Fisher X-202-C Nightmare

[DirkSpec]

Hello,

I bought this X-202-C from eBay recently and witnessed a higher level of evil when it comes to description deception. This was listed as an amplifier which blows the fuse immediately when turned on therefore no "further" testing was possible, which turn out was not the case. As I brought it up slowly with the light bulb and variac, everything went fine till I reached full line voltage. At that moment, I was prematurely happy and confused, as the description was not matching the situation. Suspecting nothing, I moved on and ordered replacement parts.

Something bothered me however, and I woke up in the middle of the night and started checking the output transformers, and right away it was apparent that one of them was not measuring right. These transformers are marked as T1158C116 (1 and 2) and the primary in one was open from center tab to one side.

I have removed that transformer to open it up, hoping that it is just the solder connection which may have failed during transportation, but no, it was not the case. I was surprised to see that there was an unused feedback tab (Class AB Ultra-linear operation?). The primary winding was good to that tab, but from that tab to the one side, there seems to be the problem.

I am assuming that this is the end of the road for this transformer. I am now considering my options. It seems like there are more 500C or 800C or even X100 transformers out there. I was wondering if the input impedance of those would be a match for these transformers? The T991-116 or T860-116 seem to use the same tubes, and I am wondering if I can replace the current T1158s with a pair?

Any thoughts?
Dirk

 

[Duke58]

You are thinking that the bad output transformer that is causing your Fisher amp to not work?

 

[freddi]

did that use the same output transformer as the KX200? My old KX200 read ~6400 ohms reflected (6400 one unit, 6398 the other) with a 7.5 ohm resistor on the 8 ohm tap and -3dB around 89KHz - both outputs nearly identical and miles better than Hammond - DCR was ~48-0-53.

 

[DirkSpec]

did that use the same output transformer as the KX200? My old KX200 read ~6400 ohms reflected (6400 one unit, 6398 the other) with a 7.5 ohm resistor on the 8 ohm tap and -3dB around 89KHz - both outputs nearly identical and miles better than Hammond - DCR was ~48-0-53.

I have checked and found out that the KX200 transformer codes are different than these. KX200 is using a pair of T908-116s.


/Dirk

 

[Tom Bavis]

The 500C output are larger than the 500B - both are EI-100 core size, 500C has 1.75" stack, 500C is 2.6", 202C is EI-112 x 2.25". So 500B will fit, 500C may (measure carefully).

 

[srh]

DirkSpec, I had the same problem with an X-100-C transformer. the cause was a failed connection between the flying lead and winding pigtail. Corrosion was the culprit. Fixed by soldering a new lead to the tail.

 

[DirkSpec]

DirkSpec, I had the same problem with an X-100-C transformer. the cause was a failed connection between the flying lead and winding pigtail. Corrosion was the culprit. Fixed by soldering a new lead to the tail.

Good encouragement, I am going to take a closer look. The thing is, the resin became very brittle after cooking for all these years and it is very difficult to follow the trace backwards. I will try to follow the lead upstream a little further and see if the fault is anywhere close.


Thanks,
Dirk