My guess is that it is a heater-cathode short in one of the audio tubes. My reasoning is that when a tube is cold the elements are not shorting but after some thermal expansion they may short out. Why it is doing it now but not before could be from turning the chassis upside/down and having a piece of crap in side the tube in question move to a sensitive area.
Electrolytics if leaky will hum first and then play which is the opposite of what is happening.
Personally, I would change ALL the caps at least in the ausio section including the power supply electrolytics.
I forgot to mention one thing. What is the voltage rating of the caps you changed? Is it the same of higher than the ones you replaced? If the voltage rating is too low that caps might breakdown under voltage.
In tube equipment a good rule of thumb is just go with a 600V rating on the capacitors. Some amplifiers and I am goin on memory here with
6CA7's may have even higher voltages to deal with.
snipped-for-privacy@winderspam.com (Derwin) wrote in news:4bAYh.5322$Dq6.2769@edtnps82:
First, you need to 'divide and conquer'. Divide the set in half and determine which half holds the problem. Is it the receiver section or the amplifier section?
Signal injection and signal tracing should let you determine which half the problem is in.
If it is in the receiver, you will need to determine whether it is in the front end (tuner), the oscillator, or the IF, or the detector.
If it is the amplifier you should again be able to narrow down the problem to what section of the audio amplifier.
It is possible that you have an open grid leak resistor. With leaky bypass capacitorys, one of them might have been 'doing double duty'. When you replaced the caps, you may have thrown away a significant portion of the grid leak.
Check for a grid that is going highly negative and cutting off the tube (plate voltage going high).
Check for open resistors.
It is also possible that one of the new capacitors is defective.
Look in a tube manual and look at the curves for the tubes used in the amp.. In an audio amplifier, you would expect class A operation, with the tube biased into the middle of a linear portion of the curve unless you have push/pull amplifier, in which case a pair of tubes would work against each other in class AB or B.
Hope this helps. ....
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bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
Some restorers claim that over 80% of the are capacitors are leaky. They replace them all, because the others are going to fail, and its easier to do the repair ONCE instead of pulling the chassis every year or two to check the few that were good.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
Yes it does, but apparently that's offensive to Meathead.
Yes, I replaced the wax paper ones first, then the electrolytics. I should have turned it on after doing the wax paper ones because that would've narrowed down the problem considerably, but I didn't. It all looked pretty straightforward and I expected it to work.. but considering the age of some of the other components and wires in there, I should've known better.
They should at least know that an ancient tube receiver is not going to have more than one input. It's rare for a tube receiver to even have a single AUX input, only high-end models had an input. I was hoping to hear from people with experience with tube receivers, and people who suggest testing a matrix of inputs clearly do not.
More like tinkerer who doesn't suffer fools gladly. Considering I've been cordial and thankful to those who have responded cordially and helpfully, why should I patronize the jerks? As long as non-jerks respond, which they have, anything posted by the jerk-squad is superfulous, and can be either ignored, or ridiculed. Either way they're useless responses so it doesn't matter how or if I reply to them. I've been using usenet for long enough to know that any time I post to any group looking for information, half of the responses are likely going to be from socially-deranged usenet-lifers. Socially-deranged usenet-lifers are always in denial and don't realize that they are socially-deranged usenet-lifers. Some of the time I think they even believe they are offering helpful advice, because if they don't pepper their initial reponses with insults they expect immense gratitude, even if what they said was inapplicable or irrelevent.
Of course. And from now on, if I don't respond to a question that assumes I am dumber than I am, assume the answer is that I wasn't that dumb, Ok? For example, if the next thing someone asks is if I plugged the power cord into a power socket in the wall, assume that I did when I don't bother responding.
If I didn't know that I had to replace caps with an equal or higher voltage rating, I wouldn't have tried re-capping the unit in the first place. In fact, I would think that anyone who didn't know that wouldn't know the difference between electrolytic caps and wax paper ones anyway.
The first two paragraphs were helpful, but I certainly don't understand why you would recommend replacing caps I just replaced. Checking to see if one of the new caps I installed is bad is one thing, but replacing all the new caps I just installed with another set of new caps sounds like an excersize in throwing money down the toilet and nothing else.
non-electrolytics are not polarized, and doncha think I would've double, triple, and quadruple-checked the orientation of the electrolytics I just installed BEFORE posting here, knowing that doing so would be opening myself up to A) redundant or irrelevent responses and B) abuse from the usenet-lifers who consider any post for advice to be troll-bait?
