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Title: loud hum, no signal Post by: SoundPerf on March 14, 2011, 02:12:30 AM Hello all,
Ok, time to swallow my pride and ask for some help. Just finished building and firing up new HRM 50. After making sure nothing smoked using a dummy load. I plugged in a speaker and turned it on and first thing was squealing due to OT primaries backwards. I emailed Nik about this becuase the layout and photos show opposite wiring. He said go with layout but that is wrong. So I reversed and the squealing stopped but I'm left with a crazy loud hum, like something is very shorted to ground or wired backwards. Along with this there is absolutely no input signal getting to the speaker. I'm a bit frustrated right now, because I took my time building and have been going over it with a DMM, scope, and my eye checking my wiring, and can't figure it out. :( I'm throwing this out there right now, even though I haven't taken any photos and haven't gotten key voltages yet in hopes that is might jog somebody's expertise and point me in a direction. The wife is sleeping right now and the hum is so loud that I can't mess with it much more tonight without bugging her. I will get some photos and voltage check tomorrow. Any help will sure be appreciated. Thanks. Title: Re: loud hum, no signal Post by: T Wilcox on March 14, 2011, 03:19:54 AM Hey Soudperf
Im sorry to here the trouble but so far no smoke lets get this figured out! You have 50watt xfmrs just like myself probably . On my build I only copied the color scheme from the layout but if you have the same colors and it still does that i also read that some of them have been wired backwards on the 2ndary. I am having similar problem on my jsx and found broken tube by inserting to roughly (oops) Title: Re: loud hum, no signal Post by: SoundPerf on March 14, 2011, 04:33:46 AM On my build I only copied the color scheme from the layout but if you have the same colors and it still does that i also read that some of them have been wired backwards on the 2ndary. Just to verify, you're saying you heard that these Ceriatone OTS output xfrms 2ndary have been wired backwards? It's after midnight here on eastcoast so I'm going to call it a night, but thanks for the quick return. Tomorrow i'm going to dig in and get measurements written down. I have a bad habit of taking data and not writing it down thinking I'll remember. I know better. I'm too old for that crap. :-[ Plus, start looking for bad connections. I've been reading about tightening down the relay & rectifier boards too much and causing problems. I may have gotten over zealous. Although I do remember all the HT voltages seemed OK. Anyway thanks...c'ya tomorrow. Title: Re: loud hum, no signal Post by: T Wilcox on March 14, 2011, 01:26:06 PM Sorry I think I meant primaries
I will try to find thread I remember whoever wrote the thread said that about half of theOTS builds experienced no output on startup because the OT wires were backwards As far as the loud Hum that could be something else. Title: Re: loud hum, no signal Post by: SoundPerf on March 15, 2011, 01:00:15 AM Here are some images of the build.
I hesitate to post these voltages because they're obviously whacked, but here it is. One thing that seems rather important is that I'm measuring 380Vdc to ground on the shield/ground of the speaker output. It's just there and not on the chassis. Thank God. So it seems to me that something is wired incorrectly, but I can't find any faults in my wiring compared to the layout. I still have some things I want to check. What's the best way to test the OT for proper wiring? Pin1 Pin3 Pin4 Pin5 Pin6 Pin7 Pin8 V1 4.15 .041 .050 -.632 V2 421 360 0 .004 V3 422 340 0 298 V4 37mv 481 480 -49.3 479 36mv V4 37mv 481 480 -49.3 479 39mv OT CT=480 (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0347.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0348.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0349.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0351.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0365.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0352.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0353.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0354.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0355.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0358.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0360.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0361.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0363.JPG) (http://home.comcast.net/~soundperf/myfilelocker/myphotos/HRM50/IMG_0364.JPG) Title: Re: loud hum, no signal Post by: erwin_ve on March 15, 2011, 08:35:47 AM Can you measure(amp off!) the resistance between First node of the filtering and the Ot secondaries?
And then measure resistance between all filter nodes to their respective plate resistor leads. Measure all cathode to ground resistance. The voltages at v2 , v3 are scary; it looks like there is no grounding for the cathode resistor and bypass cap for v2 and v3. Other things: *edit* At the power tubes; keep the grid wires away from the screen resistors. At the pre amp tubes: keep grid, anode and cathode wires away from the heater wires. Title: Re: loud hum, no signal Post by: sduck on March 15, 2011, 06:13:50 PM Something around your speaker wiring is way wrong - the sleeve of these jacks should connect to ground, and hence the chassis.
Title: Re: loud hum, no signal Post by: SoundPerf on March 15, 2011, 08:20:21 PM Yes, let me declare this now. Mr Todd Wilcox had sent me an email of his finding that I did not have the ground to chassis of the output jack. I'm in the middle of fixing this right now. This ground is of utmost importance, tracing back this grounds the components that erwin_ve was indicating. Besides the screen.
