Leader LSG1300S


2007-07-25 2:36 pm
Hi Papa,

Look for precision, single turn, 1k pots, like these:
Precision Pots Single-turn
This seems to be the "cheapest" from among them (do check if it fits mechanically):
Precision Pots Single-turn
Maybe you could ask for a sample...

I have three of the above generators, an eBay purchase of a lot, originally from a collage, all damaged.
It was the output stage that was damaged in all of them, plus some other things.
Some of the range switches (a lot of them, if you ask me) are flaky, though I have not cleaned them yet.

There is a problem with R407, the 51 Ohm resistor in the 40dB output divider. If the output DC level is pushed towards either of the supply rails (+/-15V, you can do that with the output "DC Offset" control), the resistor is overloaded, it would dissipate 4.5W!
R401 and R403 in the 10dB and 20dB divider stages could similarly be overloaded (2.3W, 3.7W).

Obviously the output stage circuit is not foolproof either.
Maybe they should have picked 600 Ohm output impedance instead of 50 Ohm, it would have eliminated the problems with the output stages.
It is possible that they felt 600 Ohm would be unsuitable for the max 2 MHz output frequency.
Though the HP-204D has 600 Ohm output impedance, and operates to max 1.2 MHz.

Regards, Peter
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