Another X-202-B In The House!!

notdigital · Sep 6, 2014

I was warned some time ago that this Fisher thing is a bit addicting. Well, yes it is; and in line with that addiction comes a x202b to the fold.

It was advertised at auction as working but needing some help. Well, as Dave mentioned a bit ago in one of his threads, "working" is a rather loose term. Likewise, "acceptable" will vary with each of us depending on the respective intensities and compulsions regarding the Fishers we all have come to know and love. As for me, simply put: I've had this thing a week looking forward to a winter project; cracked it open a few days ago; and it's already driving me nuts!!!!!!! So here we go.....

It was advertised as having a broken switch. No big deal. The prior remedy was to wire it up to the HIGH FILTER slide switch with what appears to be 22g wire. I won't mention that the "new" connection was wrapped in duct tape but hey, none of it was anywhere near acceptable.

I looked at the old switch and saw outward evidence of arcing. Then I noticed something: the housing of the switch proper came in two parts and was EXACTLY the same as that sold by a popular switch vendor (who has run out of switches.) I trolled around for pot/switch combos until I found a suitable replacement. Instead of it being DPST it is SPST and it fits like a glove!!! So for those of you with broken switches fret not. If the switch case comes in two parts, the actual mechanical switch is easily available and replaceable. Just dig around at auction under Clarostat or Centralab until you see what you need :thmbsp:

Now for the questions:

1) The armored cable has 3 wires running to the switch. The colors are different from the 800/500/400 series. Here yellow runs to the transformer, blue runs to the convenience outlets, and white goes to AC. If I kill the convenience outlets by disconnecting the blue wire, does it matter which lug the white and yellow wires go to??

2) I intend to install a thermistor which is absent in this unit. However, I have a .1uf, 100ohm, 400v snubber sitting around doing nothing. Would attaching it across the switch terminals have any negative impact?

3) Was the armored cable soldered to the switch/volume pot case originally?

As I poke around this unit I'm sure other issues will become obvious. Until then, thanks in advance for the help and guidance.

sipuser · Sep 6, 2014

Sorry, can't help with your questions but wanted to ask was it hard getting the two cases a part?

I haven't had to do this yet and the last time I looked at mine I didn't see a easy method to pull these a part.

Good luck figuring this out.

notdigital · Sep 6, 2014

Look at second pic. The very back of the assembly contains the mechanical switch. It is mounted to a case that has three tabs along the top and three tabs along the bottom. Pry open the top 3 tabs with a small jewelers screw driver or something similar and work the case until the bottom tabs disengage. Now look inside the 2 part case you'll see 3 tabs which connect the switch to the case. Pry open those three tabs and dismount the switch. Dat's it

Be mindful that my unit had a TWO part switch case. The replacement switch I had purchased from the Metal guy some months ago was a single case switch. The replacement switch I mounted to the x-202-b appears to be exactly the same as the original Centralab switch except that it is a SPST switch whereas the early originals are DPST. Other than that, the guts are the same.

When I have nothing better to do, I'll see if I can tear apart the toasted switch to see if it can be rebuilt.

dcgillespie · Sep 6, 2014

Not -- Congrats on your purchase -- and yes, I can certainly commiserate with not receiving your B in an ethically correct "as advertised" condition! But, I am sure you'll have it in shape in no time.

1. With only two terminals and the blue lead tied off, it matters not which of the remaining wires goes to which switch terminal.

2. Typically, simply placing a .02 uF across the switch terminals will minimize arcing, and also limit current flow through the transformer better than the much larger cap in your snubber package will, when the switch is in the off position.

3. The cable is typically not soldered to the control assembly, but there was a metal cap that went over the terminals of the old switch that had a U cut out in the side of it for the wires to pass through, and the armored cable to butt up to. The cap was typically soldered to the rear case of the control to hold it in place. It provided complete shielding of the AC power wiring.

Good luck with it!

