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Fisher 250T still cooking

Discussion in 'Fisher' started by bill-g, Sep 14, 2014.

  1. bill-g

    bill-g New Member

    Messages:
    21
    Location:
    Minneapolis, MN
    I turned 62 today, and thought I should post a tribute to my Fisher 250T.

    Still using it as my main amp. Here, I'm guessing this is regarded as a sterling virtue, but by most other people as a symptom of pathology. Maybe this is changing though. Just think of all the hi-fi equipment I haven't tossed in the landfill.

    Bought used in 1972. When I found it, I remembered drooling over one on display in the window of TEAM Electronics back in about 1969. Bought for $200, and have kept it running all these years. Not without some effort though....

    Several times over the years, opened it up to blow out the dust, clean the pots, and check & adjust output bias.

    One big improvement was to replace the RCA jack panel in the back with an aluminum plate and better jacks. The original was a piece of copper clad fiber board with cadmium plated jacks swedged into it. I started hearing radio stations on the aux and tape monitor circuits, I finally realized some sort of contact diode thing was happening in the ground leg where the cheapo RCA shells were pressed into the copper with no solder.

    Replaced the stock 330/33 ohm headphone divider with 160/160 ohm resistors, works well with headphones of all impedances.

    Replaced the big capacitors with bigger ones long ago.

    I restored a Pioneer SX-939 last year (I thought..), and had retired the 250T to the garage. Turns out, I missed a few things in the SX. There are a few more caps needing replacement, and the DeOxit cleaning of the too may switches didn't quite hold.

    Put the Fisher on the bench, gave it a good cleaning with DeOxit including all the Tune-O-Matic pots, and it swapped places with the Pioneer. Found a nifty 6-way stereo patch box on that I use to handle all the inputs I couldn't manage before. Tune-O-Matic still works. Phono preamp is still pretty damn good.

    FM tuner drifts a bit as it warms up. Since it's varactor diode tuning, suspect this is due to power supply regulation.

    There's a zener diode with a series thermistor that looks to be a voltage reference in the power supply. Thinking about solutions to this, but maybe that's worth a new thread.

    Front panel and knobs looking a little rough due to age and some poor cleaning choices, but still attractive as a receiver "of a certain age". Probably helped that it's been kept in frequent use all this time.

    BTW, thanks to mhardy6647 for posting the link to the scanned 1970 Allied Radio catalog! I browsed and found the 250T in there. Way cool.

    Long live the 250T.
     

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  2. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    Bill. Look at the Serial # on the back. According to the Service Manuals for the 250-T and TX any unit from 73896 and above is a 250-TX.

    I got mine earlier this year. Gutsy little bugger. Very nice tuner. No problems with drift.

    The Zener with the thermistor is the Regulated supply for the Tune-o-matic varactor tuning. 30V 1W Zener. I changed out the zener when I rebuilt the power supply. The thermistor changed value with a hair dryer on it for 5 seconds so i left it. The other Zener is a 15V 3W for the FM Front End 15V regulated supply . and 15V Muting /MPX board supply; plus the 11V Muting/MPX supply.

    The 250-T and 400-T use the same service manual. The 250-TX is separate. Both are available @ http://www.hifiengine.com/manual_library/fisher.shtml . You do have to register, but it's free.
     
    Last edited: Sep 14, 2014
  3. bill-g

    bill-g New Member

    Messages:
    21
    Location:
    Minneapolis, MN
    32294, guess it's a T. Did you change the zener because it had failed or just in the spirit of preventive maintenance?

    I suppose what I should do is observe the regulated supplies with DVMs from cold start and try to see if there's actually any correlation with the tuner drift.

    I was looking at the power supply board a while back to see if I could figure out a way to bypass that regulator circuit with a TL783 in a more or less non destructive fashion. Guess just swapping out the zener and/or thermistor (if they're really the problem) would be a lot more reasonable.

    Thanks for the info!
     
  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    I shotgun my power supplies with the exception of parts I can't get or have no info(very rare) on which in this case was the thermistor. Pre-emptive Tactical 1st strike. Do the power supply 1st and everything then falls in line.
     
  5. fred soop

    fred soop Super Member

    Messages:
    2,035
    +1
    If the power supply isn't working properly, all other bets are off.
     
