Most Common Parts Needed For Fishers!

[Tom Bavis]

Thermistor: CL-90 is only rated for 2A - save it for the 6V6 / EL84 amps. I used CL-70 in mine, CL-80 is good too. You CAN use the CL-90 in the secondary (B+ supply), but the primary side is better for reducing stress on the power switch.

Inline fuseholders aren't UL approved for AC line voltage - replace the original with a chassis mount one (there ARE circuit breakers that will fit the 1/2" hole too...).

 

[cc43fan]

Now we've all got something to point the new guys to without pulling what little hair we've got left, out! I hate trying to remember where I put all those numbers and parts at.

Larry

And with a tip of my hat, I say thanks.

 

[cc43fan]

Knob brights?
non-beveled non-fading: Bizzy Bee http://www.angelfire.com/biz/bizzyb/
beveled: Ebay.
Thermister: Make sure one leg goes to one of the two primaries of the power transformer. I usually use them as an in-series replacement for the wire that goes between one leg of the fuse receptacle and the extra AC outlets. The thermister replaces the connector wire. The goal is to eliminate arcing in the switch upon turn-on.

Is it possible to see a pic of how this thermister is connected? Maybe a sketch on the schematic ? This sound like a very good safety feature and I'd like to make this a part of my restore.
Thanks for all of the vast knowledge here.

 

[drewbolce]

Here is a chart of the various CL series thermistors.

 

[cc43fan]

Here is a chart of the various CL series thermistors.

Thanks! I'll take all the reading material I can get. Any chance of info on the correct way to install? (I'm a rookie)

Thanks for any and all help

 

[bhamham]

I put mine on each leg of the PT primaries and used CL80s - others may do it differently but it seems to work well - X marks the spots - in series.

 

[cc43fan]

I put mine on each leg of the PT primaries and used CL80s - others may do it differently but it seems to work well - X marks the spots - in series.

Thanks Bruce,
That's what I was looking for!

Chuck

 

[jaba1971]

Broken Fisher 500 TX

Gentleman,
I have a Fisher 500 TX that is showing 54 volts on the right side speaker posts when the unit is turned on. The left side which works fine shows 0 volts does anyone have any ideas as to what could be the cause of this or where I should start looking.

 

[Fisherdude]

First, wecome to AK!

Unfortunately, you've posted a specific question about a 500-TX inside an existing thread that's about a completely different topic. Not very many members will see it in here. You should go ahead and start a new thread in the Fisher Forum titled: "Too much voltage on 500-TX speaker terminals" and you'll get much, much more helpful input.

I'll wait until you do that and then I'll delete this post for you.

And good luck! You should get lots of help, and the 500-TX is a very nice receiver!

 

[AlTinkster92]

I just bought 6 festoon dial lamps (used) for a 500C for replacements for my 800C, for 15.00 bucks was that a good deal? Thanks

 

[Fisherdude]

I just bought 6 festoon dial lamps (used) for a 500C for replacements for my 800C, for 15.00 bucks was that a good deal? Thanks

Yup, that's good. :yes:

 

[audiodon]

A minor set of modifications to the existing circuitry in these units is often recommended. Here is the best description of why these modifications are recommended and the effects on the circuitry.
This is cross-posted from a restoration thread.
http://www.audiokarma.org/forums/showpost.php?p=5694423&postcount=19

 

[larryderouin]

To clarify Don's post above, the modifications are mainly for the 800C and 500C. The 400 can also use these upgrades with slight modifications (tube pins are different on the 7868 vs the 7591's, etc.).

Larry

 

[jaguar06]

Wrong thread.

 

[hammondcrazy]

How about a tuning condensor or whatever they call them,, the thingie with the plates. I may need a new one for my Royal Electra if I can't unfreeze this one!!! Who would sell them?

 

[larryderouin]

No longer available. And it's specific enough that it wouldn't benefit this thread.

Larry

 

[bktheking]

Is there more information or a step by step that elaborates on Dave G's post on the additional mods involving screen resistors mods and the rest?

 

[larryderouin]

http://www.tronola.com/html/maximize_tube_life.html

Dave G's original article. Screen resistor mod in there and why. IBAM you'll need to search the Forum. There has been a glut of 500C,400, and 800C rehab's in the last 18 months. You should have no problem finding them.

