Using Volume Control without AC switch

[audmod01]

The X-101C I have is missing its original volume control. I did manage to find a Fisher dual volume control without the AC switch (not a type that can have one added). I see that there is some room between the front panel and the chassis front behind that. I am considering the possibility of adding a small cam to the volume control shaft (perhaps by soldering) and using a microswitch to do the AC on-off function. Another possibility is to use a slide switch where one of the original slide switches was located. I am doing Dave's X-101C modifications and the High Filter switch position could be used as I am deleting that part of the circuitry.

Another possibility is to use a separate bracket behind the front chassis panel to mount the volume control recessed more to the rear and add a microswitch there. The shaft on the volume control I bought is about 2 inches long, so I have plenty of length to play with.

Has anyone else considered using a microswitch?

Joe

 

[dcgillespie]

The micro switch is a neat idea! Or, could the rear cover of your existing control be changed out for one that accommodates a switch?

Dave

 

[Dadbar]

REpurposing the noise filter is a great path. Honestly...will you ever need that function for anything?

I did something similar with my HH Scott 299, repurposing a phase reversing slide switch for power. It was a function that I was pleased to ditch

 

[audmod01]

Dave & Dadbar;

Thanks for responding. Unfortunately the volume control I was able to obtain does not provide for the addition of an AC switch. The end of the shaft has nothing to trip a switch even if I could find a switch to use. It also does not have the nubs on the rear section control that would snap in place on one of the switch units that many have repaired. Of course it would be possible to solder such a switch if the rest of the control had the correct internal parts for activating a switch.

Do either of you know the correct AC current ratings for the switch that Fisher used for so many of their amps and receivers?

Thanks.

Joe

 

[dcgillespie]

Each section of the switch is rated at 3A.

Dave

 

[audmod01]

AC Switch Rating

Dave;

Thanks, that is just what I needed to know. I just received the Fisher jewels I ordered. I ordered a set of three colors to get the one (green) that I needed. These came from Charles Allen of Sugarlaf Key, FL.

Joe

 

[gadget73]

I'd probably go with larger than the stock current rating if possible. Seems the original is a wee bit marginal. 5 amps would give you a nice buffer methinks, though having a thermistor in there for slow starts would probably sort it out too.

 

[audmod01]

Gadget73;

Yes, I agree on the current rating. I just ordered an Electroswitch D4G0405S 4-pole 2 to 5 position (adjustable) 30 degree make before break rotary switch that I can use to replace the missing Mode switch. It is coming from Allied Radio (remember them?). They had this in stock for $26.97 each. I also ordered some CL-80 thermistors and will use two on the AC input. These will soften the inrush current for any switch I choose.

The Electroswitch I chose is about 1/2 the price of the Grayhill switch I was first looking at, but has the same switching characteristics I was looking for. Mouser carries the Grayhill switch and it is in stock but about $56 in qty. of 1 each.

I have some DPDT 2-posn panel mount switches on hand. I need to check the AC current rating. They may be adequate, especially when paralleled.

 

[notdigital]

Dave;

Thanks, that is just what I needed to know. I just received the Fisher jewels I ordered. I ordered a set of three colors to get the one (green) that I needed. These came from Charles Allen of Sugarlaf Key, FL.

Joe

Can you post some pics of the jewels?

 

[audmod01]

Front Panel, Jewels, Knob & Volume Control

Here is a photo of the front panel with the green jewel mounted and illuminated with light from behind. At the top are the other two jewels, amber and red ones plus a knob and volume control all obtained through ebay.The green jewel fits exactly into the existing hole in the front panel. All I had to do was carefully remove the old glue before inserting the new jewel. It snaps in place

The knob I managed to get was exceptional condition and complete with the insert. I have five of the small inserts with the small indicator dash on order and should receive them within a few days.

I spent time this afternoon assembling the LV power supply with the fixed negative bias circuit. I am about 2/3 done on that. I have a piece of plexiglass that is 1/32 inch thick and with 4 twist-ties at its corners being glued to the chassis. It will be both the attachment means for the prototype board and the insulation between the backside of the LV power supply and the chassis metal. The glue should be cured within a day or so. I will post some more pictures when the LV power supply is completed and mounted.

Joe

 

[fred soop]

.....
I have some DPDT 2-posn panel mount switches on hand. I need to check the AC current rating. They may be adequate, especially when paralleled.

Paralleling contacts does not increase the switching current. The carry current can be added but when switching, one contact will always make or break slightly before the other, and will sustain most of the arcing.

 

[Chip Chester]

You can use the microswitch to control a remotely-mounted relay, or electronic substitute, and make the current capacity nearly anything you want. Even add speaker connect delay if it's not on the receiver already... and if you want/need it.

Chip

 

[audmod01]

Microswitch Usage

Chip;

Thanks for the suggestion. If I search diligently, I may find a microswitch with the required 3A or even 5A capability and not need the extra relay. The relay is always another way to go. If the LV power supply has a few extra mA to spare, a relay activated from one of the 11.6VDC rails could be used to activate it. That way only the 25.2VAC transformer would have to be switched and its current demands are small compared to the rest of the unit.

I hope to get the LV power supply finished today if all goes well. I will post some more pictures.

Joe

 

[audmod01]

Slide SW AC Current Rating

I looked up the slide switches I bought recently and they are rated at 11A @ 125VAC so they should work OK with capacity to spare. One nice aspect of their design is that the contacts are not just folded and crimped into position but are also stabilized with a high temperature epoxy material. These contacts do not wiggle at all as the switch elements slide. They are a better quality part than the OEM slide switches. These are normally supplied to Fender for guitar amplifier application.

Joe

 

[audmod01]

More on Micro-Switches

Today while searching for another Item I ran across four Omron micro-switches which current nomenclature calls "Snap Action Switches". The term micro-switch seems to have gone the way of DoDo birds. In any case, they are still available in various designs, some of which include small attached levers for actuation. Generally micro-switches need to be mounted in such a way that their snap action trip point can be adjusted for best results either by moving the switch and re-fastening securing hardware or by bending the attached lever. The particular micro switches I have are older (discontinued) Omron brand model 28Z1R, rated at 15A capable of starting a 1/3 HP electric motor at 125VAC or 250VAC. This is more than adequate for any of our Fisher amplifiers or receivers. This model has one normally closed and one normally open contacts and three lugs, one of which is a common connection. They are designed for push-on connectors, although wires can be soldered to the connection lugs.

Now that I have candidates for the implementation of a micro switch, I think I will pursue that method. It will involve mounting the volume control with a rear direction offset bracket to provide space for an actuating cam on the control shaft and a way to mount the micro-switch.

The fact that a longer shaft volume control will have to be used along with the extra mounting bracket(s) may discourage this method in some applications. You would have to be the judge.

Joe