valve tester – Bartola® Valves

Ba DHT Spice Model

I really love the Ba DHT preamp, if you need the gain in your system, is likely to be one of the best sounding DHT preamps in my experience. As received many requests for the SPICE model for the Ba DHT, here it is:

**** Ba TRIODE Composite DHT *****************************************
* Created on 10/13/2017 18:33 using paint_kit.jar 2.9
* www.dmitrynizh.com/tubeparams_image.htm
*
* Traced and model by Ale Moglia valves@bartola.co.uk
* (c) 2017 Ale Moglia and Bartola Ltd. UK
* www.bartola.co.uk/valves
*———————————————————————————-
.SUBCKT DHT_Ba 1 2 3 4 ; P G K1 K2
+ PARAMS: CCG=1P CGP=3.8P CCP=1P RFIL=7
+ MU=14 KG1=8940 KP=84 KVB=5232 VCT=-3.5 EX=1.47 RGI=2000
* Vp_MAX=350 Ip_MAX=10 Vg_step=1 Vg_start=0 Vg_count=11
* Rp=4000 Vg_ac=55 P_max=1.5 Vg_qui=-48 Vp_qui=300
* X_MIN=75 Y_MIN=51 X_SIZE=492 Y_SIZE=530 FSZ_X=1192 FSZ_Y=679 XYGrid=false
* showLoadLine=n showIp=y isDHT=y isPP=n isAsymPP=n showDissipLimit=y
* showIg1=n gridLevel2=n isInputSnapped=n
* XYProjections=n harmonicPlot=n harmonics=y
*———————————————————————————-
RFIL_LEFT 3 31 {RFIL/4}
RFIL_RIGHT 4 41 {RFIL/4}
RFIL_MIDDLE1 31 34 {RFIL/4}
RFIL_MIDDLE2 34 41 {RFIL/4}
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 34 1G
C1 2 34 {CCG} ; CATHODE-GRID
C2 2 1 {CGP} ; GRID=PLATE
C3 1 34 {CCP} ; CATHODE-PLATE
D3 5 3 DX ; FOR GRID CURRENT
D4 6 4 DX ; FOR GRID CURRENT
RG1 2 5 {2*RGI} ; FOR GRID CURRENT
RG2 2 6 {2*RGI} ; FOR GRID CURRENT
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N)
.ENDS
*$

You can download the file here: Ba spice triode model

Teflon Sockets

I’ve got a set of teflon sockets from Jakeband. These are fantastically made to order. Luciano from Jakeband sent me in addition some samples which I will use in the eTracer which I will bring along to ETF.19.

Honestly, these are fine pieces of craftwork. For example, you can measure and let Luciano know the diameter of your 845 (or any other transmitting valves) when ordering these valves so they fit perfectly.

I’ve used these sockets on my projects for years and am very pleased have to say. Of course you pay a premium price as these are hand-made with fine materials. In my opinion, these are worth every cent.

Also I had a pair of RCA sockets, look at them:

They are made on a single piece of tellurium copper. First coating in pure silver 99.99% thickness 18 microns and the second coating Gold 24 K 3 micron thick. Sterling job!

You can contact Jakeband directly to order your sockets. Just use the form I posted years ago here.

Aa DHT Preamp (Part I)

Obviously it was time to test the little brother of the “Ba” DHT. In particular, as I have such a low DAC in place now, I need the gain. With nearly a gain of 30, it’s an attractive fellow to work with.

First good sign is that it doesn’t pick up as much hum as the Ba. That’s good, nevertheless I placed a back copper plate which acts as enough earth shielding to keep the Ba quiet.

I worked with my breadboard to find a good “sweetspot”( at least electrically) for this valve. Given the low signal source level, I aimed for a low bias. I played with my fixed bias setup before replacing it with the SiC bias board. I found that 2V/160V was very good in terms of keeping the distortion profile to minimum. Here is what I ended up with:

Only 2 SiC diodes are enough. The source follower PCB is mandatory given the low anode current. I run it at 20mA (hot) to get best results of the stage. Rest of the circuit is very simple, achieving a gain of about 30. Here is the distortion profile:

There is no shielding and you can see some minor IM distortion with mains hum. Harmonic decay is nice with H2 being strongest. THD is very low at 4Vrms which is good sign. Let’s see the frequency response now:

Nearly 140kHz of bandwidth which is plenty for the stage. Great response. I just need to plug this one in and listen to this promising German DHT.

eTracer Build and Review

Tracing valves: an obsession

Since my early days of valves and DIY audio, I developed an obsession around testing and tracing valves. This led me to design and build my analogue curve tracer which I used for many years successfully until I build my uTracer, which was a great innovation in curve tracing. I do have many valve testers (some which I made myself) so why building another one?

