Category: valve tester

6ж52п / 6Z52P in triode mode

I have only one 6ж52п which measures within specs:

Operating point in pentode:

  1. Ia=42.1mA @ Va=150V/Vs=150V
  2. gm=4.47mA/V
  3. Is=4.4mA

Triode curves:

6z52p triode

 

Triode SPICE model:

6z52p triode SPICE model-published

 

And resulting SPICE model:

**** 6Z52P TRIODE ******************************************
* Created on 11/17/2013 19:25 using paint_kit.jar Version 2.4 Beta. May 2013 
* Curve traced and model by Ale Moglia 2013 valves@bartola.co.uk
* Curves image file: 6Z52P TRIODE
* Data source link: www.bartola.co.uk/valves 
*----------------------------------------------------------------------------------
.SUBCKT TRIODE_6Z52P 1 2 3 ; Plate Grid Cathode
+ PARAMS: CCG=13.5P CGP=0.5P CCP=2P RGI=2000
+ MU=76.5 KG1=34.7 KP=252 KVB=1272 VCT=-0.11 EX=1.39 
* Vp_MAX=200 Ip_MAX=200 Vg_step=0.5 Vg_start=0 Vg_count=8
* Rp=4000 Vg_ac=55 P_max=11.2 Vg_qui=-48
* X_MIN=64 Y_MIN=48 X_SIZE=421 Y_SIZE=530 FSZ_X=995 FSZ_Y=675 XYGrid=false
*----------------------------------------------------------------------------------
E1 7 0 VALUE={V(1,3)/KP*LOG(1+EXP(KP*(1/MU+(VCT+V(2,3))/SQRT(KVB+V(1,3)*V(1,3)))))} 
RE1 7 0 1G ; TO AVOID FLOATING NODES
G1 1 3 VALUE={(PWR(V(7),EX)+PWRS(V(7),EX))/KG1} 
RCP 1 3 1G ; TO AVOID FLOATING NODES
C1 2 3 {CCG} ; CATHODE-GRID 
C2 2 1 {CGP} ; GRID=PLATE 
C3 1 3 {CCP} ; CATHODE-PLATE 
D3 5 3 DX ; POSITIVE GRID CURRENT 
R1 2 5 {RGI} ; POSITIVE GRID CURRENT 
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N) 
.ENDS 
*$

4-65a Triode Curves

Tracing the transmitter valve curves

20131102-171745.jpgI posted several times about my 4-65a SE Amplifier and also traced in the past the curves using my analogue curve tracer to get a view of the loadlines of this fantastic DHT in triode mode.

Now that I have the uTracer I traced again the curves including grid current and A2 anode curves which are very handy for this type of transmitter valve.

My tests were conducted with the following heating and bias setup:

  • DC heater using Rod Coleman regulator @ 6V and 3.5A
  • Cathode connection to the negative filament terminal of the regulator and valve.

Continue reading “4-65a Triode Curves”

4P1L model improved

 Improving the DHT model in A2

After playing for some time with the uTracer, I found that the tracer wasn’t measuring accurately A2 curves. Ronald clearly advised me (as explained on his site) that uTracer wasn’t designed for this purpose although there was a great trick to use the screen driver to generate the A2 curves and also measure grid current. Measuring grid current is key in A2 mode so a better grid current model can be derived to better simulate the non-linear and low impedance behavior of the grid in positive bias.

My incarnation of the uTracer is not neat. I’m using my existing analogue curve tracer. As shown in the pictures below, my current tracer have a plethora of sockets and just adding right jumper cables for anode, cathode, screen and grid connectors will still give me the flexibility I had with my analogue tracer

Additional 3,300uF capacitor across C13 to help A2 traces
My version of the uTracer
uTracer using my analogue tracer sockets 🙂

The process of generating the A2 curves (and SPICE model) starts by plotting the normal curves. The uTracer is great for this. Then you have to overlay the A2 curves in Excel (or whatever tool you prefer) to combine both set of curves.

Continue reading “4P1L model improved”

uTracer up and running

After a stupid mistake which blew the PIC, I finished today my version of the uTracer. A quick trace of an CX-226 RCA Radiotron can be seen below. This is an incredible digital tester. I need to test it properly and do some comparisons against my analogue tracer, but as everyone would expect,the digital tracer has superior capabilities in terms of data manipulation and representation.

Highly recommended. Ronald provides a sterling service and specially when I damaged the PIC and send me a replacement at no cost!

