Radiohead Posted June 16, 2002 Share Posted June 16, 2002 I acquired a pair of 1975 Khorns about five months ago and purchased an Eico HF-81 about three months ago. For the past three months the Eico has been working flawlessly while my Yamaha receiver collects dust. Last night I am watching the World Cup game and my Eico had been running most of the day. I had listened to some music in the morning and then left the unit on planning to listen again later that evening. This is a sub-question I have. Should I be turning the unit on and off everytime I use it or can I turn it on and leave it on the whole day or maybe even two to three days at a time? Anyhow back to the story...the unit had been on for maybe 6-7 hours without the cd player running tunes through it and while I am watching the game I start to hear/feel this really low level humming noise coming from the speakers. After about 2-3 minutes the hum starts to escalate in volume and continued to rise until it reached the maximum volume level I had the Eico set at. It wasn't serious thank God, I had it between 1 and 2 on the volume. Anyhow, my question is what the heck is causing it? I know it's coming from the amp but how do I eliminate it? The other thing I didn't like was when I turned the amp off there was this slight little popping sound appearing as though it was coming from the tweeters. That popping sound had never occured before yesterday. Any thoughts or solutions would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 16, 2002 Share Posted June 16, 2002 Sounds like one of the Electolytics is taking a dump on you to me. Don't run the amp till you or a trained tech fixes it !!!!! I'm sure this may start a heated debate. But I personally won't leave any of my vintage amps on if I'm not present and listening to them. You never know when it could develop a serious problem and if your not there to turn it off you could smoke a tranny and render your amp useless. But turning on and off is hard on tubes. Especially with a amp like the HF-81 that doesn't have a soft start rectifier at least I don't think the EZ-81 is soft start. I'm sure someone will correct me of I'm wrong. Craig ------------------ HH Scott 299 Amp HH Scott LT-110B Tuner HH Scott P-87 Turn Table JVC JL-F50 Turn Table Sony CDP-CA7ES CD Drive 1985 Walnut Heresey I W/Layne Audio Woofers KSW-15 Subs>c> This message has been edited by NOS440 on 06-16-2002 at 11:03 PM Quote Link to comment Share on other sites More sharing options...
Radiohead Posted June 16, 2002 Author Share Posted June 16, 2002 Thank you very much NOS for taking a stab at my problem. I was hoping someone was going to respond. I disconnected the amp yesterday after turning it off and unfortunately had to reconnect my Yamaha receiver. I was shocked to hear how different it sounds now, compared to a few months ago when I hooked up the Eico. I have officially been spoiled by the tubes. Anyhow I guess I will have to be on the look out now for someone capable of analyzing my problem locally. Do you have any suggestions for where I should begin to look? What would the person's title be that I would need to look for? Also, I had the wires connected to the 8 Ohm outputs on the back of the amp. That is where I was supposed to connect them too correct? It's not supposed to be the 4 Ohm is it? What would happen if they were hooked up to the 4's? Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted June 17, 2002 Share Posted June 17, 2002 IF it is a low level hum that is getting louder, one of the first places to suspect is the Power Supply caps which, if they are stock, are the two orange beasts under the side with the PS trans. This is a fairly simple fix and easy to find parts. See below to see the caps and for some ideas of replacements. The cost of the parts is very inexpensive; the labor from a shop is where the ducats add up. It could be other electrolytics as NOS said but the first culprit if the PS Caps are stock is here. When they go bad, this type of hum sufaces. If you have no experience or feel nervous about this, a good tech or friend with soldering/tube experience is preferable. As for the amp on or off, I personally would not turn it off and on a few times a day as this puts MUCH more stress on the components. If you are listening, leave it on. Sounds like your amps is pretty much stock here. BEfore leaving it on while not around, I would really make sure it is up to snuff. No heated debate here. I leave my tube amps on more than 99% of the people in here and this is my personal preference. I have found components to last longer and be more trouble-free this way. Doing this with vintage tube gear is far more of a gamble and you might not elect to do this which is understandable. I will add that most of my problems with tube equipment has come either turning it off or on. While you may not want to leave it on for days at a time, if you are listening of and on during the day, dont turn it off and on each time. This is putting heavy stress on the amp. Once my EICO was up to par, I left it on for long periods with no problems. This is me. To be on the safe side, many would elect not to leave the tube gear on while unattended. As for the connections at the rear, what are your speakers? IF they are rated at or around 8ohms, this is a proper connection. If they are in the 4ohm range, connect to the 4 ohm taps. Most have this rating on the rear if you do no have your manual. kh ps- interior wiring page with pics and hints for HF-81: http://home.earthlink.net/~eico_hf81/eico_hf81_wiring.htm ------------------ Phono Linn Sondek LP-12 Valhalla / Linn Basic Plus / Sumiko Blue Point CD Player Rega Planet Preamp Cary Audio SLP-70 w/Phono Modified