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Eico 147A voltage issue




 
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Author Topic: Eico 147A voltage issue  (Read 110 times)
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KK4MSA
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« on: September 10, 2017, 11:49:31 AM »

Hello everyone. So I had this 147 a sitting around for a couple years, in really good shape, I wanted a signal tracer and this model came highly recommend. So I picked it up. I replaced the filters, put bnc's on the front, replaced a few resistors, typical "restoration" work, also replaced the "gain" knob on the front because there was a burnt spot and it was fried.. Power cord was cut when I got it so never powered it up beforehand. So fired it up, noticed the magic eye "dead spot" was significantly brighter than normal, I have other pieces that use the eye tube, so I noticed immediately it was pretty much all green, a little lower in intensity than "normal" but still pretty much solid. So as with any cap job, I rechecked my work several times as well as went over the whole underside connections as per the manual, as it is a really good layout. All is good, only resistor I didn't replace in the filter section is the 68k that is between the 2 10uf 400v filters, but it checked good, right in spec @ about 67 k. I also checked the caps on my Heathkit it11 to make sure I didn't have bum caps. Then after being on for a couple mins, I noticed the 6aq5 had the blue/purple haze inside, and was about to burn through, so I shut it down, pulled the tube out, fired it back up and the magic eye was a little more normal looking, hmm, well long story short I'm getting a little over 400v on pins 5 and 6 of the aq5, suppose to be 260 and 265, getting over 400 out on pin 7 on the 6x4, I'm getting 317ac on pin1,nothing on pin 6 with tube in, but with the tube out, I'm getting 320 Ac on 6. So I know this is a pretty long post, just hoping someone may know what The problem is or works on one and can tell me there voltages. It may not matter but I'm also getting 380v on pin 1 of The 12ax7,
I have replaced the aq5's just to make sure that it wasnt something with it, altho all the tubes "test" good,but I have to figure out what this issue is. The rectifier tube is getting really hot also after a min or 2, naturally,  Again, caps are in correctly, i have rechecked this several times, as well as went thru the manual step by step at least 3 times to make sure something wasn't hooked up wrong., nothing was or is burnt (yet) anywhere else other than the "gain" knob i replaced, and the thing does function, no weird noise in the speaker when powered up. getting voltages of 310-320vac on pin 1 and 6 of the 6x4, 400+ vdc pin 7, put a new 6aq5 in it, as soon as it had a second to warm up, i could see the purple haze inside the tube, and would have just melted if i didn't power down.

ere is what the resistance measurements look like,


tube,      pin ,         my measurement,        manual

6x4           1                 325                      250
                6                 306                      250
                7                 over 150k             100k

12ax7        1                260k                    270k
                 3               -2.4k                     2.2k
                 6                325k                    330k
                 7                10m                     10m

6aq5         1                 390k                   470k
                2                 330                     330
                5                 1.2k                    1.15k
                6                 1.1k                    1k
                7                 390k                   470k

1629 eye tube was spot on
I also have 14.1vac across the eye tube pins 2 & 7,  pin3 calls for 18vdc,im getting 408vdc on pin 4 calls for 260v, the - voltage on pin 5 calls for .-8 im getting .-7, so same problem with this tube as all the others, i have 400+v rather than the 260-300vdc the manual is calling for. im not sure why i am getting such high voltage, tubes check fine no short.

I have 15vdc across the cathode resistor on the aq5,the socket's were loose, but I checked all continuity and all was good, I also pushed the pin holders closer together on all tubes.

When the gain is up I'm the rf position, I can turn it all the way up and can tell its working, i hear the normal buzz you get from an amplifier, I can touch the rf input BNC and I can tell I touch it, not a huge change, but a change none the less, and the eye tube does move somewhat when i turn the gain up also, the eye closes a tad when the gain is turned up, and when i touch the bnc it opens slightly but I have to shut down after a min or two because I don't want to melt anything down. Again the spot in the eye tube that's suppose to be not green is that way for a sec, then you can tell green starts to fill in the longer its on, same thing with the aq5 out, the whole tune will start to be all green, you can tell where the unlit part is suppose to be tho.


sorry for such a long post, but i wanted to add all the info i could in hopes that someone may be able to help, or has had a similar problem. thanks in advance for your help.
i have attached a few pics of the 6x4 and 1 of the 6x4 and the aq5


* x41.jpg (202.51 KB, 1024x615 - viewed 9 times.)

* x42.jpg (189.73 KB, 960x576 - viewed 7 times.)

* x43.jpg (156.12 KB, 800x480 - viewed 8 times.)
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KK4MSA
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Posts: 2


« Reply #1 on: September 10, 2017, 11:50:27 AM »

3 more
 if more pics are needed i can upload


* x44.jpg (165.17 KB, 800x480 - viewed 7 times.)

* x45.jpg (153.43 KB, 800x480 - viewed 11 times.)

* x42 (2).jpg (252.27 KB, 1050x630 - viewed 8 times.)
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