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Fisher X-202 Rebuild

Additionally, when I disconnected the load resistors and connected actual speakers, I had nothing out of channel B.

I found that if I removed the S to 8 jumper and connected between G and 8 on both channels, both speakers would come to life.

Of course, once there was sound coming out of the speakers, it was breathtaking.

I've listened to a lot of SS amps, ranging from modern amplifiers with black magic buck boost converters to produce power out of thin air, to the true raw power amplifiers of the 1970's Marantz 2385 (amongst others).

The sound produced with within this amp has a depth and clarity, with a dynamic unlike anything I've heard before.

Call it psychosomatic, given the months and months of labor I've put into this unit, but I don't want to listen to it too much for fear that I would get used to that sound.

Of course, it's funny considering that I grew up with this stereo. I would turn it on almost daily and the only thing I cared about was how loud I could make it and not make the neighbors complain. Other than that, it produced sound, and that was the extent of my care. I could have cared less about quality.
 
2 -- The channels are out of phase most likely because you need to flip the phase reverse switch with the configuration you had.

Interchanging the scope leads on one channel effectively grounded the output of that channel through the common ground between the two channels at your scope input.

Super, super job you've done!

Dave
 
I seriously could not be any more happy with the result. The sound is so clean, even with the volume turned way up, there is no hiss, there is no hum. I don't even have the bottom plate on or the tube shields. Fantastic!
 
Truly magnificent work you've done. All I did was recap my 202. What you have done with yours is just incredible! Wish we could have an audio "showdown" with them both! I'm sure you would win!
 
I thought tonight I'd give the amp some break-in time, and the source would be my iphone.

Harmless enough, sounds beautiful through the tube amplifier. Despite being digital music compressed and streamed, it sounds better than it ever has via SS.

Something caught my attention though. It wasn't until I donned some nitrile gloves to do some other work in my basement, and I went to check something on the phone, did I feel like it was continuously vibrating softly...

I took off a glove and noted that in an ungloved hand it felt calm. In the gloved hand it felt like it was vibrating. In the gloved hand and touching it with the ungloved hand, it was calm.

I figured it really isn't vibrations that I'm feeling, but rather electricity... So, I got my DVM. The result was a bit more than I expected (as referenced from earth ground)


IMG_1415.jpg
 
The iphone is no worse for wear getting this nice flow of juice through it. Even when it's plugged in and charging(non grounded plug) it seems no worse for wear. However, will the same be true if plugged into something like a computer which has a grounded plug?
 
2 -- Definitely some leakage for sure -- but what is really concerning is that there is 207 volts of it on a 120 volt device.

For starters, what is the "earth ground" you are referencing? I suspect that something may be up with that. A good earth ground will be isolated, but electrically equivalent potential wise to that of the neutral side of the AC line in a proper installation. If the earth grounded lead of your meter is in fact referencing that potential, then there can be no more than 120 volts of leakage, since there is no more than that potential between the hot side of the AC line, and ground. If you can provide more information on this side of your connection, it will help tremendously.

On the iphone side of your meter connection, it must be assumed that touching the case of your iphone is electrically the same as touching the chassis of your Fisher. This should be confirmed. Your Fisher does not use an internal AC line bypass cap connected between one side of the AC line and the chassis, so any internal leakage must come from wiring issues (which I doubt), the power switch (possible, but not the most likely cause), or the power transformer, which is the usual point of leakage. Such leakage is typically harmless, being produced by capacitive coupling inside the transformer between the coil form, and the core. But again, even in a worst case scenario, if there was a direct short between the coil and core (highly unlikely) at the point representing the high side of the line, it would only produce a 120 volt potential between the chassis, and a known, verified ground, as provided by your electrical system. So, this side of your connection needs investigation as well.

Finally, try reversing the AC plug of your Fisher and see what change in potential that produces. As well, don't forget any OTHER devices plugged into your Fisher, that may have their own leakage, causing the Fisher to then show leakage. Tuners and the like are famous for this.

Let us know!

Dave
 
Earth ground is a reference created by an alligator clip attached to electrical conduit about 5 feet from my home's load center. The conduit is bonded to the box, and the box is both bonded to the water line coming into my house as well as a rod driven 10feet into the soil.

I have plans to run an actual dedicated wire from the terminal strip inside the box to my work area, it's just one of those things that hasn't happened yet!!!

