Help with schematic understanding

sumo · 30th April 2009, 04:52 PM

Hi, recently I've been looking for a 2A3 based SE amp to build and I have come across this page:

http://www2u.biglobe.ne.jp/~tossie/YZ-2A3-J.html
(This guy has a LOT of amp designs with schematics and pictures. Delete the "YZ-2A3-J.html" from the link. Worth a look!

)

Its in Japanese but the schematic is pretty clear and there's a close up of the innards which helps a lot but, I am unsure about one thing

In the schematic there is a connection from one of the 6.3v filament wires from the transformer to between a 39k and 100k resistor. Its marked 65v. This is the first time I have seen this and I was wondering if anyone knows what it might be for? Some kind of bias?? Now I'm a bit a noob still so this might be a bit of a stupid question but I'd really appreciate some of your knowledge

Thanks!

zigzagflux · 30th April 2009, 05:10 PM

Looks like they are elevating the 6.3V supply for the IDHT to a positive 65V DC. Having a positive heater with respect to the cathode keeps noise down.

Poindexter · 30th April 2009, 06:11 PM

It also keeps the Vh-k rating of the driver tube from being violated. You might want to go to the TDSL and see what that rating is for the 6C8G. I'm not familiar with the tube.

I disagree strongly with the way this is implemented here. I don't like to attach it to only one side of the heaters, as we can get a hummy circuit this way. If there's a center tap on the 6.3v winding, attach it there. If there's not, use a pair of splitter resistors to attach it to both sides of the heater line, as see:

Aloha,

Poinz
AudioTropic

sumo · 1st May 2009, 06:21 PM

Thanks for the help guys

That helped a bit. But what is Vh-k ? Its not in all the spec sheets. Is it Plate voltage? Or voltage between the heater and plate or something?

pointy · 1st May 2009, 06:30 PM

it may mean the directly heated cathode (see image)

leadbelly · 1st May 2009, 06:35 PM

Quote:

Originally posted by sumo
Thanks for the help guys
That helped a bit. But what is Vh-k ? Its not in all the spec sheets. Is it Plate voltage? Or voltage between the heater and plate or something?

It's the maximum allowable voltage between heater and cathode. It is in every full datasheet, just not necessarily identified as Vhk. V could be a U, k could be c, and so on.

sumo · 3rd May 2009, 12:07 AM

Aha! Thanks for that! Now it makes a bit more sense

30th April 2009, 04:52 PM	#1
sumo diyAudio Member Join Date: Jun 2008	Help with schematic understanding Hi, recently I've been looking for a 2A3 based SE amp to build and I have come across this page: http://www2u.biglobe.ne.jp/~tossie/YZ-2A3-J.html (This guy has a LOT of amp designs with schematics and pictures. Delete the "YZ-2A3-J.html" from the link. Worth a look! ) Its in Japanese but the schematic is pretty clear and there's a close up of the innards which helps a lot but, I am unsure about one thing In the schematic there is a connection from one of the 6.3v filament wires from the transformer to between a 39k and 100k resistor. Its marked 65v. This is the first time I have seen this and I was wondering if anyone knows what it might be for? Some kind of bias?? Now I'm a bit a noob still so this might be a bit of a stupid question but I'd really appreciate some of your knowledge Thanks!

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30th April 2009, 05:10 PM	#2
zigzagflux diyAudio Member Join Date: Oct 2006	Looks like they are elevating the 6.3V supply for the IDHT to a positive 65V DC. Having a positive heater with respect to the cathode keeps noise down.

30th April 2009, 06:11 PM	#3
Poindexter diyAudio Member Join Date: Oct 2004 Location: Maui, Hawai'i, USA	It also keeps the Vh-k rating of the driver tube from being violated. You might want to go to the TDSL and see what that rating is for the 6C8G. I'm not familiar with the tube. I disagree strongly with the way this is implemented here. I don't like to attach it to only one side of the heaters, as we can get a hummy circuit this way. If there's a center tap on the 6.3v winding, attach it there. If there's not, use a pair of splitter resistors to attach it to both sides of the heater line, as see: Aloha, Poinz AudioTropic

1st May 2009, 06:21 PM	#4
sumo diyAudio Member Join Date: Jun 2008	Thanks for the help guys That helped a bit. But what is Vh-k ? Its not in all the spec sheets. Is it Plate voltage? Or voltage between the heater and plate or something?

3rd May 2009, 12:07 AM	#7
sumo diyAudio Member Join Date: Jun 2008	Aha! Thanks for that! Now it makes a bit more sense

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