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Old 4th May 2007, 01:58 AM   #1
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Join Date: Mar 2007
Location: Newark, DE
Question Replaced pulled tubes with a resistor?

I've grown weary of trying to sort out my little single ended EL84 project, so I've turned to my Harmon Kardon A230 for a while. In case you are wondering, the SE amp is mostly working fine. It's still biased too high, but it runs fine if I keep it on the Variac with the line voltage turned down to around 115 VAC.

Anyhoo, I have a HK A230 which I picked up off eBay for cheap a couple years back. I'm not sure it has a whole lot of potential, but I'm still keen to make it work well enough for basement or garage duty. The OPTs have no 4 ohm secondary taps, and no screen taps on the primary. They look awfully small to me, too. All the coupling caps are ceramic discs - at least I can fix this.

Here's my question: I pulled two 12AU7 tubes and one 12AX7 tube which made up the phono preamp and tone control circuits. I don't intend to use these parts, so it made sense for me to just bypass them and remove the unused components. At least, it seemed reasonable until I realized what was supposed to be the 215V supply to the AF amp and phase inverter had jumped over fifty volts. Without the load of the phono and tone tubes, I've upset the power supply.

So, I've decided to "correct" this problem by sticking a 30k ohm, 5 watt cemented resistor where the missing tubes used to live. It seems draw the right amount of current, and the supply voltages appear to fall back in line.

Is this a big mistake? What am I overlooking?
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