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nodiak 22nd June 2008 12:55 AM

Simple Simple SE questions
Can I omit the board mounted C1 and C2 electrolytics and instead use motor runs (that I'll mount on the top plate)? If so should I match exact values of 120uF and 47uF? ( I have 100uF and 50uF motor runs so far).

Certainly more questions to follow. In fact if any one else wants to use this thread for S SE build questions please feel free. I'm sure I'd like to read the answers as well.

Thanks, Don

I'm one of the worst at getting this project finished. Am making another surge to get more done.

Tubelab_com 22nd June 2008 02:19 AM

Yes, you can leave the board mounted caps off of the board and use external motor run caps. No they do not need to be the exact value. The values that you have will work fine.

nodiak 22nd June 2008 03:55 AM

Good deal. Thanks George.

alexmoose 22nd June 2008 05:52 AM

Hey Mr Tubelab,

recently when you turned a Simple SE into a PP amp, and you used Local (plate to grid) feedback, did you ever think of how this could be implemented in the Simple SE? I really want to try this out, it may just be the fix to my Fostex problems See my other thread.

Thank you


Tubelab_com 23rd June 2008 12:38 AM

The feedback could be applied the same way with a resistor from the 12AT7 plate to the output tube plate. Something in the 100K up range. In theory it is not going to work, but I haven't tried it. Plate to grid feedback relies on a driver with a relatively high output impedance. If the driver had zero output impedance there would be no feedback. A triode driver has a low output impedance which does not remain constant with applied signal. A pentode has a fairly high and constant output impedance which is why you see this done with pentode drivers.

I had wired the triode driver in a cascode (with a mosfet for the upper device) for my experiments. This configuration kind of works like a pentode. Serious board butchery was required to do this. I have plenty of boards, and 3 that are built up for experiments, so I am not afraid of ruining one. That particular board is on its way out since it got coated with capacitor goo when I got carried away blowing up 6V6's. I can take all of the parts off of a board using a propane torch and use them to build a new board. It takes me about an hour total.

Ty_Bower 23rd June 2008 01:19 AM


Originally posted by
I can take all of the parts off of a board using a propane torch and use them to build a new board...
I wish I could see a video of that... :)

alexmoose 23rd June 2008 01:22 AM

Okay! this is very informative, However, The Reason I ask is a bit different, which is why I must ask another question.

Mr. Nelson Pass recommends that full range drivers be powered with a current source amplifier (Pentode). So when this local feedback is applied to a pentode (giving it Triode-like curves), Does it still behave as a current source, or does it become a Voltage source like its cousin the Triode?

Tubelab_com 23rd June 2008 02:00 AM


I wish I could see a video of that..
OK, maybe next time I do some I can make a video. I have a few boards laying around that I want to take the sockets off of. The process isn't complicated, but does make a stink, so it must be done outside.


Mr. Nelson Pass recommends that full range drivers be powered with a current source amplifier
Some full range drivers like to be fed with a current source, not all. A current source has a high output impedance, and a very low damping factor (near zero). Many speakers will exhibit poor bass control when driven with a current source. A voltage source has a low output impedance resulting in a very high damping factor.

A pentode tube has a high output impedance. A triode has a far lower output impedance. NFB applied to either tube will lower its output impedance. The higher the feedback, the lower the output impedance. Most pentode amplifiers have feedback applied to lower the output impedance even if the distortion is already low enough.

The output impedance of a non feedback SE pentode amplifier can be in the range of 6 to 10 ohms. A non feedback triode can be in the range of 2 to 4 ohms. These are neither good voltage or current sources. A typical solid state amp with a big bunch of feedback can be in the range of 0.01 ohms, nearly a "perfect" voltage source. Nelson's "First Watt" series of solid state amps have a high output impedance (100 ohms maybe) making them look like current sources. The literature that I read explains that they were not for just any speaker.


Does it still behave as a current source, or does it become a Voltage source like its cousin the Triode?
If you apply feedback to a pentode it will begin to look like a voltage source. Apply enough feedback to any tube amp, and it will start to look, and sound like a solid state amp, if there is enough gain to support the feedback.

ciagon 23rd June 2008 06:46 AM

I have a couple beginner questions as well.

I just recently learned about motor run capacitors but I don't fully understand why people use them. They seem to be much larger and more expensive that electrolytics. Is there an advantage of using them (other than cool looks)?

Also, has anyone added a headphone jack to a Simple SE? If so, I am curious if you used resistors or a transformer and what values were used.

spacemen12 8th November 2009 01:56 PM

I am looking to built a simple se and I have some questions:
1. What are the characteristics that I should look for a choke for this amp (Inductance, DCR, current)? I know c-14x and c-24x from Triad, and Hammond 193[J-H] would work, but I may get something in a local surplus center.

2. What is the difference between "metal oxide film" and "metal film" resistors? How can I make the difference between the two in a surplus store?

3. Is the FRED diode failure problem solve? Is it still there if there is no standby switch?

4. Fellow Canadian, what is the best method to achieve low shipping cost (with brokerage and all the hidden fees)? I am particularly thinking of the output transfo and power transfo (heavy).


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