Switch/fuse/light wiring question...

I can never seem to remember the right way to do this. I need to wire in the switch/fuse into the 120 VAC circuit coming into this 175-67. But I can't remember how to tell which side of the AC line to wire it into.

Here are the wire by number choices....



1 is one side of the incoming 120 VAC which is wired straight into the red/black primary of the power transformer.

2 is the other side of the incoming AC, with a new Y2 cap across the two incoming VAC wires. As pictured, it's a dead end.

3 & 4 are the terminals of a SPST switch

5 & 6 are the terminals of a fuse holder (2A/250V slow-blow)

7 is the other PT primary, cut out of the old Molex connector.

8 & 9 are two unneeded filament supply iwres, most likely 6.3V that were also cut out of the Molex. I'd like to use these to decrease my incoming AC, since that woulod put me right about at 117 VAC given the usual 123 VAC I see here.



OK so as I see it, I want to go essentially with increasing numerical order...wire 2 to 3, 4 to 5, 6 to 7. that would put the fuse in fornt of the PT.



How do I know I'm on the "hot" side of the incoming wall current?

Also, where do I put the filament wires to drop the wall current?

Lastly, I have a 120 VAC neon light as a power indicator. It will need to be wired across the 120 VAC.





I figger I'll wire one side of the light into 2. and the other into 6.


Anyone have any comments, suggestions, or corrections before I screw this up?...:scratch2:

Way I do it, is put the fuse on ONE side of the AC line, and the switch in the OTHER. That way, if the switch is off... if there's any sort of short anywhere, the fuse will blow, and EVERYTHING will be disconnected from the AC line. Could save it from fire...

On the 175... note that the AC power cord has one side with a rib on the wire, and the other wire is smooth. Ribbed usually means "hot", while smooth is neutral. That's how I treat 'em. I wire the switch to the hot, and the fuse to the neutral side. YMMV, but that seems to work well for me...

Regards,
Gordon.

Does it have a 3-pin grounded or 2 pin polarized plug (one blade wider)? With the original plug, either side could be hot. To meet modern safety standards, it would have to have a grounded cord (all exposed metal grounded), a non-flammable bottom cover, and the AC wiring as follows: Hot wire from cord to rear terminal of fuse, side terminal of fuseholder wired to switch, switch to transformer. Other transformer lead would go to AC neutral. Switching the neutral is allowed if the hot lead is switched (both sides of AC line).

I wouldn't use the extra 6V winding to "buck" the AC line, as I don't know how well it's insulated - could be wound next to the other 6V winding, with only enamel between them.... a separate transformer won't have that issue.

Tom I think it has the original cord, a non-polarized version. The wide plug on the polarized 2-prong is the neutral, correct?

I suppose I can add a polarized plug....:scratch2:

I'd do: Using a polarized power cord, neutral (wider plug prong) to one side of the power transformer. Hot side to fuse, then to switch, and then to the other side of the power transformer.

As for using the extra 6.3VAC winding, I'd insert it between the neutral and the power transformer. But you need to get the phasing correct. Only real way to know if it's correct is to turn the amp on, measure the heater supply before inserting it, and note it. Then do the insertion of the extra 6.3V winding (but in such a way that you can easily change it). Now turn it on and measure the same heater supply. If it went down, then you have it correct. If it went up, swap the extra 6.3VAC wires around, and then check it again. Once you have it good, then do a neat connection.

wa2ise said:

As for using the extra 6.3VAC winding, I'd insert it between the neutral and the power transformer. But you need to get the phasing correct. Only real way to know if it's correct is to turn the amp on, measure the heater supply before inserting it, and note it. Then do the insertion of the extra 6.3V winding (but in such a way that you can easily change it). Now turn it on and measure the same heater supply. If it went down, then you have it correct. If it went up, swap the extra 6.3VAC wires around, and then check it again. Once you have it good, then do a neat connection.

Click to expand...

By heater supply, you mean the max voltage put out by the PT at the first/40uF cap? I suppose I could always measure it without first, just to see how close to spec it is....

And you don't have any concerns about shorting out the PT internally????:scratch2:

analog addict said:

By heater supply, you mean the max voltage put out by the PT at the first/40uF cap? I suppose I could always measure it without first, just to see how close to spec it is....

And you don't have any concerns about shorting out the PT internally????:scratch2:

Click to expand...

I was thinking of measuring the voltage present at the heater terminals of tube sockets, but the DC voltage at the first 40uF cap will also do. You just want to see it lower by about 5% when you're done.

Ideally, each winding in the power transformer should have no connection to any other winding. So shorting internally shouldn't happen. Oh, maybe the 6.3VAC secondary may not be rated for 1.4KV "hi-pot" isolation like the primary should be, but transformer makers usually used enough inter-winding insulation (usually special purpose paper) so it should not be an issue. They also have to worry about the high voltage secondary arcing over to the heater windings, so they have an incentive to insulate everything well. And I suggested having the extra winding on the neutral feed side, to reduce the amount of voltage that would exist between it and other secondaries, for an extra margin of safety. This assumes the use of a polarized plug and correctly wired outlets in your house.

I've done this on Magnavox console amps, and it works fine for me, no problems.

wa2ise said:

As for using the extra 6.3VAC winding, I'd insert it between the neutral and the power transformer.

Click to expand...

OK, lemme see if I have this right.

I'm going to use 1 in the picture above as the neutral side, since that will make it easier to wire the hot side.

I'm going to unsolder the red/black primary, and instead connect one of the brown or yellow/brown wires (8 or 9) in its place.

Then I'm going to connect the other filament wire to the red/black primary.

When I change the power cord, and power up the amp, I'll measure the voltage and see if it's higher or lower than stock, and switch 8 & 9 if necessary.

Do I need the rectifier tube in place to fire it up and play with the filament phase/bucking mod voltages?

Would I be endangering anything by not tubing up the rest of the amp?

Thanks!...

analog addict said:

OK, lemme see if I have this right.



Do I need the rectifier tube in place to fire it up and play with the filament phase/bucking mod voltages?

Would I be endangering anything by not tubing up the rest of the amp?

Thanks!...

Click to expand...

That should do it. As for having the rectifier in and other tubes not in, only issue is that the filter cap might be overvoltaged. So, best course of action is to have no tubes installed, and measure the 6.3VAC heater voltage as seen at a tube socket.