Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Reduction => Topic started by: crackaddict on September 10, 2014, 08:22:07 PM
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Hi,
I finished my Reduction build tonight and did the resistance checks. Before I plug it in for the voltage checks, I need to know if there are any risks due to some anomalies.
- Terminal 27 showed 1Mohm, not the fluctuating "*". To me this seems like it should be right based on symmetry between A and B sides (seems like it should be an equivalent to terminal 6). Is this wrong in the manual or do I have a problem?
- Similarly terminal 31 is more of an "*" -- definitely not an OL. But to me this should match with terminal 2 from a symmetry perspective. Again, is this wrong in the manual or do I have a problem?
Finally, checking the four corners which are connected through the transformer to the bell end:
- Terminal 43: Should be 0 ohms but comes in at 179 ohms. I used gun blue and satin lacquer on the bell end, but tried to scrape through the coating around the holes. Apparently not a good connection through the lacquer...
- Terminal 48: shows zero ohms. Connected straight to ground lug, so makes sense.
- Terminal 49: Settles in at 6.8 ohms, but not zero. Again, probably not a good connection through the lacquer?
- Terminal 54: shows zero ohms. This tells me the bell end is grounded.
Based on all the above, it looks like the bell end is grounded, but two of the screws are not. Yet those two screws connect to terminals which are not used. What's the risk in leaving things the way they are?
Thanks!
Derek
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You're good to go on the voltage checks.
The only important transformer cover ground is the screw that has the ground wire connected to it.
The other measurements are just there because folks will want to measure those terminals, and seeing "OL" on a couple of those terminals might help to identify a grounding issue with that one critical screw.
-PB
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Hi,
Thanks for the go-ahead. I did the voltage check today and would love to get your feedback on a few things:
1) The A side is generally quite a bit lower in voltage than the B side. Where 70-90V is called for, "A" trends from 67V to 74V (Terminal 2 = 67.3, other A terminals ~ 73V), whereas "B" trends around 80V+.
2) Terminals 10 and 23 never quite settle down at zero; they oscillate +/- 10mV.
3) Several terminals which should be 0V, which have nothing connected but are touching resistors, show positive voltage (T3 = 100mV; T28 = 80mV; T30 = 105mV...). Also, Terminals 46 and 47 show 40mV and 30mV respectively, though nothing is connected. I can't quite explain this... (Note, T5, which also touches a resistor, measures 0V).
4) Similarly, the terminals between the small caps (T12 and T21) show 5mV and 10mV.
5) Terminal 6, which should be 0V, shows 43mV.
Is there anything to worry about there?
Final question. I've been building all these amps (Steremour, Reduction, Crack) and buying vinyl in advance of actually buying a turntable. I don't want to make a rash decision on a TT, so I probably won't have one for a week or two, and I want to use the time to install my Integration upgrade.
Given what looks like successful resistance and voltage checks, would I be OK to install the upgrade right away, even without having checked out the Reduction with an audio source? Or should I really wait until I get a TT, to see if the audio checks out prior to upgrading?
Thanks again,
Derek
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You can swap the tubes to see if those high voltages move side to side.
Something like 40mV is 0.04V. If you get a voltage that is less than 0.1V, that is close enough to 0 in our gear to call it zero. Some meters lose resolution at low voltages anyway, so it's best not to worry too much about those voltages.
-PB
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Hi,
Good idea! I swapped the tubes and the following happened (with the 70-90V terminals):
T2*: 67.3V --> 79.8V
T7: 74V --> 73.2V
T13: 73.2V --> 72.5V
T14: 73.4V --> 72.5V
T15: 74V --> 73.2V
T18*: 80.4V --> 67.3V
T19*: 79.8V --> 66.7V
T20*: 79.6V --> 67.6V
T26*: 80.4V --> 67.4V
T31: 73.5V --> 72.5V
So everything around 73V stays about the same, but the terminals which showed 80V and 67V flipped (highlighted with asterisks). Looks like it's the tubes. Is this amount of variation OK?
And do you have a recommendation regarding installing the Integration upgrade before an audio test, given that I won't have a turntable for a week or two?
Thanks a lot,
Derek
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The purpose of an upgrade is to improve the sound. If you never hear the sound, do you improve it?
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I'm just anxious to get the best setup going ASAP. I guess I really should give it a listen for a while before installing the upgrade.
I'm planning to pick up a turntable this weekend: either a VPI Traveler (cartridge unknown), which is beyond my budget, Pro-Ject Xperience Classic, or Rega RP3. I'm still wondering if the voltages look ok?
Derek
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I would consider the voltages ok, built mine not so long ago & found similar variations with different tubes.
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OK, thanks!
Derek
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You need only worry about voltages that are 15% out of spec.
As the tubes run in, say the first 50 hours, voltages will settle out. So sit down and listen for 50 hours before messing with anything. You will be pleased.
Then take the voltage readings and you will see they have changed closer to the target. But, again, only 15% out of spec needs any attention.
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Good idea. I record all the voltages, so I'll check all three amps (Crack, Steremour, Reduction) over Thanksgiving.
Derek