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RE: Have you seen the amp? Have you traced and prepared a schematic diagram?

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In Reply to: RE: Have you seen the amp? Have you traced and prepared a schematic diagram? posted by jeffreybehr on March 21, 2014 at 20:42:38

Sorry, I didn't mean to offend. I just wanted to warn anyone coming across this thread in the future not to follow the schematic blindly.

The rectifier connections for the 6EM7 supply and the 5v filament supply are shown incorrectly. The transformer leads are shown going to the + and - output terminals rather than to the AC input terminals.

On the other hand, the 300B power supply's rectifier is shown correctly. The voltage doubler only needs two diodes so the full wave bridge is being used only for two of the four diodes. That's why the fourth terminal of the FWB is left unconnected.

While I have never examined a Coincident amp, these points seem pretty clear just from looking at the schematic.

I am intrigued by the high-voltage supply supply and curious why Blume used the 5U4G. As shown the tube rectifier isn't being used for rectification at all. The amp would work fine with the 5U4G removed and a bypass wire inserted in its place (although the voltage would be a bit higher). I assume the tube was used to add a tube "flavoring" and not just for marketing purposes.

Follow Ups:

RE: Have you seen the amp? Have you traced and prepared a schematic diagram? - sonicboom 11:39:28 03/22/14 (0)
Good catch on the power supply connections. For these two supplies to be wired correctly, the upper right and lower left diodes should be reversed on the existing schematic.

As for the rectifier tube, I would hazard a guess and say that it was probably included in an attempt to reduce/minimize switching noise from the SS diodes.
Very interesting - Metralla 07:23:16 03/22/14 (2)
I am intrigued by the high-voltage supply supply and curious why Blume used the 5U4G. As shown the tube rectifier isn't being used for rectification at all. The amp would work fine with the 5U4G removed and a bypass wire inserted in its place (although the voltage would be a bit higher).

That's quite fascinating.

Regards,
Geoff
- RE: Very interesting - Goetz 00:26:05 03/26/14 (1)
  The tube rectifier creates a softstart behaviour as well, and aside of its sonic flavour it extends life of the valuable tube !
  Cheers
  G�tz
  - RE: Very interesting - Salectric 06:39:30 03/26/14 (0)
    That would be true of an indirectly heated rectifier like a 5AR4 but not a directly heated one like a 5U4G. This was discussed elsewhere in this thread.

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