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Richard Allan CG10 Find - Some "New-Old-toys"

Posted 21st March 2017 at 11:49 AM by googlyone

Years ago I moved from the country back into the city. This was a move that required me to clean out heaps of stuff that I really didn't want to clear out. In our old place we had two houses on the block, one of which had been converted into an enormous studio room with NO walls, and a 14 by 14 metre shed. To say that I amassed a collection of speakers and stuff would be an understatement.

One of the things I got rid of were a pair of Richard Allan CG-10 drivers that I never got around to sticking in a box. Indeed, I never even got around to measuring their parameters.

Recently on EBAY I came across a pair of these...

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I was surprised at the condition of these - the cones look new. Needless to say they are not, the date code is 1973.

I have measured and used the CG-12, HD-15 and a bunch of other Richard Allan drivers in the past and found them...
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Did I REALLY do that?

Posted 12th March 2017 at 04:49 PM by googlyone

in my electronics workshop I have always had a stereo. Eight years ago I looked on the shelf and decided there was all the makings of an integrated preamp - DSP - Crossover and four power amplifiers.

That is the price of always making an extra board or two when I build a "thing" - you end up with a massive collection of bits.

I duly shoe-horned this lot into a case that is about 3" high. Tuned it up and didn't think a lot more.

Fast forward 8 years to two weeks ago, and there I was listening to the radio while wondering what to build next, and I thought the left tweeter sounded a bit low.

I swapped input to the amp L-R, and yep, it was. Odd - as the DSP treats L and R exactly the same, there is no balance control in there. So I swapped the speakers. Hmm, it wasn't the tweeter. It was inside the "box".

So I popped the lid, and found this...

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Hum in Aikido Cathode Follower (ACF)

Posted 7th March 2017 at 03:00 PM by alexcp (My DIY projects)
Updated 13th March 2017 at 09:20 PM by alexcp

I purchased an Aikido Cathode Follower 2 (ACF-2) All-in-One 9-Pin PCB from The PCB is designed by John Broskie, the editor of Tube Cad Journal (, and the flexibility that he designed in is quite remarkable. The PCB allows to test various configurations, which is often not a feature of a design committed to a PCB. The quality of the PCB is outstanding; it withstands multiple soldering and desoldering without complaint. It is an outstanding product IMHO.

The schematic seems to be simple, with a cathode follower loaded by a triode current source. JJ E88CC with 221ohm cathode resistors shows 0.003% THD with pure 2nd harmonic, and select 6N1P-VI achieve 0.005%. (My 6N1Ps are hit or miss; some of them have much higher 2nd harmonic, and some of them have a mix of 2nd and 3rd at Ia=6ma and Ua=140V).

As I tested my ACF, I noticed excessive hum at its outputs - audible buzz in the speakers and 0.15% THD+N, well above the THD.
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