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Demystifying the Cascode

Posted 15th May 2010 at 12:25 AM by Miles Prower

Basic Cascode

Click the image to open in full size.

This is what the schemo of the cascode looks like. Rk serves to establish the Q-Point bias for the lower triode, and Rg is its DC grid return. Rp is the passive plate load. The voltage divider connected to the grid of the upper triode establishes its Q-Point bias.

So why would you want to do this? What you have here is a cascade of a grounded cathode stage driving a grounded grid stage. The GC topology has the advantage of a Hi-Z input. However, its high frequency performance is impacted by a high Cmiller that only grows worse with increasing voltage gain.

The GG topology avoids Cmiller for excellent high frequency performance, but it suffers from a Lo-Z input. It's not very often that a Lo-Z input is desirable. However, you can combine the two in a manner that work together. The Lo-Z of the GG stage loads down the plate of the GC stage, reducing its gain...
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Some more progress on my Baby Huey PP EL84

Posted 4th May 2010 at 10:24 PM by Bas Horneman (Bas Horneman's blog)

Unfortunately the paintjob is slowly chipping away on the edges...
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Active inductor substitutes

Posted 3rd May 2010 at 02:45 PM by DougL
Updated 14th September 2010 at 07:34 PM by DougL

Here is a circuit I like.
Not excessive voltage drop, no absolute expectations on voltage or current.


A link to the discussion in the Tube Forum
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power supply for 150w 8 ohms

Posted 3rd May 2010 at 02:01 PM by klewis
Updated 19th January 2011 at 01:53 AM by klewis

a dual secondary 40+40Vac transformer will give ~58 to 59Vdc.
With good smoothing and a well built amp you can easily achieve 150W into 8r0.

If you want to have the ability to drive a 4ohm load then you will need to double the smoothing capacitance and double the VA rating of the transformer.

For 150W into 8r0, a 300VA with +-20mF will do.

My 230:40+40Vac gives +-58.5Vdc when fed with 240Vac and the amp bias is 220mA. It gives 170W into 8r0 from a 3pair output stage.

The power supply application note is available at

build the right half of the PSU in the app-note (Fig.1) and instead of all the soft-start/relay fun, put a thermistor, CL60, in series with the primary leads of the transformer.


Andrew T notes on sizing...
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Guitar tone pot and caps

Posted 1st May 2010 at 02:52 PM by Wayne737

I have a quetion about guitar tone potentiometers and capacitors. A build I'm working on has a preamp. Must the tone control be before the preamp? And all the tone control is at the first part of the potentiometer. I want it to adjust the tone across the entire potentiometer. Would that have to do the the potentiometer, capacitor, or how it is wired?
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Shunt Regulator Wiki

Posted 26th April 2010 at 01:50 AM by DougL
Updated 28th April 2010 at 07:43 PM by DougL

Here is my brothers response to the first version of the Shunt Regulator wiki. I actually wrote it for him so he could get a clue of what I was babbling about.


Это бумажное средство приблизительно столько же, сколько эта электронная почта будет означать для Вас. Я думаю, что это хорошо написано. Вы будете нуждаться в этой связи, чтобы выяснить то, что пятку я только что написал Вам, поскольку это находится на русском языке.

http: //


Here is a translation:
Arcs, This paper means approximately so many, this how much electronic mail will indicate for you. I think that this is well written. You will require in this connection in order to explain that the fact that I recently wrote heel to you, since this is found on the Russian language.

For thoes of you that are curious, the article is here:
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Posted 25th April 2010 at 12:58 PM by taro2ss


I may be writing a article for audio products of JAPAN on diyAudio blogs from today.

Thank you.

My DIY portable headphone amplifier.
Click the image to open in full size.
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3 way speaker

Posted 21st April 2010 at 01:48 AM by clemmtec

I want to build a speaker that has very stong
bass,and clean not the noise kind. what woofers or sub woofer would you recommend ?
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Research for My first Horn Speaker.

Posted 19th April 2010 at 09:57 PM by DougL
Updated 28th April 2010 at 07:44 PM by DougL

This is my foray into the dark side.
The only horn speakers I have ever heard was a K horn being driven with a Phase Linear 700.
Could not stay in the room.
Now I am curious if it can be better.

I have a 3 DCX2496 and 6 channels of amplification, so I will start with an active system.

My goal is to get the drivers close to 100db or higher efficiency.
I want to be able to experiment with low power amps.
I am also frugal, so I want to use low cost waveguide components.

Compression tweeter
Direct radiation mid

JBL 2123 is my starting point Second hand only.

B&C 6MD38 99db $89
B&C 8PE21 98 db $100
B&C 10MD26 100 db $160
B&C 10HPL64 98 db $130

Here is an example speaker.

I will start a thread after...
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Projects, Projects, Projects..

Posted 16th April 2010 at 06:07 PM by kevinkr
Updated 16th April 2010 at 06:19 PM by kevinkr

Like most of us here I seem to have more projects than I can handle. Just added another one - I'm going to do a simple little 6BQ5/6V6/7C5 based SE amplifier for nostalgia. (My first tube amp as a teenager was a 6BQ5 SE)

I've just added to the stack by ordering a pair of 6V6/6BQ5 SE OPTs from Tony over at Twin Audio. The price with shipping was pretty hard to beat, and I figure that the effort they put into building their amplifiers probably is also reflected in the quality of the parts they use. This amplifier will be pretty simple, most likely using pentode mode with some cathode feedback, a single stage high mu triode driver, and some limited global feedback to get the output impedance down. Hopefully I can make enough power to drive the HCC with it. I could conceivably incorporate the baffle step correction into the input of this amplifier if it is dedicated to driving the HCCs. As a firm believer in the benefits of fixed bias the output stage will incorporate that....
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