I joined the Fisher family!
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Thom 2230
Active Member
Ok Larry I have gotten the under carriage photo enlarged and have spent a little time looking over it. A smaller copy will travel with me. When we started you said you would start with the incoming power and follow it out to the speakers. I would assume that is power supply 1. Right next door is the bias supply, I am not sure what that is. Is the gate power passes through to power the unit?
Larry, I've been following this thread, and I can say it takes a special kind of dedication to the fisher-rescue cause to take as much time & mental effort as you have to impart such knowledge on this unit, not to mention newbie safety training. Now, I won't have to do as much brain-picking /pestering when I finally get to my 400 (God knows when that's gonna be!)because that work's done. If I could, I'd email you not just one, but a case of beer for that!
And my Condolences on your recent loss. That void may take a while to fill, lose yourself in distractions for now until you're used to the new normal. de k8cat
And my Condolences on your recent loss. That void may take a while to fill, lose yourself in distractions for now until you're used to the new normal. de k8cat
Catmanboo;
I'm just passing on what I've learned(and remember) from Dave G, Mark the Fixer, Echowars, and all the others. Compared to a lot of them I'm a rank amateur. Concentrate on one or two brands and sub specialize on certain receivers so the load isn't too much. A 6pk of Coke would be fine. No beer. Besides all the meds I take that alcohol interfere's with, I've never been able to tolerate the taste. a very weak Rum and coke, maybe once or twice a year is my limit. Even when I was in the Navy back in the 70's I didn't drink. So I would always be the designated driver. I got free cokes, soda water or whatever. I'm still the designated driver. Let the wife get blitzed, which when we did go out, was fine with me. (The pervert that I am, LOL!)
I'm just passing on what I've learned(and remember) from Dave G, Mark the Fixer, Echowars, and all the others. Compared to a lot of them I'm a rank amateur. Concentrate on one or two brands and sub specialize on certain receivers so the load isn't too much. A 6pk of Coke would be fine. No beer. Besides all the meds I take that alcohol interfere's with, I've never been able to tolerate the taste. a very weak Rum and coke, maybe once or twice a year is my limit. Even when I was in the Navy back in the 70's I didn't drink. So I would always be the designated driver. I got free cokes, soda water or whatever. I'm still the designated driver. Let the wife get blitzed, which when we did go out, was fine with me. (The pervert that I am, LOL!)
Thom; The Main POWER SUPPLY is broken into 2 sections on the 400 physically. However on the schematic it's all one section. The single can cap in supply #1 and 1 section of the 3 section cap in supply #2 are actually what's called a voltage doubler. They are wired in series to increase the voltage from 110 to about 400v DC. Look for C-57c (bottom 1/2) and C-56 on the schematic. The Voltage comes out a AC and is rectified by CR1 and CR2. Then it goes into the main filter caps (which act as a reservoir and a ripple filter). Between each section you'll note a large wattage resistor (above 1w) which drops the voltage to the next can. At each succeeding section the voltage is lower, which is used by a different area of the unit.
The 400 is a fixed bias unit. Simply put Bias is the voltage used to set operating loads in the tubes. Note on the schematic there are 4 diodes in a square configuration with the AC Voltage from the transformer coming in in the middle of the upper and lower pairs. The ends at 9 oclock and 3 oclock are DC voltage. 9oclock being DC+voltage and 3 oclock being DC- voltage. The DC- voltage continues on past the 4 12ax7 heaters and ends up on the output tubes at pin 2/6 (these are tied together). Changes in this voltage determine how many watts the tube actually puts out. Too much bias (voltage toward ZERO) and the tube burns out quickly, while too much bias voltage lowers the wattage output with attendant distortion and lack of power. If you want the technical version Dave G can do that. BIAS is important to operation of the tube. So it has to be set correctly. The BIAS section also provides DC- voltage to the tube heaters to lessen hum and noise. AC Voltage is used in the non critical area for heaters.
The POWER SUPPLY (all together) is arguably the most important part of the unit. Poor operation of the Power supply causes extra distortion, poor or no operation of the tubes, etc. So we rebuild that 1st. That way we can be assured of correct to very close voltages on the output's and othr sections when it finally started for the 1st time. NOTE: For clarification, I'm using the 48001 and up Service manual for all part designations.
The 400 is a fixed bias unit. Simply put Bias is the voltage used to set operating loads in the tubes. Note on the schematic there are 4 diodes in a square configuration with the AC Voltage from the transformer coming in in the middle of the upper and lower pairs. The ends at 9 oclock and 3 oclock are DC voltage. 9oclock being DC+voltage and 3 oclock being DC- voltage. The DC- voltage continues on past the 4 12ax7 heaters and ends up on the output tubes at pin 2/6 (these are tied together). Changes in this voltage determine how many watts the tube actually puts out. Too much bias (voltage toward ZERO) and the tube burns out quickly, while too much bias voltage lowers the wattage output with attendant distortion and lack of power. If you want the technical version Dave G can do that. BIAS is important to operation of the tube. So it has to be set correctly. The BIAS section also provides DC- voltage to the tube heaters to lessen hum and noise. AC Voltage is used in the non critical area for heaters.
