Fisher Four-hundred Fotos?

mhardy6647

mhardy6647

Lunatic Member
I have realized that I have a bunch of reasonably good (well, by my non-photographer standards) 'before and after' photos of the innards of a couple of Fisher 400 receivers I've re-habbed in recent years.

Would anyone be interested in these being posted? I'd be happy to, if folks were interested.

Thanks for your attention!

P1000562.jpg
 
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Count me in, Mark....

I have a stock, near mint 400 that would be nice to compare with a re-done unit.
I wouldn't mind seeing some nudes to get an idea of what i'm in for.

Whattayasay?

Regards,
Crazy John.
 
OK, sounds like a mandate.

I will post some stuff starting tomorrow (for my own convenience).


Upon reflection, I should offer a big DISCLAIMER

* I am not a professional, nor even a particularly skilled amateur.

* I've done two of these, but they worked when I was done (better than when I started).

* I offer no guarantees on the quality or even the appropriateness of the techniques I've used.

* There are pros here who will do this sort of thing, excellently, for you if that is your intent and desire. You get what you pay for :-) I am not competing with them, nor endeavoring to undermine them!


That being said, the Fisher 400 is a nicely engineered, laid out, and constructed receiver. Documentation is relatively easy to find. Most parts are readily obtainable and reasonably priced. It's pretty spacious below decks; good for a tyro. Try recapping a Pioneer SX-34/Allied 333 sometime!

The end result of a Fisher 400 rehab is a very nice receiver with a little sweat equity.

Watch this space...
 
Baseline: "Before" renditions of the undersides of two Fisher 400's.

First, an earlier one, with the Siemens selenium bridge rectifier for the bias/DC filament supply. This earlier 400 also has a 6HS6 instead of a 6BA6 in the (?) first IF stage. The later 400's also, apparently, had 4 IF stages instead of 3. See: http://www.audioasylum.com/audio/tubes/messages/183979.html

Richards400belowbefore.jpg


Now, here's a later 400. This one has a silicon bridge rectifier already. This may or may not be original, but there's no doubt that later 400's used a silicon rectifier for the bias supply. This one probably has one more 6AU6 than the other, but I cannot verify that. AK member BKville could weigh in on this if he wishes -- this one's his!

Fisher400belowbefore.jpg
 
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Here's a closeup of the power supply and output stage of the older 400 from above. You can see the bias supply on the top left. The bridge rectifer's mounted on the chassis with two screws. That old, cardboard-covered 1000/1000 @ 35V electrolytic has to go!

The HV P/S "starts" to the right of the bias supply. You may be able to see the two silicon rectifiers used to rectify the B+ supply there by the undersides of the first electrolytic filter for the HV.

The output section's at top center. The green power resistor you see appears to have been replaced at one time. This particular 400 shows evidence of lots of heat around the output tube sockets. When it came to me for recapping, the 7868's were very weak and at least one's plates were glowing red. Time to change coupling caps.

Since this one had a selenium bias rectifier, it was also time to re-do the bias supply.

The stuff to the right is all radio -- I don't (can't) mess with that!

Richards400outputsbelowbefore.jpg
 
Okey-dokey, let's take a look at that bias supply.

First, the older 400, with a selenium bridge rectifier. An old selenium bridge is probably delivering less voltage than it was s'posed to, so the bias supply is probably "less negative" than the -17V Fisher called for. The -17V, IIRC, was already running those (until-recently) rare 7868's pretty hot to begin with, so things have probably only gotten worse!

Here are two views of the bias supply in the older 400. The flat, silver-colored Siemens bridge is readily visible "in front of" the twin 1000 uF electrolytic. Just remember that the bias supply is negative, so the 5.6k ohm resistor is soldered to a "ground" lug, not the positive lug, of the electrolytic. There's a 15-ohm power resistor on the positive lug of the bridge. I assume this is the DC used for a couple of the filaments in the high-gain neighborhood of the 400, but I didn't actually check.

oldbiassupplywithseleniumalt.jpg


IMPORTANT NOTE: Please point out any blatant errors in my text by post or PM. I will fix them ASAP!

oldbiassupplywithselenium.jpg


For comparison, here's a before shot of the bias supply in the newer 400. You should be able to see the silicon bridge (black thingy with 4 spaghetti-insulated leads) to the left of the twin 1000 uF electrolytic.

oldbiascap.jpg
 
Here's the rebuilt bias supply on the older 400. The selenium bridge's been replaced with a plain-vanilla silicon bridge, mounted in place with one of the studs from the old selenium bridge. The old electrolytic was replaced with two generic 1000 uF@ 50V electrolytics. The 5.6 k bias resistor was replaced -- prevailing wisdom suggests about 2.7 k here, but I have used a 3 k... it's what I had! No worries, we'll actually be able to measure the bias current later (after a fashion), so we'll see what we get.

Richards400biasafternoflash.jpg


N.B. It might look like that 15 ohm resistor is shorting out to the bolt you see below it, but it's actually well "above" it in three dimensions.
 
The hard work's done!
OK, on to coupling caps: The originals are two 0.047 @ 600V and two 0.047@ 400V. A little cost-cutting, there. I have crudely marked them on the attached photo (from the older 400). These bad boys have to go...

oldcouplingcapshighlighted.jpg
 
In BKville's 400, these were replaced with 400V 716P's and 600V 715P's, due to space limitations. In the other 400 I've done, I used the 600V Illinois caps (available from AES) to replace all four.

Sorry this photo is even worse than some of the preceeding ones!

Fisher400outputsafter.jpg
 
Dude, I think the photos are great! I applaud you for sharing your experience in such detail :thmbsp: We need more of this kind of stuff IMHO :thmbsp: Well Done and keep it coming, Jay
 
jaymanaa said:
Dude, I think the photos are great! I applaud you for sharing your experience in such detail :thmbsp: We need more of this kind of stuff IMHO :thmbsp: Well Done and keep it coming, Jay
Click to expand...
I agree with Jay. Thanks for sharing.:tresbon: Loren
 
Nawww... I don't want to see the pictures...

Oh, too late now! :D

Pictures, we don't need no stinkin' pictures! :tongue:

Scott (By the way, the pics are great! :thmbsp: )
 
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