 

[larryderouin]

Courtesy of DREWBOLCE (It's his drawing!);

IBAM (Individual BIAS ADJUSTMENT MODIFICATION) PARTS LIST AND SCHEMATIC. Mainly for the 400-500C-800C. I don't see any reason it won't work with slight modifications for other 7591/7868 based FIXED BIAS units. Matter of fact i modified this for my Sansui 1000A (changed resistor value) and it works just fine. R117-R120 are the Grid resistors that are changed( were originally 330K) for use with primarily the EH and JJ variant's. Make sure the coupling caps are changed to .1uf (see edit at bottom) when the resistors are changed.



ON THE 400.



On the 800


And now we have Dave Gillespies Balance/BIAS board. It's basically a universal variation (my words not his) of what FISHER did in in their higher ended amps/integrated. You balance the pairs with 2 of the pots (one per side), then set the BIAS. You get the BIAS improvements of Drews board, with a null when balancing out the pair (null meaning 0.00v) to equalize the loads. I've used both, and with an UNMATCHED QUAD, Dave's board works better to equalize the tubes. With new matched tubes from McShane, it's 6 of 1, 1/2 dozen the other. In any event BOTH WORK WELL, and I'll leave it up to you as to which one you use.



EDIT on 01-09-2022. about 6 years late, but better late than never...... NEW VALUES FOR THE Grid return resistors (330K originally), and coupling caps (0.047uf originally)! 0.068uf and 220KΩ maintain R/C timing of the original parts to within 2%. This is for ALL TUBES regardless of age (old stock or new stock). HOWEVER!!! If you use and IBAM or IBBA to vary the bias and have it set to 75% to 80% of maximum dissipation of the 7591's, no changes to the grid returns and coupling cap values are needed.

 

[larryderouin]

Screen Resistor Mod layout

I can't draw using a computer for shit. Hopefully you'll get the Jist.



On the 400 you are going to just add a 100oHm resistor to the screen Power lead to the jumper between pins 1 and 7. Disconnect the Screen buss wire from pin 1. Then connect the wire FROM Pin 1 to the free end of the resistor. KEEP THE RESISTOR LEADS AS SHORT AS POSSIBLE. See Improved setup for 7868 below!

On the 500B/C and the 800 B/C Pins 4 & 8 line up across the tubes so FISHER made one Jumper buss wire instead of 4 different screen wires.
1.) Cut the Buss lead at Pin 4 on Tube V13 for 500C and V10 on the 800C (inboard most tube).

2.) Separate the tubes at pin 8 and pin 4 on each tube. You'll end up with a jumper on eeach tube from 4 to 8.

3.) Solder a 100oHm resistor to each jumper keeping the lead as short as possible.

4.) Cut a piece of wire long enough to reach across the tubes. Cut insulation @ 4 places to solder in the resistors.

5.) Solder Each resistor's remaining end to the buss wire. Solder the END of the BUSS WIRE to the wire you cut in Step 1. Insulate with heatshrink.

You should have something that looks like the bottom drawing in both cases. On the 7868 the jumpers will orient up and down. PINS 1 & 7 are the 7868 SCREEN's. drawing has been revised to reflect the correction..



11-16-2014Revised to show 7W resistor 1.2K to 1.5K depending on model unit On 7868 it connects to the buss wire as above.

On 7591's There is an improved setup. Thanks to Dave Gillespie for the improvement.

7591 ONLY IMPROVED SETUP
1.) disconnect the old buss wire from the tubes. cut and remove the buss wire from between the output tubes.
2.) run a new wire of sufficient length to daisy chain the tube sockets at pin 1.
3.) install a 100ohm resistor to each tube socket from pin 1 to pin 4. Pin 1 is not used and is not connected internally.
4.) connect flying end of the 7W resistor to one of the center tubes. PIN 1. It must be before the 100ohm resistors.
5.) Connect the new buss wire to each tube's pin 1 in turn. Solder all connections.
Larry

7868 ONLY IMPROVED SETUP (Similar to 7591 except for Pin #)
normally.
1.) Same
2.) Change to Pin 8
3.) resistor to pin 8 to pin 1. Pin 8 is NOT used normally
4.) Connect the 7W resistor to one of the center tube pin 8.
5.) Same except for pin 8.