Tom Mobley Posted January 13, 2003 Share Posted January 13, 2003 Maybe this is the reason for the buzzing I've never been able to get rid of. The two yellow wires coming out of the PS are showing 365 volts, according to the schematic it should be 340V. The red wires are showing about 305V, should be 280V. What could cause this? All of the voltages coming off the PS are about 25V too high. I could understand if they were low, but too high? What's up with this? Anybody got a parts Eico for sale? I really want to try a different PS. Tom Quote Link to comment Share on other sites More sharing options...
lynnm Posted January 13, 2003 Share Posted January 13, 2003 The buzzing has nothing to do with the voltages you are measuring per se. You most likely have bad capacitors or possibly a bad tube or tubes in your preamp section or failing that in your output section Buzzing/humming typically is related to a fault in the signal path or in the power supply to the amplifier: (1.)A fault in the power supply section - look for problems with the power supply caps or the choke - ( If their is one ) - check the ground connections in particular. (2.) If everthing checks out in the PS section check out the preamp section. If the hum is extreme regardless of the source selected look for a bad ground at the selector switch . Is the hum present regardless of input selection ? If so it is likely a tube or if the tubes are OK then something within the signal path between the preamp and power amp sections. If the problem is specific to a particular input then the odds are that it is a grounding or signal line problem and you need to check out all leads to that input. Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted January 13, 2003 Author Share Posted January 13, 2003 I've already replaced the PS caps with Atoms. also replaced the can cap. cleaned all grounds in the amp too. It's the PS itself that's vibrating and humming. it hasn't been related to any in the incoming signal, does it without anything being hooked up besides the power cord. I've replaced all the tubes in the amp with NOS or Telefunken. None of this has affected the PS buzz at all. What I'm wondering is how a PS makes higher than rated voltage? The faults I can think of lead to lower output voltage, not higher? Anybody got any bright ideas? See previous thread titled something "help with Hf-81 hummer" for all the stuff I've tried on this. Tom Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 13, 2003 Share Posted January 13, 2003 Tom, didn't we compare voltages across the board between are amps and there Identical ?? What I bet you need to do is adjust the cathode resistor value up. This problem is common in HF-81's. If this is just the transformer itself vibrating and buzzing I would change this 2 resistors to 185 ohms or so. If it seems to limit the problem but it persist go higher. Oh and try to match these fairly close like 5% or less is better. Craig Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted January 13, 2003 Author Share Posted January 13, 2003 Mark, My line voltage runs between 117--119, never see it outside that range. Yes, the buzzing is coming directly from the PS, is also audible in the speakers. There was a glob of wax-type stuff on the bottom cover directly under the PS when I got it, I scraped it off and didn't think too much about it. I figured it was because of the bad rectifier tube that was in it. Is this a clue to something? I see a reference to this in the Roger Stevens stuff on Kelly's website. His was because there was some some battery charger device generating interference in the AC line. Craig, We did measure a bunch of voltages on the bottom of the thing over the phone once, I can't remember what the numbers were. I recall that we found what you expected to find, but I didn't know if you were looking at a schematic or measuring voltages on you're own amp. The main one I remember was at the solder lug in the middle-back of the bottom where the 340V red leads to the two OPT's hook up. I recall that it was right according to whatever you were referencing, but now it's 365, shows to be 340 on the schematic. Have you got a HF-81 PS you could loan me long enough to test this out? Or a parts amp I could buy? I really need to get this straightened out before I start the Super HF-81 project. I've gotten the situation worked out about eliminating the tone controls while retaining the line stage. The amp is pretty cleaned up now, no tone controls, no cbalance pot, new vol pot. It actually sounds pretty good to my untrained ear. I think I need to go to a 100K vol pot to get some vol adjustment back, but that about the last remaining issue besides this buzzing deal. Tom Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted January 13, 2003 Author Share Posted January 13, 2003 Mark, I mean I can hear and feel buzzing in the PS itself, along with some buzzing in the speakers. I can hear and feel this PS buzzing with no speakers or source hooked up at all. Tom Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted January 13, 2003 Author Share Posted January 13, 2003 Hmpf, was duplicate post, but we can't delete our own posts? Too bad. Tom Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 13, 2003 Share Posted January 13, 2003 Mine does the same exact thing but not as noticable it also quits after it warms up and I don't get it thru the speakers though. I still say changing those resistor values will minimize this. It sounds to me like the transfomer was stressed at one time or the other and needs a little relief it can't handle the load. Have you tested the value of the 2 resistors in question ? They are 2 large 165 ohm 5W power resistors hooked to pin 3 of each pair of output tubes. Check there value and let us know they usually are up in a 170 to 175 ohm. Raising these reduces the load and helps cool the amp. I personally wouldn't do this with a healthy running HF-81 but I have heard others have and it help with this problem. Oh and Tom no I don't have a spare to loan you wish I did. I'm not all together sure the one I'm using is 100% heathy. Craig Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 13, 2003 Share Posted January 13, 2003 I think most would would hard pressed to get a Eico power supply transformer to run cool. The wax melted off the paper in the windings to my geuss. You could try a variac, run the voltage up to where the Power trannie starts mechanical buzzing. Once you know where the buzzing occurs, then try a autoformer connection limiting the voltage to the primary of the power supply transformer. Under the mechanical buzzing voltage. Don't ask me how, I'm in way over my head anyway. One of my HF-12 trannies does the same, I don't want to believe the tranny is bad, it still works, but, you know..... Quote Link to comment Share on other sites More sharing options...
