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Picked up Fisher Electra VIII console this weekend. Worth repairing?

Discussion in 'Fisher' started by grindfix, Dec 3, 2018.

  1. grindfix

    grindfix Full time hobby Subscriber

    Messages:
    583
    Location:
    New Albany, OH
    This thing came from Estate sale and was plugged-in by sale organizers, so no use for DBT or variac on it.
    Radio works in both channels through the hum of Amp power supply. (hums without input)
    This amp is hybrid using tube voltage amp and drivers into choked transistor output.
    Turntable is german Miracord and it tries to spin. Dried-up idler wheel I'm guessing.
    I was hoping that it was all tube unit and now not sure what to do with it. Woodwork is in pretty decent shape with minimal dings. It is cherry but color of the finish is not attractive to me. It does not appear to be very desirable or valuable unit. 5 german made Fisher branded 12AX7 tubes are the highlight.
    What would you guys do with it?
     

     

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  2. 1ontop=

    1ontop= Active Member

    Messages:
    278
    Location:
    Croswell in the Thumb, MI
    A couple of years ago I purchased a 1948 Bendix AM FM SW Radio Phonograph at a resale shop. Thought I might do some repairs on it .. never did. Tried selling it for what I paid (not very much) and got no takers. This summer I put it on Facebook "take it away free". A few months passed with no takers. Finally just a couple weeks ago an older gentleman called me and came by to pick it up. So happens he worked in a TV repair shop in the 60's and repaired all sorts of tube equipment. You may try that or drop it off at your local charitable resale shop.
     
  3. Catmanboo

    Catmanboo AK Subscriber Subscriber

    Messages:
    529
    Location:
    Atwater, ohio
    service the TT, clean it up & use it or flip it.:needpics:
     
  4. grindfix

    grindfix Full time hobby Subscriber

    Messages:
    583
    Location:
    New Albany, OH
    It’s at my shop and between cars. I was hoping to move it to better lighting to take pictures. I need to find schematic for it and pull amp out when it gets slow at work. My plan is to test tubes, replace electrolytic caps and see what it sounds like. It starts to hum as soon as power is turned on. Since this amps final stage is solid state I better replace main filters first. Probably source of the hum.
     

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  5. audmod01

    audmod01 Super Member

    Messages:
    1,293
    Location:
    Tioga, TX
    I would say it is worth restoration. The fact that it is mostly operational shows that it will not take too much effort to get back to good performance. The slow turntable is likely a combination of motor needing new lubrication in its bearings and general removal and renewing of lubrication to the spindle bearings and sliding trip mechanism under the turntable disc. There is a large gear with teeth and cam surfaces that needs to have the old grease removed with a suitable solvent such as lighter fluid, then renewed with Lithium grease.

    The hum in the output is likely due to aged electrolytic capacitors in the power supply. There are people here who are well versed in restoration of the Fisher consoles - ask. You will likely be able to do the work yourself with some help.

    Joe
     
  6. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    37,030
    Location:
    Southern NJ
    They're an interesting design. Larry can fill you in on particular do and don'ts for that one. ELL80 tubes driving germanium output transistors.
     
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  7. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    Identical to mine. Good Amp once the Caps are replaced. DO NOTE that the finals are Germanium. I would remove them one at a time, clean the chassis, mica spacers and the transistors, and regrease them. Can you take a better picture of the Amp that is straight on with the Fuse area highlighted. It may have the original adjustment pots for setting BIAS. DON'T MESS WITH THEM! They were the absolute WEAK point in the amp. There was a fix by FISHER that made it nonadjustable. Mine has the fix and runs just fine. Search C.E. VIII or 49A back to 2009. I did mine back then along with a 59A for my Futura VI. I put individual caps underneath at their sources instead of wiring them at the CAN's. Keeps all the POWER SUPPLY in the corner.

    Manual for the '65 C.E. VIII is on FISHERCONSOLES.COM.
     
  8. fred soop

    fred soop Super Member

    Messages:
    2,033
    Germanium Power Amplifiers - Some of this has been covered in the 600-T restoration thread but is of interest for other units as well, including this one.

    First, if the amplifier is working and you are not going to do a complete overhaul, DO NOT TOUCH the bias adjustment pots, as noted by Larry. These are open underneath, may have various small critters residing in them, and if they lose contact during adjustment, may blow up the entire amplifier.

