Earthquaker Devices - Bows
- Manfred
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Before longer time I had got an EQD bows for repair, now I found my handwritten drawings from the signal path of it.
Here the redrewn schematic:
Here the redrewn schematic:
- Manfred
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Here the schematic once again with the read voltages.
- Manfred
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Here the shot that I have made.
- Manfred
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The BOWS has a more symmetrical clipping than the NPN rangmaster.Seiche wrote:So this is an NPN rangemaster with full range mod?
Only the transistors emitter seems to be biased differently (100R instead of 3k9).
- Manfred
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I built the circuit on breadboard for measuring the values.
It was hard to find a OC139 of a bunch of 100, which matches nearly the read DC-values of the orignal device,
there fore is necessary to set the bias setting for the rest of the bunch.
It was hard to find a OC139 of a bunch of 100, which matches nearly the read DC-values of the orignal device,
there fore is necessary to set the bias setting for the rest of the bunch.
- Manfred
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Yes, it is.Seiche wrote:So they are probably using a transistor with Hfe = 35, am I understanding this correctly?
I took out the transistor of the circuit after the measurement and then I read its values by means of my semiconductor analyzer.
- Manfred
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I remembered having a bunch of BF128C transistors which have a lower Hfe, so I have replace the OC139 by it for a test.
The input seriell circuit made of the 10k resistor and the 100n capacitor was to be adjusted to maintain the gain and the frequency response.
I replaced 10k by 27k and 100n by 47n.
The result looks not bad, but maybe a bias adaption is needed to obtain better results.
The input seriell circuit made of the 10k resistor and the 100n capacitor was to be adjusted to maintain the gain and the frequency response.
I replaced 10k by 27k and 100n by 47n.
The result looks not bad, but maybe a bias adaption is needed to obtain better results.
- Manfred
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I must correct the transistor type, I had mistakenly read B instead S.
It is the SF128 transistor made in GDR.
According to sources in the Internet it could be can be replaced by a BC140.
It is the SF128 transistor made in GDR.
According to sources in the Internet it could be can be replaced by a BC140.
- Manfred
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In order to make a circuit comparison, I just ordered BC140-6 and BC140-10 transitors.
- Manfred
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As anounced, the comparation trace graphs using the BC140-6 and the SF128C transistors.
The resulst are very similar.
The resulst are very similar.