Hofy Posted January 13, 2003 Share Posted January 13, 2003 If you do decide to replace the power transformer, look for other Eico amps using a #30021. I dont know what other ones used this but it is what the HF81 uses. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 13, 2003 Share Posted January 13, 2003 Hiya, Tom: I can relate to this problem. It sounds like you may have some RF-noise creeping into your system, since that can sometimes manifest itself as more of a buzz rather than hum. Rectification can sometimes be cured by a couple of different filters, including "grid stoppers." This is simply a resistor (often between, say 1K and 10K ohms)in series with the input to the grid. Try these on your input or preamp tubes in the amplifier. But, if there are grid resistors present (likely that will be the case) the grid stopper is put in position AFTER the grid resistor, which is referenced to ground. Otherwise, one can get excessive attenuation, loss of high frequencies, etc. Try this, it really might help. Start with maybe 5K ohms, and reduce or increase as needed. Use a carbon comp. resistor, which is less prone to RF pickup and oscillation, which is what you are trying to do away with. These are cheap and plentiful at Radio Shack. Your voltages are a little high, but not that much. You might also have a bad capacitor (which can be bridged with a known good one to test it), or check dropping power resistors between filter sections. You can also add resistance with appropriately large power rating to bring your voltage down. Give those grid-stoppers a try, at least. They are easy to install, and can save lots of difficult hunting and testing. Make sure things like transformer laminations are tight by lightly snugging up bolts on the tranformers (this is probably not the problem, though.)filament snubber can also sometimes help problems like this. Find out if the amps buzz with and without an input signal, which can help you locate where it's coming from. Does this amplifier use DC on the filaments, do you know? What voltages are you getting on the filaments? Does this buzz change when you move interconnects around while they are plugged in? I found my Moondogs were pretty prone to noise related to RF and EMI, and much improved the problem by turning the bottom plate into an active shield (simply grounding it to the main chassis ground) Do an internet search on Grid stopping risistor, or simply grid stopper. There is a wealth of info out there, including schematic diagrams to help clarify proper installation. Good luck, Erik Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 14, 2003 Share Posted January 14, 2003 I would bet you a dime to a dollar that the Power transformer is just weak from over stress. I still say change the cathode resistors to ease the load on it and your problem will disappear ! The only other option is to have it rewound or find a replacement. This noise has nothing to do with RF sneaking in. This is a physical vibration of the Power transformer having trouble delivering its rated current demand. The voltage readings have nothing to do with this its not that its putting out 365 VDC its how much current its being required to produce that its having trouble delivering. This is a common problem with the HF-81. You have tried every part under the sun in the amp. Just try the cathode resistor trick if it minimizes the problem you know your problem. Craig Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted January 14, 2003 Author Share Posted January 14, 2003 Craig, Erik, et al, Thanks to you guys for taking time to help me this issue. At this point I've come to the conclusion that it's the PS itself. As Craig noted I've tried about eveything under the sun on this thing, not has nothing fixed it but nothing has even changed it. It's basically doing exactly the same thing now as it was doing the day I got it before all the caps, tubes, grounds, experiments, etc. 'm going to look into having it rewound, anybody know who reliably does this? The reason I've been holding off on this is that the amp sounds really good out the speakers. It might be worthwhile to just let it buzz. It had a shorted rectifier tube in it when I got it, that may have contributed to the problem. I'll run a Google search on transformer repair stuff. Anybody know what the voltage is supposed to be on the wires that go to the hum pot? They're labeled X and Y on the schematic and I'm not thinking the voltage there now is correct. I really don't know the answer to Eriks' question about the AC/DC stuff, anybody? Tom Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted January 14, 2003 Author Share Posted January 14, 2003 I found a company: Heyboer Transformer Inc. 17382 Hayes Grand Haven MI. 49417 (616) 842-5830 http://www.heyboertransformers.com/index.shtml e-mail: heyboertransrorm@novagate.net (looks like a typo in the email addy) Boatanchor transformer rewinding. They have a print of the 30021 tranny, are willing to make and sell one for $65 shipped. I signed up for one. The guy there said it sounded like mine got too hot, probably while the bad EZ-81 was in place. He claimed my transformer buzzing issue would be fixed by "re-varnishing" which he claims is a simple service he can provide. When the new one comes in the old one goes back to be re-varnished, see what happens. Should be interesting to see what turns up. Tom Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted January 14, 2003 Author Share Posted January 14, 2003 Mark, de-mytifying is one of the few things I'm good at. It's amazing what can be found out by calling somebody up and asking the right questions. I could tell the guy I talked to at the transformer company was an old-timer (read: vast experience). He knew right away what I was talking about and what I needed. His re-varnishing process invloves soaking the tranny in some kind of varnish and then baking it in an oven. This is not a rewind, that costs substantially more. They also offer that service, but a new one is cheaper if they've made it before. Tom Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 14, 2003 Share Posted January 14, 2003 I wish I could remember the website that showed how to revarnish it yourself. It wasn't too difficult, if I recall. I do remember them saying that the use of a junk oven outdoors or out of the home enviroment would be the best option. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 14, 2003 Share Posted January 14, 2003 Wow this is cool. Did you happen to ask him if he can also fix output transformers ? What is really cool is there right here in michigan although I have no clue where grand haven is I suspect its on the other side of michigan toward Chi town. this will be the unltimate solution to your problem. My suggestion was just a band-aid Craig Quote Link to comment Share on other sites More sharing options...
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