Snagged a Fisher 400 - resto time!

Discussion in 'Fisher' started by Thumper, Jun 27, 2017.

  1. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    19,960
    Location:
    Glen Burnie Md.
    With those readings and with one pot maxxed on one side, I'd say you got some worn out tubes. Which pair is maxxed? From what I see it's probably V16 and V17. Swap both pairs and try it again to rule out the circuit's.

    Whats the pin 9 voltage???
     
  2. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    I changed out those phono tube grommets - what a pain! And I have 3 caps left from metalbone's kit - in the mpx section - C214, C221 and C222. The first one is doable, the last 2 NO WAY! Them suckers are buried!

    Then I swapped V15 and V16 and rebiased it (Larry I'm pretty sure the circuit is good - I measured the range at all 4 tube sockets before I even put the power tubes in).

    V14 .307
    V15 .307
    V16 .256
    V17 .253

    If I try to bring 16/17 up any higher then 14/15 go up too. B+ is 410 across the board. I think I need new tubes.

    Plus I swear the left side sounds better (hotter bias), but maybe it's the janky volume pot messing with me. Mark wants $125 for a new one, I might bite on it.
     
  3. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    19,960
    Location:
    Glen Burnie Md.
    The IBBA/IBAM BIAS adjustment IS interactive, so back and forth is normal. Bring 16-17 up and readjust 14-15. It'll take a few tries and they'll eventually settle down. The Right side tubes are right at the bottom of the good sounding range (about 28ma). You'll get increasing distortion below 28ma. Bring the two lower tubes up as high as they;ll go without redplating, then adjust the other pair to within 1-2 ma of the 1st pair. See if you can get all 4 at 30ma.

    With 410V B+ V14 and 15 are putting out 12.587watts per tube. V16 and V17 are putting out 10.496 and 10.373w and with screen dissipation figured in the numbers go down a little....... V14-V15 11.357w V16-V17 9.266w and 9.143w.

    33ma would get you 13.53w - 3ma = 12.5w. 36ma would get you 14.76 - 3ma = 13.53w. 13.53w is at the bottom of the 70%-80% ideal range for a 7591/7868. Maximum dissipation of the 7591/7868 is 19W. 70% is 13.3w 80% is 15.2w.

    Generally I find that old stock 7868's in 400's are in poor shape. They work of a fashion but they won't all come up to spec. You end up getting old stock on E-PREY which is a crap shoot. I just bite the bullet and get a quad of matched NEW STOCK EH7868's from Jim McShane. Never had a bad one from him.
    The only downside to this is the pin size, which is slightly larger and stretches the socket leaves slightly, enough so that old stock tubes won't make contact.
    They are good tubes, but like any russian 7591 family tube don't come up to original Old stock 7591 family tubes. Close. But close only counts in golf and Hand Grenades.

    Larry
     
  4. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    I swapped V15 and V16 (back the way I had it before) and managed to get all four at 31mA +/-1mA. Sounds much better now!

    About to the "dancing eye tube fix" next. I'm sure the thing could probably use an alignment at some point as well, but I'll have to farm that one out - above my pay grade!
     
  5. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    19,960
    Location:
    Glen Burnie Md.
    Tune it for 100.7 (the bay.) See if you can get it in fairly strong, and not overshadowed by WBIG 100.3 or DC101 101.1. If either of the surrounding stations negate 100.7 it may need peaking. Next try 90.9 WETA(DC) and 91.5 WBJC(Balt). Both classical. WETA is historically a hard station to get in Glen Burnie as a lot of DC Stations are unless the transmitter is North of DC. WETA's transmitter is in Arlington and DC blocks a lot of the signal between here and there. But here's the rub. They have a 75KW transmitter for a class "B" transmitter and the cap is 50KW last I heard. They got grandfathered in. As you're a bit closer to D.C., you may get them equally or nearly so. Then go up to 105.7 and listen to the Sports talk station (I only use it for aligning and peaking). It should bring in very good reception. There's 107.3(WRQX) that should come in good. If the dial is off PM me and I can come down and give you a hand with it.
     
    cantonkid likes this.
  6. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    Larry,
    I can't get 100.7 at all, and barely 100.3 (it's strong one second and weak the next, depending on where I am in relation to it like it's using me as an antenna, weird). 90.9 and 91.5 are both loud and clear. 105.7 (know it well, huge Os fan!) comes in but not clearly. 107.3 comes in great.

