Another X-202-B In The House!!

[notdigital]

OK, here we go:

A) Each of the outputs is connected, in pairs, at pin 5 with either a red wire or a blue wire. Each pair is connected to one of the 10ohm just north in the pic. All blue and red wiring at pin 5 to 10ohm resistors go bye bye. In place, a single 10ohm 1/4 resistor on bare pin 5 to ground. Yes?

B) For screen stability resistors: working from tube at extreme left to right in pic, remove all wiring connecting the tubes at pin 4; connect a wire to pin 1 of each tube so that they are all connected. Attach 100ohm resistor between pin 1 and pin 4 of each tube. Pin 1 at tube on extreme right is connected to C-50. Yes?

 

[dcgillespie]

Perfect on both counts. Of course the pin 4 to 8 jumpers remain in place as well as shown.

You also might notice the error on the schematic regarding the take off for the screen grids. The schematic shows the cap that they connect to is within C51, but it is not. It is within C50 as you correctly state. C51(A) is really fulfilling what the schematic shows as C50A, and visa versa.

Let us know how it turns out!

Dave

 

[notdigital]

All done with the output section. Now to focus on the top can caps.

I don't understand the values that were stuck in there however (except for the 40uf to 50a--at least that is what I think it is). In any case, I think I'm gonna restuff these with schematic values if I can find caps that'll fit.

 

[dcgillespie]

Not -- Very nice work indeed!!

As an option, remember that the rear most can (hi side doubler cap) can be replaced with a new can cap of exact value but higher voltage to replace the original can without having to go through the restuffing effort. I used a 4 X 50 uF can with each section rated for 350 vdc, paralleling all the internal caps to make a 200 uF at 350 volts. It is exactly the same height as the original cap, and available from AE.

It appears that what the previous tech did was to replace the low side doubler cap (with the one glued in at the rear of the chassis), keep the original high side doubler cap in place, and then strap both doubler caps with a an additional 100 uF 500 volt cap for added capacitance (mounted in at the front of the chassis).

Keep up the great work!

Dave

 

[notdigital]

Not -- Very nice work indeed.

Thanks Dave. But a bit of a hiccup. As I sat down to look over the cans I decided to check all the caps that were replaced. Remember me being leery? Well, lo and behold, C-43,44,45,46 should all be .047uf. I guess someone felt getting 3 out of 4 was close enuf. Arghhh. Another cap added to the list.

Also, C-13, 14, 21, 22, 33, 34 should all be 50uf, 3v; Prior tech installed 100uf's in all those positions. Leave or change??

It appears that what the previous tech did was to replace the low side doubler cap (with the one glued in at the rear of the chassis)

Yup, that little bugger is 270uf. 50-b is 200uf per schematic. However, the parts list has it as 20uf. Another typo??

Speaking of typos, I didn't catch the 50a/51a mistake in the schematic. I saw that the screens were physically connected to 50a. Just letting you know I'm not that smart

As an option.... I used a 4 X 50 uF can with each section rated for 350 vdc, paralleling all the internal caps to make a 200 uF at 350 volts.

I saw that in Al's unit. :thmbsp: But I have a box of orphan caps that I have to use up. Might as well. I don't mind stuffing; keeps me out of the bar :yes: Besides, the way I look at this, it was supposed to be a winter project so by my figurin' I'm 2 months ahead of schedule :yes:

As always, thanks for your valuable and most welcome input!!!!!

 

[dcgillespie]

On the .047s, would that not be C41 thru C44? C45 & 46 are 10 pF HF stability caps that really have no reason to be replaced over time.

The 100 uF caps are large for their positions, but should not present any problems. Ideally, low voltage tantalums are the best devices to use in this position because the operating voltage is so low. If the existing 100 uF caps are aluminum electrolytic units rated at over 35 volts, then I would definitely change them out for lower voltage devices as anything over 35 volt devices will have trouble staying formed to value in those positions.

Get stuffing!

Dave

 

[notdigital]

On the .047's, yes, my bad. My eyes drifted down one line on the parts list. C-41 through 44 is correct.

The 100uf caps are alum electro's rated at 50v. I'll get stock values---might as well.

As far as stuffing is concerned, that'll take a good block of weekend hours which, unfortunately, I don't have in the near future, fam and all. I'll busy myself with little stuff, like working on the brights which were missing in this unit. One question tho as I put together a parts list: is a thermistor recommended?? I know conventional wisdom is that one should be installed for switch protection but the thought of slow ramp-up across the board seems like a good idea. Besides, the slight voltage drop can't be bad. IF recommended, gotta find a place for it since things are pretty tight under there.

Thanks!

 

[dcgillespie]

If you install one, be sure to use a CL-80, as the oh so typical CL-90 is just too small (electrically) for this unit.

Dave

 

[AlTinkster92]

Digital, nice amp, what are those coupling caps? Never seen those before. Audio something, can't read it.

