Monday, November 22, 2010

For high frequency compression drivers, I prefer tube power. Here's my EICO HF87 power amp, which will be seeing duty on the HF horns again this year.

Originating sometimes in the early 1960s, this was a kit build. As I recall (it's been over a decade), the builder assembled it wrong, tying B+ voltage to the filament line at the 12AX7 input. As a result the amp would shock people, and probably saw very little use. I received the amplifier in a speaker transaction, and rebuilt it.

A few years back an unlit candle toppled onto the powered up amplifier un-noticed, and proceeded to melt into a puddle of wax at the power tubes. After cleaning up the amp continued to operate fine, for a while. As it turns out, wax had infiltrated the socket itself and begun to pave the way for failure.

I don't think the candle that melted down was turquoise, so it appears that there's been some reactivity between the charged circuit and surrounding substrates over the wax bridge.

I doubled the size of the above shot in GIMP, a macro attachment is certainly on my future shopping list, along with a cage for an EICO HF87.

Octal sockets are pretty easy when it comes to remove and replace, and while a single socket is the main failure point, I'm going to replace them all for good measure.

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