Simple Simple SE questions

[Junior]

Originally Posted by rknize

Those are fine except for C1. If you are using a tube rectifier especially, you really shouldn't exceed 47uF.

hi russ,
thanks for the reply.
am still learn and a lot more to learn since i am not electrically inclined. got to be careful cos do not wish to get myself hurt. what is the reason behind not exceeding 47uf? is it due to the filtering of power noise? (read some article from zero distortion about power supplies meant for chipamp/SS - lower uf is able to filter higher freq noise much faster than higher uf cap). i am assuming C1 & C2 are power supply reservoir cap & am i rite?

hi gasser-dude,
as russ replied, C1 should not exceed 47uf.

[rknize]

It has to do with the peak forward current that must be passed by the rectifier to charge the cap. Since the diode only charges the cap for about 1/4 of the cycle and the cathode can only conduct so much current at a time, this limits the size of that first cap. The data sheets for rectifiers often note this explicitly or via a table. The second cap is sufficiently isolated from the diode that is doesn't matter.

If you have no idea what I am talking about, look here:

http://www.freewebs.com/valvewizard/fullwave.html

[tubelab.com]

what is the reason behind not exceeding 47uf?

Here is my real (overly) simple explanation:

The rectifier tube supplies the power for the entire amplifier. In the Simple SE this means that one tube must pass enough current to feed four tubes, so it has a tough job.

The filter capacitors store a reserve supply of energy to feed these four hungry tubes during times when they want more than the rectifier tube can deliver. They are completely empty when the amp is switched on. The amplifier tubes don't get to eat until the resovoir is full.

Now, upon flipping the power switch the four amplifier tubes get their wake up call, and can sit at the table awaiting the rectifier tube to feed them their breakfast.

The rectifier tube is slapped out of bed, told to immediately begin filling the resovoir before it is awake yet (cathode warmed up) so that the amplifier tubes can have their breakfast. If the resovior (first cap) is too big, the rectifier tube will have a heart attack before it can fill it!

OK, overly simple somewhat stupid explanation, but that is what happens. The rectifier tubes made today seem to be of a lesser quality than those made in the past. If the coating on the cathode is not of a uniform thickness, and the plate to cathode spacing is not constant, the problem is worse.

The rectifier tube must begin to pass current as it is warming up. If the spacing inside the tube is not uniform the current will flow in one localized area, leading to fireworks inside the tube. For this reason the first cap (C1) should be kept as small as possible. If a choke will be used, a 33, or 39 uF cap might be a better choice than a 47 uF.

[P.R. Audio]

Hi everyone, I was thinking about build a second Simple SE. I was wondering if I need C12 and C22 if I am not using CFB. I was going to build it point to point. Or does that grid need to be connected to something?
I am going by the schematic on the website.
I am new at this.

[DualTriode]

Hello George and All,
This thread looks like the place to ask Simple SE questions. I am the proud user of two Simple SE’s. Just for grins I have been rolling tubes and transformers with speakers and headphones with and without feedback. The question came to mind regarding output impedance and the impact on bass response. George I recall you recommending against testing against with no load connected. There was also mentioned a spreadsheet that would calculate the Zo using two different connected load values. Is it possible to post the procedure and spreadsheet?
Thank You
DT
All just for fun!

[MellowTone]

Originally Posted by DualTriode

Hello George and All,
This thread looks like the place to ask Simple SE questions. I am the proud user of two Simple SE’s. Just for grins I have been rolling tubes and transformers with speakers and headphones with and without feedback. The question came to mind regarding output impedance and the impact on bass response. George I recall you recommending against testing against with no load connected. There was also mentioned a spreadsheet that would calculate the Zo using two different connected load values. Is it possible to post the procedure and spreadsheet?
Thank You
DT
All just for fun!

When you say no load connected, I assume you're referring to having nothing connected to the OPTs with the amp on? If so, very very bad idea. Pretty quick way to kill tubes and components in that area of the amp IIRC.

[DualTriode]

Hello,
I searched online for a output impedance test procedure. The procedure that I recall involved testing one condition with say a 8 ohm load attached and another with only the Volt meter attached. Yes with the amplifier on. Yes I know that this is bad pie.
I have given this some thought. The finger experiment goes this way.
My target amplifier has a 5000 ohm to 300 ohm output transformer. If my thought process is correct the load and the amplifier internal resistances are in series. If I connected load is 300 ohms the resistance will be 300 + Zo. Now put a sine at the input and adjust the input voltage to end up with a nice round 10 volts at the output. Now adjust the connected load so that the output voltage is half (5) of the original 10 volts. The total series resistance will now be double the original. Now measure the connected load resistance divide by 2 subtract 300 and that is the output impedance.
What do you think? Did I go south?
DT
All just for frun!

[P.R. Audio]

Hi I was just wondering if anyone has ever put in a Treble control on their Simple SE? If so does anyone have a schematic?