 

[notdigital]

AudioCap Theta 1.0uF 200V Film/Foil capacitor from, I believe, parts express. They were in the amp when I picked it up.

http://www.parts-express.com/audiocap-ppt-theta-10uf-200v-film-foil-capacitor--027-722

 

[notdigital]

Question for Dave:

Looking over the thread re: the restoration of Al's x202b I noticed that he has a cap that I am missing. (center of pic) I can't seem to find it in the schematic.

Also, in that pic there are 2 diodes, top right, that appear to be left out in your restore. Are they hiding underneath?

 

[dcgillespie]

Not -- Veeery interesting. I went back and looked at mine, and that cap is present in mine also. It is almost certainly a .01 uF 600v cap. Neither of my service manuals (Ser#s 40001 - 49999, and 50001 - 59999) show that cap on the schematic or in the parts list, and my unit falls in range of the 50001 manual. Larry????????

I would install the cap. It is connected between the PT wire going to the two B+ diodes, and ground.

The other two diodes you are referring to are in fact still in place -- in fact, they were never removed. If you look carefully, you can still see a (very) partial view of some of their leads.

Dave

 

[notdigital]

Hmmmmm.....there is evidence of the cap being there as Clippy the prior tech left remnant leads. My unit is a 50,XXX unit as well and it's not in my manual either. I scoured the net and found examples of both restored and unrestored units: some have it in, some don't. :scratch2: :scratch2: Well given the fact that it appears to have resided at that location, I'll put it in as .01 600v.

I went back on the diodes: yup, I see the leads now. Thanks!

 

[audiodon]

That filter cap to the chassis was a common and undocumented feature in Fisher gear all the way through the 400.
I've driven myself nuts looking for it.
They come in two formulations. One is the black cap as shown in your photo. The other is a white cap with a hard body and wax ends. Sometimes the white ones blow the end right off the cap. I believe I've gotten two Fisher pieces where the ends were blown out of the caps.
Sometimes I confuse these filter caps with a death cap.

 

[notdigital]

Mystery solved! Thanks Don.

Now, any ideas on the cap in post #14? I don't think it is documented either

 

[larryderouin]

The cap in post #31 is reminescent of the snubber on the 400 right at the diodes. Agree with DON on this.

Cap in #14 is the "Death Cap". But it is un-documented, at least on the copy of the service manual I have. The ancillary 110v plugs are directly off the mains, so that would make it a "death cap". It's possible it got clipped due to hum, or it shorted.

Not all changes made later got into the manuals, unless there was a subsequent 10000 series, and then not even then. They got sloppy at times with all the changes and some didn't make it in. And they even state that they reserve the right to make changes that would go undocumented, or words to that effect.

Larry

 

[notdigital]

I think you're right Larry. I think that cap is wired on one side to the fuse, the other to ground via the AC outlet (altho it is clipped) I'll check when I get home and compare to an 800c I have open. If it checks out, I'll pick up an X1Y2 and pin it in there.

Thanks guys :thmbsp:

 

[notdigital]

Well, after being distracted by other things in life, I was able to devote some quality time to Fisher restoration these last few days. As I began formulating a plan of attack, my mind kept going back to that weird balance thing I detected a while ago. In an effort to determine whether it existed using headphones, I popped a pair on and WHA? I couldn't shut the speakers off! I soon discovered that Clippy disabled ALL of the slide switches, save the Loudness Contour, by installing jumpers across the switch terminals. Needless to say, out they went and the switches were restored to their normal function. A BIG shout out to Audiodon for providing a replacement slider switch :thmbsp: Much better than what it was: http://www.audiokarma.org/forums/attachment.php?attachmentid=539659&d=1410492362

Next up was changing out the several 100uf 50v capacitors for more appropriate 50uf 16v axials; a few other caps that either weren't replaced or were missing were installed as well; closed up the power switch and capped the assembly with the top of a metal tube which fit perfectly; then the cans....

 

[notdigital]

Stuffin' The Cans...

I'll admit it, I like to stuff the cans. More work, more time, but hey, it's for me:yes: So, the high voltage/cardboard covered can got cut at the flange. Once the guts are removed, stuffed, and the can is glued together again, the cardboard covers the scar and no one would know the difference. Underneath, there is very little to show that it had been operated on. Likewise, the low voltage doubler was opened but from the bottom since the chassis hides most of the opening. Lastly (for now) C-51 was cut open and stuffed with 2 stacks of 2 caps. A little trickier to assemble but it fit.

 

[notdigital]

All in all, I think it looks better than before.... http://www.audiokarma.org/forums/attachment.php?attachmentid=539871&d=1410611187

Only the bias can remains and the major electrical work will have been completed. Next in the queue is a voltage check and how to utilize the Bias Adjust and DC Balance pots. I got some readin' to do