Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Reduction => Topic started by: OverAnalyst on August 12, 2020, 05:00:30 AM
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Thought it would be better to start my own troubleshooting post/topic instead of using someone else's.
Here's what I posted previously (yesterday morning):
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Here are my resistance measurements for the following terminals:
38 - 7.7ohms (should be *)
39 - 1.1kohms, not fluctuating (should be *, but per the previous reply, if not 0, should be okay?)
41 - same result as 39
42 - same result as 38
For the following, I get very similar to Neuronal, so I’m assuming they’re ok?
45 - * (should be 0 ohms)
46 - .7 ohms (should be OL)
47 - * (should be OL)
And assuming those resistance values are okay, I went ahead and proceeded with voltage checks. Here are my off-nominal readings:
44 - 78V (should be 180V)
45 - 77 V (should be 0V)
47 - 175V (should be 0V)
The manual I’m using is dated 7.21.19
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So I plugged her in, and instead of music, I get a hum on both speakers. The tubes do light up (so did the LED’s when doing the voltage checks). I tried the different line source selections on my preamp, and still humming. Photos below. Know the issue?
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Don’t listen to an amp that hasn’t passed its resistance and voltage tests. PB and others can jump in with more specific advice.
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I'm away from the office and PB is a bit under the weather, so our responses may be a little spotty for the next few days. As advised, don't fire up the amp again until this is resolved. Terminal 45,46 and 47 resistances are OK, as you have determined. Sorry about the misprint there, the misprinted version of the manual you got seems to be caught in our library as a ghost that won't disappear. The correct version is dated 10-3-19. We can send a link to a current version if you email us at [email protected].
With respect to 38,39,41 and 42 these resistance measurements will most likely fluctuate or progress in one direction to a high value as capacitors in that part of the circuit charge up. The 7.7 ohms at 38 and 41 looks to be a problem. One possibility is it is actually 7.7 Megohms and thus is OK. Checking your meter settings and remeasuring the resistance would be in order here to determine if that is the case. Another possibility is that the terminal is miswired and is actually reading 7.7 ohms, in which case it must be corrected before proceeding to voltage measurements.
I'm not spotting an obvious miswire in your photos. You might start by reflowing the lower holes in terminals 39 and 41 and remeasuring resistance. From the angle of the photo it's not possible to see if they are completely soldered.
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A quick example of where you can run into trouble: the cap mounted over at 31U has the lead poking out toward 32. If that lead touches 32, you will ground out the signal. I would go through and bend all the leads like that in your build over the terminal strips, then reheat the solder in those areas so it flows around the bent leads.
If your voltages on the forward 4 terminal strips are OK but you aren't getting signal, this will be a solder joint issue more than anything. I have also seen the RCA jacks installed improperly and that caused signal not to pass properly. It's also possible for debris or solder to touch between the center pin of the RCA jack and the outside body, and this will also short signal out.
If you don't see something obvious, let me know what AC voltage ranges your meter has and we can send some signal into your Reduction and look for where it gets hung up.
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Per Doc’s comments, I do indeed get 7.7ohms and not Mohms for both 38 and 42.
Per PB, I did go thru and remove some of the excess wiring, and improved the attachment and reflowed. And per Doc’s comment, I did reflow 39L and 41L.
I did another round of resistance measurements, and still get the same result. Everything checks out except for 38 and 42. Still showing 7.7 ohms.
Something I want to mention but not sure if it means anything. The first time I did resistance checks, I did get a * for both 38 and 42. But of course, being the anxious person I am, I proceeded to power on and perform voltage checks. Now 38 and 42 show this relatively low resistance. Did I screw something up here? Any possible damage to nearby components?
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How are those resistances with no tubes in the sockets?
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ahhhh, yes. After removing the tubes, I get * or 4Mohm range which match the spec. Good to go there. So I'll go ahead and perform voltage checks, unless there's anything else I should do?
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I think you can move on to voltage checks.
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so finally got back to the voltage checks. And I'm also working to the 10.3.19 manual. I have two terminals out of spec (same as first time around)
44 - 78V (should be 0V)
45 - 77V (should be 0V)
I have a couple pics if that helps....
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Those are just errors in a manual that our automated download system doesn't want to let go of. If you have good voltages up front, everything in the back is going to be working OK.
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Still get the hum on both speakers and no playback. I can slightly hear a little noise coming from the record, but it is pretty much nothing.
Back to your reply #12, I did check the RCA inlet plugs. I think I see a problem. The stack in the instructions (page 13) shows the chassis, red flat washer, washer tab, and then the two nuts. On my build, I have chassis, washer tab, red washer, and the two nuts. Looks like my red washer and washer tab are flipped on both RCA plugs. Could this be the culprit???
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What AC voltage ranges does your meter have?
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600V
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That's as low as it will go?
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ahhh, it does measure mV, but will need to dig that up. Fluke 107
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You need to set the meter to MV with the ~, then use an 1/8 to RCA cable to connect your phone to the Reduction. On your phone, download one of the many free signal generator apps and use it to make a sine wave at 60Hz. With the volume all the way up, you should see 300mV to 500mV at the ends of the RCA plugs with the 1/8" end plugged into your phone.
Let me know when you're there and we can proceed with tracing some signal in your amp.
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confirmed. I get get 400mV
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Groovy!
Plug those RCA cables into the Reduction, leave the Reduction off, then measure the AC voltage across the RCA jacks.
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so I took measurements from the nut and the center of the plug. On the both A and B sides, I read 400mV.
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OK, now you'll want to turn your phone down till you see about 10mV coming into the RCA jacks, turn the amp on, then read mV between ground and terminal 6 as well as ground and terminal 27.
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6 - Around 130mV and fluctuating
27 - Around 140mV and fluctuating
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On a side note, I take a resistance reading from the ground tab on the RCA to the nut. They should essentially have zero resistance, correct? I get about 23kOhms for both A and B side.
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I would double check that the ground tab is installed just under the nut, not under the plastic washer. In your photos it was hard to see the buss wire going to the ground lugs on the ground post, but I saw two wires folded over each, so it looks as though they are there.
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Yeah, that's what I was trying to explain back on reply #19, but poorly. I have the plastic washer between the ground tab and the nut. ARRGGGG. I'll spend this evening fixing.
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You aren't the first person to do that, don't worry!
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So that RCA ground tab/washer was the issue. It amazes me how one "little" thing can cause quite a showstopper. Just spent the last few hours listening to some records. I'm definitely pleased. I purchased the upgrade kit as well, but will wait till I'm ready.
Gotta say, it was pretty cool learning about that trace signaling. I've heard it before, but never knew what it was.
Thanks for your help and patience PB. Much appreciated.
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I'm glad you got it all sorted!