    Granted, it's in the shop with me which is 2/3rds underground and I have this crappy little antenna hooked to it (which is also underground).

    The only thing I know about FM stuff is that I spent the way too many hours trying to basement align my Marantz 2245 and ended up busting a couple of the inductor core slugs. It's at Just Audio now getting the real problem fixed (MPX board issue). Plus I have no FM test gear other than a new/used 100MHz scope. Almost bought a sencore sg165 a few years ago but didn't.

    BTW the pointer is about 1/4" to the left - I'm not afraid to mess with it but if I can pick your brain about FM stuff at the same time I'm in!
     
  7. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    Oh and did the tuning eye resistor mod - much better! Plus bit the bullet and ordered a pot from McShane. BTW - how hot should the PT get in a 400? After about an hour I can hold my hand on it for awhile, but it's not very fun.
     
  8. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    19,960
    Location:
    Glen Burnie Md.
    If you have an infrared or laser thermometer, it's infinitely better than your hand. Sounds like it's running about 140-150*F which is about right. It'll come down a few when it's set up right but will still burn you if your wife gets masochistic and holds your hand on it ("Where is the $$$??? Tell me or Burn slowly and painfully!"(shades of the old man skit on Big Bamboo!)). Mine runs right between 145-150. And that's on a late model. I haven't finished up the early one yet. But the previous early one also ran what most people would call "HOT".

    Best thing to do is get a laser thermometer @ Harbor Freight. Skin doesn't last too long being fried. Transformers are usually good up to about 190*F according to Dave and then they let go. No worries about the 400 PT getting that hot. The most I've seen is 150*F. Dishwashers heat up water to that temp. Showers are usually 120* unless you have a really old water heater. The water heaters are factory set to 120*F. And 120*F will can give you a 1st deg burn (sunburn--no blisters) 140 will leave a 2nd degree burn (blistering). Charred skin(3rd deg) comes on at about 170*F. Then time heated is a factor as depth of the burn is a factor in healing or not healing.

    You can actually use the KM-60 alignment procedure and do the same on the 400. NOTE: Z5 UPPER and LOWER instructions need to be reversed on the manual for the late model 400 (above 48001). It's fairly simple and all you need is a DMM and Mini Clips. It works good. I've got a SG-165 at the house but have not used it yet except to check separation on the MPX. I've also got a 100mHz scope that I need to learn how to use. I'm game if you are.
    I'm retired so I'm home all the time and bored senseless most of the time.
     
    cantonkid likes this.
  9. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    Larry, what scope do you have? I got a Tek 2235 a couple weeks ago to replace my 60's all tube Heathkit deal that finally kicked the bucket. I haven't really done much with it yet other than hook the probe to the internal squarewave generator and get both channels to work by fiddling around with various switches and knobs, haha. Plus I do have an IR temp gun but I also have one better - a FLIR thermal imaging camera - it's a damn cool toy. I'll snap some pics and post em soon.

    Before I even THINK about tweaking any cores or anything I wanted to test all the small signal tubes so I did that tonight. Everybody looks good but V2 and V3. V2 shows bad for grid emissions and shorts but still tests 80% (huh?) and V3 just tests weak as Popeye with no spinach.

    It's funny - FM still works (not great) but I can stand in front of the thing and lean a foot to the left or the right and make the tuning eye go from wide open to a 1/4" gap.

    Time to search for a couple weird 6V heater tubes that I don't own any of...
     