The POWER SUPPLY (all together) is arguably the most important part of the unit. Poor operation of the Power supply causes extra distortion, poor or no operation of the tubes, etc. So we rebuild that 1st. That way we can be assured of correct to very close voltages on the output's and othr sections when it finally started for the 1st time. NOTE: For clarification, I'm using the 48001 and up Service manual for all part designations.
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Thom 2230
Active Member
Good morning Larry from a chilly Iowa -2 here.
There is a lot to absorb here. The description of bias is helpful, my research last night told what bias is but not why it is so important. Tonight I'll find the pieces you have described on the schematic and on the real deal. Get back to you when I have a handle on it.
Thanks for investing your time.
Now it is off to snow removal - then work.
There is a lot to absorb here. The description of bias is helpful, my research last night told what bias is but not why it is so important. Tonight I'll find the pieces you have described on the schematic and on the real deal. Get back to you when I have a handle on it.
Thanks for investing your time.
Now it is off to snow removal - then work.
Thom 2230
Active Member
Larry, I spent an hour or so going over the schematic last night. I found the capacitors and diode you instructed me to locate and traced the wire. When going to the unit I was a little confused. Are large capacitors always aluminum cans? And are diodes wrapped in construction paper? If so I followed a yellow wire from a diode to the sockets of the power tubes. How did I do?
This is like a detective novel,what is the next step?
Have a good day.
Thom
This is like a detective novel,what is the next step?
Have a good day.
Thom
Main Filter caps are usually on top (there are some that place them underneath like the Harmon Kardon Citation series) but they are far and few between. There is a 2 section filter Capacitor underneath in the BIAS Supply section in clamps. Compare that with the pic. It's been replaced with 2 1500uf 63v UKL series Nichicon caps. Thats the one in cardboard covering as it's in the negative voltage BIAS SECTION. The other 3 are on the top of the unit.
DIODES are NEVER wrapped in construction paper. Take a picture and post it with an arrow pointing at the part. I'm thinking it's probably the Bias Cap, and you followed the yellow wire to the filaments (heaters) of the 12ax7's.
I'm really straining the old synapses here. If you bought the Hayseed caps with the BIG DUAL CAP for underneath it's one way of hooking it up and going to be impossible unless I see the bottom of the cap as I've never done one like that. With the individual caps it's a different procedure entirely. But it all works out the same in the end. Do you have a SIEMENS Rectifier bolted to the side wall next to the cardboard covered cap? Or is it a small black 4 legged thingy? If it's the small black 4 legged thingy, it's a silicon rectifier and you don't do anything with it. Note on either of the rectifiers there are 2 legs marked ~. Those are the ACvoltage legs. The other 2 are marked + & - . That should be self evident. Remove the SIEMENS Rectifier and replace with a new Silicon Rectifier. If it has a thru hole, mount it to the wall with a bolt, star washer and a nut. Take a picture BEFORE and AFTER, POST PIC. And I need type of BIAS CAP you got so I can right out a procedure for you. Need a pic of the replacement cap (Single cap dual section) PINS
DIODES are NEVER wrapped in construction paper. Take a picture and post it with an arrow pointing at the part. I'm thinking it's probably the Bias Cap, and you followed the yellow wire to the filaments (heaters) of the 12ax7's.
I'm really straining the old synapses here. If you bought the Hayseed caps with the BIG DUAL CAP for underneath it's one way of hooking it up and going to be impossible unless I see the bottom of the cap as I've never done one like that. With the individual caps it's a different procedure entirely. But it all works out the same in the end. Do you have a SIEMENS Rectifier bolted to the side wall next to the cardboard covered cap? Or is it a small black 4 legged thingy? If it's the small black 4 legged thingy, it's a silicon rectifier and you don't do anything with it. Note on either of the rectifiers there are 2 legs marked ~. Those are the ACvoltage legs. The other 2 are marked + & - . That should be self evident. Remove the SIEMENS Rectifier and replace with a new Silicon Rectifier. If it has a thru hole, mount it to the wall with a bolt, star washer and a nut. Take a picture BEFORE and AFTER, POST PIC. And I need type of BIAS CAP you got so I can right out a procedure for you. Need a pic of the replacement cap (Single cap dual section) PINS
HEY GUYS! Gonna need some help on this one. If you feel inclined to jump in somewhere Go RIGHT AHEAD. I think it's gonna be somewhat hard for me to explain some things so if you think you can do it better and get the idea across DO IT!