    If you want to adjust the bias pots, here is the process:

    1 - Power off.
    2 - Mark the position of each pot as accurately as you possibly can.
    3 - Mark which pot goes in which position.
    4 - Remove the pots.
    5 - Clean the pots with whatever method you prefer.
    6 - Connect an analog ohmmeter between the wiper and end terminals.
    7 - Adjust the pot over its range. The resistance MUST change smoothly. If there is ANY hiccup, the pot is not clean. Go back to step 5.
    8 - Reset to the marked values and reinstall.
    9 - As a final check, measure resistance from the wiper one more time. All the circuits I've seen show 10 ohm pots so the final measurement should be less than 10 ohms in proportion to the wiper position, but there could have been other values used.
    10 - The actual adjustment procedure involves tuning for minimum IM distortion using the analyzer that all of us have sitting on the bench. If you stay with the original adjustment, check the DC offset at the output. If it is unacceptably high, it is corrected by changing the bias of the upper and lower transistor pairs with respect to each other. This should be a very small adjustment and not enough to greatly affect the bias. Split the adjustment between the 2 pots.
    11 - Proper bias current at idle is 30 mA. Depending on the actual circuit, it may be possible to measure the voltage across the emitter resistor. However, some variations will have this resistor also handling current for the bias network. A direct measurement may not be trivial.

    Alternate:

    The fixed bias version of the circuit (with the diodes) is dependent on component tolerances to maintain correct bias and zero DC offset. This may or may not be accurate. On my 600-T, one channel was close to correct but the other was way off. I redesigned the bias circuit to reinstate the adjustments but make them "safe". The same could be done to replace the old bias pots.

    Here is the circuit .....
    [​IMG]

    and the revised bias adjustment network .....

    1424
    [​IMG]

    Some variations will have 2 different part numbers for the transistors. This is not critical. Also, the resistors in the bias network (R17, R19, R21, R23 and their companions) may vary from what is shown here. There are 2 keys to this modification. One is (R25, R27, R29 and its companions), the other is (R31, and its companions) the emitter resistors.

    The emitter resistors should be 1%, not because the circuit is that critical, but the measurement is. This is where the bias current will be measured. The bias adjustment network resistance is "trapped" by R25, R29, and R27, such that this combination must be between 2.5 ohms and 4.5 ohms even if the pot wiper should lose contact. The sealed Bourns pots should be reliable and the small size is not an issue. There is very little power dissipated and no real need for those original large wirewound units.

    Adjusting Bias

    Connect a voltmeter across one emitter resistor and adjust the associated trimpot for 10 mV, corresponding to 30 mA of emitter current. Turn the other trimpot in that channel to approximately the same physical position because the adjustments for the upper and lower transistor pairs interact and this will get the adjustments closer to start. Actually, you could start with both pots adjusted to mid range. Then check the voltage at the other emitter resistor. Repeat until both are adjusted. Next, the DC output offset voltage should be measured. If it is positive, then the upper transistor pair needs slightly less bias and the lower slightly more. If the voltage is negative, then the opposite. This is a very small adjustment.

    Let the amplifier "cook" for a while, then recheck the adjustments.

    Good ventilation during operation is necessary. The bias networks generate approximately 12 watts of heat and if airflow is blocked, the transistors will eventually fail.
     
  9. grindfix

    grindfix Full time hobby Subscriber

    Messages:
    583
    Location:
    New Albany, OH
    Larry and Fred, thank you for your replies. I will most likely recap it and will look into retrofitting bias/DC offset network. Regarding the sensitive idle current adjustments, I always clean pots before I touch them under power. I do first round of adjustments under DBT and set bias accordingly low so it will be on the low side when I power it direct of the wall.
    Larry, pictures you asked for are attached.
     

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  10. biscuithead

    biscuithead Me likes the eargasm retroplasm... Subscriber

    Messages:
    4,504
    Location:
    Northern Colorado
    I’d just like to add that the Elac 10f is a gem also. IMO, it is the best TT that Fisher ever put in a console. I’ve also had this exact console, and loved the sound! Great find! Stick with Larry, he will steer you right. Have fun!
     
  11. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    The BIAS Mod has already been done, looking at the empty holes where the pots were. It should be very close if not dead on. There is a Temp compensated diode (RCA 2836 or something like that) that replaces the pot. If it's very close, I'd leave it, but going with FRED's adj. board is a good bet. I'll see if I can find the pics showing how I replaced all the CAN CAP sections with individuals.
     

