Edcor GXSE5-600-15K for 300B HPA

[merlin el mago]

Could I use the Edcor for 300B for headphone amplifier of 300 ohms and 97 dB/mW?

Ratio is 25:1

15K : 600 ohms

So 300B 2K5 : 100 ohms

Specs:
Wattage 5W
Max. Current 100mA
Primary (input) Impedance 15K Ohms
Screen/Grid Tap 40%
Secondary (output) Impedance Depends on model. (mine 600 ohms)
Frequency Response 40~18K Hz., <1dBu
THD+Noise <0.1% @ 1K Hz.
Bobbin Material Nylon 6/6 GF-30
Flamability Rating Class B 130°C
Core Material M-6 29 ga. grain oriented lamination steel
Secondary Insulation (transformer) Clear air dry polyester varnish
Termination 0.187" (3/16") quick disconnects
Mounting Zinc plated steel channel/frame
Weight 1.2 lbs.
Compliance RoHS & REACH

TIA
Felipe

 

[artosalo]

That depends on the total gain of your amplifier. Do you have other stages than 300B ?
I don't see a problem with that transformer, but since the headphones require very little power, it would be good idea the put an low impedance attenuator between the opt and headphones. Especially if there are more than just 300B as amplifying stage.
This will improve signal/hum ratio.
Also a standard 3k5...5 to 8 ohms opt would be perfect for headphones.

 

[merlin el mago]

300B will need a driver?

 

[merlin el mago]

If driver needed I have 4P1L DHT or 7N7 no DHT.

I use Dave Slage autoformer AVC.

 

[artosalo]

Gain of a 300B stage with EDCOR GXSE5-600-15K and 300 ohms headphones is some -3 dB. It should be sufficient in most cases.
Since headphones are very sensitive, the filament should have DC supply.

 

[audiowize]

I would not use such a low step-down ratio. Your headphones don't need 8000mW into 300 Ohms, and noise will be very high if you try to deliver that.

 

[artosalo]

8 W ??
With a single 300B and EDCOR GXSE5-600-15K:
Some 1.5 Vrms in and 1.0 Vrms to headphones.

 

[audiowize]

True, you won't get 8W with a 15K:600.

 

[merlin el mago]

Could someone help me with the design with only 300B, looking for the net I only get two or more tubes designs?

 

[merlin el mago]

I would not use such a low step-down ratio. Your headphones don't need 8000mW into 300 Ohms, and noise will be very high if you try to deliver that.

True, you won't get 8W with a 15K:600.

????

 

[euro21]

Could someone help me with the design with only 300B, looking for the net I only get two or more tubes designs?

Felipe, most of modern 300Bs microphonic as hell, if you use it as preamp.
Try other tubes.

 

[merlin el mago]

I want to use as headphone amp?

 

[artosalo]

Look at this schematic:



You only need the output tube 300B. Leave both 6SN7 halves away and feed signal into the the grid of 300B. The value of cathode resistor depends on the supply voltage. As a headphone amplifier the 300B can be biased to quite low power dissipation. Some 10 W may be good value to start.

 

[merlin el mago]

All people said dc for heaters to avoid hum?

What B+ and what value of cathode resistor?

 

[artosalo]

Yes, DC for filaments.
Try 250 V +Ub and 820 ohms for cathode resistor.

 

[audiowize]

If you have just the 300B and a 15K:600 transformer, you will have negative voltage gain from your circuit.

 

[artosalo]

I told that in post.

Gain of a 300B stage with EDCOR GXSE5-600-15K and 300 ohms headphones is some -3 dB...

 

[merlin el mago]

One stage amp invert phase, right?

 

[audiowize]

I told that in post.

Yes, apparently once wasn't enough to derail this idea.

 

[artosalo]

One stage amp invert phase, right?

Yes (when common cathode connected).