Fisher tube chassis balance controls

[audmod01]

Balance Control Shaft

Yes I also installed a new earphone jack yesterday - another item from Antique Electronic Supply. I need to take a close look at Dave's pictures of the changes he made to the speaker switch and the wiring of the jack. I had to make a slight modification of the custom dial lamp socket to make room for the installation of the earphone jack and make sure there was clearance for insertion of a 1/4 inch plug. The lamp socket originally had a dual spring loaded set of tabs that would latch into slots in an associated bracket. It was designed for easy removal by pressing together the two tabs. I had to fold one of these back on itself to eliminate interference with the jack & plug. I will see if I can get some good photographs.

Question for Dave: which channel connects to the plug tip and which to the ring when the earphone plug is inserted? I know you said the original wiring had the two channels swapped from standard industry wiring that came later.

Yes the control shaft flat side will depend on where the flat is inside the knob. The control has to be at middle of its range and the knob will have to be held up to the shaft to see how the flat needs to be oriented.

Joe

 

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Input/Output RCA Jacks

I have been looking at the input/output RCA jacks of this amplifier. I am wondering if it is possible to install any of the new gold plated jacks to replace old corroded ones. Have any of you tried this and been successful?

The existing jacks are spaced pretty close together. I have some examples of the gold plated jacks from one source, but the rear hex nuts and ground lug are so large I doubt I can use them.

Joe

 

[dcgillespie]

Joe -- To represent the modern standard, the headphone jack should be wired so that the plug tip represents the left channel. As originally built, the jack was wired backwards.

Dave

 

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Earphone Jack Standards & Mode Sw Question

Dave, Thanks, that is exactly what I needed to know.

One more question regarding the Mode Switch in the X-101C - is it a shorting type switch (make before break) or a simple non-shorting type?

Joe

 

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Dial Lamp, Phone Jack, Balance Control

Here are a few pictures of the Dial Lamp, Earphone Jack and Balance Control installed on the painted chassis front.

Joe

 

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Parts Ordered

I ordered a switch from Mouser Electronics today that is a rotary 4 single pole triple throw sets of contacts to use for the Mode switch. I also ordered all of the resistors required for the modifications to the X-101C. I have not ordered all of the capacitors yet, but did order some that are going in the loudness circuit.

Parts will start coming in and so installation of parts depends on what makes sense at the time. I still will need to get the right size of per-board or breadboard to use for assembling the low voltage power supply.

Joe

 

[dcgillespie]

Joe -- Due to the custom design of the original Mode Switch, the connecting criteria of the contacts between the various positions really doesn't apply. In general however, they operate in a make before break fashion.

I hope this helps!

Dave

 

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Mode Switch Replacement

Dave;

OK thanks for that information. I have not found a make before break switch but have found a 4-pole triple throw rotary switch with 30 degree detents and adjustable stops which I should be able to make duplicate the functionality of the original. I may continue to look for one that has the make before break capability. The one I did find is only about $5 and has a long plastic shaft that can be trimed to proper length and a flat filed into it if needed.

Joe

 

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Dealing with Corrosion

Since both the top and underside of the chassis had considerable corrosion, I decided that I would check all the riveted ground connections. I used my Fluke 8600A multimeter and checked them all. I was pleasantly surprised to find that all the grounds are still good! I was really dreading the possibility of having to drill out large numbers of bad grounding rivets.

I also checked the tape head and magnetic phono RCA inputs to the front push-button source selector assembly. Another surprise - the guy who had cut so many other wires did not cut these wires! Others such as the Aux input leads which went to the Mode switch were cut and are dangling in the air. It shows that very little real thought went into the modifications the previous owner had made to this unit. Liberal use of duct tape served to help eliminate some obvious B+ short possibilities.

The new DPDT slide switches I received from Antique Electronic Supply have M3 x 0.5 metric screw thread mounting holes in them. I stopped by a local Ace Hardware store and found some correct size M3 screws that are long enough to mount the switches and require no added hardware to hold them to the chassis.

More later.

Joe

 

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Power Transformer Wiring Question

I have a question for those who own a X-101C which is accessible for a view under the power transformer. I forgot to make a notation as to which wire of the two red ones goes between the two electrolytics and which one goes to junction of CR1 and CR2 rectifiers. One wire is just red and the other is red with a yellow stripe.

I received the two 50uF X 4 @350VDC this morning and have installed them on the chassis. I need to know the answer to the above question so I can make sure the wires connect to the correct connection points.

