Fisher 400 Restoration Project

[Jdiesel87]

Hello I all! I've been lurking on the Fisher forum for a few months now, doing my best to absorb as much information as possible as I waited for the right Fisher 400 to come along. That time has finally arrived and I managed to get one in unknown condition, sight unseen.

I braced myself for the worst and expected it would need a full fresh, new tubes, and possibly more. While I waited for it to arrive I started to put together a shopping list of parts that I would likely need to get it up and running. I soon realized the available "kits" were of poor quality and rather expensive. I read through Dave Gillespie’s A Reference 400 Restoration thread multiple time, have a collection of bookmarks and saved posts, and a Mouser and Digikey list on standby.

Well, the receiver arrived and I need to put on the brakes. It turns out that much more work than expected was already completed on the receiver. I'm not disappointed, but I will need to take some time to assess what the current state is, what might still need to be done, and what might need to be redone.

What I was able to conclude from my quick visual inspection:

1. Its an early model 24000 serial # receiver
2. It already has EH output tubes installed
3. The remaining tubes are a mix of Sovtek 12AX7-LPS and Siemens (Japan)

4. Some internal work has been done


i. First thing I noticed is that almost every cap has been replaced with an Orange Drop

ii. The power supply section has a Panasonic 100uf 450v and a Sprague Atom in place of the blue axial. Not sure what the status of the death cap is at the moment.


III. The selenium rectifier has been replaced


iv. The large 7w resistor has been changed. I'm struggling to make sense of the other resistors on the output tubes sockets.


First question, is it possible that the big bias caps have been re-stuffed? Is there an easy way to check? I had planned on ordering the Hayseed Hamfest kit but if I don't need to that's great.

Second question, are Orange Drops everywhere a bad thing? I often see people using the yellow polyester or Knowles Illinois capacitors.

Third and biggest question, does anything major look out of place? I plan to plug it in to the dim bulb tester this weekend and see if it works.

 

[RS Steve]

It doesn't look like the cans are restuffed, HH replacements would be a good idea. Orange drops tend to make the highs very bright whenever I have used them throughout, and I have heard others say this also. Not a big deal when you have tone controls to adjust to your liking. I have used the yellow Illinois type in the preamp section and orange drops as coupling caps with good results. I would install an inrush limiter (CL-80) to help protect the power switch, and I also always install screen stability resistors and IBBM. Looks like a nice unit though, much has been already restored.

 

[Jdiesel87]

Thanks for contributing.

I placed an order for the Hayseed Hamfest kit. I can't be bothered to mess around with discrete components and restarting tubes. A bit pricey but it is was it is.

The inrush limiter is already in my cart. My fingers are crossed that the power switch is still functional and in good condition. I don't see any residue or signs of arcing. Hopefully the inrush limiter will extend the life of it.

I'm going to also order some various Illinois Yellow poly caps and maybe some Panasonic metalized poly caps to experiment with. The amp will be used to power my Klipschorns which already lean to the bright side so going full Orange Drop could be an issue.

I plan to also order parts to do the IBBM mod

Are 1/4w 100ohm carbon film still the recommended resistors for the screen stability resistors mod?

1/4w 10ohm Cathode for the sampling resistors?

Are there recommendations or changes need when running EH output tubes? I seem to recall reading that upping the coupling caps from .047uf to .1uf and lowered the resistance of the grid leak resistors was something that people were doing.

I assume that the IBBM will allow me to run the EH output tubes at the ideal voltage.

 

[RS Steve]

Thanks for contributing.

I placed an order for the Hayseed Hamfest kit. I can't be bothered to mess around with discrete components and restarting tubes. A bit pricey but it is was it is.

The inrush limiter is already in my cart. My fingers are crossed that the power switch is still functional and in good condition. I don't see any residue or signs of arcing. Hopefully the inrush limiter will extend the life of it.

I'm going to also order some various Illinois Yellow poly caps and maybe some Panasonic metalized poly caps to experiment with. The amp will be used to power my Klipschorns which already lean to the bright side so going full Orange Drop could be an issue.

I plan to also order parts to do the IBBM mod

Are 1/4w 100ohm carbon film still the recommended resistors for the screen stability resistors mod?

1/4w 10ohm Cathode for the sampling resistors?

Are there recommendations or changes need when running EH output tubes? I seem to recall reading that upping the coupling caps from .047uf to .1uf and lowered the resistance of the grid leak resistors was something that people were doing.

I assume that the IBBM will allow me to run the EH output tubes at the ideal voltage.

Yes on the screen stability resistors and sampling resistors, I use 1% versions. The modern tubes usually require a bit more negative bias voltage; there is a Dave Gillespie mod where you put the 15 ohm resistor on the negative side of the dual 1000 uf caps I believe to accomplish this. I believe it can't be done on the single can dual cap set up. This is why when I order the HH cans, I get the two separate caps instead of the can.

 

[Jdiesel87]

Ah darn I ordered the kit with the bias can capacitor. Do you recommend changing my order to get the caps instead? I probably still have time.

 

[davam]

Yes on the screen stability resistors and sampling resistors, I use 1% versions. The modern tubes usually require a bit more negative bias voltage; there is a Dave Gillespie mod where you put the 15 ohm resistor on the negative side of the dual 1000 uf caps I believe to accomplish this. I believe it can't be done on the single can dual cap set up. This is why when I order the HH cans, I get the two separate caps instead of the can.

That mod works well' I restuff my own cans so I make the bias can com positive for that .I like to keep it as original looking as possible you might em
hayseed and see if they can make the bias cap can com positive for you or change it to separate caps

 

[RS Steve]

Ah darn I ordered the kit with the bias can capacitor. Do you recommend changing my order to get the caps instead? I probably still have time.

Yes, I would.