No Michael, I said that I replacede .050uF wax paper caps with .068uf WIMA caps. Eeyore is right, it was a stupid reply.
Perhaps you should've read my next post in the thread which answered those questions, before wasting your time with your irrelevnet post? My post with those answers was posted long before you decided to post pretending I hadn't already answered those questions.
YES. Why are you even replying if you obviously have never looked inside an old tube amp?
probably
they're all glowing and I tested every tube a few months ago and they were all fine. I no longer have a tube-tester to check again, however.
All the caps I replaced are connected exactly where they were before I replaced them. What I'm thinking is that the guy who sold it to me, after having 'restored' it from non-working condition wired it up in some jeri-rigged fashion to get it to look like it was working enough to be able to sell it to me. Probably one of the caps was bad and compensating for a bad resistor as someone else mentioned. However, the wiring he added did not contribute to the 'spaghetti' much. Anyone who has ever looked inside any old electronics from before the days of circuit-boards will know what 'spaghetti' wiring looks like. Those who havent, try this: Look at a circuitboard populated with a bunch of components. Look at the traces the circuit makes on the back of the board. Now imagine each one of those traces being replaced with a wire. Now perhaps you will be able to envision the 'spaghetti' wiring that a circuit not build on a PCB will look like.. Anyway now I'm pretty much screwed. I don't own an oscilliscope so I will probably just sell off the tubes and toss the chassis. I prefer the sound of solid-state these days anyway, my interest in tube gear was a folly that only lasted a couple years.
That's because I already knew that I had replaced the caps with caps of equal or higher voltage specs. I could've written 20 pages describing every detail, but I omit the details that don't matter in order to emphasize the details that do matter. But I do understand that that particular detail matters enough that I probably should have reassured readers that I was already ontop of it.
Thanks for being one of the few responders who was able to consider the symptoms and extrapolate some possibilities from the symptoms.
That's simply not true. Please look at the following:
formatting link
and note the source selection knob on the far right of the amp.
I can select from tuner, tape, turntable, and auxiliary inputs on that receiver. It is very clearly tube powered (4xEL84). This is a 1959 era receiver. At that time, many people had a desire to hear not only radio programming, but also selections from their collection of record albums. If you purchased a separate amp.
Yes, I see you saying something like "that's not the ancient I had in mind" and I do suppose you have to draw the line somewhere when looking at various generations of technology. 1959 wasn't exactly yesterday, however. :-) Even many older systems have at least a switch between tuner and phono sources.
I don't know that I believe it when you say that it is rare for a tube receiver to have multiple inputs. I don't doubt but what yours could be different--however, we still have no model number or even a brand name to go by.
As I said before, please *don't* make it difficult. We're all here to help. Put quite bluntly, nobody here is in any way required to help you. I sincerely suggest you consider this when visiting any public forum and asking for assistance. This desire to help tends to get a bit "squelched" in the face of rude behavior.
And I still think testing your newly installed capacitors is a good idea...should you get the amp fixed, I would like to know how it played out, if you are willing to say.
the tuner isnt an input, and besides the pre-amp on the turntable input, the circuit is the same between the tape and aux inputs, it's just switched. That's what the knob you're selecting with does. What, you think they build seperate pre-amps for aux and tape inputs?
snipped-for-privacy@winderspam.com (Derwin) wrote in news:6mzYh.5305$Dq6.3498@edtnps82:
Do you have a tube manual, look up G1 of the preamp and power output tubes. Check the dc voltage when it is not working they should not be a positive voltage on them if so check the new capacitor connected to that tube. Extremely high negative voltage check the grid resistor.
Of course I assume you have a high imput impeadance voltmeter there.
I would like the brand and model # if you wouldn't mind.
Suit yourself. You're more than welcome to believe whatever you like, even when the tuner is clearly external to the amp.
:-)
That very much depends upon the design of the amplifier.
I've tried to offer some help and correction to some beliefs that aren't universally correct. All the while I've been fairly polite about the whole thing. I guess there are some people who just can't/won't/don't want to be told or helped. You seem to be one of those types. So, I won't reply any further. Good luck with your amplifier, though. I do hope you get it fixed and working well.
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