6Э6П-E and 6Э6П-ДР datasheets

Thanks to Vyacheslav Kalashnikov who kindly did all the work here so here are the translated 6E6P-E/6Э6П-E and 6Э6П-DR/ 6Э6П-ДР datasheets:

Looking at the 6Э6П-DR/ 6Э6П-ДР, there is a minor difference in the transconductance and anode current variance. Also the heating requirements are less demanding. Interesting to see though, is the fact that the 6Э6П-ДР grids can handle a bit more of extra power.

The proof is in the pudding, so we need to test the sound differences amongst these two valves and 6E5P/6Э5П!

6E5P/6Э5П and 6E6P-E/6Э6П-E in triode mode

One of the first valves I traced with my curve tracer was the 6E5P/6Э5П. It has a very good reputation when triode-strapped. I did many tests and found this one being a superb driver given is one of the most linear valves out there. Many use them as a 300B driver. I will probably implement Rod Coleman’s shunt cascode topology in my 45 SE or in a 6C4C/4P1L PSE design.

Over the weekend I traced many valves as managed to recalibrate the oscilloscope and tracer and wanted to play with some samples I had around.

Here is the 6E5P/6Э5П in triode mode:

And here are the updated SPICE model parameters:

Now, let’s have a look at it’s close brother the 6E6P-E/6Э6П-E in triode mode. It has a long life (10,000 hours against only 500hours):

Many praise the 6e6p-DR tetrode over these two, I haven’t tried it yet myself but here are the minor differences between 6E5P/6Э5П and 6E6P-E/6Э6П-E to highlight:

Both 6E5P/6Э5П and 6E6P-E/6Э6П-E have very linear curves!
6E5P/6Э5П: less anode resistance and higher transconductance compared to 6E6P-E/6Э6П-E which seems to have a tad more of gain

6P36S / 6П36С beam tetrode in triode mode

My friend Vyacheslav sent me for testing an 6P36S / 6П36С output beam tetrode which was used for TV horizontal deflection circuits in the old days. Here are the nice curves in triode mode:

Low anode resistance and high current capability with its 12W of anode dissipation make this cheap indirectly heated tetrode an interesting candidate for an amplifier. Let’s have a look at the triode model:

Happy to complete the triode SPICE model if someone can translate the Russian datasheet and provide me with the electrode capacitances.

Well, how will this triode perform in a simple SE configuration? With a low Ra, a 5K anode impedance OT will work well:

With just 55Vpp we can drive this valve to produce 2W @ THD=1.6% (without considering the driver distortion cancellation). The valve can be biased nicely at 55mA and 220V.

I’ve got the (SE) power!

For DHT single-ended (SE) topology, I have to admit that I reached to the conclusion that in my opinion either 6C4C or 4P1L are the way forward in terms of sound and cost after not being happy with the option of running the 45 in A2 mode. Both 4P1L and 6C4C sound lovely in SE despite many will say the 300B is unbeatable. Yes, won’t say a ridiculously thing such as 6C4 or 4P1L are the “best DHTs”. We all know that there are many great DHTs out there, but at a cost. Well, if cost is not a problem for you, you can chose great NOS valves from PX4, 50, 300B to 813 or 845. The latter comes with a hidden price: the power supply. I’ve been there as I’m building the 4-65a SE and most of the budget is used in the power supplies. Sound-wise, we did a side-by-side listening tests on many SE and PSE amplifiers and couldn’t find a significant different between 4P1L PSE and 300B stages. This could easily end up in loosing the tangent and falling into an endless debate about topologies, OT, driver-output stage combinations, bla, bla, bla, but in reality you can’t beat a 4P1L PSE in terms of cost and bias flexibility (i.e. you can easily get 5W from a pair of 4P1L as we will see later). I wish I could achieve the output power I like (i.e. 3W) with a 45. A 45 in push-pull is then very attractive but I haven’t listened (or build) it yet.

I have a very decent stash of both 4P1L and 6C4C, so obviously I will be inclined to get the most out of these ladies rather than continuing burning money on other NOS valves . If you are still reading this is simply because you have (or at least considering buying) 4P1Ls or 6C4Cs and you want to build a good amplifier with them.

So how much power can you get out of the 4P1L? Anatoliy did his own tests and was very pleased with the results in terms of sound. I haven’t run the 4P1L in A2 yet but here it would look like in A2:

You can get clean 5W from a pair of 4P1L running at 50mA (each) and biased at 200V. The driving requirements are only 50Vpp and we can see in the diagram above that the positive grid excursion is to just over 10-12V. Obviously the right driver needs to be used to provide the necessary grid current in A2 and also withstand the changes in grid impedance when transitioning from A1 (high impedance) into A2 (low impedance) with minimum distortion.

I don’t currently have an 2K5Ω OT gapped at 100mA, so won’t be looking at running a 4P1L PSE in A2 like this.