     

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  12. infullview

    infullview Active Member

    Messages:
    218
    Location:
    Maine
    I had the same turntable as well. It's built like a tank and the tone arm is a bit massive but it is fully counterbalanced and jeweled and can track surprisingly light. One thing to know about germanium transistors; they can be noisy. You may hear some very low clunking/rumbling sounds buried in the white noise.
     
  13. grindfix

    grindfix Full time hobby Subscriber

    Messages:
    583
    Location:
    New Albany, OH
    Larry, good to know that it’s most likely safer vs original unmodified version.
    Do you know if this bias mod was post production recall? Looks like wiper / shaft is removed and all else left in place.
    I’ll post pictures of inside when I get time to pull amp out. Catch 22 is that I’m pretty busy at the shop and no time to even think about it while it is grossly in the way and something needs to be done with it. I got it fairly cheap ($60) so I just had to have it. Thought about what to do with it came later, after my son and I got it from upstairs of the estate sale house. I will recap it. Will I keep it or not will depend on how it sounds after recap. I don't see any posts about any preamp / tuner repairs. Any capacitors worth changing there?
     
  14. fred soop

    fred soop Super Member

    Messages:
    2,033
    The bias mod started at s/n 39000 on the 600-T. Don't know if it was actually a recall but was probably done on any unit returned for service.
     
  15. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    There's one Can cap in the tuner/preamp. I've never changed it out on any of my 49-T chassis's. It's in a VERY TIGHT SPACE, so individual caps are almost always going to have to be mounted on the chassis walls, if you don't stuff the can. IT's a 4 section (60/200v-60/200-20/300-40/350v), so you'll need to use Pencil type caps to stuff the can. I would increase the voltage on the caps by 50V. 68uf/250vx2, 22uf/350v, 47uf/400V. Replace the 8uf electrolytic at the detector on the tuner (C-77). There are 4 in the Phono Section (all ceramics) that should be replaced with Films. C-9, C10, C12, C13. Then 4 on the Preamp section C44, C45, C47, C48. Those are the 9 Minimum. If you feel particularly Froggy, replace the rest of the Ceramics in the PREAMP SECTION (6), BUT Fisher used very High Quality Ceramics and these last six are fine as is. Cornell Dublier DME series Films are good choice due to space limitations in the phono section (crammed in btwn the tuner box and the chassis wall), but you can use Illinois MKP Axials for the preamp section. All 400V.
     
  16. grindfix

    grindfix Full time hobby Subscriber

    Messages:
    583
    Location:
    New Albany, OH
    Larry, did you replace rectifier diodes? I bet you did. What did you use? Bridge rectifier looks like a good option for power amp section.
     

     

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  17. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
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    I used 1n4007's in the 1st one (49-T), and a 4amp "tabletop" bridge in subsequent units. On the Can cap in the middle you'll see that most all the leads from it end up at the 390ohm resistors along the back wall of the chassis. I put individual caps right there on the Terminal strips btwn the resistors where the leads terminated. The two cardboard can's get 4700uf 100V stuffed in them. Be careful as they are ISOLATED from the chassis by the Fiber inserts. You can get new ones from AES if they crack (and they more often than not DO). If you don't stuff them, you can put a couple of Terminal strips along the side in that corner and wire the new caps up as long as they aren't grounded (Voltage doubler) to the chassis. Let me see if I can find the pics of the 49A and 59A chassis' I did 1st. (the 59A is essentially a 49A with 4 more Transistors and associated parts for more power,as used in the Futura and Ambassador for 1964 and 65.)
     
    Last edited: Dec 10, 2018 at 7:26 PM
  18. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    I found pics.
    #1. This is the 1st one I did. The markings are self evident.
    49A and 59A amp porn.JPG
    I used 1n4007 diodes for the Rectifier in this one. C20A was moved subsequent to this pic, to the right most T-strip at the 390ohm resistors at the top of the pic.

    #2 & #3 are of 2nd unit. Note placement of Caps. The diodes were not replaced in this one, and it's still running fine.
    100_4563.JPG
    100_4561.JPG

    Last is the 3rd 49A I did for a friend of THERED1. Note the 4A "TABLETOP" Rectifier. The caps with the tape on them are the 4700uf 50V replacements for the Voltage Doubler Cardboard caps. This unit is run everyday.
    100_4567.JPG
    100_4568 modded.JPG

    100_4570.JPG

    Larry
     
  19. grindfix

    grindfix Full time hobby Subscriber

    Messages:
    583
    Location:
    New Albany, OH
    Thanks Larry,
    I’ll post my progress when I get to it.
     

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