More to come shortly…cx226 RCA test

Improving the valve curve tracer (part 3)

Didn’t take as long as I thought to build the new anode current sensor for the valve curve tracer. A simple PCB was used to solder directly the components for a quick solution. Here is how it looks:

DPP_0008

 

valve-tracer-sense02

I tested this new circuit with some valves from high transconductance to low current ones. The current amplifier works like a charm. I used a CCS first to calibrate the x10 output and found a great linearity from 1mA up to 100mA. Currently I used my bench power supply to test this but I’m planning to do some major surgery to the tracer and include this sensor inside the main chassis.

With a dual 15V supply the AD8479 can work with up to 600V in common mode. This is perfect for my tracer and can be used to sense anode and screen currents.

Tracing a 49 NOS valve
The proof is in the pudding!
Wired anode current sensor
Curve tracer and new anode current sensor

 

Improving the valve curve tracer (part 2)

After some feedback from the DIYaudio forum clearly the INA122 was a killer in this application as no differential signal was used at the output stage. Despite having an INA122 around, I looked at an alternative option with a good op amp I had at hand. The LM833 is a dual low noise op-amp that can do the trick here:

valve-tracer-sense02

Continue reading “Improving the valve curve tracer (part 2)”

Transconductance tester

Introduction

IMG_0580For some time I’ve been postponing the conclusion of a half-finished project. This is one of the many projects that I have around as many of you, but it was time to complete it as just some minor bits were outstanding.

My interest in measuring valve transconductance was very high since my early days of involvement with hollow state technology. The old valve tester I acquired didn’t measure it, I tried many ways to measuring it with different methods until I settled with using a CCS load and an AC meter as described here.

The problem I found though was that my true RMS AC meter in low scale (i.e. 100mV AC) didn’t like a significant DC voltage drop across the sensing resistor. Not sure why, but either way I wasn’t happy either without decoupling the anode to the sensing part of the circuit when using high voltages.

Continue reading “Transconductance tester”

2e24 DHT

IMG_0369 SMALL It was suggested to me recently by Piotr to explore the 2e24 after looking at the 2e22. This small directly heated pentode have about 10-12W of anode dissipation depending how it’s wired. I suspected this DHT in triode mode will have a high anode resistance so as soon as I managed to get hold of a sample, I submitted it to the mercy of my curve tracer:

Continue reading “2e24 DHT”

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:

6E6P-DR6E6P-E и 6E6P-DR

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!

 

2Ж27Л / 2SH27L / 2Z27L

2J27L photo1

I was looking at my valve stock when I found the 2SH27L/2Z27L Russian universal directly heated pentode and asked myself the question of whether this could be a good candidate for a DHT pre-amp.  This little fellow was developed alongside the 4P1L after the second world war and was intended to be operated by batteries.

IMG_3530If you remove the aluminium screening case, you can discover a lovely valve inside.

 

 

 

Looking at the key characteristics we can see that:

  • Heater voltage: 2.2V
  • Heater current: 57mA
  • Anode voltage: 120V (200V maximum)
  • Anode current 1.9mA (2.5mA maximum)
  • Transconductance: 1.9mA/V

The heater requirements are minimum (120mW) so this could be easily run from batteries. I was intrigued by this valve working in triode-mode. How will perform?

Let’s have a look at the  characteristic curves first:

2j27L triode LARGEThe anode resistance is high, about 12K. The gain is also high for a DHT, so 16 is attractive for a pre-amp depending on the specific use/need.

What about its linearity? Let’s look first at the distortion at low signal levels (1Vrms output):

2J27L THD Vo=1Vrms

The distortion is very low, which is great for the preamp, however looking at the triode performance at large signal levels we can find that the linearity is not that great: 0.2% @ 10Vrms output:2J27L THD2 Vo=10Vrms

Obviously the optimal bias point for low level signal is not good for large signal as grid current kicks in and distortion goes up. Limitations on anode voltage and current may impact our capability of pushing the bias point further right in the curve to avoid grid current al large signal.

If we look to reduce the anode voltage supply we can see that distortion increases but a good compromise point is Ia=2mA, Vgk=-2V and Va=72V in which THD is 0.026% @ 1V rms.

A 70V HT supply is more attractive, however if we think about using this valve in a preamp with a cathode follower output driver like this one, then the HT supply requirements will be enforced by the latter.

Finally, if anyone is interested in playing with this valve and simulate the preamp in SPICE, here is a quick model which I haven’t tested yet:

2j27L spice model2Z27L-Triode SPICE MODEL