Thanks Steve
Franco
Is there switchable push-pull <-> single-ended mod?
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- Kagliostro
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- Joined: Wed Dec 30, 2009 12:09 am
- Location: Italy
Re: Is there switchable push-pull <-> single-ended mod?
pdf64, correct for the resistors.
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- Posts: 260
- Joined: Fri Apr 18, 2014 8:29 am
Re: Is there switchable push-pull <-> single-ended mod?
The position to connect the 2.2M resistor in the larmar ppimv is generally known as between pin 1 and pin 2.(like below) I know that it is a role to replace 220K grid leak in parallel with 250K pot.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.
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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Re: Is there switchable push-pull <-> single-ended mod?
You draw it correctly.
Pdf64 was pointing out that I draw them wrongly, and he is right.
Pdf64 was pointing out that I draw them wrongly, and he is right.
Re: Is there switchable push-pull <-> single-ended mod?
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
TT
- martin manning
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Re: Is there switchable push-pull <-> single-ended mod?
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.
Re: Is there switchable push-pull <-> single-ended mod?
^ +1 on this.