Fisher 500b crackle issue

Discussion in 'Audio Hardware' started by Guy Gadbois, Apr 23, 2015.

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  1. indy mike

    indy mike Forum Pest

    The JJ's are easy to get and inexpensive - you won't break the bank if you pick some up. You might want to track down a tech who can check your 12AX7s for noise.
     
  2. Analogman

    Analogman Well-Known Member

    How does a "tech" check a tube for noise? (without a scope and the whole receiver, and even then?)

    Why, in every thread involving an "I need advice on a problem" question does everyone immediately starts recommending buying something? Based purely on anecdotal, even purely coincidental experience and in a lot of cases hearsay? In my trade that's called "shot gunning" or "parts hanging"

    What's wrong with using a logical, process of elimination diagnostic approach and actually locate and diagnose the problem accurately? On the first try?

    How do you feel when those scummy rip-off mechanics (who are all independently wealthy from ripping you rubes off, selling you crap that you didn't really need) do that with your cars? Just keep trying things until something works? ('cousre that's the perception that most of the motoring public enjoys regardless, even if they are lucky enough to stumble into a real mechanic who knows what in the hell it is he's doing, and is ethical)
     
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  3. chervokas

    chervokas Senior Member

    Well, it's a very good idea to keep extra tubes around anyway. Tubes fail. After some number of hours of use and depending on how hard they're used by the circuit in question, they'll lose strength with possible changes (again depending on the circuit) in tone, output, distortion. Any individual tube may go noisy or problematically microphonic at any time. It happens. Those great old production tubes can last a long time and even a lot of new production preamp tubes in most circuits can run for thousands and thousands of hours, years of satisfactory use (not so much output tubes). But at any given time, especially with vintage gear, there may be a need to change tubes -- a tube may go bad, a part like a 50 year old resistor may fail taking a tube out, or a problem may pop up in one channel or another, as here, where you need to do troubleshooting, and often the first step in troubleshooting tube gear is checking for bad tubes which can involve swapping in known good tubes/replacing obviously bad ones. Plus, a lot of the fun in owning tube gear is in tube rolling. Yeah, Telefunken 12ax7s may sound great and be highly thought of, but maybe you'd prefer something else. I have no experience with JJs but I've used the New Sensor-made Sovtek 12ax7LPS as quick, cheap replacements when needed, and I actually like their sonics, at least in guitar amps, quite a bit.

    You seem to be hesitant to pop the top on the receiver and move the tubes around but I think you should get over that. An owner of tube gear is going to be called upon to change tubes. It's like changing lightbulbs or guitar strings -- you're not going to call an electrician every time a lightbulb needs to be replaced or a guitar tech every time a string breaks. Try the standard troubleshooting procedure for crackling in one channel of a tube amp -- first check for a bad preamp tube in the offending channel by swapping them L/R as discussed in this thread (that's what the tech is going to do first anyway), to isolate the offending tube or tubes. Then replace those if they turn out to be the problem. Keep known good spares around. And if tubes don't turn out to be the problem, bring the amp to a tech. Don't run around changing things least likely to be the problem -- like speaker wire -- or buying extra stuff that's completely unreleated -- like power conditioners -- until you've done the basic first step of troubleshooting: checking for bad tubes, and based on Analogman's experience w/ this amp, bad phase inverter pots.
     
  4. adamdube

    adamdube Forum Resident

    Location:
    Elyria, OH USA
    I mentioned buying a cheap JJ input tube to help figure out his issue....nothing more, nothing less. They are inexpensive and make easy testing parts to work out issues like this (maybe a bad tube).

    Easy trigger.....
     
  5. adamdube

    adamdube Forum Resident

    Location:
    Elyria, OH USA
    I think the power condition recommendation was based on the notorious Fisher volume control. It was not meant to solve the crackle issue, just prevent another one on the receiver. Like @action pact said.....and I agree, they do make our Fisher's sound better since the power is cleaned up. Have you tried one on your Fisher?

    When looking at issues like this, we would be remiss as a forum not to offer assistance when a potential receiver killer, like the volume control is, is out in the open screaming to be fixed. Especially when $100 bucks or so will save heartache and disaster.
     
  6. chervokas

    chervokas Senior Member

    I don't have a Fisher. But the poor OP is trying to solve this problem of a persistent crackling noise in one channel of a vintage tube piece, and he's tried every kind of thing except what pretty much anyone normally would and should do as a first step presented with such symptoms -- check for a bad tube.
     
