6GM8/ECC86 Tube preamp for 30VDC supply

[lineup]

The heater uses 330mA at 6.3V. Which means the heater has a resistance of around 19 Ohm. The circuit I will use switches a resistor of 56 Ohm in parallel with the constant current source. So, for a number of seconds will be like 80mA across the resistor leaving around 250mA across the heater.

Then after the delay there is 327mA for the heater.

Here is my heater circuit:

 

[kodabmx]

Fancy! How much current is this circuit able to provide? Would it do 2X current for 6N6P? EDIT: of course. The 317 can do 1A even if it's fake. Here's my circuit.. SMPS, not battery. LOL

 

[lineup]

The ECC86 system with TDA2050 Gainclone

How much gain would this tube circuit give? The TDA2050 power amplifier needs 0.39 Vpeak at the input.

I have changed the circuit to have 2.7k anode resistor. Across this resistor is like 12V. The triode is coupled in parallel = 1 tube per channel.

 

[lineup]

I got home the material today. Now is time to construct.

Biggest problem are the 2 tube sockets. The tubes are to sit on top of my box. The box is of massive aluminium. Think it is like 2.5mm thick. Now the sockets have a diameter of 21.5mm. That is the size of holes I must make. But how? This is my problem now.

I will order something for my drillmachine - stegborr. Means step-drill. It drills step by step a bigger hole. Can make 30mm holes max.

 

[kodabmx]

I also use a step drill, and it's a vast improvement over a hole saw. 9 pin sockets usually require a 7/8" hole, 22mm is probably easier to find than 21.5mm and will work fine. Here in Canada I can't even find metric drill bits!

 

[lineup]

Yes, the step drill I am buying has a 22mm step. This will do perfect.

 

[kylej1050]

Here in Canada I can't even find metric drill bits!

Metric stepped drills can be had very cheaply online. I just recently acquired a set of them. Not sure why, just wanted to fill out the toolbox.

 

[kodabmx]

Good to know. I'm waiting for this to go on sale: MAXIMUM M2 Steel Step Drill Set, 3-pc | Canadian Tire
But I use these: Mastercraft Titanium Nitride-Coated Step Drill, 2-pc | Canadian Tire They go on sale for $17 every couple of months.

 

[lineup]

This is the one I'm going to order. The price rather high. Like 40 €uro

 

[catd]

Hello!

This kind is more flexible, for any diameter

reichelt.de
BOHRER BS3-30,5

(Can't put the correct link here)

 

[lineup]

Thanks I could search for the BOHRER. Looks really good.

 

[U130421]

According to Philips datasheet ,curves B shows very linear transconductance variation on Va= 25v Ia 5ma Vg=0.7v . At this operating point the tube generates exclusively even order harmonics . It works from 3ma to 7 ma .

 

[lineup]

Yes. -0.7 is a good point. There was another guy in beginning of this thread that mentioned vgs -0.75V I will look at what you recommend. 25V 5mA

This is my latest thinking.. I use 0.70 Volt in the cathode. The anode voltage is 23 Volt. This gives 7 Volt across the anode resistance. This gives a ration 10:1.

Each tube delivers around 4mA and they are in parallel to lower output impedance.

 

[lineup]

I am thinking using slowstart is not necessary.
Not when I will use LM317 in Constant Current mode to supply the tube.

Also I have changed about using TRIODE in parallell.
I now design for using only one half tube per channel.

 

[lineup]

Here is my diagram of Headphone Amp.
Tube does the voltage gain
and a couple of transistors the current buffer.

 

[lineup]

Headphone amp based on ECC86 low volt tube

Today I finally got a good spice model for ECC86.

* ============================================================== 
* ecc86 LTSpice model 
* Rydel model (5 parameters) mean fit error 0.0841046mA 
* Traced by Wayne Clay on 03/31/2021 using Curve Captor v0.9.1 
* and Engauge Digitizer from Philips datasheet. 
* ============================================================== 
.subckt ecc86  P G K 
    Bp  P K  I=((0.06448068329m)+(0.02426328916m)*V(G,K))*uramp((11.97388325)*V(G,K)+V(P,K)+(5.140204023))**1.5 * V(P,K)/(V(P,K)+(0.5451602865)) 
    Cgp G P 2.0p ; 0.7p added (1.3p) 
    Cgk G K 3.7p ; 0.7p added (3.0p) 
    Cpk P K 2.0p ; 0.2p added (1.8p) 
    Rpk P K 1.0G ; to avoid floating nodes 
    d3  G K dx1 
.model dx1 d(is=1n rs=2k cjo=1pf N=1.5 tt=1n) 
.ends ecc86

The provider is @cogsncogs

So, I start this thread again with a new circuit.
The circuit has got rather low THD distortion.

 

[lineup]

The circuit. THD is 0.15%

The voltage gain is like x8.
This is a circuit for 32 Ohms headphone.

 

[kylej1050]

The current handling ability of that little 6GM8 is quite surprising.


Will you be breadboarding this design to give it a listen?