• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Pitiful X-202

C43 is the filter cap for the DC heater/bias supply. The stock values work fine, but if you increase them, there is little point going over 2200 uF each.

C46 is the primary filter cap. The only caps you can safely increase within that cap isC46A and C46D. Sections B & C serve the output tube screen grids -- if you want to increase them, then you will definitely want to install Screen Stability resistors first.

C55 is the secondary filter cap. You can increase values there with little concern if you want to.

C46A can be increased somewhat in this case due to the presence of the resistance Fisher provides between the cathode of the rectifier tube and the first filter cap. I wouldn't go over 60 uF as a total value if you chose to increase it.

Dave
 
Dave: what are your thoughts on replacing the power cord on a Fisher X-202?

my cord is looking a bit tired but still seems intact with no cracks, etc.

however, it's pretty short at only 5ft in length

is it worth the trouble to replace the cord, and if so do you have any recommendations?... eg. 2-prong polarized, or 3-prong with ground

also wondering about how to determine the correct polarization orientation regardless, now that all wall outlets have this feature

I'm mainly concerned with safety & reliability for this, but it would be great if anything could improve SQ as well (and of course, a nice new cord, especially something thicker always looks impressive...)

PS: I also plan to install a CL-80 inrush current limiter

thanks!
 
Stay with a two prong cord -- do NOT install a green wire AC ground cord. Such cords are fine for modern equipment that does not mix chassis ground and audio ground. But the old equipment has the audio ground operating at chassis ground, so the installation of a an AC ground power cord on vintage equipment then causes nasty ground loops to form with any other pieces that have their audio grounds tied to the AC line, such as cable and satellite receivers.

Fisher always intended the AC switch to operate on the neutral side of the power line -- this to minimize hum from an AC switch located so close to sensitive audio circuits (i.e., the volume control). The best approach is to use a polarized two prong cord, with the neutral side wired to the AC switch, and the hot side to the fuse post. Additionally, the X-202 does not include an AC bypass cap. If you want to install one for minimum hum, then install an X-Y rated cap from the neutral side of the line (before the switch), to the chassis.

A CL-80 is the correct device for the 202, and should ideally be installed on the hot side of the line in series with the fuse post.

Dave
 
thanks Dave!... as usual your response is top-notch

what capacitance value do you suggest for the X-Y rated AC bypass cap?
 
thanks again Dave!

on your other X-202 thread ("Adding DC Bias/Balance Test Points to the X-202"), under PERFORMANCE MODIFICATIONS you mentioned this item:

1. Removal of the permanent LF filter circuits included throughout the design.

I'm very interested in this modification... do you have any more info on this mod, what it does, and what's involved?

if it's doable by a mere mortal, and has a noticeable impact on SQ, then I might like to try it

I'm currently ordering parts, so this would be the ideal time for me to consider adding this to my list...

thanks
 
I will try to get something posted soon with pics. In the mean time, for parts you will need to order 1.0 UF 250 vdc caps for installation at C26 and C53 (Sams), and .027 uF 250 vdc caps for installation at C31 and C58 (Sams). This will address the passive filters, while the active filters only involves parts removal (C20, C47, C24, C51 Sams). When removed, a wire should replace these caps.

Dave
 
thanks Dave

wow... this looks pretty complicated (ie., I wouldn't have much of an idea of why I would be doing some of this!)

what stands out for me is just how different these parts are: not just in values, but in capacitor types, and locations in the circuit... seems to be all over the map

Q1. is there any chance that I might be looking at a different parts list / schematic?... my parts list shows stock values as:

C26 = ceramic 30uuf, N150, 1000V
C53 = electrolytic, 8uF, 50V
C31 = mylar, .68uF, 250V
C58 = ceramic 15uuf: N75, 1000V
---------------------------
C20 = mylar, .01uF, 250V
C47 = electrolytic, 25uF, 6V
C24 = ceramic .02uf, 20%, 500V
C51 = mylar, .047uF, 400V

Q2. should the new caps all be *film* caps, ie, metallized polyester or polypropylene?

Q3. what does this mod accomplish, and what has been your experience with in real life? (ie., is it worth it)

thanks!
 
Note on my last post that I had the word "Sams" in parentheses -- this meaning that the component designations were referring to the Sams schematic, as opposed to a Fisher schematic.

The new caps should be of the film type of your favorite choosing. Modern film types are such that even the 1.0 uF cap can be had in a reasonably small size as a film capacitor. As to the composition of the capacitors, that's a game I got out of decades ago, when numerous well controlled double blind tests I participated in (on both sides of the curtain) concerning the capacitor "question" failed to produce any consistent preference or notable change in delivered performance among the participants, and failed rather miserably. Therefore, I leave that choice up to you.

In my opinion, the modification is not one so much of improving the sound from yesterday's sources, but of allowing all of the LF information of today's sources come through unhindered. In comparison to my un-modified X-202, the low end is fuller, but more noticable is the fact that it is more solid and defined on today's mediums that contain sufficient LF material to put a spotlight on that end of the audio spectrum. In the side by side comparison with my unit, the subjective impression was not that the modification boosted the bass but rather, that the bass through my unit was filtered -- which it was. When my X-202 retires its hat as being a reference unit, I will install the modification in it.