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  7. Analogman

    Analogman Well-Known Member

    Relax, not attacking your remarks
    Notice I acknowledged that the 12AX7 very well MIGHT be the problem if not part of it
    No arguments
    But there is hardly anything "cheap" about buying crap if you don't need it
    That's what I'm talking about
     
  8. adamdube

    adamdube Forum Resident

    Location:
    Elyria, OH USA
    A JJ 12xa7 can be had for less than $15 - cheap enough, and we do agree it might be a tube. Having a good known working tube is paramount to figuring these things out, to a degree, for a non tech. It's just the "Why, in every thread involving an "I need advice on a problem" question does everyone immediately starts recommending buying something?" portion that seems, to me anyway, a precursor to an argument.

    Also of note, even if he doesn't buy a spare tube to test with, moving around his current tubes will require him to power off the unit several times, thereby causing stress on a known troublesome part, the volume/power control. I think it's essential to preempt the failure of this part.

    I get what you're saying though, sometimes these request for help do end up with the obligatory post saying buy this or that, without it helping any. But in this case, everything recommended to buy is essential for running a Fisher Tube receiver.
     
  9. adamdube

    adamdube Forum Resident

    Location:
    Elyria, OH USA
    I agree, starting with a bad tube and swapping them out is key. Like I said in the above post.....that volume control will fail, it's just when. And turning the amp off an extra 10-15 times while moving tubes around just makes it happen sooner. Preventing this is all I am trying to do.....and for $100 or so, well worth the investment..That fisher can run for another 40 years if taken care of, the OP should start right away.
     
  10. indy mike

    indy mike Forum Pest

    It would be great if everyone were comfortable cleaning/tensioning tube sockets, being able to handle a soldering iron to replace noisy resistors or leaky caps (and dealing with the potentially lethal voltages involved when working under the hood), or even just swapping around pairs of tubes to see if the noise moves with the swap. The fact is, a lot of folks are leery of doing that sort of work themself. Unfortunately, owning tube gear is best suited to those who are comfortable rolling up their sleeves and being comfortable doing some maintenance chores on their own - if not, then off to a tech you'll go.

    How do you check a tube for noise/microphonics? Aside from using the piece of gear the tubes are in (which is suspect if the gear isn't operating to spec), you could use the Maxipreamp II tester: http://maximatcher.com/maxipreamp.html

    That's on my list of like-to-have pieces of gear to go with the Maximatcher power tube tester and a B&K 747B tester I currently have. I've tested tubes for a few folks here, and I'd like to be able to have a small signal/preamp tube tester like the Maxipreamp tester that can check for noise so folks can have the quietest tubes go into critical areas like a phono stage.

    The Amplitrex AT 1000 tests for microphonics: http://www.amplitrex.com/at1000.html

    Vacuum Tube Valley offered a preamp tube tester that had noise/microphonics checking capability: http://www.amplitrex.nl/vacuum-tube-valley/dual-triode-characterizer/

    George Kaye also made a tester that tested for noise/microphonics as well. Your suggestion of the scope etc. is also valid, though the most impractical choice for casual tube users:

    None of these are inexpensive pieces to purchase, and truth be told are impractical to buy unless you plan on buying/selling tubes - you're looking at $500+ for any of those as used pieces, and the VTV and Kaye pieces have been out of production for some time.

    You're absolutely correct about there being folks who are ready to rip someone off - computer repair shops, car mechanics, tube vendors, model train repairmen. I'll venture a guess that there's more honest folks offering repair services than weasels ready to rip your flesh.

    Not everybody running tubes has access to a tester, and my suggestion to pick up a couple inexpensive JJs was based on the idea that new production tubes were probably tested and working properly. Swap in the JJs and see if that caused a change in the noise problem - under $40 buys a pair of tubes that can act as spares when the inevitable death of a tube occurs, or have them handy if a comparison with currently used tubes or a new purchase tube that comes in is required; not everyone running tubes has a stash of working pulls or NOS replacements on hand. Even the revered Telefunken turns up working less than ideally at times. I just tested a a small stash of used ones a forum member sent to me (hello, Adam :wave:), and found a number unusable because of section imbalance.
     