THOM. This isn't gonna be an overnight deal. It's gonna take a good while (a month or more) so don't get impatient. IT will eventually get done. Have you got the METALBONE KIT yet???
THOM. This isn't gonna be an overnight deal. It's gonna take a good while (a month or more) so don't get impatient. IT will eventually get done. Have you got the METALBONE KIT yet???
Thom 2230
Active Member
Ok Larry we are moving on down the road! The large cap in the bias section is one of the pieces I mistook for a diode. The second pice I was thinking was a diode is a black cardboard vertical cylinder up topside next to the large transformer. Now what are the two aluminum cans in power section 1 and 2 on the top side? These are what I thought were the caps.
Thom 2230
Active Member
Tonight I will take some detailed photos of the 400 to clarify things. (hopefully) I will also post photos of the parts I've purchased so you cad see what I have to work with.
Have a good day, hope your other charges here in AK have a better basic understanding of electronics than I do.
I'll drink a Coke in your honor today!
Thom
Have a good day, hope your other charges here in AK have a better basic understanding of electronics than I do.
I'll drink a Coke in your honor today!
Thom
On the 400 you have 4 CAN CAPS. 1.) Dual Section BIAS CAP UNDERNEATH. 2.) Cardboard covered single section (upper 1/2 of voltage doubler) 3.) 4 section can cap next to it. 4.) the 3 section can cap at the front (contains the lower 1/2 of the voltage doubler. ) These consititute the Filtering and what I liken to a battery for the POWER SUPPLY. It's a bad analogy but the only one I have at the moment. Right now I'm suspect at your capability to do this by posts. If you can't identify main filter caps, how are you to identify other caps, resistors, diodes, etc. in the unit. I really wish there was someone close enough to you that could sit over your shoulder and physically show you what, and how to go thru an overhaul. Having said that, take the pictures and send them on. LEts see what you have 1st.
Larry
Larry
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Thom 2230
Active Member
Hello Larry, hey there has been no word from Dean - everyone's life is busy.
In the mean time I'm sending photos of the parts I've purchased to do this job, perhaps this will offer a starting point.
In the mean time I'm sending photos of the parts I've purchased to do this job, perhaps this will offer a starting point.
Attachments
Between the Hayseed caps (when they arrive) and the Fisher DOC parts, you've got the basics for a Factory stock rehabilitation. Considering your level of experience, I would NOT recommend you do the de-emphasis (mono or Stereo). You can do the DIODE/BIAS RECTIFIER to start with, AFTER the HAYSEED Can's Arrive, and you follow explicitly directions and DO NOT TRY TO GET AHEAD. SLOW GOING IS BEST. Rushing brings on more problems and injuries. And that's one thing WE DO NOT WANT!
UNPLUG THE UNIT, COIL UP THE CORD and put it in a PLASTIC BAG, TAPE IT UP!
Remove ALL JEWELRY from fingers, wrists (includes watches).
When working on circuits, capacitors will carry some charge unless discharged. Take a 1000ohm 5w resistor and ground out one of the power cap sections. Clip with alligator clips to both ends. Use a meter on dc volts to check voltage on each section. When all show 0 volts, THEN and ONLY THEN are you able to work inside the unit.
Basically it's a replace like for like parts. Some of the parts will be somewhat different. But they are compatible like for like.
1st thing you will replace is the BIAS Diode Bridge. That's the table looking thing in the bias/rectifier bag.
On the block the are 2 corners marked ~ (catercorner from each). These are the AC Voltage from the Transformer. Remove each wire from the SIEMENS and attach it with solder to the NEW BRIDGE. The other two corners are marked - and +. These are your DC Voltages. Make DAMNED SURE YOU get these right, or your bias cap underneath will go CHERNOBYL on you. Connect the wires as close to the body of the Bridge rectifier as you can and trim off the ends. Mount to chassis where the old siemens rectifier WAS. WHEN DONE TAKE PICTURES AND POST. Then let me know when the new can's come in from Hayseed. STOP AT THIS POINT.
UNPLUG THE UNIT, COIL UP THE CORD and put it in a PLASTIC BAG, TAPE IT UP!
Remove ALL JEWELRY from fingers, wrists (includes watches).
When working on circuits, capacitors will carry some charge unless discharged. Take a 1000ohm 5w resistor and ground out one of the power cap sections. Clip with alligator clips to both ends. Use a meter on dc volts to check voltage on each section. When all show 0 volts, THEN and ONLY THEN are you able to work inside the unit.
Basically it's a replace like for like parts. Some of the parts will be somewhat different. But they are compatible like for like.
1st thing you will replace is the BIAS Diode Bridge. That's the table looking thing in the bias/rectifier bag.