Dave
 
I've heard of Sams being mentioned on AK, but always figured they were just someone's "photocopies" of the original manufacturer's paperwork

stupid question, but how do I go about getting a copy of the Sams schematic (and parts list) for an X-202 amp?... are they posted somewhere?

thanks
 
Last edited:
Not a stupid question! Sams is an independent publishing company that takes manufacturer's equipment, and draws out their own schematic of the unit based on the unit provided to them. In a Sams "Photofact", they identify where each component is actually located in the chassis, give specifications for the various transformers and other parts (by measurement) not specified on a Fisher schematic, and also provide voltage and resistance readings at each tube pin in the unit. It is a somewhat more in depth servicing aid than the service manual that Fisher provides, and can be used as a cross check to ferret out schematic errors which can exist both in the Fisher and Sams schematics. Sams copies any adjustment procedures offered by Fisher in their photofact files. The Sams Photofact for the Fisher X-202 is Folder #4 in Binder set #526. There are AK members that have many of the Sams folders scanned that will email them to you (post a request), or you can check the auction site, where original Sams folders are often available. If you do a search for this model, a Sams folder for it may come up if one is currently being offered. Also google it to see if you can find one that way that you can download. If you cannot find a Sams schematic, I will try to do a cross reference for you when I get some free time.

Dave
 
thank you!... actually, I think I already have it... "set 526, Folder 4", Date 4-61"

I'd always wondered about this document... I got confused when I tried to use earlier, it since part numbers seemed weird (compared to what other web posters had referenced)... it also some data that I wanted that was different... for example, B+ voltage at output tubes shown as 370V (Sams) vs. 390V (Fisher)... so I started using the actual Fisher document because I assumed surely they must be the authority

which is the better one?... wouldn't Fisher's be?

geez, how confusing: 2 sets of drawings and data for the same thing, that use similar -- yet different -- part numbers!

I'll try to figure out which parts are the equivalents, and then decide if I want to tackle this "LF Upgrade"

thanks
 
Fisher was notorious for running changes in their equipment, and often issued multiple service manuals to cover different serial number ranges of the same piece of gear. (The differences between the first and second generation of the MPX-100 are probably the most extreme example.) Sams usually didn't issue as many versions, so they often didn't cover ever variant - but they did have the advantage of working from a completed piece of equipment, so they'd sometimes catch things that were changed between the engineering department drawing up the initial schematics and equipment going into production. And sometimes they made errors.
 
That's the nice thing about Sams. Since I've already given you the Sams part number, you can just look at their under chassis pic, look for those part numbers, and then know exactly where those components are.

Good luck with it!

Dave
 
here are the part # equivalents between the Sams and Fisher schematics for the parts involved in the "Low Frequency Upgrade"

SAMS = FISHER (spec uF/V)
=================================
C26/C53 = C31/32 (0.68/250 mylar)
C31/C58 = C44/C45 (0.01/250 mylar) * Sams schematic shows incorrectly as 0.1uF
C20/C47 = C7/C8 (0.001/1000 ceramic)
C24/C51 = C27/C28 (0.001/1000 ceramic)

...and I'm going to go ahead with this mod... seems like a good idea, and now that the part #s make sense(!), seems pretty doable

thanks!
 
Dave:

please confirm it is OK to use 250V rated resistors for the 10 ohm Bias, and 100 ohm Screen Stability resistors... both are 1/4 W rating, and these do not seem to come in 350V (which I've heard should generally be used in tube equipment)

thanks
 
The voltage across all of these resistors is no more than a couple of volts under a worst case scenario, so even the lowest voltage rated components will be fine to use.

Dave
 
thanks Dave, you've been a super help to me so far... your (quick) advice and information is phenomenal -- and hugely appreciated

my parts should arrive tomorrow (via the quick-ship miracle of Digikey...), then I need to pick up a few supplies locally, and then need to make time to start on this work in earnest

getting pretty stoked now!... the more I look at this Fisher, the more I like it... sure it worked and sounded pretty good as-is, but I'm pretty confident that my completion of the previous restoration plus a few improvements will end up in a success story
 
what is the correct order of the front-panel jewel lights?

I believe that mine are all original an unaltered and they are ordered:
green | yellow | red | yellow | green

however, most similar Fishers I see on the web are different:
green | yellow | red | green | yellow

I think I've seen maybe one other like mine out there... is any one way correct?... personally, I kinda like the symmetry of mine

???
 
The Fisher order, looking at the front from left to right, is in fact Green-Yellow-Red-Green-Yellow, if maintaining authentic appearance is important. Some also favor the symmetry you suggest. In reality -- and I don't mean this in any negative critical way (because I like their looks as well) -- they were really kind of an appearance gimmick, since the switching sequence of the lights can be interpreted in different ways, and in some of the ways that Fisher did, it simply makes no sense at all. Personally, I go for the authentic look and just enjoy the light show!

Dave
 
You must log in or register to reply here.
Back
Top Bottom