Joe

 

[dcgillespie]

Joe -- It really doesn't make any difference which way the wires are connected, but Fisher traditionally connected the red one to the diodes, and the red/yel stripped one to the junction of the two doubler caps.

Dave

 

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Power Transformer Wiring Question

Dave;

Thanks for that data point. I pretty much thought the same (no real difference from the standpoint of operation). I wanted to put it back the way it was to start with. Since the chassis had been messed with previously, I did not have a reference point. I did look closely at one of the under chassis views of Don's unit and it appeared the Red/Yel wire was connected to the junction of C26A + terminal and C25 negative terminal. So I was right about the original connection point.

I was looking at the low voltage power supply and ordered a suitable size prototype board from MCM Electronics plus some heat shrink tubing and extra Deoxit. I have a 1/32 thick piece of plexiglass I can put between the low voltage power supply board and the chassis metal. It appears that the total vertical space in that area is 1 inch. So 1/32 plus 1/16th for the board leaves the rest for components but needs to allow some space so that nothing will touch the bottom chassis cover.

Joe

 

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HV Power Supply Re-wiring

I spent some time this afternoon cleaning duct tape residue from some of the HV power supply wires. There was also some dark brown residue from something that changed the red wire of the secondary until it looked brown instead of red. The red/yel wire was also covered with some of the same residue plus some duct tape residue. The whole area looked so crummy that I decided to remove all components from the terminal strip where the rectifiers are. In the process I discovered that so many wires had been connected and disconnected in the past that there were many stray wire strands that were almost shorting across from terminal lug to lug.

Another issue was found with the solder that had been used. It took more heat than normal for good solder and generally had made rather suspicious connections. I manage to remove all parts and cleaned the terminal strip. Then each lug was cleaned one by one of all stray wire strands and then fresh solder was used to flush away the old solder. Things cleaned up quite nicely.

After that was done I could see that the red/yel wire could easily reach one of the twist lugs (normally ground) of the floating 200uF Electrolytic capacitor. So that lead was attached and soldered. Then another twist-lug of the floating electrolytic near the mating 200uF electrolytic was wired to the adjacent half-round symbol section of that capacitor. Each 50uF section of each of the electrolytics were connected to their mates on the same capacitor, thus placing all the sections of each capacitor in parallel. The result provided 200uF working capacitance from each capacitor.

The original silicon rectifiers were still there, but had been subjected to so much heat over time due to who knows how many soldering operations, that I am going to replace them with 1N4007 rectifiers. The original rectifiers were the metal case types and some past solder operations had compromised their insulation near the outer case and the active lead just fractions of an inch nearby. When I am done I will take some pictures showing the wire routing. When finished I believe it will make future troubleshooting easier with wires and components in plain view.

I also spent time cleaning duct tape residue from the output transformer wires. That adhesive becomes quite hard and difficult to get off, but will eventually soften and let go. The oldest transformer had some leads that had changed color significantly. The cleaning helped restore those lead colors almost to original hue.

I will try to get some pictures of this area tomorrow and post them.

Joe

 

[gadget73]

Sounds like someone was using 50/50 plumbing solder. That stuff doesn't lay worth a damn. If its acid core solder, it will also eat up component leads. You'd notice the corrosion from that.

 

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Solder Used in Prior Mods

Yes, I have seen plumbing solder used before and it leaves behind a residue that basically destroys the equipment. Fortunately this one did not have plumbing solder, but must have been a high lead content type that just did not do a good job and would definitely not have been my choice. It reminded me of some solder I bought as a teenager and used on my very first Heathkit.

We had a scare last evening. We were under a tornado warning, so we had to run to our daughter's house next door and get in the storm shelter. We had our excitement for the night. Fortunately the tornado passed by without doing any damage here. My prayers go out to those who lost homes and other property or were injured.

Joe

 

[dcgillespie]

Absolutely! Glad you're OK! The power of Mother nature can go waaay beyond formidable. When you've experience it, it's undeniable, and can reduce your world to nothing in moments......

Dave

 

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200uF Capacitors Installed

Dave;

Yes, and thank you for your thoughts. We thank God for his protection always.

I managed to get the two constructed 200uF @ 350VDC capacitors installed on the chassis this morning. I had already wired all of the 50uF sections together on both. I spent time making an insulating cardboard sleeve for the one that has 1/2 the power supply DC voltage on its outside surface. It is important to do that to provide protection against shock hazard or accidentally shorting out the B+ circuitry.