    Last edited: Apr 25, 2015
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  11. The Pinhead

    The Pinhead KING OF BOOM AND SIZZLE IN HELL

    Now THAT's PITA !:laugh:
     
  12. chervokas

    chervokas Senior Member

    Not really. It's not like it happens all the time or it's endemic -- though with the state of a lot of pulls being sold as NOS and the current quality control of a lot of new production tubes it does mean you should buy from a good dealer who does sufficient testing and burn in. But every now and then you might have to change some tubes. I mean, I have four tube guitar amps, and a bunch of tube hifi equipment and it's not like I'm finding that tubes go noisy on me or fail all the time at all (at least since I stopped trying to find noise free blackplate RCA pulls). I gotta change lightbulbs in the house, oil in the car, heck, even repot house plants more often than I have to change preamp tubes. Power tubes, especially in guitar amps, well, those you can go through quickly, but that's a different animal where you looking for distortion and pushing things hard.
     
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  13. Steve G

    Steve G Senior Member

    Location:
    los angeles
    if you open up an amp it's pretty easy to see a leaky cap. at least in my experience. it's the one with the gross looking gunk all over it.
     
  14. Analogman

    Analogman Well-Known Member

    Only useful if framed in a larger narrative, which it seldom is
    For someone who is already at a loss for what to do next and already dealing with understandable trepidation (this is all new), all that does is promulgate even more anxiety
    In other words, either offer an additional suggestion WITH a context or further explanation OR prioritize and KEEP IT SIMPLE
    The OP is already aware of the switch weakness, I am certain he can manage/process the switched power strip recommendation on his own, in fact, he already has
    He said so
     
  15. Analogman

    Analogman Well-Known Member

    Only IF it's leaking and only if you know what you are looking at
    The Fishers don't use electrolytics in the coupling stages (nothing to leak) and the B+ filters are multi-section can type electrolytics (sealed)
    The under chassis big brown cardboard tube cap for the bias supply is about the only cap on these models that ever shows any clear signs of leakage, and even then it is often just a stain (and the staining is often the result of something else)
    We don't even know what his amp still has or doesn't still have
    Dispensing advice without even seeing at least a photo of the underside is ill advised
    The best and most responsible advice at this point (without having any specific information), besides the moving things around and try to eliminate, narrow down the source, is for him to do what he's going to do; take it back to the person who serviced it
    Curious, how many tube amps have you overhauled?
     
  16. AndrewS

    AndrewS Senior Member

    Location:
    S. Ontario, Canada
    Yep. I was angry just reading that...
     
  17. Analogman

    Analogman Well-Known Member

    You misunderstood, I was being facetious; but I am happy that we can agree on so many other things!
    When auto "mechanics" employ the "try stuff" or "let's try this" to see what happens diagnostic techniques the whole trade is branded as incompetent (hang on artists).............yet when threads like this are born, that's the first thing folks do, start in with the litany of "stuff that happened to me"; aka, the "shotgun" approach
    They don't want it "done" to them yet they unwittingly give cause for it to be done to others.......follow me?
    It is also the same approach used by 95% of the auto repair "do it yourselfers" and has only gotten worse with the coming of the internet age; "buying and trying"
    I try at every opportunity to encourage folks to THINK about the problems they encounter with the machines in their lives and become more confident in their own abilities to separate the crap from Shinola
    It also spreads one of the most wonderful experiences a person can have; figuring things out on their own
    But I'm rambling and it's irrelevant, it was a joke

    As for your post, nice work no complaints............but it quite the tangent to be off on when for right now the focus is to avoid as much confusion and anxiety as possible and help this guy get his problem resolved in as simple and direct a manner as possible...............us rambling on about advanced level "hobbying" only brings further confusion and anxiety to the mix
    We can talk about all the other things he needs to do, and buy, after he gets over this hurdle AND HOPEFULLY posts some pictures of the actual amp's underside so the guessing, digressing and speculation can stop
    The dude just wants his amp fixed

    Maybe we should start another thread? As for your tester lusts and comments? I only rely on "testers" but so much
    Beyond basic integrity (health), the only way (ultimately) to know how any given bottle or envelope is going to behave, including noise, is to put it in a circuit under a working load
     
  18. adamdube

    adamdube Forum Resident

    Location:
    Elyria, OH USA
    Yes he implemented one, but only after it was recommended in this thread. Until then he had not. Please tell me about your experience with power conditioning and Fisher tube amps. Because my experiences mirror @action pact - it is a dynamic difference. Please point out to me where I added any equipment to his setup without keeping it simple and in context.

    Cheap power strips from Home Depot do not filter power, just replicate plugs with a fuse inline. Having a unit like the Belkin will also allow for other hardware, Table, DAC, CD, etc to also have filtered power. And if he uses a TV on it, it's miles better. Really sharpens up the blacks and colors.
     
