If you're real careful you can fry egg's on one. Or the tip of your finger......(Look Ma, the FBI can't print me now! 
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A Reference 400 Restoration/Modification
- Thread starter dcgillespie
- Start date
kentuckycat
Active Member
Well, I guess I'm done. I wasn't crystal clear on the noose resistors but from all I read - I cut them out. I reached out to Jim McShane for a few questions that I couldn't find the answer to on AK and he was a big help. I wasn't sure what my options were for having one weak 7868 tube, so I bought a new EH set from tubedepot. McShane was fresh out of 7868's. So I guess that's it. Done. The 400 will be my music source / space heater for the balance of the winter. arrivederci
kentuckycat
Active Member
As a follow-up:
- while I was waiting for parts I built a cool little buck transformer time machine and set it for 1964. Up is 115v, down is ~110V and center is off. I’ll use that power switch to turn on the 400 instead of the original Fisher switch.
- I wanted to buy a chromecast audio but the used price got stupid. I found a cheap little Amazon basics device called an audio extractor, dug my old video chromecast out of the junk drawer and plugged it in to the extractor then into the DAC. Works perfectly. Same quality streaming as the chromecast audio.
- thirdly, I see what the fuss is about with these Fishers. Up until yesterday my favorite amp was my Kegger/Blueglow SE KT88- which sounds awesome. The 400 digs deeper and has better separation. Looks cool, too.
- while I was waiting for parts I built a cool little buck transformer time machine and set it for 1964. Up is 115v, down is ~110V and center is off. I’ll use that power switch to turn on the 400 instead of the original Fisher switch.
- I wanted to buy a chromecast audio but the used price got stupid. I found a cheap little Amazon basics device called an audio extractor, dug my old video chromecast out of the junk drawer and plugged it in to the extractor then into the DAC. Works perfectly. Same quality streaming as the chromecast audio.
- thirdly, I see what the fuss is about with these Fishers. Up until yesterday my favorite amp was my Kegger/Blueglow SE KT88- which sounds awesome. The 400 digs deeper and has better separation. Looks cool, too.
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kentuckycat
Active Member
I finished the above receiver and love it, so I bought another one on ebay two days later. $218 bucks cheap. Non-working and the photos showed some issues. It showed up this week and it was packed incredibly well. It's an early one, so I wasn't expecting a nearly flawless chassis, but that's what I got. The whole thing had a thin film of cooking grease covering it. That might have been what protected it so well.
However, the aluminum plate that separates the output tubes from the transformers was missing, so I fabricated a new one out of a scrap of aluminum. The threaded fasteners that hold it in place are very specialized so I wasn't sure what I was going to do about that. I went to the hardware store thinking that a solution might jump out at me and it did! Thumb screws. I drilled a hole in wing nuts and riveted them to the aluminum plate and viola! Except for being shiny, it's pretty much an exact match. Fits perfectly.
The bracket that holds the magic eye tube in place is also missing but miraculously, the plastic iris was floating around in the box. I'll have to MacGyver a solution to that one. Also, not a single original Fisher knob, which is a bummer. The tubes are a Heinz 57 variety of odd, probably unmatched tubes. Someone did a bush-league job of recapping two of the can caps but I'll be replacing all of that with new ones from Hayseed. As advertised, it doesn't work, so I'm trying to figure that out now.
However, the aluminum plate that separates the output tubes from the transformers was missing, so I fabricated a new one out of a scrap of aluminum. The threaded fasteners that hold it in place are very specialized so I wasn't sure what I was going to do about that. I went to the hardware store thinking that a solution might jump out at me and it did! Thumb screws. I drilled a hole in wing nuts and riveted them to the aluminum plate and viola! Except for being shiny, it's pretty much an exact match. Fits perfectly.