So, a reading taken from the neutral wire of the outlet I was using to the ground point I was referencing from reads 200mV. The hot side reads 121.9VAC

When I connect one lead to the amp's chassis, and the other to that ground reference, I have a standing voltage of 1vac(odd...but I'll blame that on solar winds, the position of venus in the solar system, and excessive florescent lights in my basement)

Once I plug in the amp(still turned off), I have 63vac from chassis to earth ground.

Reversing the plug gives me 3.2VAC (still turned off)

Without touching the cord's current position, turning on the amp gives me 117VAC. If I touch the chassis, it drops to 27VAC...

Reversing the polarity of the cord, and turning the amp on, I get 185vac, touching the chassis reduces it to 32vac.

Yesterday's 207 and all readings today were taken with no accessories connected. (yesterday's only had the iphone and nothing more)
 
Interesting. I wonder if something else is riding on the AC line, that is somehow adding with the AC voltage to produce a higher than normal AC potential. However, with the reading changing so much by simply touching the chassis, it proves that the voltage is capacitively coupled to the chassis, and not produced from a hard connection. Is your meter running off of an AC adapter, or battery power?

Dave
 
A few details perhaps worth noting...

Prior to the rebuild and since the rebuild, the Center channel light is always dimly lit. If you select the center channel on, it turns on bright, but otherwise is always dim...

Not sure if this is considered normal operation either, but the rebuilt cans, they get quite warm after some time of operation. Not sure if it's heat produced from within, or if it's just conducted from surrounding heat sources...
 
Well, I thought it was a fluke last time I powered the amp, but channel B was dead at initial startup. After a few seconds the speaker popped and it came to life. Powering it again, it was still alive and well, and did not fault.

It's been a few hours and I just powered it and channel B was dead again. I investigated the cause... I found no controls on the front panel to have any influence (during the rebuild process they were all thoroughly cleaned and exhibit no dead spots or crackle when adjusted).

What I did find was V8, the Phase inverter/voltage amp for channel B makes the loud pop in the speaker when the tube shield is tapped upon. No other tubes make any noise. Well, despite bringing these tubes to a shop to have them tested, I think this one slipped through the cracks. May need a new tube here. Perhaps I'll change both channel A and B's at the same time...just to keep things even.
 
Interesting. First I'll note that V7, (the phase inverter/voltage amp for channel A) was the tube I noted with the Mullard flash, while V8 didn't. V8's heater also glows dimmer than V7's... I swapped V8 and V7, and found that when V7 was in V8's position, it behaved just as it did in the V7 position...at least in regards to mullard flash and heater brightness. Tapping that results in channel B popping is still present. In fact, I found that if I tap anywhere near V8 I can produce the pop out of the channel B speaker. If I tap near V7 it doesn't produce any noise. It has to be very localized to the V8 tube socket. (though tapping on the side of the chassis by V8 causes the noise) Of course to get the sound when tapping on the chassis around V8, I have to use the plastic handle of a small screwdriver. Tapping with only my finger works on V8 only.
 
Looks like you found it. Either you have a cold solder joint, or an intermittent component. It is a 50/50 chance that either could be the culprit.

Good luck with your hunt!

Dave
 
I noticed the center channel light on mine would dimly glow as well after I installed new bulbs. With an original bulb, it doesn't seem to glow with the center channel switch "off". It's the only bulb that reacts that way.
 
The center channel lamp is in fact designed to glow dimly with the unit turned on, but the center channel turned off. This allowed it to act as a power indicator, even if the other bulbs burned out. By operating the bulb so dimly, its life span under that operating condition could last multiple generations. To achieve the proper illumination level when in the dim mode of operation, it is important to use the correct bulb so that the proper voltage drop will be produced across the dropping resistor that powers the dim operating mode.

Dave
 
Interesting! I wonder why there was no mention of that in any of the literature. I thought there was something wrong when it came on with the switch off. So it really should always have THREE bulbs glowing when "ON"--the dim center and one "A" and one "B" (Stereo or Reverse) or both "A"s (Mono)?

Maybe I should replace the old bulb then.

Additional: Forgot that I had found this on "that auction site" that was included in a recent X202 auction. It does say that the Red light serves as a "Power On" indicator...
 

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