Fisher 400 recap

[mgarry81]

Hey I recently started recapping a Fisher 400 I bought a few years ago and have a few questions. The receiver was all original caps and tubes when I bought it and sounded pretty good as I thought. The left channel started becoming weak so I took a peek and found the coupling caps was leaking. I replaced the four .047uF coupling caps with .1uF as I have seen recommended again and again. I know the reasoning in changing the caps value is to accomodate a new set or EH output tubes but since I have the original 7868's is that a problem? Also, I noticed I should change the grid resistors from 330k to 220k; do I need to do that immediately or only if I switch to modern tubes?

I also added the 10ohm resistors to the cathode side of the output tubes for the protection and ability to measure bias voltage of each tube. Next, will be the selenium rectifier, 1000v filter caps, diodes, and death caps. Does anyone have some good pictures of that section restored on their 400?

Thank you very much for all the knowledge shared on this site already. There is no way I could have gotten even this far on this restore without you guys. The receiver already sounds amazing with its new coupling caps I can't imagine once the bias it brought back up to above spec. This is my first piece of tube gear and it now has such deep dimensional sound I'm now a huge believer.

 

[larryderouin]

Mike: You need to change the grid resistors asap. The caps and resistors work as a set, and you can get an instability by putting only 1/2 of the set in. New or old tubes, no difference. With them being 7868's no problem.

Get the Bias Supply builty up 1st. Then wok on the power supply, the can caps, and suvh. Bias and POWER supplies must work as designed or all else won't fal into place as thought.

The 500 is a breeze to work on compared to an 800C. A lot of the same parts, in the same places, but a lot more stuff.

Larry

 

[mgarry81]

Thanks Larry, I bought the resistors already so I'll change them with the bridge rectifier and filter caps. I have yet to pick up the electrolytics to replace the multi section can caps that sit up on the chassis so that will be the next order. I notice some guys do not change the large cans unless there is an issue with one but I figure if you already this far might as well. Is there any harm in testing with all new except the large cans?

 

[larryderouin]

None that I know of unless the can's are bad. I did my 400's can caps last, and tested each section as it was finished by firing up the whole thing. Then ran it for about a month or two before I had the can's replaced. I went the Hayseed Hamfest route and they made custom can's to my spec for each one. overall for the set about $10.00 cheaper than Antique Electronic Supply and they are exact values/voltages.

Larry

 

[audiodon]

Aside from reliability issues:

Replace coupling caps to change the tone.
Replace power supply diodes and caps to increase apparent power and make it get silent faster.
The 400's a wonderful unit.

 

[mgarry81]

Ultimately I would like to change all of the cans in the power section to get the most power out of it. How do you think this will drive my B&W 602 S3 bookshelves? Obviously totally different vintage. I know tube and solid state power is different and my Yamaha CA810 at 65wpc runs them well. How does the 400 do with half the wattage output?

 

[larryderouin]

It'll do fine. 95% of your listening is in the 1st 5 watts. The only real difference is headroom for Bass and Midrange Peaks. The Yamaha has a bit more headroom if you want to get frisky with the volume.

Tube and Solid State power is the same. You can't change physics. Watts is Watts. The only difference is how they measured them back then. If you use the 1974 ICC protocols it works out to 32watts for the 400 and 65 Watts for the Yammie. But there is an added attraction to tube units. You can use them as supplemental heaters in the house when it's cold

You'd be surprised at how the 400 handles modern speaker and even vintage speakers. It may be the BOTL of the tube units FISHER made from 1963 to 1967, but it kicks some butt. The Yammie has an edge to it that the FISHER will have smoothed out. I find the FISHER somewhat LUSH sounding, kind of laid back. You may or may not like that sound.

Again. The FISHER will handle the speakers just fine, but it will sound different than the Yammie.

Larry

 

[mgarry81]

It is exactly what I love about the 400. Not as raspy and pumps out the lows perfectly. With this recapping every time I hook it up to test in between sessions it just keeps getting better. The depth of the soundstage is amazing. And your right at least if my boiler were to fail I could probably heat the house with this thing .

Last night changed the bridge rectifier, filter caps, and changed the grid resistors to 200k. Now I have the death caps, diodes, a few more electrolytics, and then on to the mpx section. They look like a whole lot of fun in that cramped space.

After the last bout of rehabing I took readings across the cathode to ground resistors I had installed. Three read around 22 and the fourth at 25. Does that sound like my output tubes are ok or is a new matched quad in my future?

 

[mgarry81]

Finally finished the Bias section and output section. Next is the FM which I should get to if I can bear to take it out of service for a few days. I uploaded a bunch of high resolution photos of the work on my site. Any photo can be clicked on for high resolution.

www.mikegarry.com/fisher-400-restoration

Aside from my amateur soldering skills I would appreciate any criticism from you guys. The sound coming from this thing is excellent and although they are warm the output tubes do not seem to be as hot as before and the output transformers are much cooler. I am thinking of already pulling out the cheap coupling caps and going to orange drops but I would like to change other things first.

Thanks again guys for all your help on here it has really made this very enjoyable!

 

[audiodon]

With three output tubes at 22ma and one at 25, you're fine. It should last.