I found some white cardboard material from a discarded frozen food container and cut pieces to cover the smallest OD of the can and wrapped until it was even with the largest OD rim at its base. Then another layer was added to cover all including the bottom rim and top portion of the can. I used a parallelogram shaped piece of the cardboard for this. Each layer was both taped and glued to the surface of the can. The parallelogram shaped piece was cut to meet at the right dimension to mate smoothly with the other end of itself. Then I used Adobe Photoshop and created an outer label mentioning the 4 sections and the final 200uF value and voltage rating. This was also made with a final parallelogram cut shape and taped and glued to the last layer of cardboard. There was a top circle piece of cardboard with another part of the printed label material glued to the top of the can. The top edge of the side cardboard had been rolled over and this last outer label paper was also rolled over the top circle covering. The final result looks much like an OEM insulating sleeve and provides the protection for the user and service personnel that is needed.

The top view of the chassis shows the push-button input selector switch board cleaned up. It had a lot of dust collected on it from having the top cover left off for years. Now it can be seen easier and this will facilitate installing replacement coax cables to it.

In the process I reconnected the power transformer secondary HV leads and the LV filament windings. I replaced the OEM can type rectifiers with some plastic body 1N4007 rectifiers, which are 1A @ 1KV rated and smaller in physical size. The OEM fuse holder had been replaced in the past with a newer type that went too far back inside the chassis and would have interfered with adding the LV filament power supply, so I found a fuse holder from my parts bin that was shorter front to back and installed it. I still have to work on the AC wiring. Some of the leads will probably have to be extended. I am also looking for a better AC cord to use.

I have a small 1.57 in. X 2.75 in. prototype board plus some multiple colors and sizes of heat shrink tubing coming from MCM Electronics soon. I will soon order the IC, bridge rectifier, transistors and other parts to do the rest of the modification.

It is keeping me busy.

Joe

 

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Resistors and Switch Arrived

Today I received the $5.00 4-pole triple throw switch I may use for the Mode switch of this unit. After removing it and checking fit to the chassis front painted panel, I noticed that although the shank is made to fit the 3/8 in. chassis hole, the shaft is not 1/4 inch as expected. Somehow I failed to notice this when I ordered the switch. Another issue with the switch is that it is not a shorting or make-before-break type. That may present loud pops in use if the control is switched unless the volume is turned down first.

Although I could probably use this switch, the shaft OD being less than 1/4 inch means that I would probably have to shim the inside of the mating knob to get it to mate well. Even then, it might prove to be unreliable. I do not think it would be practical to put a metal sleeve over the shaft to bring it to the 1/4 inch OD. The measured OD of the shaft is 15/64 ths. or .2285 inches (5.80mm). This is .0215 inches less than 0.25 inches. Half of .0215 would be .01075 inches thick metal sleeving to fit over the switch shaft or inside the knob shaft opening. I would have to investigate what metal thickness gauge would be close to that.

Although it costs more, Mouser does have a 4-pole triple throw switch with a nice 1/4 inch metal shaft which is also a make-before-break switch. The downside is that its cost is 10 times that of the lesser switch I just received.

If anyone knows of a suitable 4-pole triple throw make-before-break (shorting) type switch that I could use, please let me know. One aspect of the Mouser switch I spotted on their site is that the information as to number of switch positions is confusing. It says 2,3 position. I may have to call Mouser and talk to someone in their parts department to sort that out.

At least all the resistors requires for the modifications have arrived. Some of those 1/4W resistors are quite tiny!

Joe

 

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Re-wiring of Preamp Heaters

I finished rewiring the filament circuitry of V1- V4. Since Fisher had used yellow and green for filament wires on the power transformer, I used a similar approach for the preamp wiring. Fisher used white wire to connect the V1 - V4 tube filament circuits. I stayed with the white wires for V1 and V3 interconnect while the grounds for pins 5 of each tube connected to the center ground & side ground lance right at the sockets. The pin 4 connection from V3 has a yellow wire going back to the location for the LV power supply board. With V2 & V4 I connected pins 4 to ground at the tube socket center ground and side ground lance. Then pins 5 of V2 & V4 were connected with white wire and a green wire from V4 pin 5 leads back to the LV power supply board location.

I spent some time pre-wiring a new loudness switch and soon will install that assembly in the chassis.

Joe

 

[EastPoint]

This is incredible. Thank you for rescuing and resuscitating this poor amplifier.