Well, Chris Chang from Essues Technologies developed a fantastic new digital curve tracer for valves, the eTracer. There are a few things which will grab anyone’s attention on this curve tracer. Firstly, the power supplies can accommodate a large range of valves which the uTracer can’t. HT can go as high as 750V @ 300mA and the grid supply down to -170V! This is exactly what you need to test your transmitting valves or even a 300B. Secondly, the tracing speed is surprisingly fast. This is a nice feature, specially when you want to trace pentodes at various screen voltages to develop a Spice model for example.

Build process

Continue reading “eTracer Build and Review”

6GE5 Pentode Model

A quick trace of a NOS Tung-Sol 6GE5 measuring around 113%:

Derived the Spice models using Dekker’s ExtractModel tool. The uTracer has a limit of 200mA so it’s not possible to trace the extended set of curves for this valve. However, this is not a limitation to produce a good model.

Here is the triode matching:

I run a set of curves at various screen voltages from 100V up to 200V at 25V steps to generate the pentode model The saturation effect is visible on higher currents above 140mA as you can see below:

Below is the triode model, you can dow Continue reading “6GE5 Pentode Model”

Valve Leakage Test

Years ago when I built my analogue curve tracer I added a small, yet very effective valve leakage test circuit. Due to my laziness, I failed to test a transmitting tetrode which I bought on-line and despite being NOS it damaged my uTracer. I followed the repair and re-calibration process and got the tester back again running, however, I regretted not having used this simple one step test I normally did before. Lesson learned, now I do use it back again!

Here is the circuit in case you don’t have a proper tester and you want to build something similar yourself:

You can test for leakage current using a simple amplifier made out of a NPN transistor and an indicator. In this case I used a Russian Neon (80V/0.5mA) and the existing supply on my tester (+/-80V). You can replace all this with a simple LED and the supply you have at hand. The circuit is designed to turn on the bulb when 5 μA leakage current is provided on the base of Q1 thanks to grounding the valve element next to the one under test. So for example if we want to measure cathode to grid leakage, we simply ground the cathode and we connect the tester to the grid. Same process is repeated with the other valve elements.

When I asked for some help in the DIYAudio forum, someoone gently recommended this text. Unfortunately I don’t read German, but what I got out of this adivce was:

valves with poor vacuum (i.e. failed the test described on the procedure in 18A)
1. preamp valves with less than 4 μA are usable
2. output valves whit less than 10 μA are usable
Valves that are good and show little Gas on the gas test:
1. should have less than 0,6-1μA for preamp valves
2. And should have less than 1.5-2μA for output valves

So the 5μA threshold was good enough in my view. It does work well and the beauty is that when neon light is very dim is an indication that it may be a workable valve despite the tiny leakage in particular with output valves.

Hope this helps

Ale

HY1269 curves

I’m a big fan of the thoriated-tungsten filaments and I value them not just because they do look very cool, but fundamentally due to how they sound in a single-ended stage. I hope to build a nice push-pull amp with these type of valves soon.

I found a pair of HY1269 valves recently. This valve is not well-known amongst the used ones out there but they do have some interesting characteristics as a directly heated tetrode that would be interesting to consider it for a plate-to-grid (Schade) feedback configuration. With its 30W of anode dissipation capability, it’s a good candidate for an output stage. However, it’s quite likely that you will have to drive it in A2 to get the most out of this valve. Like designs using 811a and similar transmitting valves, the HY1269 can be operated in class A2 even with no signal on the grid.

As per my “Robustiano” design using the 6P21S, it would be nice to see extracting 6W or more out of this transmitting valve. I’m sure that the thoriated-tungsten touch will provide a lovely sound if properly implemented.

Continue reading “HY1269 curves”

6P21S tetrode curves and model

Time ago I generated the tetrode curves for this great directly heated tetrode using my analog curve tracer. I originally used this tetrode in triode-mode. Although it’s a good candidate for a SET amplifier with its 21W in triode-mode, I always wanted to find out how it will perform with Schade-type anode to grid feedback. Building an accurate beam-type tetrode model was key. Luckily now, Derk Reefman has developed an accurate model for these type of valves.

I also worked with Ronald Dekker and insisted him to build in the “Schade” feedback capability in the uTracer using software rather than hardware:

Continue reading “6P21S tetrode curves and model”

4П1Л / 4P1L Pentode Curves

A versatile CCS load

I’m a heavy user of CCS loads. I generally use them to test my valves regardless of using my curve tracer or not. I tried multiple CCS types in the past with good results until I ended up burning one FET or protection zener or whatever due to the abuse of it.

Testing high current loads is not easy at high voltages. The DN2540 is rated at 400V. Not enough. You can use an expensive 01N100D which is another depletion 1KV MOSFET that has a lower Ciss (54pF against 200pF) or you can look at the cheaper enhancement FETs which require a different bias arrangement. If we are looking at modifying the classic cascode self-bias pair, it is a convenient opportunity to improve the VDS bias of the lower FET to improve the frequency response by lowering the Ciss. Remember that in a FET the Ciss is proportional to the VDS. The classic cascode pair has a disadvantage as the lower FET is biased with VDS lower than 1-2V to ensure the upper FET is biased correctly.

Continue reading “A versatile CCS load”