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Transistor numbers?

Posted by altecaddict (A) on January 7, 2007 at 10:22:09

Hello All, I've got a situation here that's kicken my butt. I'll try to keep this breif and to the point. I recently re-capped a Fisher model 59A amplifier in my old Ambassador console (sentimental value). This amp is a hybrid which uses 6HU8s in front of transistor outputs. The transistor part is where I get into trouble, as I am really just a solder slingling tube DIY guy. All went well with the recap, and the old girl was singing more beautifully than ever, when I noticed that one output heatsink was considerably warmer than the other. This particular amplifier has a variable resistor for each pair of transistors (two pair per channel). Not being able to locate any service info., I decided that I would measure the voltages across the cooler channel's vriable resistors and compare it to the hot channel. Well, one of the resistors on the hotter channel was running 900mv while the others were at ~350mv. When I attemted to adjust this, I discovered that the control was filthy and felt like it was full of gravel. The instant I turned it, the voltgae jumped, and the fuses in that channel blew. (ooops) I then decided to clean these controls, so I took readings of the ones that were working properly (~6ohms), cleaned them all, and readjusted back to 6ohms. The one channel is fine, but the one that blew the fuses, blows them instantly on application of power. I'm thinking I may have blown up a transistor along with the first set of fuses (one transistor measures different readings from the others with an ohm meter?). My thought was to replace all the transistors, and get hold of the bias setting info. Problem is, I can't figure out how to decode the part numbers on the transistors. One side is RCA, and one side is Sylvania. It would appear that this amp had a major channel failure at one time because one of the interstage TXs is newer allong with the different transistors. The two Sylvy numbers are ECG121 620KI, and ECG121 651K1. The RCAs are TR 35144 VFW274 5A, and 35524 VFC 4L. If anyone recognizes these numbers, or could point me in the direction to find out how to cross them to something, I would be most greatful. Oh, and of course if anyone knows where I could find a service manual on Fisher Hybrids of the 60s, that would also be a tremendous help. As a matter of fact, I'm open to any and all advice at this point. Thanks for reading, Jay

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