Dave

notdigital · Sep 6, 2014

An hour or so ago curiosity got the best of me and I fired it up. Thank goodness, it works. A little hum and scratchiness here and there, dead cap bodies all over the place, the usual dirt and dust, blown bulbs, et cetera and et cetera. Ah, what da hell. Gives me something (else) to do

Thanks Dave on the connections; I'll pass on the snubber and cap figuring I have several switch replacements stored away in the event of failure; and I gotta fashion a shield for the switch. Man, an old film can is never around when you need one :yes:

I'll pick away at this thing as time allows. If the preview is any indication, I'm in for a real treat

sipuser · Sep 7, 2014

notdigital said:
Look at second pic. The very back of the assembly contains the mechanical switch. It is mounted to a case that has three tabs along the top and three tabs along the bottom. Pry open the top 3 tabs with a small jewelers screw driver or something similar and work the case until the bottom tabs disengage. Now look inside the 2 part case you'll see 3 tabs which connect the switch to the case. Pry open those three tabs and dismount the switch. Dat's it

Be mindful that my unit had a TWO part switch case. The replacement switch I had purchased from the Metal guy some months ago was a single case switch. The replacement switch I mounted to the x-202-b appears to be exactly the same as the original Centralab switch except that it is a SPST switch whereas the early originals are DPST. Other than that, the guts are the same.

When I have nothing better to do, I'll see if I can tear apart the toasted switch to see if it can be rebuilt.

Thanks Not, I understand and see how you get to the tabs inside now. :thmbsp:

fred soop · Sep 7, 2014

notdigital said:
.....
It was advertised as having a broken switch. No big deal. The prior remedy was to wire it up to the HIGH FILTER slide switch with what appears to be 22g wire. I won't mention that the "new" connection was wrapped in duct tape but hey, none of it was anywhere near acceptable.
.....

If that high filter switch has been used as a power switch, you may want to consider replacing it. Like the power switch, you should be able to disassemble it, allowing for swapping the plastic handle from the old switch into the contacts of a new switch.

dcgillespie · Sep 7, 2014

Not sure where my head was, but in my last post I indicated that the armored cable butt up to the switch cap on the back of the switch. It does, but it also solders to the switch cap as well -- but not to the control.

Sorry for any confusion this caused.

Dave

notdigital · Sep 7, 2014

dcgillespie said:
Not sure where my head was, but in my last post I indicated that the armored cable butt up to the switch cap on the back of the switch. It does, but it also solders to the switch cap as well -- but not to the control.

Sorry for any confusion this caused.

Dave

Dave, in the several pics of UNDISTURBED switch/pots that I've seen, there's always been an unraveled coil of the armored cable soldered to the housing somewhere. In some restores, I've seen that detail omitted. The unit I have has no evidence of the armor being clipped; not even close. Given the attention to detail (or lack thereof) in other areas, I think I would have seen some indication that the armor was clipped. But nada. Nevertheless, I think the better practice would be to tap it to the case so that's what I'll do.

Thanks for following up.

Fred: I haven't examined that high filter switch as of yet. I'm sure it needs cleaning up. If the contacts are eaten up, I'll change it out. Thanks for the heads up.

NoTransistors · Sep 11, 2014

I am still waiting for ME to fix my humming X-202-B.
Best of luck. It is a wonderful amplifier.

notdigital · Sep 11, 2014

Tech ME is always busy with other stuff. Happily the ME that is working on my unit got a few hours today to devote the task. I told him not to be too ambitious; just get it cleaned up for now.

While I can't wait till I can hear it at full glory, today I'll give ME a break

:yes:

dcgillespie · Sep 11, 2014

NO -- If the hum in your B is more of the illusive nature, and not garden variety filter cap stuff, you might check out my recent thread on solving an illusive hum in this model as well. The problem was nothing more than poor lead dress from the factory!

Dave

AlTinkster92 · Sep 11, 2014

That was my X202B Dave was referring to... sounds great now by the way.

notdigital · Sep 12, 2014

Had a little time the last couple of days poking around the 202 and managed to do a lot of cleaning. I found the phono tube grommets to be typically hard as a rock so I changed them out. I temporarily connected the newly installed switch and reconnected the High Filter switch that had been serving power switch duty.

In looking things over I found a few things out of order. Like using 12ax7's in the 7247 positions, like forgetting to snip out a resistor after installing a replacement, and finding what I believe to be a death cap disconnected. I looked over the schematic as well as the parts list and couldn't find that .01 600v cap. So question:

One end of the cap is connected to AC. It appears that the other end was originally connected to a terminal of one of the convenience outlets which eventually leads to chassis ground. I plan to install a proper X1Y2 cap here but I'm wondering why it was clipped? Hum??

dcgillespie · Sep 13, 2014

To me the bigger question is why was it ever installed? It was almost certainly not part of the original build, which can be very nicely quiet without one. I'd make things right in the unit first before immediately jumping to replace it. Then you can determine if its actually needed -- and if so, why.

