Another tube limiter
« on: April 03, 2005, 10:55:48 PM »
Scanned from one of my old books, I present:

Presto 41-A (724kB PDF)


Another tube limiter
« Reply #1 on: April 03, 2005, 10:58:44 PM »
Thats Funny,  I Just posted in brewery about peoples thoughts or experiences on building a Gates Sta-Level.

thanks for the PDF
Tube limiters..yum!

gary o

Another tube limiter
« Reply #2 on: April 04, 2005, 08:37:43 AM »
Thanks NYD I love old limiters wonder how one of those ones would sound.

Gary O.

Rob Flinn

Another tube limiter
« Reply #3 on: April 04, 2005, 09:36:06 AM »
I like the look of this circuit, with its healthy 520v coming of the rectifier valve.  No messing around there !!!  Although, sadly, it is regulated down a bit after this point.
regards Rob

gary o

Another tube limiter
« Reply #4 on: April 04, 2005, 09:55:16 AM »
Healthy 520V not if ya put yr fingers on it haha....hi Rob & anyone, I like the look of this one too seems to be a lot of regulation I take thats what that bottom part of the circuit is doing.There is another pentagrid limiter floating about Kloin 1126 I think,when I posted it asking if anybody knew what it may sound like, it took a right kicking PRR said it would shread transients.....wonder how this would fair.

Another tube limiter
« Reply #5 on: April 04, 2005, 11:28:02 AM »
This thing looks cool.


Another tube limiter
« Reply #6 on: April 04, 2005, 12:27:52 PM »
I actually have a friend who has one of those. He picked it up some years ago from a horse racing track for cheap. They ran the announcer mic through it. He absolutely loves it.

It is a big sucker though.  :shock: :cool:


Another tube limiter
« Reply #7 on: April 05, 2005, 02:17:05 AM »
> Healthy 520V

Wasteful 500V. Why do you want big voltage in a limiter? The output is limited. We are not talking headroom here: the whole idea is to smash peaks.

You need enough voltage on the vari-gain stage to get a decent signal-crap ratio. Higher voltages allow higher signal before distortion, but this is a slow process. Doubling the voltage quadruples the heat but only gets 6dB more dynamic range on a system that runs 100+dB at any reasonable voltage.

You want regulated voltage on the vari-gain stage because its control voltage is proportional to plate voltage. If you let B+ wander from 200V to 300V, that's about 3dB variation in output limiting level, which is far too much for a well-tuned radio transmitter or disk cutter. I don't know why they bothered regulating the power output stage. Maybe they had too many 2A3s lying around.

> pentagrid limiter ... PRR said it would shread transients...

Transient clipping has nothing to do with pentagrid. It is the R-C coupling out of the vari-gain stage, and the common-mode voltage range of the next stage. Look what happens when you go over limit level. You reduce current in the vari-gain stage to reduce gain. Both plates shoot up from 120V at rest to around 200V for 6dB gain reduction. The next stage, in this and many designs, can only take about 2V-5V common-mode input voltage before it saturates. It does so by grid-conduction, which shorts-out the signal on the plates of the vari-gain stage. Until the coupling caps charge-up to the new voltage on the vari-gain plates, it is clipping, not limiting. This has many advantages, if you are not perfectionist about your audio. You can lighten-up the attack time, making less load on the rectifier driver. You don't get such a bobble around the gain control feedback loop. The output IS "limited", your transmitter does not go "splatt" into adjacent channels, or lose the load on the class-C driver and bobble it. And we all knew that a few milliseconds of clipping would not annoy the listeners.

One thing Dave did not point out, but did come up in a recent thread: note that they drive grid 1 with audio plus control, and grid 3 with just control. Remember what these grids are supposed to do in the radio that they came out of. If it would give good GR when just driving G3 with control voltage, we could easily dispense with the input transformer. It seems like a good plan. However it is very rarely done, and I suspect it isn't really any better.


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