X-101-C McShane kit electronic restoration

[3l3ctron]

I purchased the kit a few months ago, and now I’m getting started. This is the biggest job I’ve yet attempted, and can use the resident experts’ assistance here. I’ll be moving slow, because I love this machine and want to avoid mistakes. It’s the best sounding piece of equipment that I have!

I’ve been looking things over, and doing a lot of tracing inside the chassis versus the schematic. Many of the passive component replacements that Jim selected have different values than the original. So, lots of triple and quadruple checking of things.

 

[3l3ctron]

1st look underneath.

 

[3l3ctron]

A couple of these ww resistors look like they’ve been getting pretty hot.

 

[3l3ctron]

Some previous work appears to have already been done to repair the on/off/volume pot which at this time works perfectly.

 

[Omegaman]

Best of luck
Take your time, plenty of pictures and ask lots of questions

One step at a time and don't guess, Plenty of people to assist

I did a McShane install on my Fisher 800c and it still plays beautiful three years later

 

[3l3ctron]

It’s probably not the popular choice around here. But, I don’t intend to stuff the old can caps. I’ll use the clamps he sent me to mount 2 of the new caps to the chassis.

 

[3l3ctron]

The 200 uf black can cap C25 was replaced with a 560 uf/400 volt “very low esr” type. The dual section can next to it C26 was replaced with the same single section 560 uf type.

It appears the “missing” 40 uf section will either jumper from C27 the 40/40/20/20 multi section cap (instructions are to make the 20/20 sections together in parallel), or from the single 47 uf axial. But, I haven’t installed those yet. Because, I haven’t worked that out. I’m a little confused there... I may put a small terminal strip in there to make it more neat near those currently non terminated leads. But for right now I’ve just clipped them together.



Another view

 

[3l3ctron]

Also, C22 was replaced with a 220 uf low esr radial type. I had to make a jumper for it to reach it’s terminal.

 

[3l3ctron]

Yeah..The terminal is in.

 

[3l3ctron]

I have questions now..

1. Does the negative lead of C26a need to be connected to a ground terminal, since it doesn’t have the same kind of soldered-to-chassis twist connectors as the can it replaced, or does the new chassis clamp function to ground it to the chassis also? The former is what makes the most sense, but wanna check first.

2. The positive lead of C26b (now a 47 uf axial) goes to the same place as the others on the new terminal I installed. It looks like the negative lead should also go to the same ground as the negative terminal on C26a. Is that correct?

 

[3l3ctron]

After more tracing and meditation, I believe that I have found the answer to my questions above.

C25 was never grounded like the other can caps to begin with. It was mounted isolated from the chassis on its’ board which was riveted to the chassis. It was wired to C26a/b which was grounded.

On the new C26a I ran a 600v wire from the common lug to a new ground terminal I installed. R62 used to run to the grounded twist tab. I re-routed that to the same new ground terminal.


Then the C26b 47 uf axial’s negative lead also goes to the new ground terminal. I also swapped out R62, R74, & R79-82 to the new higher wattage ones in the kit (those worried me because of my color blindness, but it actually was a breeze since I know how to use my DMM testing the old resistor’s values to verify).

There’s not a lot of clearance there, but it fits.

 

[3l3ctron]

C27a/b/c also was installed into the chassis last night. Grounding the twist lugs to the chassis was difficult. It isn’t as pretty as the factory’s work, but there it is..

Also, C27c is now 40 uf after wiring the 2 x 20 uf sections together in the new 4 section can - now making it 40/40/40.

For now I’m waiting to solder some of this stuff into place until my lay-out is verified.

 

[3l3ctron]

I added the new cathode resistors to pin 5 (x 4) tonight.

 

[3l3ctron]

No comments from the peanut gallery..ok

I’ve soldered all of the connections in place, and tested the ground connections with my DMM.

Next up...Attach 8 ohm loads to the speaker terminals, and power up with the dim bulb to test.

If everything is good from there, I’ll continue on with the audio path caps and grid resistors. I probably won’t have time to get started on any of that until after the weekend though.

 

[larryderouin]

3l3ctron. Looks good to me. One thing tho. ON CATHODE BIASED FISHER GEAR the MAX GRID resistor for the 7591/7868/6gm8 family is 1megohm. so unless those 330K resistors have drifted, leave them be. Do you plan on adding screen stability resistors (100ohm 1/4 Watt)?? would be a real good idea.

EDIT NOTE: The 1 megohm GRID RESISTANCE value is noted in the 7591/7868/& 6GM8 Tube Data sheets in the Tube manuals.

 

[3l3ctron]

3l3ctron. Looks good to me. One thing tho. ON CATHODE BIASED FISHER GEAR the MAX GRID resistor for the 7591/7868/6gm8 family is 1megohm. so unless those 330K resistors have drifted, leave them be. Do you plan on adding screen stability resistors (100ohm 1/4 Watt)?? would be a real good idea.

Hi, Larry. Thank you for dropping in.

I’m basically following the kit instructions. And, the 330k grid resistors will be replaced with 200K Ohm .5 watt MF (x 4).

Regarding the screen stability resistors, can you explain it to me better why it’s a real good idea?

 

[larryderouin]

3l3; The main reason the Grid returns are dropped in value is the value exceeds the maximum grid resistance(300K) for a FIXED BIAS circuit. As the great majority of Fisher integrated amps are Cathode Bias a maximum resistance of 1 megohm (1 million ohms) is permitted as noted above. The X-101-C is cathode bias, so the 330K need not be changed. I have a 101-B using Russian Tung-Sol Re-Issue 7591's and with the 330K grid return resistors show no ill effects.

A little light reading with regard to keeping output tubes (both old stock and new stock) happy and healthy, by Dave Gillespie. This will explain why way better than I can. http://www.tronola.com/html/maximize_tube_life.html. Once you read that and understand why the need for screen stability resistors, we'll show you how and where to install them.

 

[N8Nagel]

I purchased the kit a few months ago, and now I’m getting started. This is the biggest job I’ve yet attempted, and can use the resident experts’ assistance here. I’ll be moving slow, because I love this machine and want to avoid mistakes. It’s the best sounding piece of equipment that I have!

I’ve been looking things over, and doing a lot of tracing inside the chassis versus the schematic. Many of the passive component replacements that Jim selected have different values than the original. So, lots of triple and quadruple checking of things.

Tell me more about this kit... have same unit looking pretty shabby sitting on the kitchen table right now; undecided whether to fix or flip.

 

[3l3ctron]

Tell me more about this kit... have same unit looking pretty shabby sitting on the kitchen table right now; undecided whether to fix or flip.

I ordered it from Jim McShane, and contacted him through his website via email.

http://www.mcshanedesign.net/

 

[N8Nagel]

OK I will contact him. I thought he only sold tubes and kits for HK based on looking at his website. I really could use just an easy resto on this one as it's cosmetically challenged.