  10. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    19,960
    Location:
    Glen Burnie Md.
    I've got a few 6ab4 and 6ba6's. I'll cull out a couple of them for ya. Sounds like the OSC-MIX (V2) is wonky. Plus the 6ba6 (V3 1st IF) is weak. That will cause the problems with you acting as an antenna or an attenuator.

    I got a TEK 2235 (AN/USM-488) last year. Need some lessons on it.
     
  11. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    Larry, that'd be great! We all know e-prey tubes are a crapshoot...

    If you wanna bring your scope down we can play around with them some - I've got an audio sine-square generator so I could at least show you the very basics. I'm just waiting on some replacement probe tips and a couple of other accessories I ordered first (everything's in the mail).
     
  12. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    So I went to remove the PI noose resistors tonight and like a numbnut I snipped the wrong ones - the 150k feeders to pin 3. I have probably a thousand resistors here but no 150k's, at least not 1/2w. Then went to do the PI adjustment (method 2 in the stickies) and I don't think these pots even have a pin 3?

    [​IMG]2017-07-31_10-27-25 by rickenbacker_man, on Flickr

    I ordered replacements some time ago with another order but I guess I wasn't paying attention, they're 50k instead of 500k. Two steps forward...
     
    Last edited: Jul 31, 2017
  13. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    19,960
    Location:
    Glen Burnie Md.
    Pin 1 and pin 3 on the TUBE! On a 3 pin pot, you'd use the center pin and either of the outer. AES( www.tubesandmore.com ) has the pots fairly cheap too. Which means the shipping will be more, although you could get the resistors at the same time.
     
  14. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    On the TUBE! I had that revelation this morning before you even said it Larry... it was one of those nights I guess...

    I swung by a local electronics place on the way to work and it was closed. Guess it's one of those mornings, too.
     
    Last edited: Aug 1, 2017
  15. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    19,960
    Location:
    Glen Burnie Md.
    Local Electronics Place??? What's the name and where!!???!!?? It's gotta be closer than Baynesville Electronics was(Timonium) b4 they closed.
     
  16. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    It WAS called Mark Electronics in Beltsville but closed as in closed for good! They stocked a good amount of resistors and caps and whatnot so it was a good standby for me in case I forget something in a mouser order or a time like this when I need two stupid 150k resistors... So I just ordered a 365 piece 1/2w assortment off of amazon instead which supposedly will show up today.
     
  17. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    I fixed my WHOOPS! from last night after new resistors showed up tonight then did the the PI adjustment (original pots seemed fine). Holy hell - not sure if it was that or the noose removal but it sounds WAAAY better now! The PI pots were off before - at like 1 O'clock and now closer to 3. There must have been some distortion present before that I didn't notice because I was blindfolded by "new amp awesomeness syndrome".

    And I'm a Klipsch guy so shiny monster cables and gold connectors don't interest me much. I use lamp cord for all my speaker wires. If it was good enough for Paul, it's good enough for me.
     
    cantonkid likes this.
  18. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    19,960
    Location:
    Glen Burnie Md.
    Went over to Thumper's place y'day after. Brought my 2235 scope, and after a bit of "here's what I've got" including about 2200 watts worth of Tube AMPEG and a couple other brand Bass Amps, we got down to brass tacks, taking a look at his 400.

    His problems consisted of weak reception which stemmed from a couple of things.
    His antenna consisted of a speaker looking square from Phillips from the 90's or 00's. Moved it around while on a weak station and the bars on the 400 moved in and out like it should have.
    And he had a couple of Very weak RF/IF Tubes (V2 and V3).

    Suggested a directional yagi on a rotator to get best results from any of the receivers, and or tuners in the house as he's literally in the deep fringe zone for most Baltimore stations and in the good to fringe zone for most all DC stations. Most stations from each area literally overlap each other as a number of them are 200mHz apart and are sometimes hard to get good selectivity out of them.

