Kalamazoo Model One

[Gerry Rzeppa]

I came across this little beauty today and was wondering how they manage to get away with leaving out the usual caps on the cathode circuits. What effect does that have on the amp's performance, reliability, etc?

[cbass]

I guess it improves an amps reliability less electrolitics. To dry up. They aren't getting away with anything. Adding the cathode bypass caps would increase the gain at all frequencies being produced if its big enuff . you can boost just the higher frequencies with a smaller cap

[cbass]

Also I suppose an el84 is easier to drive than a 6v6 so not as much preamp gain is needed

[Jana]

It was cheaper to make--electrolytics cost money in those days. Either that or they were concerned with the flow backing up and having to call a plumber.

[Bob S]

What Jana said.

[Gerry Rzeppa]

Thanks, guys. Your responses, in conjunction with a nifty calculator I found, tell me all I need to know. The calculator is here:

http://www.ampbooks.com/home/amplifier- ... capacitor/

[cbass]

Yup they got some nifty calculators ultimately its up to the ear though

[tubeswell]

I hope Jana's plumbing analogy is sinking in.

Another way of saying this is that the cathode bypass caps shunts any AC that would otherwise appear in the (unbypassed) cathode resistors to ground. In case that might confuse Gerry; in terms of 'electron flow', the electrons are being pulled from the ground return, through the cathode resistor, on their way to be boiled off from the cathode, and then head towards the plate. With each subsequent increase and decrease in tube beam current (that results from corresponding changes in grid voltage), the voltage across an unbypassed cathode resistor would otherwise increase or decrease - in proportion to the tube current and the cathode resistor's resistance. This reduces the overall plate-to-cathode voltage (and hence reduces the voltage gain) within the gain stage from what it otherwise would be with a bypass cap in place.

But the effect of the bypass cap is that it discharges (electron-replenishes) on the 'increasing' tube current part of the signal cycle, and then releases that (+ve) charge (electron-depletion), as the plate sucks some elections out of the +ve pole of the bypass cap, during the otherwise decreasing-tube-current part of the signal cycle. In this way the cap charging supplements the periods between peaks of tube current going through the cathode resistor. The overall effect is to hold the cathode voltage relatively constant w.r.t. the plate. This enables more (plate-to-cathode) voltage gain throughout the signal cycle. The bandwidth of this 'extra' gain is determined by the RC combination of Rk and Ck - and we get back to our frequency equation which you know all about Gerry.

[LeftyStrat]

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[Gerry Rzeppa]

Another way of saying this is that the cathode bypass caps shunts any AC that would otherwise appear in the (unbypassed) cathode resistors to ground. In case that might confuse Gerry; in terms of 'electron flow', the electrons are being pulled from the ground return, through the cathode resistor, on their way to be boiled off from the cathode, and then head towards the plate. With each subsequent increase and decrease in tube beam current (that results from corresponding changes in grid voltage), the voltage across an unbypassed cathode resistor would otherwise increase or decrease - in proportion to the tube current and the cathode resistor's resistance. This reduces the overall plate-to-cathode voltage (and hence reduces the voltage gain) within the gain stage from what it otherwise would be with a bypass cap in place.

But the effect of the bypass cap is that it discharges (electron-replenishes) on the 'increasing' tube current part of the signal cycle, and then releases that (+ve) charge (electron-depletion), as the plate sucks some elections out of the +ve pole of the bypass cap, during the otherwise decreasing-tube-current part of the signal cycle. In this way the cap charging supplements the periods between peaks of tube current going through the cathode resistor. The overall effect is to hold the cathode voltage relatively constant w.r.t. the plate. This enables more (plate-to-cathode) voltage gain throughout the signal cycle.

Now that's a very good explanation. It seems that once we get inside a valve, where convention dictates that we talk about actual electron flow, we're all speaking the same language. All I'm trying to do in the other thread is to maintain that same "electron flow point of view" throughout the rest of the circuit.

The bandwidth of this 'extra' gain is determined by the RC combination of Rk and Ck - and we get back to our frequency equation which you know all about Gerry.

Which is why that calculator I mentioned above is so nifty. Machines are just so much better and faster at math than people...

[pops]

An unbypassed gain stage will also have a flatter frequency response, but again as jana said it is cheaper

[LeftyStrat]

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[LeftyStrat]

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[Blackburn]

Can we toss this thread in the incinerator with the other? The usual caps...

Jana offered the best help.

http://www.google.com/search?client=saf ... 8&oe=UTF-8

[NickC]

C'mon ya'll ........ wake up and smell the bacon!

Gerry Rzeppa - Scrambled Eggs & Toast

http://4praise.com/cgi-bin/files/m3u/6007.m3u