The bracket that holds the magic eye tube in place is also missing but miraculously, the plastic iris was floating around in the box. I'll have to MacGyver a solution to that one. Also, not a single original Fisher knob, which is a bummer. The tubes are a Heinz 57 variety of odd, probably unmatched tubes. Someone did a bush-league job of recapping two of the can caps but I'll be replacing all of that with new ones from Hayseed. As advertised, it doesn't work, so I'm trying to figure that out now.
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kentuckycat
Active Member
Update: The unit was not as advertised. It works perfectly. The speaker switch was in the off position. (hee-haw). I guess I got a pretty good deal on ebay. Does anyone have a line on a set of Fisher knobs?
I'm not sure why I didn't get any voltage. You could be right and I might have had the MM set to AC. I tried it again a few hours later at a higher voltage and I got a voltage reading. So I twisted the knob on variac and BAM, music! (after fiddled with the speaker switch). I really love that sensation of hearing music coming out of an amp that I've been working on. thanks for your response!
kentuckycat
Active Member
The schematic shows a double pole switch so I’m guessing the one on my unit is a replacement. Looks like the previous owner didn’t know what to do with the wire leading to the outlets so it was left dangling. Would it be safe to wire the outlets to the single pole switch or should I just shrink wrap that lead?
Thanks!
Thanks!
You can make the outlets unswitched by taking the extra lead and tapping it into the hot lead before the switch. OR tape off the leads and not use the outlets.
kentuckycat
Active Member
Larry, I didn’t even think of this until I read your reply- I power the 400 via a buck transformer. I think I’ll tape them off like you suggested. No sense in putting the extra burden on the switch or the external transformer. Thanks for helping me think that one through! Jeff
Mark Davis
Active Member
Dave I am new to the Fisher 400 restoration hobby and am trying to figure this out. I tried posting these questions to the parts sticky but did not get a reply. I think it was buried to far down. I apologize for a double post.I picked up a 400 at a estate sale pretty reasonably. I did the Dim bulb test everything looked fine. I had some Red plating on two 7868 tubes so I turned it off. I did not have a variac at the time I do now. I have not tried it on the 400 as I was told not to power it up again. I have read your thread A Reference 400 Restoration/Modification. I am trying to get to a baseline to start before doing additional Mods. From what I understand I get the main Caps from Hayseed Hamfest. The other components that need replaced I tried Jim Mcshane but he said he is extremely busy to try him in a month. I also went to Metalbone but he said he is not filling orders now and may not. He lost a hard drive so he couldn’t even send me the directions. (I think it would help on newbie like myself.) I am searching for a list of components that need replacing so I can try and source these myself. I have the service manual so if I knew the Designation / Symbol I have the specs. (Unless there are suggested improvement components from the specs.)
You said to replace the following as a must.
A. All electrolytic caps in the B+ power supply, DC Heater/Bias supply, MPX, and Ratio Detector circuits. (Is this what I Replace C55, C74, C76, C77 A,B,C, C78, C210 anything I am missing)
New top side can caps are installed to minimize the intrusion/need of otherwise new under-chassis components required, which helps to minimize clutter and maintain the look of the original Fisher build. ( I replace with Hayseed Hamfest Kit - C75, A,B,C,D)
B. Both HV (B+) rectifier diodes. (Not sure here SYMBOL ????)
C. The selenium rectifier with a silicon unit if so equipped. (Replacement - 8A 400V Rectron: Mouser # 583-BR84)
D. Both AC Bypass caps.(Not sure here SYMBOL ????)
E. Phono preamp and MPX mylar coupling caps. Replace Mylar Caps(C19,C20,C47,C48,C49,C62, C63, C64, C65, C214, C221, C222)
F. Any other component showing signs of stress, is out of production tolerance, or through troubleshooting has been determined to prevent less than designed/expected performance.
What else should I be looking to replace for a start. Looking to get a solid base line before other Mods?
You would not have a list of the capacitors and other components to replace would you? I started looking and sourcing this stuff from different vender’s looks to be a challenge. Not to mention I am not 100% I have the right components.
