Help Saving 400-CX SA-100 and 100-R Tuner

Discussion in 'Fisher' started by moondogtn, Oct 10, 2017.

  1. moondogtn

    moondogtn AK Subscriber Subscriber

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    Good evening to all the fisher gurus. I am hoping y'all are willing to help a first timer do this as I have never worked on tubes. I have done some solid state repairs with guidance from members here. I am willing to listen. I can solder and know some about electronics. Test equipment I currently have are Goldstar O-scope, DBT, Fluke DMM, Eico Power Supply, and two tube testers. I am pretty stoked to attempt this project providing I can get the much needed guidance necessary not to butcher these units. I believe they are in decent cosmetic shape under the dirt and dust. So far, I didn't do anything to them at all, not even wipe off dust as I want to do this in steps.

    Backstory, I traded a friend for some stuff he wanted and I got this trilogy of Fisher tube equipment. He purchased at an auction and it has not been tested. I am excited to get this and want to do my best to get it back in action. He did wipe down the amp. The preamp has a transformer that isn't original but he included a (functional) triad original transformer in the trade for install.

    I don't have a variac but plan to get one soon. I have a DBT. I am not in a rush as I have work, school, and a family but just want to take my time and do it right.

    I attached some pics. Here is a link to the google album.

    https://photos.app.goo.gl/zKpqyv1AOSTiWUP02

    If more are wanted, please just ask. Thanks

    Edited as I figured I would add the test equipment although I have never used tube tester so I will need to figure that out. Also, added google album.


    Bill
     

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    Last edited: Oct 11, 2017
  2. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Moon -- You'll find plenty of good folks here to help you with your restoration efforts when you get to them. Properly restored, you will really enjoy the pieces you have.

    Until you get to that though, from my post #26 of this thread:

    http://audiokarma.org/forums/index.php?threads/1961-fisher-president-vi-restoration.766491/page-2

    A pic of the bottom of your 400CX would be greatly appreciated. In particular, when turned upside down, with the rear facing you, focusing on the components that are connected to the third tube from the right.

    Otherwise, when you need some help, just ask!

    Welcome to the AK Fisher forum!

    Dave
     
  3. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    If the tuner chassis is in good shape, keep an eye out on eBay for a replacement faceplate. Sometimes they're found on otherwise damaged units that are parted out. Helluva nice system you'll have there when you're done!
     
  4. moondogtn

    moondogtn AK Subscriber Subscriber

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    Dave, I appreciate your optimism. I’m hopeful but in uncharted territory. I attached a few pics and also added to the album in google photos. Please let me know if these will suffice or I can get more


    I would like to get started but not sure where to begin.

    Cleanup?
    Power test?
    Purchase variac?

    I noticed one of the 12AT7 tubes is missing on the preamp.

    Sam, I’ll set up a watch on eBay for one and keep an eye out.

    Bill
     

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  5. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Hi Bill -- Thanks so much for the pics. It confirmed what I was looking for.

    Since you're new to tubes, a step at a time is the rule of the day. Certainly get things cleaned up first. Check the stickies on this site about doing that properly (i.e. safely), so that you don't damage any graphics or metalwork in the process. You'll certainly want to replace the one missing 12AT7. Depending on which one is missing, either one or the other channels won't work, or both won't work with one of those tubes missing.

    Your skills and ambition will determine whether to get a variac, or not. Both it and a DBT will let you slowly restart a vintage unit without causing any undue damage. You've already got a DBT, so I'd work with that for the moment. Otherwise, a variac with a builtin watt meter is indispensable if you plan on doing enough work in the future to warrant the purchase.

    It might be best for you to start with the preamp first, because it appears to be the biggest challenge at this point. It appears that someone had to replace the power transformer with external components of unknown specification. As well, unfortunately, there is no Service Manual or schematic available for this rare unit -- unless you came upon one when you acquired these units -- but that shouldn't stop you from doing a basic restoration on it. There will normally be two components that are invariably already bad on this unit -- the selenium rectifier -- originally mounted up high on the inside of the unit near where the phase switch is located, and the can filter capacitor associated with this rectifier that is mounted right in front of where the power transformer normally resides. It appears that the rectifier for this power supply now must be located externally with the new power transformer, because there does not appear to be any inside the unit anymore. For the can, you can either have one custom manufactured (nobody makes an inventory item to replace the original can), or use two discrete caps to replace the original, while leaving the original in place for appearance purposes. These components form a low voltage DC power supply to power most (but not all) of the heaters in the tubes of the unit. When they go bad, the unit will either not operate, or take a very long time to warm up due to the very low voltage produced by the supply for the heaters. You will ultimately want to replace the B+ filter caps as well, but they usually last longer than the DC Heater supply caps do, which is why you start with them first.