Instead, I have a pair of LL1623/60mA which can provide a varied set of transformation ratios: 5K6Ω, 3KΩ and 1K6Ω.

With this OT I could then easily get 2-3W out from a 6C4C or 4P1L PSE as we shall see looking at the loadlines.

Continue reading “I’ve got the (SE) power!”

4P1L PSE load line

A pair of 4P1L can be easily matched, so 4P1L PSE is a great cost-effective option to deliver +3W single-ended warm sound in A1. Having investigated filament bias, harmonic content, now is time to look at this configuration in a bit more detail.

I have at hand a nice LL1623/60mA which can be configured to 3KΩ:8Ω. After looking at the loadline here is what I think it should play well to deliver 3W:

Va=250V, Ia=60mA, Vgk=-22.9V
The pair of 4P1L will equate to mu=8, gm=12mA/V and Ra=690Ω
Vg= 41.6 Vpp

A driver with some headroom to provide at least 80Vpp should be fine for this SE amplifier. Without looking at harmonic cancellation, this stage should deliver 3W at about THD=1%. Clearly proven that I will not readapt the 45 for A2 🙂

EDIT – 17th March 2013

Just realised after reading Imzen’s comment that the maximum Pa used is incorrect. 4P1L is a 9W device when triode-connected. So here is the correct loadline for a 5K OT:

As we can see, it’s better to run this valve in PSE as you will get just 1W in SE with 1.5% THD when biased at 220V/40mA…

4-65a SE Amp: HV3 supply

Building the HV3 (+330V Supply)

I could easily say that by now I’m tired of building power supplies. Yes, I’m and fundamentally can’t see the day when I get to fire up this amplifier.

Filament supplies and three stacked power supplies is the price I’m paying to get a completely cap-less and DC coupled A2 amplifier. I guess that my analysis once completed will be made with full perspective of every single implication of this amp: iron, heat and weight. Yes sir, this is a heavy-weight challenger.

I guess that this specific HT power supply design is quite flexible as could be easily reused in many of the projects I have in mind, which unfortunately keep growing.

Good thing is though, I can make these supplies pretty quickly, but don’t do this at home ok? There is serious HT involved. I don’t have pets or kids (but do have a wife) and these supplies should be hidden and away from any poking curious finger.

The final design is similar as the one used before. Could be adapted to choke input, but with the components I had at hand, this supply is very well filtered. It provides only 15mV ripple noise which at 330V is a lovely noise floor around -87dB:

The mains transformers are Weiss (excellent quality) which has screened windings. Instead of having a full Graetz valve rectifier and waste more heat (and use more damper valves), the rectifier is hybrid using a pair of UF4007. Capacitors are oil and polyester ones for the output HF decoupling on each rail. Each channel will feed a Salas SSHV2 shunt regulator which will provide the stable DC reference for the 46 driver stage and bias point for the output 4-65a stage.

Bad news is that, there is one supply left to be built before I can test at least one channel!

Loud

Sweating the 45… (Part4)

Last week I looked at optimising the 45 loadline in A2. Clearly we shouldn’t be attempting to get more than 2W from this valve without a significant level of distortion. However, having about of 3W would be attractive for the transient response of this amp.

So how will this circuit perform in a simulation? Let’s see what the spice results are:

The THD is significantly better due to the harmonic cancellation between the two stages. The driver distortion is 0.3% at full tilt (150vpp) and this could be improved. I guess the 6e5p could do better, but interesting to see how the cancellation of harmonics may play around. The new operating point and the stacked supplies will demand different MOSFET parts of 1kV for sure…

Driving the 45 in A2 (Part3)

What about driving it at full tilt in A2?:

The driving signal has to be about 160Vpp to provide maximum swing, so power is:

${P}_{out}=\frac{\left( Vmax - Vmin\right)\cdot \left(Imax-Imin \right)}{8}$

${P}_{out}=3.36W$

H2 distortion:

${D}_{H2}=\frac{1}{2}\frac{\left(Imax + Imin \right) -2 \cdot Ip}{\left(Imax-Imin \right)}$

Which yields a whooping 6%!

Driving the 45 in A2 (Part 3)

Ok, the previous operating point wasn’t optimal from a musicality perspective. As suggested by 45, I reworked the load line for 36mA/275V and anode load of 5.6KΩ (which is what I could get with my OT):

The driver should now provide $V{}_{gk (pp)} = 2 \cdot (+20V + 55V) = 150Vpp$ .

The output power will be around:

$P{}_{a}=\frac{1}{2}\cdot i{}_{ap}^2 \cdot Z{}_{a} = \frac{1}{2} \cdot (36mA)^2 \cdot 5.6K\Omega \cong 3.6W$

Efficiency would be around 36% in theory. Happy if around 3W can be obtained from this valve here with a reasonable distortion…