I am fairly handy an Electrician by trade and can read schematics. I built industrial control panels for years. Electronics are new to me and I am reading some of the Rider books to learn.
Thanks in advance for any help.
You said to replace the following as a must.
A. All electrolytic caps in the B+ power supply, DC Heater/Bias supply, MPX, and Ratio Detector circuits. (Is this what I Replace C55, C74, C76, C77 A,B,C, C78, C210 anything I am missing)
New top side can caps are installed to minimize the intrusion/need of otherwise new under-chassis components required, which helps to minimize clutter and maintain the look of the original Fisher build. ( I replace with Hayseed Hamfest Kit - C75, A,B,C,D)
B. Both HV (B+) rectifier diodes. (Not sure here SYMBOL ????)
C. The selenium rectifier with a silicon unit if so equipped. (Replacement - 8A 400V Rectron: Mouser # 583-BR84)
D. Both AC Bypass caps.(Not sure here SYMBOL ????)
E. Phono preamp and MPX mylar coupling caps. Replace Mylar Caps(C19,C20,C47,C48,C49,C62, C63, C64, C65, C214, C221, C222)
F. Any other component showing signs of stress, is out of production tolerance, or through troubleshooting has been determined to prevent less than designed/expected performance.
What else should I be looking to replace for a start. Looking to get a solid base line before other Mods?
You would not have a list of the capacitors and other components to replace would you? I started looking and sourcing this stuff from different vender’s looks to be a challenge. Not to mention I am not 100% I have the right components.
I am fairly handy an Electrician by trade and can read schematics. I built industrial control panels for years. Electronics are new to me and I am reading some of the Rider books to learn.
Thanks in advance for any help.
Before we get into particulars, We need to know the serial # to verify it's an EARLY or a LATE Model. FISHER noted serial # range on the front cover of the manuals. Also do YOU have the Service Manual for the range your serial is in. These are the serialed 400 manuals at fisherconsoles.com.
400 Receiver (s/n 10001-19999)
400 Receiver (s/n beginning 20000)
400 Receiver (s/n 20001-29999)
400 Receiver (s/n beginning 48001)
The last 2 are the most used. If you feel comfortable using another by all means but remind us of what manual you are using. Keeps us all at least in the same county.
The manual is a good source of parts values and voltages. About 80% of the caps in the 400 are ceramics and usually DO NOT require attention. Mainly you'll be doing lytics and most of them are in the power supply, and other sections as you noted above. Lytics that are <1uf get replaced by low noise lytics (Nichicon UKL or similar low noise).
Take some pictures of the undercarriage (Hi-DEF) overall of the chassis. Then quarter the chassis with a little overlap up/down and side to side, so we don't lose any parts off picture.
400 Receiver (s/n 10001-19999)
400 Receiver (s/n beginning 20000)
400 Receiver (s/n 20001-29999)
400 Receiver (s/n beginning 48001)
The last 2 are the most used. If you feel comfortable using another by all means but remind us of what manual you are using. Keeps us all at least in the same county.
The manual is a good source of parts values and voltages. About 80% of the caps in the 400 are ceramics and usually DO NOT require attention. Mainly you'll be doing lytics and most of them are in the power supply, and other sections as you noted above. Lytics that are <1uf get replaced by low noise lytics (Nichicon UKL or similar low noise).
Take some pictures of the undercarriage (Hi-DEF) overall of the chassis. Then quarter the chassis with a little overlap up/down and side to side, so we don't lose any parts off picture.
Mark Davis
Active Member
Larry I have service manaul 400 Receiver (s/n 10001-19999)
Attached are the pictures you asked for.
I did the Dim Bulb test and then plugged it in to 120v. Thats when the Red plating happened.
Question should I try powering up the amp with a Variac now that I have one? Or no until parts are replaced.
Thanks for your help.
Attached are the pictures you asked for.