    The preamp is the heart of the system. If it doesn't function, all ability to control the system is lost. But to get it going, you're going to first have to make sense of all the external transformers that were added at some point in an attempt to make the unit operational. Draw out on paper what all that represents. Detail pics of the transformer adventure will let us help you decipher what's going on there. From what I can see, the twisted purple and white leads should be supplying about 30 vdc (positive relative to the chassis) to the unit. Inside the unit, the original purple is the positive lead. The red and orange lead are supplying high voltage to the rectifier tube, while the remaining leads supply 6.3 vac (relative to ground) with a tap at about 5.5 vac to power the indicator lamps.

    If any terminology throws you here just ask. Restoring this equipment will be a long, involved process for you, depending on your skills and learning curve. But this is as good a place to jump in and start at as any. Let us know!

    Dave
     
  6. moondogtn

    moondogtn AK Subscriber Subscriber

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    I’m not sure what they have going on here so I can’t draw out this circuit without more information.

    I attached a picture which may be better if I flip unit right side up and remove the cover but I would like to get large transformer sorted out first. The brown/white twisted pair are attached to a small terminal strip above the master volume switch if it unit were sitting right side up. This is soldered to a purple/white twisted pair and is the soldered to a standard plug?

    I also notice the smaller transformer (2nd to last pic) is not hooked up to anything.

    Large transformer (3rd to last pic) is probably going to get replaced with the original triad transformer but I took pictures of wiring for reference. It’s difficult to differentiate colors so I am planning on using numbers to label each and remove transformer tomorrow if time permits.

    I can power up and test the transformer once I get it disconnected. I will also test the original triad transformer(last pic) to confirm good as I think it’s best to go back with that rather than the behemoth they had installed?

    I hope this helps. I have not had any luck sourcing the schematic for this unit although I asked a friend who is looking through his files.



    Bill
     

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  7. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Bill -- Now I see how the repair was being executed:

    1. The large power transformer must be supplying the HV to the rectifier tube (310-0-310) for B+, and almost certainly the 6.3 vac to power the rectifier tube heater, and the heater of the 12AX7 on the right end of the unit when it is upright and facing you.

    2. The terminal strip you refer to is an added piece that has four discrete diodes connected to it to replace the original selenium bridge rectifier pack that has been removed.

    3. The 25 volt Stancor transformer must be powering the four diodes to become the DC heater power supply in the unit.

    3. The only absolutely unknown element then is of the yellow-green-blue leads connecting to the terminal strip on the side panel of the unit -- what does the blue lead connect to coming from the transformer package? The Green and Yellow leads should be supplying 6.3 vac to power the heaters mentioned in #1 above, while the Green and Blue leads should be supplying about 5.5 vac to power the front panel indicator lamps -- but I don't see any source for that in the external transformers, unless that is what the disconnected transformer was for. What does the blue lead connect to in the transformer "array"?

    You will definitely want to remove the terminal strip with the four diodes attached and install a silicon bridge rectifier to do that job properly. While the existing approach no doubt works, having so much un-shielded AC floating around the volume control area is a recipe for disaster with regards to hum.

    The "original" Triad transformer may be original to the unit when you or someone before you got this unit, but it is not the original Fisher transformer. Lacking that, it would be best to use the Triad transformer -- but depending on whether that transformer contains a hum strap, it may be better to leave it as an external piece rather than mount it to the chassis. Mounting a transformer without such a strap will increase hum many fold. Check to see if the transformer has one -- I can't tell if it does from the overhead shot provided.

    For reference, I've included a shot of the new silicon bridge rectifier I've install in the unit I have here that replaces the old selenium rectifier pack, and is mounted where the old selenium device was located. You can likely disregard the power resistor associated with that installation. It is there to emulate the voltage drop of the original selenium device so that the peak current drawn from the (still original) power transformer remains as it was when the selenium device was installed and still good. Without the resistor, the lower voltage drop of the new silicon device would cause increased heating in the power transformer which is not good for its long term dependability. Since you are in a sense "rolling your own" transformer configuration, the resistor may not be required in your case, but I highly recommended it when the original transformer is still in place. I'm seeing a number of these units with replaced power transformers -- it may be because such precautions were not taken. The cap associated with the installation is effecting one of the two caps in the DC Heater supply can cap that is bad in this particular unit. The second cap is located near the can cap itself. The can has been left in place for the sake of appearance, but serves no electrical function anymore. The Brown and While wires are the AC leads from the original power transformer (originally connecting to the selenium rectifier pack), and the Black and Purple leads (also originally connecting to the selenium rectifier pack) are the original leads carrying the DC down to the can cap. Anyway, you can use this pic as a reference for a more appropriate way to install a bridge rectifier in place of the four discrete rectifiers currently installed in your unit, which will ensure that no hum is contributed by the heater supply into the audio circuits.