I don't know if its just a optical illusion, but it appears that the original 22K resistor is cracked, so possibly with it open, some tech just bridged it with a new component. Still, a very poor way to go.

The unit needs 7247s in the positions where it is called for. One half of V4 and V5 are cathode followers, which are required to drive the low impedance volume control circuit, and remote control volume circuit, were that option ever used. The 12AX7 is simply not capable of drawing enough current in that section of the tube to adequately drive these circuits.

Looks like you're well on your way now --

Dave

notdigital · Sep 13, 2014

dcgillespie said:
To me the bigger question is why was it ever installed? It was almost certainly not part of the original build, which can be very nicely quiet without one. I'd make things right in the unit first before immediately jumping to replace it. Then you can determine if its actually needed -- and if so, why.

I guess why it's there will forever remain a mystery. All I can say is that whoever put it in is crazier than me!! The connected lead was very neatly wrapped and soldered and the cap was very carefully tucked away behind the wiring in that area. I pulled it out once I didn't see it in the parts list/schematic. Maybe the factory tech installed it and he/QC clipped it once it was discovered that it wasn't needed. Oh well, in any case, I'll drop it to a "maybe" item on the punch list.

I don't know if its just a optical illusion, but it appears that the original 22K resistor is cracked, so possibly with it open, some tech just bridged it with a new component. Still, a very poor way to go.

Naw, that line is dust. The tech just dropped the ball on it. The resistor's twin is clipped. Besides, the prior tech's MO is to clip and tap solder the replacement. Curiously, BOTH original resistors are well within spec. :scratch2: :scratch2:

The unit needs 7247s in the positions where it is called for... The 12AX7 is simply not capable of drawing enough current in that section of the tube to adequately drive these circuits.

That explains some volume weirdness I found when I first fired it up. I wasn't sure what was going on since I didn't have a copy of the Operating Instructions so I just made a note to come back to it. (THANK YOU Vintageaudio123 for the scan, and for sharing it with the rest of AK :thmbsp

Looks like you're well on your way now

Well, while I'm happy the unit works and, so far, there haven't been any real head bangin' problems, I'm not looking forward to the next phase which is removing all the dead bodies, pigtails, and other detritus. :no:

Perfectionist impulses do have drawbacks :yes:

Thanks for the advice Dave.

dcgillespie · Sep 13, 2014

Man oh man, that thing has got new power supply caps spread out all over the place in it. I hate that for you, as it will entail a good bit of work to clean it up besides the other items you've mentioned.

You might remember a recent thread where I recapped the B+ and low voltage power supplies of an X-202B here:

http://www.audiokarma.org/forums/showthread.php?t=603467&page=3

You might check out the pics in posts# 38 and 44 to give you some ideas for how it can be done in a neater fashion.

The good thing is, it can all be fixed up to your liking!

Dave

notdigital · Sep 13, 2014

Way ahead of you Dave! One of the very first things I did was to read x-202-b rebuild threads, especially yours. Al is one lucky dude! I haven't decided exactly what to do yet but I'm inclined to restuff particularly since the "replacement" caps are all funny valued :scratch2: :scratch2: But another question:

As I was looking over the removed caps, I caught site of the black one--.015uf. I peeked over to C-36 and C-36 off pin 7 of the inverters (where the .015 used to live) and the prior dude put in .022 caps. Leave it there or replace with proper value?

Given the above, I'm going to check the schematic values against what was later installed. I'm a little leery now.

In the meantime, I think it's a little neater now.

dcgillespie · Sep 13, 2014

.015 uF is the correct factory value. It, together with the 820K resistor from pin #7 to ground helps to establish a built in LF filter. Going a little larger wouldn't hurt things today, with .022 in fact being a good value to use. I wouldn't go any bigger than .03 uF at that location.

Already looking better! Watch out for that big 8.2K resistor going between the cans on the two decks. It is stretched tight in the original build. That is what caused the initial problems in Al's unit in the first place. The tension caused the terminal in the can on the upper deck to break away internally from its connection inside the can, leading the the symptoms he described.

Dave

notdigital · Sep 13, 2014

Whew, wasn't looking forward to replacing those. Thanks Dave.

Now I'm gonna peek over at the outputs. Lemee study that section as I'm sure I'll have a question or two.

Another X-202-B In The House!!

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