Amplifier Welborne Labs 2A3 Moondog Monoblocks Cable DIYCable Superlative / Twisted Cross Connect Speaker 1977 Klipsch Cornwall I w/Alnico & Type B Crossover system one online / alternate components / Asylum Listing f>s> This message has been edited by mobile homeless on 06-17-2002 at 09:25 AM Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 17, 2002 Share Posted June 17, 2002 Mobile is correct I forgot that EICO used those Axial lead Caps under the chassis. If your handy at all you can replace them no problem. If you don't feel comfortable and can't find anyone local to fix it let me know and you can ship it to me and I'll go thru it completely if you pay for the parts and shipping. I enjoy working on these amps and would love to have a nice HF-81 to listen to and compare to my Scott's while a repair it. This is why I would donate my time. If he decides to send it to me while were at it we should replace the Coupling Caps to wouldn't you say Mobile ?? What would you suggest would be his best Option Cap wise ? Craig Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted June 17, 2002 Share Posted June 17, 2002 If Craig is nice enough to do this fix for you, I would highly recommend it as he has come a long with in a very short time. I have seen pics of his soldering/layout work and it looks good. He appears to have good attention to detail and shares a love for vintage tube gear, something that the average tech in many a modern audio shop does not usually exhibit. Most of the people that have written my since my EICO site has been up, have learned to do the soldering work on their own. There have been a few, however, that have taken it in to shops. One person I know took his EICO into to Raleigh, NC at Audio Advice, a high-end shop that does sell tube amps and has a pretty good tech. Work done? Those two orange PS caps replaced with Nichicon MUSE at 47uF. Total cost? $125 ($10 for parts although they charged $20). Time it takes to do this mod? About 30 minutes if SUPER careful, even faster if good with the iron. So you see how the LABOR really adds up. The second experience was even worse. A guy in Holland had all Conrad-Johnson gear but wanted to hear what the EICO could do in his second system. He got one on ebay for $150. Then found a guy online to go over the unit and bring it up to spec. He was in California (I will post his place when I remember). The guy ended up saying it needed all sorts of stuff and replaced pots, caps, some resistors, tubes, sockets etc. Total cost? YEp...... $600! This was a complete ripoff as the guy sold him everything at double markup and gave him stuff he didnt need while keeping the EICO/Mullard tubes and putting in Sovtek in place. IT was a disaster that could have been avoided. He has a major site online but these guys can be CROOKS. Unfortunately, the Holland guy gave him the go-ahead before talking to me. Moral is, it's best to learn this stuff on your own if you have the abilitiy and time OR get someone that you trust or better yet, a friend like NOS to help for a moderate fee. As for the caps, many are saying the Auricaps are a good option in the coupling positions. They are more expernsive, but a lot of the guys are like them. A cheaper alternative is the 716P Orange Drops (better than 715p). Still, if you are getting a great deal with NOS, I would probably spring the extra ducats for the Auricaps which are not that bad price-wise. There are many opinions and all have validity here. I would say to keep the values around the same as the stock settings as I have found that increasing here can make the amp sound slightly more ponderous and thick. I would personally opt for the 600v Auricaps at .033 for the output stage coupling caps and .1 at 600v for the line stage caps. IF you buy 10 caps from the main distributor, you get a price discount. If NOS is going to be in there, I would also do the output tube cathode bias resistors getting them as closely matched as possible. I personally would keep them stock at 165 ohms but others have moved them to 180 ohms at 5-watt to make it run cooler (the voltage in most househoulds was a bit less in the day). I like the sound stock so much, I dont want to change here. There are other options to the circuit but to remain simple, I would elect to leave the choices stock. Fixed, user adjustable bias does have the potential to sound better and is more flexible. I would leave stock as it performes very well I have found. Regardless, Craig is very kind here to offer his assistance and could be saving you some serious ducats. kh ps- I just noticed something... ARe you saying that the hum INCREASES when you up the volume? This is a bit different. THe PS caps problem should remain same level of hum regardless of volume of amp. Please clarify here. This message has been edited by mobile homeless on 06-17-2002 at 10:49 AM Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 17, 2002 Share Posted June 17, 2002 Mobile, That's a good point on the hum increasing with volume ! The heath Kit I'm working on had lots of Hum and static and at first I thought it was the Can Caps and it ended up being the EL84's were bad. He could have some tubes going south also. To any effect if he opts to send it to me I'll test all the tubes and match them in curcuit best as possible with my Hickok 536. I have all the spare parts from my basket case EICo I sold so I have the stuff to trace the problem down. Anyway he goes the 2 axial's should be replaced for safety sake. Thanks for your kind words. I get allot of joy out of working on the Amps in my spare time. I really never charge anyone yet but I do take Tips LOL !!!! Craig Quote Link to comment Share on other sites More sharing options...