    I hope this helps!

    Dave
    SAM_2249.JPG
     
  8. moondogtn

    moondogtn AK Subscriber Subscriber

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    Dave, I have a few things to report. I apologize for it taking so long.

    1. I labelled the wiring and removed the old transformer. I can now move that preamp around much easier.

    2. Odd thing is that wiring goes directly to a plug, no transformer in between. I attached a photo. I read your post and will plan on replacing this with the silicon bridge.

    3. That little transformer wasn't hooked up at all.

    4. Those leads were attached to the large external transformer. I thought I attached pics. I will do that now. I also updated the shared album in google photos. I hope someone will let me know if you aren't able to view.

    BTW, you were correct. I misunderstood in thinking the Triad transformer was orginal. What is a hum strap? I did google it but no dice. I attached another shot of the Triad. Hopefully, it will show you what you need to see.

    I am unsure where to start?

    Testing transformers? If so, easiest/safest way? Hook up to 120 and carefully check secondary voltages?

    Edit: I actually have what I think Is the correct schematic for this unit. I’ll look at it closer as soon as time permits to confirm.

    Bill
     

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    Last edited: Oct 18, 2017
  9. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Bill -- A hum strap is the wide copper strap you often see going around the outside of the laminations, but under the end bells. It does NOT go through the cut-outs in the EI stack (it would represent a shorted turn if it did). Often, the strap may be painted black making it harder to see, but you'll either see it, or you won't. There's no in between. The strap helps to minimize any stray leakage of magnetic field from the transformer, making for quiet operation when powering sensitive circuits. Without the strap, it's a recipe of ensuring hum -- particularly if the chassis it is mounted on is a steel one.

    OK. Looks like they were using the 5V winding of the big transformer to power the 5.5 volt lamp circuit, and the 6.3 volt winding of that transformer to power the AC heater circuit. The Stancor P6469 transformer was powering the makeshift bridge rectifier mounted on the added terminal strip. As to why there is a plug on that wire, who knows -- but GET IT OFF OF THERE!! I surely hope that somebody didn't think that the purple and white wires were where the AC power was supposed to be applied to!! If it was a convenient way to make a disconnect for the connection it was about the dumbest way it could be done. The chance of plugging that straight into the wall is waaaay to great. The Triad transformer was likely supplying the HV to the rectifier tube.

    So the existing setup is using 3 transformers to make it work. I think I'd investigate trying to get that down to two transformers, as the chance of finding one transformer manufactured today that could provide all the necessary voltages is slim to none -- and Slim left town........

    I note that there is someone on the auction site selling a Fisher power transformer that was said to be for a preamp (search Fisher Preamp). You might inquire of this person as to the various windings the transformer has to see if it would work.

    Best --

    Dave
     
  10. bhuskins

    bhuskins AK Subscriber Subscriber

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    I know a little about this unit as well Dave and the triad transformer was a separate purchase and has/was not utilized with the unit whatsoever. It was recently purchased with the intention of fully replacing the transformer on the board and getting everything back to one chassis.
     
  11. bhuskins

    bhuskins AK Subscriber Subscriber

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  12. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    The triad transformer could no doubt fill the need for the B+, 6.3 vac heater, and even 5.5 volt source for the indicator lamps if a dropping diode is used to provide that source. You would still need a separate transformer to power the DC heater supply though, which is apparently what was done to the unit in the picture above. Do you have any experience with specifically the unit pictured above? I'm wondering how that unit is relative to hum in the phono preamps as compared to the humless operation produced by the original power transformer.

    Dave
     
    Last edited: Oct 20, 2017
  13. moondogtn

    moondogtn AK Subscriber Subscriber

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    Dave, I couldn’t say regarding hum but bhuskins should be able to.

    I should be able to make some progress documenting and cleaning up this weekend.

    Bill
     
  14. bhuskins

    bhuskins AK Subscriber Subscriber

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    The one above was flawless and awesome....
     
  15. moondogtn

    moondogtn AK Subscriber Subscriber

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    That’s what I was hoping to hear. I’m taking baby steps. I removed the bells and the tubes, labeled ziplocs with locations, and put them in a safe place. Next step will be to start cleaning chassis. I haven’t exactly decided as I don’t want to be so aggressive as to remove lettering. I’ll post up any progress.

    Bill
     

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  16. moondogtn

    moondogtn AK Subscriber Subscriber

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    I am not getting to devote much time to this project but am still trying to squeeze in some research and gather information. I came up with a partial parts list and a picture that I plan to add to mark up as I go along. I noticed the frako caps C54, C55 were the same as the other frako caps 25 uF vs the 250 which is shown on drawings and partls list. What do frako caps actually do in the circuit? I ordered a variac that should be here by the end of the week.
    Here is the initial list. Quantities may need to be adjusted but I wanted spares to have on hand. Please let me know if my format is wrong here and I will modify it.