    On that note after looking over his work on the 400, which was very good, I made a couple of suggestions for ground placement of the IBAM, cutting out the 68- ohm resistors for the AUX/TAPE interconnection, adding 2 more film caps to the phono section (.022uf across pins 1 to 6) and a couple of semi dry solder joint, which he fixed on the spot, we swapped the 6ab4 for one of my spares which did better on his B&K 747 than my Philco 9100. Reception was a bit better. Then we swapped the 6BA6 (V3) for a brand new Sylvania Red label, and reception went from mediocre to very good on the little Phillips. Honestly I don't think now that a dipole in the garage would make much difference unless it was mounted on the roof.

    After the tubes were replaced, Baltimore stations started coming in very good. Then a 12ax7 (V13) crapped out suddenly so after troubleshooting we found it and it was replaced along with V12 with a pair of Russian Tung-Sol 12ax7's. As he's done the "Noose" correction, the Russian tubes should hold up their end of the deal. If they don't, he's got a cigar box full of domestic and european OLD STOCK 12ax7's he can test for matched sections and put 2 in.

    Upshot is he's gonna get some new RF/IF TUBES for spares, and I'll be available for helping him with the alignment with the RF/IF and then look at the MPX via Fred's "Beethovens brain on drugs" setup. So far his restoration of the 400 is very good to outstanding. He did a couple things I hadn't seen before, and the implementation of that is outstanding. He's got a brand new BORG Volume pot/switch from Mark Oppat which will go it shortly and everything will be as it's supposed to be up front. I have no doubt he'll do that install as well as the rest of his restoration.

    It was a pleasure meeting Thumper and his wife, and we had a productive and fun afternoon. Gonna have to do it again.

    Thumper: OHIGHWAY (Rick) has a Audio get together in the fall that the guys from Va., Pa., and N.J. come down for, plus the local Md. Bunch. Great bunch of guys. I'll let ya know when it is and I want you to come. It's really fun, and calorie intensive! Plus you can hear a couple of really nice setups Rick has with Klipsch-Horns.

    Larry
     
    Last edited: Aug 7, 2017
    cantonkid likes this.
  19. RS Steve

    RS Steve Tube Junkie Subscriber

    Messages:
    7,414
    Location:
    Jupiter, Florida
    That's great Larry, wish I had a few tube owners close to me to team up with on occasion, I feel like I'm on a deserted island at times here. Glad you were able to make progress, tuner function is becoming my only weakness on my restorations.
     
  20. Thumper

    Thumper Active Member

    Messages:
    210
    Location:
    Laurel, MD
    Thanks to Larry for coming down and taking a look at my 400. We had a good old time talking tubes and shooting the breeze.

    BTW Larry, you're off a bit - at last count I'm "only" at around 1,800 watts worth of total tube bass amplification... LOL

    I retested the original V13 last night and it tested fine - I think I was hitting test button 2 on my 747 instead of 1. I guess in my head since we were testing the 2nd half it would be TB2 instead of TB1 without looking at the book. Always RTFM! Anyway, I reinstalled both original PI tubes and it still works fine - I suspect the problem was that dry joint on one of the screen resistors. It worked fine for the last two weeks or so so I guess it didn't like being poked at as you were pointing it out to me. Anyway, all water under the bridge now...

    Larry also loosened up my dial cord string as it was tight as all getout. I thought it was a little too tight but I didn't know how to adjust it. He also moved my indicator over a little to get it more lined up. Still off by a hair, but it's close enough for government work.

    I'm off to order some RF/IF tubes... I'll look in my box of random audio crap tonight too as I think I might have another antenna in there. That little phillips thing works ok but I want to at least try out a better antenna to see what we get.

    Couple more things to button up on the 400 and then I'll call it done for now, unless we decide to get the alignment a little better or if I decide to try to wrap my head around the EFB stuff.

    Thanks again Larry! Let me know when that get together is - I've never heard a pair of KHorns but I've always wanted to.
     
    Last edited: Aug 7, 2017

Share This Page