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A tale of two Fishies - X-101-C integrated amp restorations

Appreciate the info Dave, you're a wizard. I think I'll hold off on them for the time being, as this was a seldom used system all it's life and had all original tubes. I've got a bunch of other projects lined up on the bench, one in particular that I'd love to pick your brain about, but I'll likely add the resistors at a later date. Thanks, as always, for the clarification.

Alan
 
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While I've got you, I remember reading that you had some other recommendations for this unit. Changing screen grid resistors maybe? I don't remember specifically. Is there anything, while its still in testing phase, that you would have highly recommend I take care of now? Appreciate the help
 
Contrary to yours, my experience with these units is that they in fact run quite warm, and run the output tubes rather hot as well. Today, if using the Russian tubes in the cathode string, they tend to not pull quite as much current for a given voltage applied to the heater, which in turn lets the unit run somewhat cooler at the prescribed bias point. But most typically, tubes manufactured in the 60s will cause the unit to run pretty hot when biased correctly.

At the very least, I have always recommended installing a small power supply to not only power the small signal tube heaters, but also convert the output stage to fixed bias operation. This effort is fairly involved, but will typically up the real power level of the unit by nearly 50% (producing about 27 watts RMS at 1 kHz with both channels driven). If you add EFB(tm) into the mix, then the unit is basically capable of 35 watts RMS per channel under the same conditions. Beside the huge payoff in tube life, the unit runs much cooler than stock, and distortion drops significantly as well. This was the subject (in part) of my thread on the X-101C, of which this thread became a part of.

I believe that Audiodon may still have the unit that was the subject of this thread, so he may be able to comment more about it since he would have had it for quite some time now.

Dave
 
Yes sir, and thanks for your response. I agree, and I spoke too soon, about the heat. Indeed it still is running rather hot, it just took longer to get there. I guess while it's burning in I'll go through all the details of the unit you're talking about. I remember leafing through it but I guess a more thorough reading is required. Once again thank you, and all of you guys, for the responses and for the trail of data for us to follow.

Alan

Edit; when I say it still runs hot, it does. Hotter than any of my other gear. BUT, absolutely nowhere near as hot as it did before the rebuild. I can touch the transformer now, with the part of my hands that I actually can feel, and keep it there. Whereas before, my skin n actually blistered up.
 
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So I've got my hundred hours of break in on the new capacitors. Today, after getting a package Saturday, I replaced the 2.2k 7w resistor, out of the five I bought one was exactly 2.2k, and the 'death cap' with an orange drop as well as tidy up anything that didn't look 'good enough' for me. Now I'm just waiting on the rest of my
Knob brites and I can get my x-101-c and fm-200b into my living room system. Thank you all for your assistance and inspiration. I look forward to future projects and bs'ing!
I also re-checked the bias after today's surgery. Looks good to me. Had a mini freak out after I set the bias I turned the volume up a bit and heard a slight hum, reached in with the wooden end of a small paintbrush and it got louder. Decided to take a break, put the bottom cover back on and turn the unit right side up. Powered it up and she was dead quiet. Whew! Scared me. Does the bottom cover act as shielding?

Alan
 

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I'm finally getting the last pieces together to button up my 101. I will be, temporarily, using the FM 200B without restoration. It seemed to work great on the bench, and I'll have it located, in the rack, where I can remove it to do some work to it. Got all of my knob brites glued on today-still missing a knob on the tuner- cleaned the dial glass, replaced the #47 bulbs. I gently rocked those dial bulbs out, that look like fuses, and cleaned them. Niether of them worked. I powered up to make sure the 47's lit up, they did, and so did the dial bulbs! Nice!
Anyway. Question; I replaced the old burnt diodes I the x-101-c with in4007's. They seem to work fine, but would RG4C diodes be more appropriate? Thanks folks.

Alan
 
The 4007 diodes are already a step up in durability over the original diodes, which most often are found to still be in serviceable conditions in vintage Fisher equipment. The RG4C would be a step further yet dependability wise, and is high speed to boot. You can install them if it will give you greater satisfaction, but in terms of any real dependability or performance improvement gained, that is highly questionable. The claimed sonic improvement due to the use of ultra high speed diodes is next to impossible to demonstrate on a scope, let alone hear.........

Dave
 
Ps, Dave, I wasn't considering the 'snake oil' factor. I just wanted to make sure that what I put in was adequate for the circuit. I like to do things once.

Alan
 
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