SONY C17B 6DH3 tube replacement question

[la-2a]

Hi, I want to replace the 6DH3 tube in a Sony C17B (CP-3 PSU ) which is making a lot of noise. There are a few candidates available. The problem is that I measure 250V on the tube. I'm not sure whether a 5840, 5703, 6S6B-V can handle the high voltage. The heater voltage is 6.2V. What do you think, will this work? Unfortunately I have little experience with tubes. Would it make sense to reduce the voltage and how? Thanks for your suggestions. Check the attach files.

 

[capacitorless]

If you haven't seen this thread about the 6s6b-v already, there is some great information about that tube.

 

[la-2a]

Thanks for your suggestion. I looked at the specifications of the 6DH3 tube and the maximum anode voltage is 160V. The comparison tube AC 701 can manage a maximum of 200V. My question is whether I need to modify the power supply or whether the replacement tubes 5840 , 5703 can actually handle 230V. I was a little confused that the original tube in the C17B has 230V at the plate according to the schematics, even though the tube specifications say 160V.

 

[capacitorless]

It looks like the 6s6b(-v) goes up to 250v on the plate depending upon operating conditions.

I had to retrieve the English datasheet translation that's linked in the above thread from the Internet Archive (great place to send donations) and it's attached in pdf format.

One comment made is about running that tube at a reduced heater voltage, to reduce heat buildup. It uses 200ma of filament current at the rated voltage, fwiw. Hope this is helpful.

 

[Khron]

Thanks for your suggestion. I looked at the specifications of the 6DH3 tube and the maximum anode voltage is 160V.

Yes, ANODE voltage, as in "voltage between anode and cathode". As in, not necessarily "overall supply voltage"

Most tube stages will have at least one resistor between the tube and either supply rail (B+ or ground), if not both. With some current flowing, there WILL be some voltage drop across said resistor(s) - Ohm's law, anyone?

So while not impossible, the tube is somewhat unlikely to see the full supply voltage across it - only if it ends up completely closed / non-conducting, when the input signal is at its most negative, but that will be beyond the clipping point.

 

[capacitorless]

I just wanted to point out the the CP-3 schematic shows a 200v option on the secondary of the power transformer.

 

[mjmajilton]

Yes, ANODE voltage, as in "voltage between anode and cathode". As in, not necessarily "overall supply voltage"

Most tube stages will have at least one resistor between the tube and either supply rail (B+ or ground), if not both. With some current flowing, there WILL be some voltage drop across said resistor(s) - Ohm's law, anyone?

So while not impossible, the tube is somewhat unlikely to see the full supply voltage across it - only if it ends up completely closed / non-conducting, when the input signal is at its most negative, but that will be beyond the clipping point.

Continuing that thought, at 0.7ma of current, the cathode will be at 140 volts.

 

[la-2a]

Thank you @capacitorless great suggestion, I totally overlooked it. I was able to reduce the voltage by 40V. Now I measure on the connected microphone B+ Voltage pin 2 to 4 = 215V and pin 2 to 3 = 177,4V. Despite the new tube, the microphone has noticeable noise.