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Quote:
Originally Posted by artosalo View Post
I think that it would be useful to test a higer gm driver (ECC88...6N6P, 6J9P (E180F) etc. etc). The problem with ECC82 is its low gm and thus too high output impedance.

Have you notice that the buffer does not need to be grounded by simulation or in practice too ?

When the cathode resistor of the buffer stage is removed, the total current is reduced, but also the transconductance of the buffer, which is fatal to the linearity of the buffer stage.
I didi try this yesterday with the EL84 buffer stage, it seems to work very well. I still have to hook up my scope to see how it performs, but for now my ears tell me its good
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