864 / VT-24 DHT curves

This is one of the other great DHTs I received from Vegard Winge for tracing.

Here are the curves and the SPICE model: 864 DHT Composite

The SPICE composite model based on Dmitry’s:

**** 864 VT-24 DHT Composite ******************************************
* Created on 03/16/2013 19:30 using paint_kit.jar 
* www.bartola.co.uk/valves
* Curves image file: 864 SMALL.jpg
* Data source link: 864 SMALL.jpg
* Created by Ale Moglia valves@bartola.co.uk
*----------------------------------------------------------------------------------
.SUBCKT TRIODE_864-Composite 1 2 3 4 ; Plate Grid K1 K2
+ PARAMS: CCG=2.3P CGP=5.3P CCP=1.3P 
+ MU=7.14 KG1=13560 KP=98 
+ KVB=1.88 VCT=-0.07 EX=1.41 RGI=2000
* Vp_MAX=200 Ip_MAX=0.008 
* Vg_step=2 Vg_start=0 Vg_count=11
* END PARAMS -----------------------------------------------------------------------
* cathode resistor is 4.4 ohm, the pins K1 and K2 are 1.1 ohms from the ends of it
RFIL_LEFT 3 31 1.1
RFIL_RIGHT 4 41 1.1
RFIL_MIDDLE 31 41 2.2
E11 32 0 VALUE={V(1,31)/KP*LOG(1+EXP(KP*(1/MU+V(2,31)/SQRT(KVB+V(1,31)*V(1,31)))))}
E12 42 0 VALUE={V(1,41)/KP*LOG(1+EXP(KP*(1/MU+V(2,41)/SQRT(KVB+V(1,41)*V(1,41)))))}
RE11 32 0 1G
RE12 42 0 1G
G11 1 31 VALUE={(PWR(V(32),EX)+PWRS(V(32),EX))/(2*KG1)}
G12 1 41 VALUE={(PWR(V(42),EX)+PWRS(V(42),EX))/(2*KG1)}
RCP1 1 3 1G
RCP2 1 4 1G
C1 2 3 {CCG} ; CATHODE-GRID
C2 2 1 {CGP} ; GRID=PLATE
C3 1 3 {CCP} ; CATHODE-PLATE
D3 5 3 DX ; FOR GRID CURRENT
D4 6 4 DX ; FOR GRID CURRENT
RG1 2 5 {RGI} ; FOR GRID CURRENT
RG2 2 6 {RGI} ; FOR GRID CURRENT
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N)
.ENDS
*$

Hope this is useful…

Ale

307a DHT in triode and Schade feedback

Vegard Winge kindly sent me some great DHTs for tracing including the 307a directly heated pentode. The sample traced is not an original Western Electric but a lovely Raytheon RK 75 307a NOS. There is limited information of this valve in triode mode and the folks at DIYaudio are looking at potentially using it for a DHT headphone amp.

This valve has a filament of 5.5V and 1A and an anode dissipation of 21W in class A (including screen dissipation) when triode-connected.

Let’s see how this valve performs in triode-mode:

How well can we match a triode model for this valve?

Continue reading “307a DHT in triode and Schade feedback”

The Shunt Cascode Driver

A heavy-weight driver

Rod Coleman came up with a brilliant design recently which baptised as “shunt cascode” driver. For those who cannot stand a pinch of sand in their circuits, I suggest you skip this post now. This hybrid circuit is actually a folded cascode if we consider the book terminology. What makes attractive of this design is its outstanding performance against the classic multistage designs aimed at achieving a large drive signal for output stages such as 300B, 6C4C/2A3, etc. I personally haven’t build it yet but according to Rod the sound is superb.

Before building a stage which will replace my current 45 SE driver, I thought it made sense to analyse the circuit and understand why is claimed to be such a great alternative for today’s designs.

Continue reading “The Shunt Cascode Driver”

Russian pentodes in triode mode

After some proper time tracing the curves, here are a set of Russian high-frequency pentodes in triode-mode for comparison. I was looking at closer ones to D3a and these are the ones I had at hand and wanted to include in the tests:

	6Z5P	6Z9P	6Z11P	6Z49P-D	6Z51P	6P15P	6E5P	6E6P-E	D3a
Vf [V]	6.3	6.3	6.3	6.3	6.3	6.3	6.3	6.3	6.3
If [ma]	450	300	440	300	300	760	600	610	315
Pa [W]	4	3.75	6	3.4	3.5	13.5	10.6	8.8	4.5
Gm [ma/V]	7	35	33	17.75	29	16	32	25	34
μ	44	36	40	44.3	79.5	22	30	34	68
Ra [Ω]	6K2	1k	1K2	2K5	2K7	1K6	960	1K3	2K
Ia [ma]	16	29	40	15.7	23	52	50	30	22
Va [V]	252	125	150	200	150	250	200	200	200

Well, as you can see in the table above, the 6e5p and 6e6p-e (both tetrodes) were included in the list. Some interesting points to highlight:

Continue reading “Russian pentodes in triode mode”

26 DHT Preamp Gen2 by Rui Lourenço

Rui's 26 DHT preamp in operation — Rui’s 26 DHT preamp in operation

Here is a great post by Rui Lourenço who finished a sublime incarnation of the 26 DHT preamp Gen2. I hope you find this post as inspiring as delightful it is for me to see someone taking my 26 DHT preamp version to the next level of perfection. I think Rui’s pictures will speak for themselves showing the great craftsman skills and amount of effort and dedication put into this art work.

My Type 26 Tube Preamplifier adventure – by Rui Lourenço (Portugal)

I’ve started my interest in diy audio about 2 decades ago, basically at that time because I had no means of buying some of the fantastic equipment’s I saw in several Audio Shows, also because the bug was there, and some of my friends were doing it. Today, fortunately I have the means, but the bug was kept and personally I believe that good implemented diy projects can most of the times be several notches above commercial products, or otherwise you would have to spend some important thousands of Euros to acquire them at a similar performance level. You all agree that the personal filling of achievement vs your friends drop jaws when looking to some of the wonderful projects we find everywhere, is also very good.

Continue reading “26 DHT Preamp Gen2 by Rui Lourenço”

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…