Radiohead Posted June 19, 2002 Author Share Posted June 19, 2002 Sorry I haven't responded back in a few days. Been busy with summer school. I can't thank you enough for the offer Craig and I would like to take you up on it. I am going to reconnect the Eico today and see how long it takes for the hum to show up. Last night I took the bottom of the unit off to check the wiring and everything looked pretty good, but then again I am not quite sure what I am looking for. The orange caps had .25 MF written on them. At least thats what I think they said. I am at school right now and can't check but will update this post as soon as I get home. As far as the hum is concerned I don't think it is getting louder when I turn up the volume knob. It just starts as a low hum and progresses to a certain level where it maintains that level until I nudge/shift the amp and then it stops. It's really quite strange. If the hum starts to occur a simple nudge or bump of the unit causes it to go away temporarily. Then awhile later it shows up again and I repeat the process. I unfortunately do not have a tube tester yet so I have no idea as to the status of these tubes except for the fact that they all seem to light up quite nicely. The tubes are: 2 - 12AU7(RCA's I believe), 4-12AX7 (2 GE & 2 Baldwin GE??), 2 - 6CA4 (Sylvania with AGS above the name), and 4 - 6BQ5/EL-84 (Brand new JJ Tesla with less than 10 hours on them according to the gentleman I purchased the unit from). Anyhow on another note, the guy gave me an Eico FM tuner as well that I finally got to work after figuring out the connection. Its model number is HFT-90, same as the one I saw on Mobile Homeless' website. Surprising how good it sounds for a mono tuner. If you don't have any objections Craig I wouldn't mind sending you that unit as well to see what you can do with it, if anything, to make it better. I want to thank you again for the offer. I am really quite surprised to see such friendly people on a BB. It is nice to know that there are still people willing to help others out there. I will update this again later this afternoon when I get the Eico up and running to try and describe this hum in more detail. Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted June 19, 2002 Share Posted June 19, 2002 If you BUMP the unit and the hum goes away, then this is most probably a wire grounding out somewhere and not the caps. The hum would not be disappearing if it were the PS caps. My guess is a wire or connection has moved. Check your speaker wiring connections at rear to make sure they are clear of the other terminals. My guess is something simple. Regardless, you PS caps will need replacing in future. The EICO HFT-90 is a nifty little tuner and can sound VERY nice on uncompressed FM. If gotten for the typical price of below $60 (sometimes in the $20 range), it's a great deal. I have a whole page on my unit when it was for sale but have not put it back up. kh ------------------ Phono Linn Sondek LP-12 Valhalla / Linn Basic Plus / Sumiko Blue Point CD Player Rega Planet Preamp Cary Audio SLP-70 w/Phono Modified Amplifier Welborne Labs 2A3 Moondog Monoblocks Cable DIYCable Superlative / Twisted Cross Connect Speaker 1977 Klipsch Cornwall I w/Alnico & Type B Crossover system one online / alternate components / Asylum Listing f>s> Quote Link to comment Share on other sites More sharing options...
Randy Bey Posted June 19, 2002 Share Posted June 19, 2002 or more to the point, a wire 'not' grounded somewhere. Loose ground connection, in other words, or a high resistance solder joint. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 22, 2002 Share Posted June 22, 2002 Radiohead, The Offer stands and if you want to send the tuner that is fine also. As long as it doesn't need alignment I can give it a once over for you. Does it pull in stations strong ?? Usually tuners don't have the problems Amps do because they produce very little heat so there's not much to be done to them. Mobile is right if you move the amp and the hum comes and goes its a connection problem somewhere. It could be a dirty tube socket also. I still recommend you have the amp given the once over for reliable usage. Email me at craigostby@comcast.com with your phone number and the best time to call you and we will setup shipping it to me if you want. Craig ------------------ HH Scott 299 Amp HH Scott LT-110B Tuner HH Scott P-87 Turn Table JVC JL-F50 Turn Table Sony CDP-CA7ES CD Drive 1985 Walnut Heresey I W/Layne Audio Woofers KSW-15 Subs>c> This message has been edited by NOS440 on 06-22-2002 at 07:55 AM Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 22, 2002 Share Posted June 22, 2002 Mobile, Off the top of your head do you know how many and of what value are needed to replace all the signal Cup Caps in HF-81 ? Craig Quote Link to comment Share on other sites More sharing options...
tunebucket Posted June 23, 2002 Share Posted June 23, 2002 I have the same combo ,Khorns and eico, and it's out of this world. Me too...had a low full bodied hum emanate one day. Being trained as a youngster to whack on the side of the TV to improve performance I proceded to ...gently...wiggle and prod the tudes and above chassis components. The metal can cap turned out to be the piece that when pushed this way or that made the hum.I sprayed the big solder lug on the bottom with deoxit and positioned it just so and that solved the problem until I could replace it. Got a new can from vibroworld for $30 shipped.No more hum dead quiet.Also any other parts you wish to upgrade ala mobiles and roger stevens eico pages are worth dollars on the penny, each replacement kicked mine up a notch or two.What a HUGE SOUND.Gotta love it. Mabey it's your can too...hope this helps Quote Link to comment Share on other sites More sharing options...
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