Friday, October 14, 2011

Continuing contemplation of the Teletronix LA2A as I shift and shuffle the new workbench into a useful state. Here's an early revision schematic I found at The Bottle Garden studio site, the absence of a LIM/COMP switch points to a first revision so far as I can tell.

Signal path: From the input transformer signal passes through cascading halves of a 12AX7 and into a cathode follower built on stacked halves of the 12BH7 feeding the output transformer (through a DC blocking cap).

Supporting electronics: Input signal is split into a strapped 12AX7 voltage gain stage which feeds the 6AQ5 which drives the luminescent panel of the T4 through a DC blocking cap. The T4 then, when fired, illuminates the CdS cell which decreases resistance, effectively draining more signal to ground before it hits the grid of the very first gain stage of the signal path.

So, the resistive drain of the CdS cell will always be in circuit, before any signal amplification. I'm making the leap to the conclusion that the CdS element has a tremendous impact on overall voicing and characteristic of the device. I'm also shooting down the statement of relief in my previous post regarding mica dominoes in circuit. They are not, unless you believe subtle frequency nuances of the side chain amplifier driving what amounts to a light bulb are going to play much of a sonic role. Which brings me to the electroluminescent element, it makes sense that the characteristics of this are going to play a large part in actually driving the CdS cells into their lower resistance state.

I bought this octet of NOS General Electric CdS cells at auction, I'm hoping that with the ability to play with series/parallel configurations I can come somewhat close to the static response range of the Clairex CL505. Since there was no data sheet I could find, this does amount to a shot in the dark.

1 comment:

MKULTRA said...

You said 12BH7.

The 12 volt equivalent of bacon.
Great all around driver. Epic for
headphone amp.