I did the Dim Bulb test and then plugged it in to 120v. Thats when the Red plating happened.
Question should I try powering up the amp with a Variac now that I have one? Or no until parts are replaced.
Thanks for your help.
Attachments
maybe try it on the variac at about 60 volts. verify the bias supply is operating somewhere near 1/2 of the expected voltage, and confirm the output tube coupling caps are not leaking. Quick and dirty way of doing that is to measure the voltage across the 330k grid resistors on the output tubes. Good caps will show no voltage drop across the resistor, leaky ones will indicate voltage drop.
Leaky caps or weak bias supply will both cause excessive current in the output stage, which is what red plating really is.
I like to get some idea of basic functionality before doing a major overhaul but thats just me. Sometimes that just isn't possible but if I can do a temporary patch to get things working more or less as-found to see if it works or has some obvious major problem I do that. Not really looking for sound quality but I want to know if both channels work, the controls respond basically like they should, the tuner works, etc.
Leaky caps or weak bias supply will both cause excessive current in the output stage, which is what red plating really is.
I like to get some idea of basic functionality before doing a major overhaul but thats just me. Sometimes that just isn't possible but if I can do a temporary patch to get things working more or less as-found to see if it works or has some obvious major problem I do that. Not really looking for sound quality but I want to know if both channels work, the controls respond basically like they should, the tuner works, etc.
Mark Davis
Active Member
Do you do this with the tubes in or out? I agree with trying to get to a baseline thats were I am trying to get to. I was reading something about testing with the rectifier tube in but all other tubes out. Does that apply to the 400. I think it was on another tube radio site.I assume my first step would be the Hayseed Hamfest caps.
No rectifier tube in the 400. Tubes IN. That will load the transformer so the voltages aren't so high they don't make sense. And tubes in complete circuits so you can take voltage readings almost everyhere and compare them to bogey values on the schematic.
You got yourself a VIRGIN! coupling caps 1st. Then Hayseeds, then all the rest of the basic upgrade stuff. Get rid of those "Black beauty" caps (blackaxials with theyellow stripe or colored stripes.), Dogturds (black or brown epoxy dipped). Leave the Erofol's for now.
When you do the Hayseeds do all the 1-2-3-4watt resistors between the can sections. Replace that Humungous 1.2KΩ 7Wwith a 10W Ohmite. Add 100Ω1/4w screen stability resistors, 10Ω 1/4W cathode resistors, and at least IBAM or IBBA (Individual Output tube Bias adjustment boards).
One of 2 things as far as the redplating. Condition of the tubes (could very well be at end of life) or the bias circuit is gaffed to the point where the bias voltage is too much(Underside BIG CAN cap leaking) for the tubes (non adjustable right now). OR BOTH, which isn't too farfetched considering how hard the tubes were run. Rebuilding the bias cap part of the circuit to get correct voltages is paramount to tube longevity. Adding an individual tube bias adjustment (whether IBAM or IBBA) will add to your pure sanity quotient. So rebuild the WHOLE POWER SUPPLY 1st. We'll go from there.
You got yourself a VIRGIN! coupling caps 1st. Then Hayseeds, then all the rest of the basic upgrade stuff. Get rid of those "Black beauty" caps (blackaxials with theyellow stripe or colored stripes.), Dogturds (black or brown epoxy dipped). Leave the Erofol's for now.
When you do the Hayseeds do all the 1-2-3-4watt resistors between the can sections. Replace that Humungous 1.2KΩ 7Wwith a 10W Ohmite. Add 100Ω1/4w screen stability resistors, 10Ω 1/4W cathode resistors, and at least IBAM or IBBA (Individual Output tube Bias adjustment boards).
