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Post by Boomzilla on Aug 13, 2016 14:11:03 GMT -5
One of my Heathkit amps plays fine. The other is so low in volume that it's barely audible.
I've checked the component values and wiring (twice), so I'm suspecting that there's a bad tube in there somewhere.
The amps each have four tubes - a rectifier (EZ81 / 6CA4 / 6BW4), an input tube (dual triode 6AN8) and a pair of output tubes (EL88 / 6BO5).
Is it fair to assume that either the rectifier or the 6AN8 are the most likely suspects?
I have spares for all tubes, and can troubleshoot via substitution if need be, but I thought I'd ask first.
Thanks kindly - Boomzilla
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Post by audiobill on Aug 13, 2016 14:12:53 GMT -5
Boom, swap all the tubes across amps at once, for starters.
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Post by Boomzilla on Aug 13, 2016 14:30:48 GMT -5
Since I lack a tube-tester, probably a good idea...
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Post by novisnick on Aug 13, 2016 16:55:32 GMT -5
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Post by Boomzilla on Aug 13, 2016 23:46:52 GMT -5
Other things going on for the moment... Will change them tomorrow.
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Post by sidvicious on Aug 14, 2016 2:46:41 GMT -5
I agree with Audiobill and yes a rectifier can take an amp down. I had one tube in my no longer owned Audio Research VT-100 mkIII stop lighting up and I had it serviced right away and a point in the bottom of the tube socket had to be re-soldered and could have taken out a resister.
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Post by Boomzilla on Aug 14, 2016 3:50:31 GMT -5
Troubleshooting plan for Heathkits:
1. Swap ALL tubes from amp A to B & vice versa. Does problem change channels? Yes = It's a tube. No = Triple check wiring & parts on non-working amp.
If step 1 is Yes = Change tubes in non-working amp starting with rectifier, then driver, then output tubes.
2. Once amps are working, evaluate volume levels & tone from each. If identical, good. If tone or volume are different, then change tubes on lower-volume amp starting with driver, then output tubes.
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Post by audiobill on Aug 14, 2016 6:06:01 GMT -5
Likely the first driver tube after input - that's likely the gain stage.
What rectifier tube does this amp use?
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Post by Boomzilla on Aug 14, 2016 8:39:39 GMT -5
6CA4
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Post by audiobill on Aug 14, 2016 9:14:19 GMT -5
Compare the pin 3 voltage to ground for each rectifier - be careful, high B+ voltage!
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Post by Boomzilla on Aug 14, 2016 9:45:56 GMT -5
Tube substitution is easier - Will proceed in a few minutes.
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Post by Boomzilla on Aug 14, 2016 11:14:57 GMT -5
At trial one, the right amp worked, left didn't. After switching tubes, one amp to another, right amp still works, left still doesn't. Conclusion: It isn't the tubes & it's time once again to verify wiring & parts values (AGAIN) for left amp.  |
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Post by audiobill on Aug 14, 2016 11:55:52 GMT -5
Good Work!!
email me a pic of left channel internals.
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Post by Boomzilla on Aug 14, 2016 12:55:21 GMT -5
Well...
I'd installed a 470K resistor where I should have had a 47K. Now both are on song! Review soon in "Boomzilla's Journey" thread.
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Post by Boomzilla on Aug 14, 2016 13:25:12 GMT -5
The left channel internals are embarrassing - I'm not showing them to ANYONE! LOL BUT (and this is the important part) they WORK.
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klinemj
Emo VIPs 
Official Emofest Scribe
Posts: 15,098
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Post by klinemj on Aug 14, 2016 15:02:28 GMT -5
Ohm my, I can't really "resist" making a comment...
LOL!
Mark (glad you found the issue quickly!)
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Post by bluemeanies on Aug 14, 2016 19:18:32 GMT -5
audiobill______audiogod!
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Post by audiobill on Aug 14, 2016 19:20:48 GMT -5
Audiodemon more likely!!!
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Post by Boomzilla on Aug 14, 2016 21:05:49 GMT -5
So that would make me the "AudioMoron..." LOL
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