Old terminal strip conversion

[mrn1ngstr]

Ive reassembled a Dukane 1U460A, converting mic input to cliff jack, and Ive got cliff jacks for 4 and 8 ohm outputs. The old terminal strip also has lugs for 70v and two 25v balance. One of the 25v transformer leads goes to one balance lug and the 4 ohm. The question I have is what do I do with the other 25v lead? Right now Ive got it taped off. I copied the factory schematic with the values written in- the original had a table of values so small I almost had to get a magnifying glass to read them. Let me just say sorry cause its a mess... On the bottom left of the schematic is the new wiring. Once this thing is good to go, Im going to start tweaking some values and playing with my scope until its useable.

[martin manning]

Yes, just tape off the other 25V lead (yellow, per the original schematic).

[mrn1ngstr]

Cool. Thats what I figured but I wanted to make sure. Here is another question then. When I switched the pilot lamp out for an resistor/LED/diode rig, it dropped the filament voltage down to 5.75. Is that going to cause problems? My thinking is no, just might not have as big of an electron cloud to pull from. A little less output?

[martin manning]

Put the diodes and resistor across the outer legs of the filament winding (not CT to one leg) so you are using the whole 6.3 (ish) volts, and choose a resistor that will limit the peak current to around 30mA, say 220 ohms for a red LED. You may be fooling your meter the way you have it, so the 5.75VAC reading may not be accurate.

[mrn1ngstr]

You were right. I ran it across the two main filament lines and the voltage went up to 6.1v and it may just be me but the led looks brighter. It looks like some plate voltages went up too.

[martin manning]

It's certainly well within spec now, but I'm wondering why the filament voltage isn't running high. The power transformer was made assuming 1950's line voltage, and you are sure to be ~5% above that now... measure it and see.

[mrn1ngstr]

The PT has two different primary leads, one for 127VAC and one for 117VAC. When I got it the 127 was hooked up and 117 was taped off. Thats how I kept it.

[martin manning]

All good then!