On the block the are 2 corners marked ~ (catercorner from each). These are the AC Voltage from the Transformer. Remove each wire from the SIEMENS and attach it with solder to the NEW BRIDGE. The other two corners are marked - and +. These are your DC Voltages. Make DAMNED SURE YOU get these right, or your bias cap underneath will go CHERNOBYL on you. Connect the wires as close to the body of the Bridge rectifier as you can and trim off the ends. Mount to chassis where the old siemens rectifier WAS. WHEN DONE TAKE PICTURES AND POST. Then let me know when the new can's come in from Hayseed. STOP AT THIS POINT.
Thom, heed what Larry says PRECISELY. I,too, am apprehensive about someone undertaking a project of this magnitude absent prior experience & familiarity with electronic theory,component identification and verifiable soldering skills. I can liken it to someone unfamiliar with woodworking tools, methods/procedures attempting cabinetmaking using rare, expensive materials. please take no offense! I'd hate to see bad things happen to your prize piece that would be difficult +/or $$$ to undo or correct.
Please consider finding an old junk radio or tv built with the same style of construction and practice unsoldering, removing & replacing wires & parts to gain experience & confidence. When your soldered connections are indistinguishable from the originals, you're good to go.
Also recommended to get a resistor color code chart & learn how to read the colors on resistors. You don't want to mix any of these up!
We're all on your side here, man. You gotta learn to swim before you jump into deep water. And if you havent, take pictures up close of your rcvr prior to starting. You'll be glad you did. Years ago, I had to replace the rca input strips on my Fisher x-101-d amp. I took pics of the area to be worked. Once I got the pics back from developing (I did say years ago!), I had everything needed to proceed. Those pics were worth more than a page of notes. Still have it today. Yesterday I dug it out of long-term storage, serviced it (clean chassis, check toobs, hose down switches & pots). damn thing still works!
We expect a play-by- play commentary on your project. Good luck & have fun!
Please consider finding an old junk radio or tv built with the same style of construction and practice unsoldering, removing & replacing wires & parts to gain experience & confidence. When your soldered connections are indistinguishable from the originals, you're good to go.
Also recommended to get a resistor color code chart & learn how to read the colors on resistors. You don't want to mix any of these up!
We're all on your side here, man. You gotta learn to swim before you jump into deep water. And if you havent, take pictures up close of your rcvr prior to starting. You'll be glad you did. Years ago, I had to replace the rca input strips on my Fisher x-101-d amp. I took pics of the area to be worked. Once I got the pics back from developing (I did say years ago!), I had everything needed to proceed. Those pics were worth more than a page of notes. Still have it today. Yesterday I dug it out of long-term storage, serviced it (clean chassis, check toobs, hose down switches & pots). damn thing still works!
We expect a play-by- play commentary on your project. Good luck & have fun!
fred soop
Super Member
Todays resistor colors are not as clear as in years past and the resistors are much smaller, adding to the problem. A model railroad friend recommends using a meter and checking ALL resistors before installing. He found some smoke a few times with either misreading or parts that were simply mismarked. Yes, it does sometimes happen. I have also (maybe twice in 40 years) received resistors from DigiKey that were different than what was labeled on the bag.
Thom 2230
Active Member
Thom 2230
Active Member
Larry, the 400 has been on its back unplugged for the past three weeks. I will go through the procedure to discharge the caps FIRST. Concerning the Hayseed cans - I must have skipped a groove. These cans have not been ordered. What is a good source? And what should I ask for?
Thom 2230
Active Member
Thom, heed what Larry says PRECISELY. I,too, am apprehensive about someone undertaking a project of this magnitude absent prior experience & familiarity with electronic theory,component identification and verifiable soldering skills. I can liken it to someone unfamiliar with woodworking tools, methods/procedures attempting cabinetmaking using rare, expensive materials. please take no offense! I'd hate to see bad things happen to your prize piece that would be difficult +/or $$$ to undo or correct.
Please consider finding an old junk radio or tv built with the same style of construction and practice unsoldering, removing & replacing wires & parts to gain experience & confidence. When your soldered connections are indistinguishable from the originals, you're good to go.
Also recommended to get a resistor color code chart & learn how to read the colors on resistors. You don't want to mix any of these up!
We're all on your side here, man. You gotta learn to swim before you jump into deep water. And if you havent, take pictures up close of your rcvr prior to starting. You'll be glad you did. Years ago, I had to replace the rca input strips on my Fisher x-101-d amp. I took pics of the area to be worked. Once I got the pics back from developing (I did say years ago!), I had everything needed to proceed. Those pics were worth more than a page of notes. Still have it today. Yesterday I dug it out of long-term storage, serviced it (clean chassis, check toobs, hose down switches & pots). damn thing still works!
We expect a play-by- play commentary on your project. Good luck & have fun!