One of 2 things as far as the redplating. Condition of the tubes (could very well be at end of life) or the bias circuit is gaffed to the point where the bias voltage is too much(Underside BIG CAN cap leaking) for the tubes (non adjustable right now). OR BOTH, which isn't too farfetched considering how hard the tubes were run. Rebuilding the bias cap part of the circuit to get correct voltages is paramount to tube longevity. Adding an individual tube bias adjustment (whether IBAM or IBBA) will add to your pure sanity quotient. So rebuild the WHOLE POWER SUPPLY 1st. We'll go from there.
Mikiehepcat
New Member
That is what I was looking for. Thank you Dave for sharing your expertise.
Mark Davis
Active Member
D
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Dave, have you ever posted a drawing for Aux/Tape Monitor bleed removal, Tape Head input conversion, permanent RIAA EQ and removal of LF filter?
Maybe you have a copy you could link? Thanks!
Dave, I found Drew's post with your connection steps to convert TH input into an additional Line level input.
"1. Remove existing lead from Tape Head Input jack, and ground it.
2. Disconnect terminals 2 & 3 of the EQ package from the selector switch. Also disconnect the output of the preamp from the terminal in between the terminals where the EQ package connects to the selector switch. Since there is also an 82K resistor tied to this terminal that allows the equalized signal to flow on to the line level portion of the selector switch, this resistor must be disconnected from this terminal as well, and then permanently reconnected to the output side of the preamp output coupling cap as it was before. You now have three completely empty terminals on the selector switch.
3. Hard wire terminal #3 of the EQ package to the output side of the preamp output coupling cap.
4. Connect the Tape Head Input jack to the selector switch terminal where EQ package lead #2 was connected to.
5. Find the two terminals that connect to the OTHER END of the aforementioned 82K resistor, and determine which one is picked up when Tape Head is selected. Break the connection between these two terminals, so that the 82K only connects to the terminal that is picked up when Phono is selected, and the other terminal (Tape Head) is free.
6. Find the terminal next to where the Tape Head Input jack is NOW connected (that was originally connected to the output side of the preamp output coupling cap and 82K resistor), and connect a jumper between this terminal, and the terminal identified and freed up in step #5."
To better understand I modified the original Fisher schematic following the suggested steps. Did I do it right?
If so, it may help others. First is the original snippet of the relevant section:
And this one is edited with conversion changes:
This modification also addresses permanent RIAA EQ connection modification. I can't find a "permanent LF filter" in the schematic. Where do I find this 0.001uF on the schematic?
Thanks!
"1. Remove existing lead from Tape Head Input jack, and ground it.
2. Disconnect terminals 2 & 3 of the EQ package from the selector switch. Also disconnect the output of the preamp from the terminal in between the terminals where the EQ package connects to the selector switch. Since there is also an 82K resistor tied to this terminal that allows the equalized signal to flow on to the line level portion of the selector switch, this resistor must be disconnected from this terminal as well, and then permanently reconnected to the output side of the preamp output coupling cap as it was before. You now have three completely empty terminals on the selector switch.
3. Hard wire terminal #3 of the EQ package to the output side of the preamp output coupling cap.
4. Connect the Tape Head Input jack to the selector switch terminal where EQ package lead #2 was connected to.
5. Find the two terminals that connect to the OTHER END of the aforementioned 82K resistor, and determine which one is picked up when Tape Head is selected. Break the connection between these two terminals, so that the 82K only connects to the terminal that is picked up when Phono is selected, and the other terminal (Tape Head) is free.
6. Find the terminal next to where the Tape Head Input jack is NOW connected (that was originally connected to the output side of the preamp output coupling cap and 82K resistor), and connect a jumper between this terminal, and the terminal identified and freed up in step #5."
To better understand I modified the original Fisher schematic following the suggested steps. Did I do it right?
If so, it may help others. First is the original snippet of the relevant section:
And this one is edited with conversion changes:
This modification also addresses permanent RIAA EQ connection modification. I can't find a "permanent LF filter" in the schematic. Where do I find this 0.001uF on the schematic?
Thanks!
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