Wurlitzer 206 Amp Questions

Started by clarkleach, January 26, 2023, 04:17:02 PM

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After replacing all electrolytic capacitors the amp powered up and worked but was still very noisy.  So I replaced TR1, TR2, and TR3 with new 2N2925s from Mouser.  I also replaced all resistors in the pre-amp as well as R29 and R30 in the power supply with metal film resistors.  This has quieted the amp down considerably but it's still noisier than I would like.  It's not just hiss; there's an occasional rumble and an occasional sound like howling wind.  Now for the questions:

1.  While probing the signal path with my scope (referenced to ground), I see signal at the emitter of TR1 but not at the base of TR2.  I see signal at the collector of TR2 and can hear it from the speakers.  What is going on here?  Am I missing something?

2. I added the 6K8 and 2K2 resistors suggested for the addition of line out.  According to the service manual, this should provide about a 500mV signal level.  I'm seeing more like 50mV, with about 500-600mV at the top of the divider.  Is this cause for concern?  What's the best way to remedy this?

3.  I removed R59, R42, and C47, since they only seemed to be part of the unused mic input.  Was this a mistake?

4.  Any ideas where noise is coming from?

I've attached a schematic that I drew which is more or less "as built".