Is there switchable push-pull <-> single-ended mod?

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Kagliostro
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Re: Is there switchable push-pull <-> single-ended mod?

Post by Kagliostro »

Thanks Steve

Franco
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roberto
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Re: Is there switchable push-pull <-> single-ended mod?

Post by roberto »

pdf64, correct for the resistors.
psychepool
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Re: Is there switchable push-pull <-> single-ended mod?

Post by psychepool »

pdf64 wrote: Fri Feb 16, 2018 6:39 pm Yes, that looks good, apart from the 2M2 'fail-safe' resistor should go between the switch output and circuit common.
As the switch may fail open circuit, which would cause the power tube control grids to lose their dc reference, and result in them red-plating and burning out in short order.
The position to connect the 2.2M resistor in the larmar ppimv is generally known as between pin 1 and pin 2.(like below)
Folie2.PNG
I know that it is a role to replace 220K grid leak in parallel with 250K pot.
If connect it to the same location as the reference you show, would not that result in the grid stopper resistance being too high?
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roberto
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Re: Is there switchable push-pull <-> single-ended mod?

Post by roberto »

You draw it correctly.
Pdf64 was pointing out that I draw them wrongly, and he is right.
tictac
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Re: Is there switchable push-pull <-> single-ended mod?

Post by tictac »

There should be a capacitor after the master volume as well, and you should have 220 K or thereabouts bias feed resistors. That master volume should be completely isolated from the bias circuit ...

TT
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martin manning
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Re: Is there switchable push-pull <-> single-ended mod?

Post by martin manning »

tictac wrote: Sat Feb 17, 2018 5:17 am There should be a capacitor after the master volume as well, and you should have 220 K or thereabouts bias feed resistors. That master volume should be completely isolated from the bias circuit ...
If the pots are referenced to ground, yes, but in this type of MV the pot elements replace the 220k grid leak resistors. This circuit is more transparent because with the pots turned all the way up it is completely out of the picture, with a single coupling cap and 224k grid leak resistance (250k//2M2 = 224k) setting the LF roll-off. Adding two more large caps to isolate the pots and retaining the 220k grid leak resistors is completely safe in the event of a pot wiper failure, but the low frequency characteristics are different, and vary with the volume setting.
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roberto
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Re: Is there switchable push-pull <-> single-ended mod?

Post by roberto »

^ +1 on this.
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