811a SE Amplifier with a twist

Goodbye Jon

Sadly, yesterday heard the sad news that our friend Jon Finlayson from the London Audio Circle passed away.  Jon was an incredible person, a true music lover and passionate about life. He introduced me to most of the circle team members and enjoyed thoroughly the meeting at his place and listen to his electrostatic speakers and constantly evolving system.

I learnt such a great deal of stuff from him and will remember our conversations and how passionate and meticulous he was into doing things. In particular when I built my Starlight CD player and he helped me out with the DAC ladder resistor matching.

See you on the other side Jon.

The 811a amplifier

The last year of the pandemic allowed me to do some experiments whilst being more at home. I hooked up an 811a on the bench with the following circuit:

I reused my original D3a driver from the 300B SE Amplifier. That was an easy choice and speed up my building process. I added a PMOS driver for a “plate to grid” feedback. The feedback network was somehow tricky to trim as had limited resistors available but the combination of 2 39KΩ resistors and a 18KΩ resistor worked well. The follower helped with driving the positive grid current which is about 16mA on idle at 22.5V bias or so. The bias is actually adjusted with a positive regulator set to about 50V on the PMOS gate.

I ended up building a PCB for the PMOS driver, very simple but effective.  I used an SMPS for the filament supply and was good enough for testing purposes.

The iron was some Lundahl gapped at 90mA which I had at hand, but can be anything you want.

Power? Oh yes, could extract 16W at about 1.5% and think measured 18W before clipping.  Distortion at low power (e.g. 2W) was less than 0.4% so a nice beauty to listen to. I love the sound I got out of it, not my normal listening system and couldn’t move the whole Frankenstein down to where my speakers are with the kids around and 600V all over it (long are gone those days where 600V were everywhere in my music cabinet).

 

 

D3a Spice Model (Pentode & Triode)

My latest 300B amplifier brought me again closer to the D3a. I have to say it’s an exceptional driver for this amp as well as it can perform in a phono stage at same excellent level.

I took the opportunity to trace again one Siemens D3a NOS boxed as “POS 1.176 Q 31-X 601”. This one was handpicked as it measured at 102% (31mA) in triode mode with a Gm of 39mS.

I wanted to develop a pentode model for phono experiments so put this lovely valve back in the eTracer and used the Extract Model tool from Derk Reefman to develop the model below.

Continue reading “D3a Spice Model (Pentode & Triode)”

300B SE Amplifier Finished!

When everything was going to plan…

This build became one of the quickest and eventually the most painful from all, perhaps not really. However, it was very challenging in the end. I will tell you why in more detail. Yet, it has been a fantastic learning experience.

Continue reading “300B SE Amplifier Finished!”

E282F HP Amp

First and foremost, Merry Christmas! I hope you’re having a great time with your loved ones and good music.

Without a mood for public introspection this time, I have to say that I will celebrate this holiday the best I can. I will be hosting today with a lot of meat, wine and single malt. What else can I do? When I escape from the little ones, will get back to spin some records and hopefully work on the projects.

Merry Christmas to everyone

Headphone Amp Quest Continues

Obviously, I needed to pursue this project further. I’ve been lately listening a lot to HPs as simply is the best choice for me when the young family is in bed. In addition to this, I find the HP setup to force me to connect a bit more to what I’m listening to as I don’t get easily distracted.

Continue reading “E282F HP Amp”

D3a driver w/ Rev08 board

A friend from Canada ordered a pair of boards and I used the opportunity to test the newly arrived hybrid mu-follower (aka as gyrator) Rev08 PCBs.  He will be using these boards in the 300B design posted here.

Continue reading “D3a driver w/ Rev08 board”

A simple line stage

Driving your amp

A typical challenge we may all face is how to drive effectively our amp via a stepped attenuator or an AVC. I have a 4P1L preamp which drives very well my AVC, however, I have now an LME amp which has a wimpy input impedance of less than 7K.

How do we deal with this? A simple line stage which is capable of driving the low impedance of the amp is what we need in this case. Several options are available, however I settled down for a simple cathode follower.

Why? Because I love valves, and I wanted to play around a cathode follower design here.

vinilo A heavy load for your preamp or music source may increase distortion and we don’t want that.

I set myself the challenge to design a simple linestage with a minimum number of power supplies. I could have gone for a MOSFET follower, but hey: I wanted some hollow state stuff in there! Ok, if we look into a cathode follower as the core design, this means that we need at least an HT supply and a filament supply. If we could leverage a bucket converter, we could provide the HT from a LT transformer, probably best to look into two windings to separate the filament supply from an HT one. There are cheap ready build step-up converters for peanuts, and this is what tempted me to explore this solution.

I tested recently some step-down bucket converters and was encouraged by the noise levels and the FR.

The first design, getting us started

Continue reading “A simple line stage”

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”

C3g and D3a triode SPICE models

Using my C3g and D3a triode curves, I developed the following SPICE models:

D3a triode SPICE

 

** D3A TRIODE ************************************************************
* Created on Sat Jan 12 09:17:53 GMT 2013 using tube.model.finder.PaintKIT
* model URL: http://www.bartola.co.uk/valves/valve-curves/d3a-triode/
* Created by Ale Moglia valves@bartola.co.uk
*--------------------------------------------------
.SUBCKT TRIODE_D3A 1 2 3 ; P G K ; 
+ PARAMS: CCG=6.7P CGP=3.3P CCP=1P RGI=2000
+ MU=72.1 EX=1.456 KG1=65.625 KP=534.0 KVB=300.0 VCT=0.0557 ; Vp_MAX=500.0 Ip_MAX=0.07 Vg_step=0.5
*--------------------------------------------------
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 
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 ; FOR GRID CURRENT 
R1 2 5 {RGI} ; FOR GRID CURRENT 
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N) 
.ENDS 
*$

C3G triode SPICE modelC3g triode SPICE

 

** C3G TRIODE ************************************************************
* Created on Sat Jan 12 09:40:08 GMT 2013 using tube.model.finder.PaintKIT
* model URL: http://www.bartola.co.uk/valves/valve-curves/c3g-pentodetriode/
* Created by Ale Moglia valves@bartola.co.uk
*--------------------------------------------------
.SUBCKT TRIODE_C3G 1 2 3 ; P G K ; 
+ PARAMS: CCG=7P CGP=2.7P CCP=6P RGI=2000
+ MU=50.4 EX=1.428 KG1=199.6875 KP=426.0 KVB=204.0 VCT=0.5760 ; Vp_MAX=500.0 Ip_MAX=0.07 Vg_step=1.0
*--------------------------------------------------
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 
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 ; FOR GRID CURRENT 
R1 2 5 {RGI} ; FOR GRID CURRENT 
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N) 
.ENDS