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Anyone know what tubes are used in the phono section of the Bogen RP-230 receiver? I've looked at a schematic on line but can't figure it out. What type and where to find them in the chassis? The phono tubes are shot. Lots of distortion and hum
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Preamp tubes will be 12AX7 or 6EU7, never seen anything else used. Higher value resistors (especially plate resistors, which have high voltage across them) are often off value - I've found them completely open, and up to 5 times the marked value. And of course, any leaky caps will throw voltages completely off.
I couldn't find a free schematic on the Internet to look at but in looking at RP-230 photo's on E-bay there's a group of three tubes, possibly all 12AX7's that would be the phono tubes.
Looking from the front of the unit the group of three would be on the left side.
The two small tubes about mid point on the chassis directly behind the front plate appear to be the output driver tubes.
The tubes to the rear seem to be for the tuner section and the four larger tubes are the output tubes.
Eli is right as usual in that some or all the problems may not be tube related.
The three can electrolytics should be replaced along with any found under the chassis.
In one one pic I spotted a square gray selenium rectifier under the chassis that's right next to the bottom of a can electrolytic at the edge of the chassis that's either the B+ rectifier or a low voltage DC supply for the phono tube filaments. That should be replaced as well but if it's in a filament supply you have to be familiar with using a dropping resistor so the filament voltage with a new rectifier isn't too much.
This helps A LOT Dave! Good information
Put Sovtek 12AX7LPS tubes in the phono section sockets, just in case the unit uses AC heating. The 'LPS is a genuine 7025 equivalent, constructed with a spiral wound, hum bucking, heater.
The hum you hear may be caused by dried out electrolytic capacitors. It is a matter of routine to replace all of the 'lytics in a unit of that "vintage".
The OEM O/P tube is the 7408, which is the industrial version of the 6V6. "Reissue" TungSol 6V6s will be fine, as replacements.
Contact AA sponsor Jim McShane to fill your replacement tube needs.
If you can, please upload the schematic.
Eli D.
Thanks. Yes cap replacement is on my to do. I think the phono tubes are the offenders right now, as the line section (CD via AUX) is quiet. I did replace the output tubes with 6V6's a while back
Keep in mind that while the original parts may still be good enough for the line level inputs to sound OK, a common part like a multi-section electrolytic can capacitor may have a bad section that's associated with the phono tubes B+ voltage or parts only associated with the phono section can be bad without affecting the line section.
oh! ok good point.
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