Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on March 21, 2017, 07:32:36 pm

Title: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: kagliostro on March 21, 2017, 07:32:36 pm: I noticed a 33K resistor (R32) in an odd position (to me) on the Echoplex EP-2 PS

(http://el34world.com/Forum/index.php?action=dlattach;topic=21721.0;attach=64312;image)

Is that a Bleed Resistor ? (if it is 33K seems a very low value for that purpose but B+ is around 140V so it may be, or not ?)

Thanks

Franco
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: shooter on March 21, 2017, 08:25:35 pm: The 2 R's in the filament chain seems odd also, considering there's already a CT for filaments. :dontknow:
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: John on March 21, 2017, 09:00:38 pm: I think R32 is a "balancing resistor". Merlin talks about this in one of his books. It helps smooth out any hum that might be sneaking back on the ground side of the first filter caps, if I remember right. Although... 33K seems awfully high.
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: kagliostro on March 22, 2017, 06:29:23 pm: To me didn't seems as in Merlin circuit :dontknow:

(http://i.imgur.com/3HPjmML.jpg)

Franco
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: John on March 22, 2017, 07:49:54 pm: Ohhh... *slaps forehead* I saw what I expected to see which was a filter cap where there is none. In that case, I have no idea what that resistor is for. Could even be the schematic is drawn wrong?
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: trobbins on March 22, 2017, 09:08:38 pm: Yes the resistor would function as a bleed. Notice that the two diode anodes still go through the 100 ohm limit resistor to the first filter cap.
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: Tony Bones on March 22, 2017, 09:15:18 pm: I agree that it's just a bleeder. I also agree that it's smaller than it needs to be.
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: kagliostro on March 23, 2017, 02:40:35 am: The schematic is supposed to be correct, also because other models of the same brand has a similar arrangement

I'm prone to think definitively to the 33K + 100R as a Bleed Resistor, the value is low, but also B+ is low ...

Franco
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: HotBluePlates on March 24, 2017, 11:42:50 am: Quote from: kagliostro on March 21, 2017, 07:32:36 pm
I noticed a 33K resistor (R32) in an odd position ... Is that a Bleed Resistor ? (if it is 33K seems a very low value for that purpose but B+ is around 140V so it may be, or not ?)

The small value looks like an intentional loading of the power transformer. I don't know if this is just to achieve a design B+ voltage, or if the motor across the primary creates a need for the extra loading. Maybe PRR knows...
Title: Re: Which is the purpose of this resistor on PS, is a Bleed Resistor ??
Post by: jjasilli on March 24, 2017, 12:26:12 pm: I agree that it's a shunt, or "bleeder", resistor. As such it seems to drop the 140V B+ about .004 volts. It's hard to see a practical purpose.