• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

all dht system?

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3A5's mu is about 15, versus good IDHT "phono" tube's (triode or trioded pentode) mu: 50-100.

The DHT tubes best amplification factor is about 30 (for example EML 30a: 32).

I have several 841 DHT tubes (mu=30). It is good VAS device with small distortion even at high swing, but requires enormous plate load (over 250k) and potentially microphonic and hum sensitive. At large (line) input signal it's not issue, but phono input has mV magnitude.

Vinylsavor (Thomas Mayer) like this tube as phono voltage amplifier device loaded by transformers.

I developed phono stage (in LTSpice) with two stage 841s, but amplification is over average (below 40dB). With 3 DHT stages the implementation would be very expensive.
 
Yes, one side of the cathode is the cathode. Eric Barbour used 6.3 vdc to heat it and connected one side to ground. The tube self biases and does not need a cathode resistor. The tube is directly heated.

Looking at the tube as in the pdf diagram -
- high voltage to the top
- input to the grid
- ground
- +6.3 VDC

They are very inexpensive at about $2 each.

6S17K V UHF Triode Tubes Lot of 10 New Boxed | eBay

ray
 
OK you are correct and on closer reading of the blurb it even says indirectly heated.

It really is a curious beast, quite unlike most indirectly heated tubes with the cathode separate from the heater. Looking at the topology of the tube itself, the heater and the cathode are almost one and the same thing.

Perhaps we could say semi directly heated. I wonder if there are other tubes with this topology.

ray
 
OK you are correct and on closer reading of the blurb it even says indirectly heated.

It really is a curious beast, quite unlike most indirectly heated tubes with the cathode separate from the heater. Looking at the topology of the tube itself, the heater and the cathode are almost one and the same thing.

Perhaps we could say semi directly heated. I wonder if there are other tubes with this topology.

ray

The family that these tubes come from are called disc seal triodes . These are indirectly heated types . The DET23 datasheet details how these would be used . Note the cathode is tied to one side of the heater

http://www.mif.pg.gda.pl/homepages/frank/sheets/139/d/DET23.pdf

316a
 
Thanks for the info.

By the way, the datasheet solves a problem for me in that it points out the need for cooling the anode. I have found that the sound would go away when there was not enough ventilation and now I see why. Luckily I was using an alligator clip to hold the anode but now I will add extra mass to the clip.

ray
 
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