  19. adamdube

    adamdube Forum Resident

    Location:
    Elyria, OH USA
    This is helpful and in context.....c'mon man! You taking about generalities and auto mechanics. I am talking about solving Justin's problem. He has either a bad tube or something else wrong. While swapping out the tubes might provide some simple trouble shooting, I have also pointed out a very well known issue to a new fisher user. Rather than send him to a hardware store to buy a power strip I have shown him a better alternative that will not only keep that power switch working much longer but also provide cleaner power to his receiver, which, in my experience, has immediate sonic benefits.

    You're generalizing and throwing things at the wall hoping to make them stick. I see this all the time with your posts....always seeming to poke and jab to start some back and forth crap. Where is the damn ignore feature, I think I need to turn it on....way too much BS round here.
     
  20. Analogman

    Analogman Well-Known Member

    Yes, and recommended for another issue (topic), not the one at hand
    A typical, classic thread tangent for an "I have a problem, what do you guys think" post

    You should really try READING my posts
    I'm not trying to threaten or call into question your vast knowledge and experience and I don't think I have disagreed with anything you have suggested, just possibly the order of priority.................that's all
    I have discussed my experience with power "conditioners" in this thread as well as several others here
    The efficacy of any line conditioner is user/application specific
    I've had more than one piece of equipment that worked it's best when simply plugged straight into the wall

    And my references to auto repairs and repair people are what's called "analogies", used in an attempt to be clear with the point(s) I am attempting to make; sorry you don't appreciate my use of them..............same as painting a house (first) with a bad termite problem

    Successful diagnostics and repairs require that you prioritize your thinking
     
    Last edited: Apr 25, 2015
  21. Guy Gadbois

    Guy Gadbois Chief Inspector Thread Starter

    Really the problem is the socket. After switching the tubes around, the same socket made the crackle using different tubes. It's socket V11 for those keeping score at home. So maybe a socket replacement is in order...or a check of the wires going to that socket?
     
  22. chervokas

    chervokas Senior Member

    Take it to a tech. Could be that the socket just needs cleaning and retensioning. Could be another problem with the socket itself or maybe one of the connections to it from a part or wire. Also, that's one of the PI tubes -- did you check the PI adjustment pot for that tube with the wiggle as per Analogman's suggestion? Could be the pot there, not the actual socket.
     
  23. Guy Gadbois

    Guy Gadbois Chief Inspector Thread Starter

    New development.....the R channel now loses volume and crackles. It's gotta be a wiring issue then because it's happening on both sides
     
  24. Guy Gadbois

    Guy Gadbois Chief Inspector Thread Starter

    Here's my check up list for the tech. Have I missed anything? Advice please!

    1- Check pin connections on resistors/caps/wires

    2- Replace all the resistors on the P.I. Sockets with 1/2watt, Metal Film resistors (1%)

    3- Check/clean phase inverter adjustment pots

    4- Check contacts on tube sockets

    5- Check caps

    6- Check pots

    7- Check solder joints. Probable cause?

    8- Change coupling caps

    9- Check/replace power supply caps, selenium rectifier, coupling caps and grid resistors


    Replace selenium rectifier

    1) The two ~ leads go to the AC Leads from the transformer.

    2) The - (NEGATIVE) will go to the two BIAS VOLTAGE CAPS Negative lead(this also feeds the heaters for the 12ax7's), and the + ( Positive) will go to the 15oHm ceramic resistor, then to chassis ground.

    3) On the Negative lead, you should have -22V or so. Adjust with a resistor(1W)so the heaters on the 12AX7's are getting between 10 and 10.5V Each. They'll run good at that point, and will last longer.

    Phase inverter adjust

    1) Using an alligator clip lead, short the B+ supply point to the phase inverter tubes to ground. This would be the 320V source that appears across C78C. This is the 4 section CAN CAP.

    2.) Ground the common lead of your ohm meter.

    3.) Measure and record the resistance value that appears at pin #1 of the left and right phase inverter tubes.

    4.) Connect your ohm meter to pin #3 of the left and right phase inverter tubes, and adjust their respective phase inverter control for the respective value noted in Step #3 above.

    5.) Remove the alligator clip lead.
     
  25. adamdube

    adamdube Forum Resident

    Location:
    Elyria, OH USA
    If the selenium rectifier is still stock, there is no way I would let him touch it again.....you did say it was a refurbished receiver right?

    If that was left in there he doesn't know enough for me to trust him....#1 thing to replace....and heck I only got 300 hits for that when I googled refurbishing my 400. He should have known better.
     
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