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Bogen RP60 Power supply resistors

guinypig

guinypig

New Member
Hi,
I am currently working on a Bogen RP60. I just noticed that 2 resistors in the power supply do not have the value indicated in the schematics. R84 and R87 are supposed to be 33K but have apparently been replaced with 10K like R85 and R88.
Can anyone confirm that the value of the factory installed components is really 33K for R84 and R87 and that the schematics is right?
 

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They look like they say 3.3K to me... won't make a LOT of difference, though - as they feed the driver stages which have a plate resistor of 180K, so there won't be much voltage drop. Would be nice if Bogen showed voltages; also would be nice if they put ALL the parts in the parts list ...
 
Do they look original? If so they're probably what belong there. I've run into schematic disagreements quite often. If the part in the unit looks factory installed, go with that value.

agree that it looks like it should be 3.3k based on R84. I think the 33k is a typo.
 
I did some poking at the full schematic here. Doing some reverse math and making a few inferences, I think the voltage at points B and E should be right about 325 volts. Voltage at A should be pretty close to 350 volts. Voltages are taken with everything CCW, so it looks like thats "tape" mode, which will shut off current flow to the tuner.

A 3.3k drop resistor would mean 9 ma of current for the entire front end, which doesn't seem to be completely unreasonable. 10k would give 3 ma which also seems possible. 33k would be 0.9 ma and I'm pretty sure thats wrong. Could go through and figure out the current draw of each triode all that stuff feeds but generally if you spitball a small signal tube at 1ma for some quick and dirty back of the napkin math it won't be completely unrealistic. Looks like we're feeding 5 triodes on each channel with the tuner turned off so 3 ma could be right.

One thing I love about Bogen is the way they sneak unconventional circuits into things. Have a look at the way V15 is actually powered. The two triodes are electrically in series with one another. Cathode of the first section goes to ground through a 1.2k resistor. Plate feeds from the cathode of the first section through a 150k. Plate of that feeds from the supply through a 180k. Can't say I've ever seen a voltage amp and phase inverter wired like that before.

full schematic for anyone interested
https://www.hifiengine.com/manual_library/bogen/rp-60.shtml
 
Thanks Gadget73.
I found a manual for a Knight amplifier that uses the same power supply and the value indicated is 10k.
 
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