Fisher 800c project for 2014

Power supply complete

Here are the final changes for the McShane Kit for the power supply

See how I had to accomodate C91D where C95 was.

I ran the NEG from the new C91D back to the original C91D NEG

attachment.php


Closeup
attachment.php



That completes the changes for the power supply

Next are the screen stoppers and cathode resistors
 

Attachments

  • After C98.jpg
    After C98.jpg
    141 KB · Views: 92
  • After power supply changes.jpg
    After power supply changes.jpg
    94.2 KB · Views: 92
Last edited:
Cathode resistors

New 10 Ohm Cathode resistors on PIN 5 of each output tube

Before
attachment.php


After
attachment.php



What do I do with the 274 Ohm .5 resistors that are labeled screen stoppers on the McShane parts list?

Were the 10 Ohm 1/2 - 1 watt resistors labeled Cathode resistors on the McShane parts list the correct ones to put on pin 5?
 

Attachments

  • DSC03499.jpg
    DSC03499.jpg
    111 KB · Views: 169
  • DSC03502.jpg
    DSC03502.jpg
    125.7 KB · Views: 82
Last edited:
Getting back to post 80: You're using a 3 tab strip. Is either of the outer tabs that you are using touching chassis??
 
Getting back to post 80: You're using a 3 tab strip. Is either of the outer tabs that you are using touching chassis??

No the center tab with screw is touching chassis but the outer two are not

In the end I only used a single tab on it. The POS wired directly

Thanks
 
What do I do with the 274 Ohm .5 resistors that are labeled screen stoppers on the McShane parts list?


Look at this pic from Dave's 800C rebuild - run the resistors from pin 4 to pin 1, snip the bridging wire that connects pin 4 & 8 between each socket, then add a connecting wire to pin 1 on each socket. The big 1.2K resistors need to connect to pin 1 on one of the sockets.

attachment.php
 

Attachments

  • 800C.jpg
    800C.jpg
    152 KB · Views: 96
Were the 10 Ohm 1/2 - 1 watt resistors labeled Cathode resistors on the McShane parts list the correct ones to put on pin 5?

Yes, they run from pin 5 to ground. Make sure you move that 220 ohm resistor to its own ground too.

edit: sorry, you've already installed 10 ohm cathode resistors above.
 
Last edited:
Don; Looking good so far. (going faster than you thought it would, ain't it?)

Going back to C98. You could also connect the NEGATIVE side(along with the rest of the stuff) to the outer terminal (unused). It would get everything off the cap and actually give you a better connection circuit wise as only 1 wire/lead/etc is connected to the cap itself.
 
Don; Looking good so far. (going faster than you thought it would, ain't it?)

Going back to C98. You could also connect the NEGATIVE side(along with the rest of the stuff) to the outer terminal (unused). It would get everything off the cap and actually give you a better connection circuit wise as only 1 wire/lead/etc is connected to the cap itself.

Well, The red wire to POS was a little short to reach the outer tab and I didn't want to (lazy) run a new one so I did not use the outer tab. It reaches the C98 POS can lug fine. This was my last connection of the long day

I justified this by noting that the original C98 POS had two wires running directly to the can cap lug.

If you think that it should be rewired I'll do it

going faster than you thought it would, ain't it
I dunno, its been 10 months. But I would surely be wallowing in despair and frantically exchanging phone calls and emails if it weren't for the GREAT folk at AUDIOKARMA
 
Last edited:
Bruce; I don't recall the 220ohm resistor that you're talking about on the 800-C. I just looked at both of mine. NADA, as I reconnect it right on the riveted socket mount for those units that have it(ie: 400's). Here's a picture of BugleGirls 800-C underneath before any work done to it. No 220ohm from pin 6 on any tube. So it looks to me that it's a 400 only item.

Don; On the 400 there is a 220ohm resistor between pins 6 on one end and pin 3 on other end V16 or 17(depending on early(<48001) or late version(>48001) as a grounding point. With the addition of the 10ohm cathode resistor, the 220ohm loses it's ground, so must be moved. The closest ground would be the tube socket mounting ring. Pin6 on the 7868 corresponds to pin6 on the 7591 and pin 3 on 7868 is pin 5 on 7591. There is no corresponding part from pin 6 to pin 5 on the 800-C chassis as shown here.
attachment.php
 

Attachments

  • 100_3912.jpg
    100_3912.jpg
    172.8 KB · Views: 116
So just changing the pin 5 ground jumper to 10 Ohm resistors is all that is needed?
No additional assembly required for the Cathode resistor upgrade on the 800c?
 
Last edited:
Give the AUDIO Junkie in the striped Shirt a CUPIE DOLL!

You got it.
 
Installing the Screen Stopper modification

Here is how I did the Screen Stopper modification

Added a 270 Ohm resisitor between Pin 4 and Pin 1 for each output socket

Cut the jumper between Pin 8 (Of one socket) and Pin 4 (of the next socket)

Add a wire jumpering PIN 1 on all sockets

Move the Orange lead from Pin 8 to Pin 1

Move the 1.2k Ohm resisitor from Pin 4 to Pin 1

Before
attachment.php


After
attachment.php


Marked up
attachment.php
 

Attachments

  • After.jpg
    After.jpg
    129.7 KB · Views: 106
  • DSC03511.jpg
    DSC03511.jpg
    123.5 KB · Views: 107
Last edited:
C116 and C117

Another difference in my early serial # unit

I am down to the final components to change and I cannot find C116 or C117 on the schematic or on the board

They are just not there

attachment.php


Other images in post #95 show greater detail

I am guessing that I should just leave those parts out?

Any advice?
 

Attachments

  • DSC02416.jpg
    DSC02416.jpg
    215.1 KB · Views: 89
Last edited:
C116 and 117 are on the P.I. tube(s) on the later "Standalone" units. The Early executives didn't have it due to changes in the output section and P.I. circuits. There were a few things that threw me too when I redid mine. They aren't needed in the 63 Executive.

63 Executive
attachment.php


Standalone 800-C
attachment.php
 

Attachments

  • 63 Exec PI - output section.jpg
    63 Exec PI - output section.jpg
    107.3 KB · Views: 78
  • 800-C Standalone PI - OUTPUT section.jpg
    800-C Standalone PI - OUTPUT section.jpg
    84.5 KB · Views: 76
Thanks Larry, just less work I have to do

This is only the second difference I have noted, the first being the three 180 resistors

Whats left? The last four items on the parts list:

four 200k resistors to replace four 330k resistors R21,R22,R23,R24
four .1 uf PIO caps to replace four .047 caps C16,C17,C18,C19
two 10 pf caps C14,C15

Then a complete review of my work, checking solder joints, cap polarization, connections and wire runs

Make sure the fire extinguisher is charged

Then begin the process of powering up and measuring voltages

Then its Oh-Beer-Thirty
 
Last edited:
C99 C101 C105 C106 replacement

Here are the changes for V18
attachment.php


Here are the changes for V19
attachment.php
 

Attachments

  • V18 marked up.jpg
    V18 marked up.jpg
    118.2 KB · Views: 81
  • V19 marked up.jpg
    V19 marked up.jpg
    122.3 KB · Views: 78
Back
Top Bottom