How, I missed this? I don't know. Dumb, dumb. I know one thing even though I relied on the layout considerably, I also relied (too much maybe) on the photos. Which this connection is hard to see. I'm very use to having a schematic to check my wiring. I really missed this part of the equation. Anyway, I actually had to switch the OT primaries back around, which makes the layout correct. I powered it up did a preliminary check and the voltages are much more in line and it's completely quiet. Next is put better tubes in, bias, and plug in a guitar. Mainly just want to state where things are and thanks to all that are helping. I get tunnel vision and other eyes are needed. ;) Title: Re: loud hum, no signal Post by: SoundPerf on March 15, 2011, 08:38:24 PM Also, if you look at the 22uf filter cap on the tagboard on the wall near V1 your will see that I mixed up the 2.2k and 220k resistors. Nik found this mistake lastnight.
Ok, back to work and hopefully playing soon. :) Thanks Title: Re: loud hum, no signal Post by: T Wilcox on March 15, 2011, 10:24:07 PM I predict Soundperf will be playing his OTS tonight ;D
Thanks for the good mention BTW. I see Sduck was on right track as well. Title: Re: loud hum, no signal Post by: SoundPerf on March 16, 2011, 02:38:26 AM Yippy, It's alive....(in the voice of dr. frankenstein) ;)
Man ol man, this thing sound great and I haven't even got it totally setup yet, just biased. (using old tubes, and have HRM & PI set at 12:00). Basically, I just plugged in a guitar to try it out and ended up playing for about over an hour. Thanks again to all that have helped, including sduck, that was on the right trail. I have some question about voltages, but I'm going to start a new thread and put this to rest. Title: Re: loud hum, no signal Post by: SoundPerf on March 16, 2011, 03:36:02 AM Other things: erwin_ve, I forgot I wanted to get back with you about this. I do understand what you're talking about, I just want to clarify this a bit becuase I was trying to be conscious of this. *edit* At the power tubes; keep the grid wires away from the screen resistors. At the pre amp tubes: keep grid, anode and cathode wires away from the heater wires. A far as the power tubes, should I just try to position them by bending them farther away or do I need to completel re-route them? And the pre amp side. I had read what I think was your thread from a while back talking about moving the these wire just above about 1 cm made a nice differenct. Now I did try to do this especially with pin 3 wire. But once again, should I try to just bend them away, but keep them basically routed the same, or should I try to re-route them. And if so, can you give some pointers. Thanks P.S. Here's some new voltages. They seem a bit on the high side. Not sure why this is. But the amp is sounding darn good and quiet. Any ideas? Title: Re: loud hum, no signal Post by: erwin_ve on March 16, 2011, 09:32:05 AM Just bend the wires, it's the EMI from the heater wires that causes a degenerating tone.
Voltages are a bit high but that could also be your wallpower; when 120 is 125v, you get these voltages on the tube side(like in your chart). Title: Re: loud hum, no signal Post by: T Wilcox on March 16, 2011, 02:12:12 PM Man that is awesome,
You probably know alot more about that amp now than if you did not have those problems. I always learn more troubleshooting than just building Hey Soundperf you get your part from Malaysia yet? Im still waiting on my chickenhead knobs, they shipped on 3-11 regular postage. Just wondering if they will come anytime soon. ??? Title: Re: loud hum, no signal Post by: SoundPerf on March 16, 2011, 11:19:36 PM Man that is awesome, Believe it or not they arrived today. Mine were sent on 2/28/11. I had given up on them. So yours were sent just a few days ago. I thought we were talking about this before that? Anyway, USPS from Maylasia is very slow. So I learned a lesson....if in a hurry use UPS and not USPS. :oYou probably know alot more about that amp now than if you did not have those problems. I always learn more troubleshooting than just building Hey Soundperf you get your part from Malaysia yet? Im still waiting on my chickenhead knobs, they shipped on 3-11 regular postage. Just wondering if they will come anytime soon. ??? Yes, the best lessons are from mistakes and troubleshooting. I wanted to get to know this amp in and out anyways. Just with a bit less stress. And really the only stessful thing was being concerned about destroying a few hundred dollars worth of components. If money wasn't an issue, I would have been less stessed. ;) I would like to do another build soon and source my own parts. Maybe something with a bit lower part count. But first things first, I have a bunch of tweaking to do on this amp. I pretty sure this will become my go to amp. I had jobs on the road all day today, so I didn't get to play at all yet. I think I'm going to put in the new tubes tonight and get a bit more familiar with it. I can tell right off one thing that is so nice about these amps. They're very dynamic, but compress just the right amount when needed. I was concerned when I would read comments about them being "harder to play" or more likely to "show your flaws". But, I think it's going to suit my playing just fine. :) Title: Re: loud hum, no signal Post by: SoundPerf on March 16, 2011, 11:26:14 PM Voltages are a bit high but that could also be your wallpower; when 120 is 125v, you get these voltages on the tube side(like in your chart). Yep, I'm measuring 124v at the mains. Thanks for the help and advice. I still have some wire placement and securing them in place to do yet. |