How Chassis Rust Can Encourage Mods

[ckreymann]

So, I decided that there's no point in trying to restore my Fisher X-101-D unless I blow it out and start over. It has an almost perfect faceplate and original knobs. It's now going to be a complete rebuild with some mods. Look here and you'll see why:
http://lagunatechnics.com/audio/fisher/images/x-101-d_rust.jpg

Rust has always been a bummer that decides whether you spend time on a unit or make it a parts bucket. Sure, I've seen lots of painted amps, but that's not my style. I like to make at least an effort at maintaining original appearance and design as much as reasonable.

Naval Jelly can work on light rust but can leave metal discolored and pitted. So I fired up the random orbital sander with 180 grit metal oxide paper and sprayed a light coating of clear Permalac on the exposed metal. We'll see if it passes the test of time...I'll report back in about 40 years...

http://lagunatechnics.com/audio/fisher/images/x-101-d_clean.jpg

At the risk of sounding sacriligious, the signal path and switching in this box are extreme. I mean, there were at least six feet of wire for reverb in/out and, as was the practice back in the day, lots of tape head connectors/controls. They're outta there.

Since this means fewer connectors (which need replacement anyway 'cause they're too close together), the speaker connectors and i/o for Tuner, Aux, Phono Hi and Phono Lo fill fit on the top of the chassis.

BTW: I've posted a service manual for the X-101-D over at the fishergroup forum, but it's highly compressed and a little fuzzy (they're almost out of disk space). I also assembled a complete fold-out schematic and parts list on one page that's very legible. If interested, PM me and I'll send what I have or tell me how to post it in this forum.

Any foreseeable problems, thoughts or discussion? :scratch2:

 

[ke4mcl]

rust doesnt bother me too much. a little surface rust can be easily worked out. i dont get carried away with chassis polishing or any of that. im more concerned with sound and reliability than looks.

obviously, a beater is a much more likely candidate for mods you wouldn't do to a pristine piece.

 

[jaymanaa]

No sacralige at all. "Most" older amps can certainly benefit from modifications. Parts are better, and like you say, there's a lot of circuit "crap" that is obsolete. I've never worked on that model, but if it has a center channel, I'd get rid of all that mess too.

 

[ckreymann]

rust doesnt bother me too much. a little surface rust can be easily worked out. i dont get carried away with chassis polishing or any of that. im more concerned with sound and reliability than looks.

obviously, a beater is a much more likely candidate for mods you wouldn't do to a pristine piece.

Yep, sound and reliability are what counts the most. Unfortunately, when I see rust there's an obsessive compulsive breaker in my head that can't be reset 'till it's gone.

Glad for your comment about beater vs. pristine. Personally, if I could ever afford to get a pristine piece I wouldn't even think about mods.

Thanks.

 

[ckreymann]

No sacralige at all. "Most" older amps can certainly benefit from modifications. Parts are better, and like you say, there's a lot of circuit "crap" that is obsolete. I've never worked on that model, but if it has a center channel, I'd get rid of all that mess too.

Seems like amps can be a lot like software: Too much "feature bloat". The X-101-D was one of Fisher's last, best (arguable) amps and they loaded it with features to compete with all the other big amp names.

Yeah, the "derived" center channel gets snipped as well, as does the mono/stereo/reverse switch (like, WTF?). I'm tracing the signal path through the circuit and eliminating the unecessary crap since I'm starting from scratch anyway.

Thanks,

Chris

 

[gadget73]

The mono/stereo switch is actually a useful thing I think. I have had a few "stereo" mixed records that just sounded awful. Flipping that switch nuked it, and I got a nice clean mono sound. Reverse is also occasionally useful if you end up with tape recordings that were made with the input leads backwards.

 

[ckreymann]

The mono/stereo switch is actually a useful thing I think. I have had a few "stereo" mixed records that just sounded awful. Flipping that switch nuked it, and I got a nice clean mono sound. Reverse is also occasionally useful if you end up with tape recordings that were made with the input leads backwards.

Good point, thanks! Looks like I should keep it now that I understand why it's there.

Chris

 

[ckreymann]

No sacralige at all. "Most" older amps can certainly benefit from modifications.

My mods are fairly conservative. You can see them at:

http://lagunatechnics.com/audio/fisher/images/x-101-d_mods1.jpg

http://lagunatechnics.com/audio/fisher/images/x-101-d_mods2.jpg

Basically, after I removed the tape/reverb/center channel connectors, I put a blanking plate on the rear of the chassis. What's left on top is tuner/aux/phono hi/phono lo and speaker connectors.

If I can get all the parts connected in all the right places, this might just work...

Chris

 

[Dadbar]

reliability definitely trumps originality for a unit you will use all the time. I celebrate the excellence of your choices. The stereo/mono/reverse switch, though, is nice to have if you use headphones a lot....and for easy troubleshooting. I put one into a home brew amp I made recently...and it gets a lot of use.....

 

[Patrice B]

The mono/stereo switch is actually a useful thing I think. I have had a few "stereo" mixed records that just sounded awful. Flipping that switch nuked it, and I got a nice clean mono sound. Reverse is also occasionally useful if you end up with tape recordings that were made with the input leads backwards.

In my case, the "reverse" function of my Heathkit AA-100 leads to me discover something (really) strange:

In phono mode, one channel sounds a little different against the other side (more trebly, level slightly lower...).

I reversed the L and R leads of the TT on the RCA jacks and switch to "reverse stereo" to get the correct placement of L and R... and there's no more difference in sound quality. Strange one I must admit (resistors and caps replaced in the phono section, tubes also...), maybe something to do with TT grounding versus amp grounding, I dunno!

Sorry for the little OT subject.

So, yes, these switches are sometimes useful.

I also keep these circuits to check for balance between channels...