    Bridge Rectifier ?


    C29, 31, 36, 38, 54,55 647-UPW0J270MDD UPW0J270MDD Nichicon Aluminum Electrolytic Capacitors - Leaded 6.3volts 27uF 4x7 20% 1.5LS 10 $0.153 $1.53

    C45 Section A, D 647-UPW2W470MRD UPW2W470MRD Nichicon Aluminum Electrolytic Capacitors - Leaded 450volts 47uF 20x40 20% 10LS 10 $2.20 $22.00

    C45 Section B, C 647-UPW2W100MHD UPW2W100MHD Nichicon Aluminum Electrolytic Capacitors - Leaded 450volts 10uF 16x25 20% 7.5LS 10 $0.843 $8.43

    C50 Section A, D 647-UPW2E100MPD UPW2E100MPD Nichicon Aluminum Electrolytic Capacitors - Leaded 250volts 10uF 10x20 20% 5LS 10 $0.488 $4.88

    C50 Section B, C 647-UPW2V330MHD UPW2V330MHD Nichicon Aluminum Electrolytic Capacitors - Leaded 350volts 33uF 16x31.5 20% 7.5LS 10 $1.44 $14.40

    C46 Section A, B 647-UPW1V102MHD UPW1V102MHD Nichicon Aluminum Electrolytic Capacitors - Leaded 35volts 1000uF 12.5x25 20% 5LS 10 $0.828 $8.28

    Please advise if there are other items I should add for the initial order. I suppose I should replace caps prior to even attempting to apply power? Initial power up question, can I use the variac and DBT in conjuntion/series? Should I as an added precaution?

    Thanks

    Bill
     

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    Last edited: Nov 4, 2017
  17. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Bill -- The Franko caps are what are know as "Cathode Bypass Caps". They are low voltage electrolytic caps that act to help achieve the maximum amplification for which the stage to which they are connected to is capable. In this unit, all of the 6 Franko caps are in fact, and should be 25 uF caps. The 250 uF as specified in the Fisher Service Manual for C54 and C55 in this model is a mis-print, and should read 25 uF.

    Dave
     
  18. moondogtn

    moondogtn AK Subscriber Subscriber

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    Dave, So, will that list suffice or do you see anything that I should change or add to it(resistors or diodes) or just order the basics at this time? Am I missing anything? I don't mind ordering extra now if it prevents me having to order stuff later.

    Thank you for telling me what those frako caps do. I was wondering.

    I should have some time this weekend to get transformers leads identified and labeled.

    Also, I have searched the threads but want to make sure I understand this regarding cleaning up the brass faceplates. The below method seems to most applicable to my situation but want to ask prior to doing irreversible damage to faceplates. I assume you don't boil the faceplate...just use this mixture with a chip brush as Larry says?

    Thank you

    Bill
     
  19. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    The bridge rectifier you have chosen certainly works, but is way, way overkill. A 3 or 4 amp unit is more appropriate.

    Ditto for the use of a CL-80 current limiter. It will be hard to specify at this point if or how many of these you might need, since you are not using the original Fisher transformer. One thing is for certain however -- it won't need a CL-80 (3A device) or even a CL-90 (2 A) device, since the fuse of these units is just .5A. Any adjustment a CL device might provide will need to wait until you actually have an operating unit that measurements can be taken on. Also, if an adjustment is needed, it may not even be a CL device that is most appropriate to use, either.

    Use a Variac for power up if possible. If using a DBT, the lamp wattage will need to be much smaller than normally seen used. Do not use both together -- the interaction between them will be confusing.

    Your approach is to use individual discrete caps to replace the can caps. This certainly works, but will make for a more crowded underside that takes away from the neat orderly build if not well planned out. It also opens up the possibility of introducing ground loops if the ground leads of the discrete caps don't conform to the original ground scheme used.

    Also check the condition of the dropping resistor used in the DC Heater Supply. It's probably still quite good, but should be checked none the less. Otherwise, it's a good list to get you started.....

    Dave
     
  20. moondogtn

    moondogtn AK Subscriber Subscriber

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    Dave, I can definitely downsize the bridge recitifier. I only chose it as that was the part listed on the sticky for common fisher parts. Same for the CL-80. I removed them from the parts list. I also have a request for a quote on all the cans to hayseedhamfest. It is possible the cost will be comparable and yield a cleaner looking end product..

    I am however struggling trying to determine the dropping resistor for DC Heater supply you are referring to.....If it is the 12 ohm 7W wirewound resistor R94, then it is good. It measures exactly 12 ohms.

    On a different note, I reached out to the seller on the auction site, twice. No response either time. So, I couldn't get any info regarding that transformer.
    Thanks for the help.

    Bill
     

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