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September 15, 2019, 10:35:51 PM

Author Topic: Problem with some resistance values in Foreplay II (Rev 2.01)  (Read 223 times)

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Offline TomMasz

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Problem with some resistance values in Foreplay II (Rev 2.01)
« on: November 24, 2018, 09:43:03 AM »
I just got around to building the Foreplay II I bought in 2004 (long story). I just ran the resistance value check and some of the results don't jibe with the +/- 10-15% tolerance.

Specifically:

(these might be okay)
T4 - 31.4M vs. Infinity
T5 - 31.4M vs. Infinity
T7 - 24.3M vs. Infinity

(these probably aren't)
A1 - 340K vs. Infinity
A4 - 68.6K vs. Infinity
A5 - 68.6K vs. Infinity
A6 - 220K vs. Infinity
A7 - 340K vs. Infinity
B1 - 340K vs. Infinity
B4 - 68.6K vs. Infinity
B5 - 68.6K vs. Infinity
B6 - 220K vs. Infinity
B7 - 340K vs. Infinity

The symmetry between the two tube sockets leads me to believe I did something pretty basic incorrectly but I've looked and don't see anything obvious. Any help anyone can provide will be greatly appreciated.

Tom.

Offline Paul Birkeland

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Re: Problem with some resistance values in Foreplay II (Rev 2.01)
« Reply #1 on: November 25, 2018, 02:14:22 PM »
31,400,000 ohms vs infinity isn't really a difference. 

The 68K at A5/A4/A9/B4/B5/B9 is the bottom of the voltage divider to bias up the heaters, so that's OK.

None of these resistances are particularly concerning, I would fire it up and check voltages.

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline TomMasz

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Re: Problem with some resistance values in Foreplay II (Rev 2.01)
« Reply #2 on: November 26, 2018, 07:01:16 AM »
Thanks, Paul. I'm going to do exactly that.

Offline TomMasz

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Re: Problem with some resistance values in Foreplay II (Rev 2.01)
« Reply #3 on: November 26, 2018, 09:05:54 AM »
Voltages all checked out when I powered it up and fixed one cold solder joint. Testing the output with a 5kHz sine wave showed no hum or distortion, it looks like a great design.

Thanks again for your help.