Bogen RP-230 Restore

x2turbo

Well-Known Member
I'm new to tube gear and I recently picked up a Bogen RP-230. I've replaced all the electrolytics, including the multi-cap cans but I'm wondering if there is anything else I should replace?

I've read that the selenium rectifiers should be replaced, but I'm not sure what\where that is. Is it the square bock near the cap in the middle of the top of the picture? If so, do I replace it with a diode? Not sure what type though. Also read that if it replaced with a diode a resistor should also be used in line.

Anything else I should replace?

Sorry for all the questions but I want to make sure I've gotten everything before I fire it up. The previous owner said it worked before I bought it and all the tubes glowed, but I haven't turned it on since I got it. I have a variac arriving on Friday and won't turn it on before I have that to use.

Thanks

IMG_0671.JPG
 
Can't tell what the black box is. Can you get a close up?

If it has line to chassis or across the line caps, I like to change those to modern safety (X1/Y1) rated caps. The old ones could possibly fail shorted.

Otherwise the usual of replacing electrolytic caps and paper caps does the job most of the time. Wouldn't be a terrible idea to find out if it has any sort of bias adjustment procedure, and maybe add in some means of checking the current through the tubes if it has nothing. Can't find a schematic, so no idea what this one specifically uses.
 
Here are some closer pics. I do have a copy of the schematic. I'll scan it tomorrow.

The caps you mention, are they the ones in the second pic? I replaced the 4uf caps with 5uf Sprague Atoms.
IMG_0672.JPG IMG_0673.JPG
 
Our goal is not to replace EVERYTHING but only what needs to be replaced. That would be: electrolytic caps and paper caps. Everything else pending functionality (out of specks). Fire it up and watch the current, even without variac fuse of original value would blow if something is wrong.
 
Our goal is not to replace EVERYTHING but only what needs to be replaced. That would be: electrolytic caps and paper caps. Everything else pending functionality (out of specks). Fire it up and watch the current, even without variac fuse of original value would blow if something is wrong.


Should I have a load on the speaker terminals?
 
Yes, load on the speaker terminals.

If there are line to chassis or across the line caps, you'll see them where the power cord lands on whatever it connects to. Usually its a ceramic cap, 0.01uf or so, rated at 1kv or higher most of the time. Once in a while it'll be a more boring paper cap. The modern caps are designed to fail open, where the old types or a typical film cap can fail shorted, which is potentially dangerous if it energizes the chassis.

Still can't quite tell what the magic black box is. What does it connect to?
 
Thain, I'm wondering if it's an early bridge rectifier, looks like it may be attached to the can cap right below it.
x2turbo, is there any writing on the "magic black box"?
If it's a bridge rectifier, I've never seen one quite like that before. Almost looks like someone sanded the top down.

BillWojo
 
No writing that I can see, but I can only see 5 sides of the cube. 4 wires come out of the other side I can't see. 2 connect to leads from the transformer, not sure where the other 2 go. I didn't trace them.

With the encouragement I just got I checked the fuse and fired it up. It works!! :banana:

I hooked up some sacrificial speakers and an iPod dock and I got music. Pretty happy for my first recap of a tube receiver. It actually sounds pretty good. I don't have any high efficiency horns or anything HE for that matter other than some HPM 40, 100 and 200s which none of are probably a good fit. I do have a pair of recapped Advent OLAs. Maybe those are worth a try?

It isn't all rosy though. FM works, but FM Stereo does not. It tunes based on the tuning tube, but no sound. Maybe the selector has an issue.

Also 2 of the 4 12AX7s don't heat up. They are part of the Phono section. Either 2 of the tubes are bad or I have another issue somewhere. They are the original Bogen Mullards. I've got mixed feelings about whether it's the tubes or not. Should the tubes heat up even if Phono isn't selected?

Positive first steps though!!
 
2 leads to a transforner, and at least one out to a cap says bridge rectifier. Usually you'll see one go to ground, one to the + lead of a cap, the other two to a transformer. Definitely haven't seen that package before. Kinda has the look of silicon though. The selenium bridges I've seen were in metal packages bolted to the side of a chassis as a heat sink.

Probably it will heat the phono tubes, but not 100%. Flip it to phono and check. usually it does not switch heater supply though. It may use a DC supply for those tubes, which I'd guess might be tied off that bridge rectifier. Sometimes if it has a DC bias supply, the heaters run on that too. Other times they run off the output tubes, operating as a cathode resistor.

A schematic would help here.
 
Here is a copy of the schematic. I'll do some testing after I get home from the office later tonight.

Thanks for any advice in advance!
 

Attachments

  • Bogen RP-230 Schematic.pdf
    119.5 KB · Views: 140
ok, looks like the phono tubes are the cathode resistor. If either were completely bad, you'd get no sound and neither tube would light. If the cap across them were shorted, the phono tubes would not light but the output tubes would red plate. Weak output tubes might cause low voltage across those tubes. Low B+ voltage would also cause low voltage on the tube heaters. I would figure those probably aren't getting the full 12.6v each anyway, so they may light a bit on the dim side. Maybe turn the lights off and see if you can see anything.

Schematic does indicate a full wave rectifier for HV, so I'm guessing thats what the black box is. Possible it originally had 4 diodes and was swapped to the bridge, or maybe for some reason they decided to individually number the internal diodes. Also possible its just a production revision.

C89 is the line to chassis cap.
 
I pulled the tube protectors and turned off the lights and they are all lit be it dimly. Based on what you said that may be expected. Later on tonight when I have some time I'm going to hook it up to a TT and better speakers but even on the crappy speakers I have it hooked up to it sounds pretty good. The separation really surprises me.
 
Everything works but the phono stage doesn't have the same output level as the aux. I have an iPod connected via an Onkyo dock. At half volume it is louder than I need it thru Advent OLAs. Phono is using a Grado Red cart on a Pioneer PL-560. Maybe the cart isn't a good match the the Phonostage. Output volume is about half. Any thoughts? Issue with the tubes or expected behavior?
 
Lower level with phono isn't that uncommon. Some of the early magnetic ones were fairly hot output, 5-7mv. With a lower level cartridge, it tends to be on the quieter side. No idea what specs the Grado is but if its under 3mv, thats probably why. There may actually be a spec for what the phono stage expects somewhere, probably in sales lit or an owner's manual if you have such a thing.

I've found older Shure and Stanton carts to be a reasonable match for most tube phono stuff. They had variable levels of output depending on the cartridge and nail combo but most of them had some combo that would give enough drive to make things happy.
 
This schematic might be more readable (first page - ignore the other two) - I can likely get a better scan if not.
 

Attachments

  • Bogen_RP230.pdf
    713.4 KB · Views: 23
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