  6. bill-g

    bill-g New Member

    Messages:
    21
    Location:
    Minneapolis, MN
    Addendum:
    At some point I verified that the PS output to the Tune-O-Matic (ya gotta love that name) was drifting as the unit warmed up.
    Last summer I ran across a higher voltage 3 terminal adjustable regulator, the TL783, that can take much higher input volts (125v input-output) than the LM317's I've used for many years. I looked at the Fisher PS, and figured out where to cut traces etc, and kludged in a new regulator on a little Adafruit project board, replacing the zener and thermistor which act as a voltage reference for several of the supply voltages. Also replaced the main caps for units with twice the ratings, and all the ones in the regulated supplies. Dialed the regulator to 31.26V and bingo, rock solid tuning!
    This receiver might just outlive me. How cool is that?
    BG
     

     

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  7. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    Sounds good Bill. I gave my youngest son (Just turned 31) the 250-T along with a FISHER Branded BSR with a Pickering ATE, .3x.7 elliptical, and a pair of Minimus 25's so he and his "partner" could play LP's. I went up the other day and they had this record gouger Crosley portable sitting out and running. I just about puked. I asked him what his intentions were with regard to the 250-T set up. "You can take it back, it's too big"! WTF???? He'd been bugging me for a small setup for 3 years. No accounting for taste. I guess
     
  8. bill-g

    bill-g New Member

    Messages:
    21
    Location:
    Minneapolis, MN
    Bummer. Some folks don't get it, especially galling when they're friends or relatives. My wife would love it if I tossed all my good stuff and replaced it with some plastic Bose icecubes+subwoof. She paid about $300 for one of the Tivoli KLH reproduction table radios, but the tuning cap started going to hell after about 1 year. I opened it up, looks like a middle school maker project in there, not very serviceable. What a piece of junk. A bargain at 1/4 the price.
     
  9. Godataloss

    Godataloss New Member

    Messages:
    6
    Location:
    Lorain Ohio
    Picked up a 250t in a wonderful Barzilay console and a pair of KLH Sixes a couple months ago. So far it's blown me away. I pulled it from the console thinking I was going to clean it up and sell it, but it fit so nice in an old Fisher wood case I had, that I haven't been able to bring myself to list it. Good thing since one of my MKIII's had to go back to the shop and the Fisher is now doing main system duties hooked up to my Cornwalls. It literally rocks the house!
     
  10. Karl M.

    Karl M. New Member

    Messages:
    1
    I have a 250-T that I acquired years, uh, make that decades ago (think: early 80s) for garage use. With the presets it was great for being able to change the station by just selecting one of the other presets. So no fumbling around with grubby hands trying to tune in a different station. Just grab a rag and select a different station by pushing one of the preset buttons. (Keep in mind though that I take VERY good care of my equipment, so actually touching the unit with dirty fingers just wouldn't occur.)

    But now when listening to FM radio when it's warm out (doesn't seem to happen when the temps are on the cooler side) the audio level jumps up and down until it's temperature stabilizes. However, this doesn't seem to happen when I'm using the 250-T to listen to the "garage" computer that is connected to it. And I do get some station fade. Sometimes the audio level drops, but the station is still tuned in well (or so it seems). So I end up chasing the volume control. As I'm thinking about this, I have noticed that sometimes also the FM signal strength meter jumps up and down and the stereo light goes on and off. But it's not "linear" (sometimes this but not that, then sometimes this AND that). <shrug>

    I suppose I ought to start by doing something about replacing the zener diodes for the 15V and 30V supplies. Probably ought to use some of those 3 leg regulators.

    I also have a Fisher 200 (transistor version). It's also one of those units built by United Audio in Germany (and when you take the cover off, it shows). I've had that about 10 years longer than the 250-T. Back when that was my main stereo receiver (think: 1978) at some point it quit. I don't remember the exact symptoms but I ended up replacing one (maybe it was even 2) of the zener diodes with a 3 leg regulator. It's been running great ever since.

    So I probably ought to do the same with the 250-T. I suppose it wouldn't hurt to replace the larger electrolytics while I'm in there.

    At this point I'm pretty disgusted with broadcast TV and radio. Most of my listening at this point either comes off MP3s, internet sources like YouTube or SomaFM.com (on SomaFM Drone Zone is my typical "go to" "channel", but sometimes for an off the wall change I'll do Suburbs of Goa or one of the other "channels"). Typically I've been listening to the SomaFM through the garage computer, but last week I acquired a Harman/Kardon HK3700 receiver which is also a network "tuner" with Vtuner built into it. (This allows for the selection of a very large variety of internet audio sources.) The HK3700 is going to replace the 250-T for the garage. I already have one of the HK3700s in my workroom and I love it. Anyway, probably at this point, once I get the 250-T "fixed" I suppose I'll put it on fee-bay. I have a stack of "vintage" equipment that I probably ought to do the same with, as, at this point, I just don't see that I'm going to use it. I have so much cra..., er, "stuff" that I really need to thin the herd to make room for projects (3 cars at this point).

    Karl M.
     
  11. sgmlaw

    sgmlaw Active Member

    Messages:
    453
    What a great story. Made my evening. Thanks for sharing your decades long love affair with your 250T.

    We all have one like yours that we refuse to give up and hangs around forever. You are perfectly normal.
     

     

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