The positive feedback encouraged me to record this second video. Unrehearsed rambling on the CX-112a preamplifier. Hope this is useful to many of you and would love to hear your feedback.
Category: DHT
Directly heated triodes (DHT)
EF86 – 300B XLS SE Amplifier build
Here is a very nice build from Dan Kercher on his contraption of the 300B amplifier with auto bias. The driver is an EF86 with SiC diode biasing, the topology is a hybrid mu-follower and a source follower drives the output stage. Filaments are DC with Rod Coleman’s board:
More details can be found below:
Hi Ale, I wanted to thank you for all of your PCBs. I just finished a project that uses your Gyrators, SiC bias boards, and SiC Source Followers. I'm so happy with the results. Details posted on Audio Asylum. https://www.audioasylum.com/forums/tubediy/messages/27/276814.html Cheers, Dan
300b driver experiments
01a preamp
300B Amp in action
I think a gain of about 130-140 should be ok. Perhaps if I get around in adding the 6SF5 stage then it may be good enough.
So this got me thinking. Of course I have on my list 2 driver tests:
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 [email protected]
* (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
300B SE Amp – here we go
A Brave New World
Surely you’re as tired as I’m with COVID-19. One of the best things I can do to distract my mind is to keep myself away from social media. Every stone you turn, there is COVID or a statement about it. I won’t moan as I have a job for now and a healthy family. Some members of my family were infected but nothing major. I can only say is that the world has change. And so my day to day life looking after the young family whilst working is a real challenge. Starting my fifth week of lockdown, I have to distract somehow my mind at times, otherwise will go mad.
A New Concept
01a Preamp from South Korea
Time ago I made a set of gyrator boards for Chul in South Korea. His build skills are amazing and look at his work below. I love the structure and design, it’s simply beautiful.
Mini Hybrid Mu-follower board test
I had a go first at a mini-gyrator board using SMD. Blimey, it’s hard work to get all these crammed into such a small footprint.
I did a quick test with a D3a and worked fine at 100V/10mA (low voltage of course). It was +35dB flat up until a couple of Mhz. Even the over-current LED works!
Footprint is as small as you can get: 45mm x 25mm 🙂
More to report later!
UX-120 DHT
I’ve got hold of a NOS quartet of UX-120 Radiotron valves made in 1925. These are 95 year old beauties. Unbelievable how well conserved they are and operate.
This valve developed by RCA was the first output valve intended to be used with dry-cells (3 No. 6 cells in series). See the data sheet extract below:
There is no much data available on this valve, if you have some please share and let me know. Here are the curves I traced from a sample which measured 114%:
VT-25/801a/10Y DHT Preamp with SiC filament bias
For quite some time now I wanted to share one of the variations of the famous VT-25/10Y pre-amplifier. As usual due to work, business travel and family duties, I’ve struggled to find the time to update the blog.
Continue reading “VT-25/801a/10Y DHT Preamp with SiC filament bias”45 SE Amplifier – revisited
A unique sound
If you have a small room and high-efficiency speakers, then keep reading. If not, you can still enjoy reading about probably the best sounding output valve in my view. The 45. I wrote about it few times and have to say, it’s still one of the best. Better than a 300B but unfortunately can do only 2W. You can use it in Push-Pull and is superb. Have a look at this.