HELP Schematics for RL 12 T 15

[tubeman813]

Hi to all,

I am looking for a suitable circuit for the RL 12 T 15 tube.

It is a 15 W indirect heated triode.

I only found the schematics from "Darius".

Has somebody other informations or circuit?

What driver for RL 12 T 15?

Is the RV 12 P 2000 a good choice?

Thanks for the help.

[45]

Originally Posted by tubeman813

Hi to all,

I am looking for a suitable circuit for the RL 12 T 15 tube.

It is a 15 W indirect heated triode.

I only found the schematics from "Darius".

Has somebody other informations or circuit?

What driver for RL 12 T 15?

Is the RV 12 P 2000 a good choice?

Thanks for the help.

Lucky you! It's an interesting device.

I would try 425V/30mA, bias -20V. Using a 10K load should give 4W at 5% THD. However it's "moderate" Class A2. You need 60V p-p (i.e. 21.2 Vrms) that means you have to swing the grid between +10V and -50V.
The voltage swing is rather low in comparison to other triodes of the same class but you need some power to drive the grid. You could use a good 1:1 interstage transformer (like the Lundahl 1671/30ma) and the 6H30 at 140-150V/20-22mA.

Cheers,
45

[tubeman813]

Dear 45,

thank you for your support.

I am not a great circuit designer.

Can you help me to draw a circuit for this Amp?

I have started, but I am not sure.

Also the OPT I am not sure how many K.

You say 10 K, I have heared other saying 16 K OPT.

I also think 425 V at 30 mA is a little low.

I like to use 500 V at 25 mA - this tube can run 800 V.

Output approx. 4 W RMS - hopefully.

I will attach my "idea" of the circuit.

[45]

Originally Posted by tubeman813

Dear 45,

thank you for your support.

I am not a great circuit designer.

Can you help me to draw a circuit for this Amp?

I have started, but I am not sure.

Also the OPT I am not sure how many K.

You say 10 K, I have heared other saying 16 K OPT.

I also think 425 V at 30 mA is a little low.

I like to use 500 V at 25 mA - this tube can run 800 V.

Output approx. 4 W RMS - hopefully.

I will attach my "idea" of the circuit.

From you schematic it is clear that you don't want to go into positive grid. RC coupling is not suited for Class A2.
The max driving voltage would be 50 V peak-to-peak in your design.
Using 10K load you would get max 2.8W with 8-10% distortion.
Using 16K you would get max 2.5W with 7-8% distortion with the same driving voltage.
In general I do not recommend 16K because you will not find easily such transformer. It is very difficult to do, the only amplifier using a 16K transformer is the Kondo Audio Note Ongaku, in my knowledge!!
You could use a 8K transformer and connecting a 8 ohm speaker to the 4 ohm secondary in order to get 16K but probably you will not get a good response at low frequency. If you want to try, look for a 8K transformer with high primary inductance.

If you go for class A2 operation you can use 10K at 425V/30 ma and will get 4W with lower distortion. However you cannot use RC coupling.


I don't know the input pentode in your schematic however I would not use 500K grid resistor for the RL12T15. It is too high. I would use 220K max.

In your design you can use almost any triode with moderate internal resistance like the 6SN7, because 50V peak-to-peak (i.e. 17.7 Vrms) are not difficult to get.
If you use the 500V for the output stage you can add another RC filter and get 350-400V supply for the 6SN7. Anode resistor 47-56K, cathode resistor 1-1.2K.


Cheers,
45

[tubeman813]

Dear 45,

thanks a lot for your idea.

Let me think about my next step.

[tubeman813]

Dear 45,

I will go for the 16 K OPT.

I have ordered a pair - but it will take a while.

I also will use 430 V and 30 mA - better ratio.

I still think for driver tube.

But RV 12 P 2000 will do.

I add the loadline for RL 12 T 15.

[45]

Originally Posted by tubeman813

Dear 45,

I will go for the 16 K OPT.

I have ordered a pair - but it will take a while.

I also will use 430 V and 30 mA - better ratio.

I still think for driver tube.

But RV 12 P 2000 will do.

I add the loadline for RL 12 T 15.

With 16K better to go for 500V/27-28mA. The cathode bias should be 25-26V.
The power output will be approx. 2.5-2.7W.



Cheers,
45

[45]

P.S.

Where do you buy a 16K transformer?

[tubeman813]

Hi 45,

I ordered the 16 K OPT from Gerd Reinhoefer Elektronik.

The site is only in German.

Here the link for SE OPTs:

Eintakt

He have many very good OPTs.

Next week I get a pair universal Cut Core OPTs, 2,5, 3,5 K 4 and 8 Ohm, 15 Watts, local made.

But really good staff, cannot wait.

Also not that cheap.

Cheers,

[tubeman813]

So, I got my 16 K output transformers.

It took a long time to get these OPTs.

There was some attempts of winding them.

I will run RL 12 T 15 with 500 V at approx. 30 mA.

I will get the power transformers soon.