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Old 13th February 2009, 03:22 PM   #1
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Default help with PSE design

Can anyone in "laymans" terms tell me how to use plate curves in a PSE scenario.

Specifically,

1) I assume each triode "sees" 1/2 of cathode resistor in self bias?

2) That also means total idle current is double that of each triode?

3) How about plate voltage same or half (I think same)?

4) Plotting the load line are the currents all 1/2 and voltages the same?

5) Max plate dissipation I assume I use double the single tube value?

6) I have read the info in this link

http://www.tubecad.com/2007/10/blog0122.htm

Following this method with the curves I have and operating point I want takes me "off the chart" of available info. I think this is because of my confusion of High School Science and "Ohms law".

Does anyone have a similar method tuned to Parallel Tubes? I would like to figure this one out myself which is the reason I am not giving TOO much information as to the tube and such.

Basically what I am after is how to adapt the above method to parallel triodes.

ANY help would be appreciated and I will post my "results" for comment and criticism as soon as I calculate and develop a schematic
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Old 14th February 2009, 03:18 AM   #2
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1. Each tube has a cathode resistor. This prevents one tube from drawing more current than the other and going into thermal runaway. When you select 2 tubes in SEAMPCAD this is shown in the schematic.

2. Total idle current is double.

3. Plate voltage is the same as with one tube.

4. SEAMPCAD plots total current ( 2x one tube ) vs. the votage for a single tube.

5. Max dissipation is double that of one tube. SEAMPCAD may show %dissipation as that of one tube. Again, when 2 tubes are selected in the circuit setup this is adjusted automatically.

6. If the load line plots off the chart go to the setup button under the chart and adjust for a higher maximum current and/or voltage as needed.

Hope this helps.
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Old 14th February 2009, 03:22 AM   #3
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I assumed you were using SEAMPCAD. You may not be. Please realize that the plate resistance of 2 tubes is 1/2 that of one tube which is why twice the current is drawn.
The load resistance is 1/2 that of a single tube, i.e if 5k is recommended for one tube 2.5k could be used for 2.
If you are "off the chart" after allowing for 2x the current your operating point may be wrong.
Use the proper chart for the application, Triode, UL, or Pentode.
Triodes in pure class A SE run at a lower voltage than triodes in class AB1 push pull.
Also, each cathode resistor is calculated as it would be for a single tube.
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Old 14th February 2009, 04:00 AM   #4
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DShortt,

I am not using SE Amp Cad, I haven't made the decision to purchase it as of yet. I have downloaded the PP Design Calc and like it so far. As you are describing I think I just might go ahead and make the purchase of the SE AmpCAD, I might just go ahead and buy the whole shebang.

I don't need to use separate cathode resistors in the case of this tube because it is two pentodes in one envelope with common cathode. (I have probably given away a hint as to the tube).

I have worked it out on paper and think I have a workable design. I will post it soon.
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Old 14th February 2009, 04:09 AM   #5
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Take the graph for one tube and double the current on the y axis. Leave the voltage as is on the x axis.
Use 2x the dissipation for one tube. Use 2x the Ik for one tube. Use 2x the idle current for one tube at the operating point. Now plot a dissipation curve and plot a load line.
Feel free to post results and/or problems. Most here have done this and like to help.
Take time to do this before ordering parts.
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Old 14th February 2009, 04:22 AM   #6
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829B or FU29. SEAMPCAD does not have this tube that I know of. It also only defines tubes as triodes, a 6550 is assumed to have the screen grid tied to the plate. You can define a tube that is not included but only in triode mode.
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Old 14th February 2009, 04:22 AM   #7
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Thanks in essence that is what I did on paper. Unfortunately the 829B is a hard nut to find info on triode mode. The data I found is limited. I posted the rough draft schematic on a new thread.

Please look it over.
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Old 14th February 2009, 04:24 AM   #8
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look here
Attached Images
File Type: jpg 829b se.jpg (39.4 KB, 98 views)
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Old 14th February 2009, 04:30 AM   #9
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OK, I'll follow the new thread.
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