Posted by Walt N

March 23, 2022 - 08:26 pm

Steve, Is there a reason you suggested changing Q101 to 2N5089, but not Q102?

Posted by Steve L.

March 11, 2022 - 04:00 pm

Hi again Walt, Lo and behold I found my copy of the RP100 manual. Looks like -29V should be on pin-1 of J12 of the Record Preamp board. This goes to R55 and R56 on the board. I'll be happy to dig into this further with you if you wish but I guess this has gotten away from the Cortina, so please contact me by email. I think you have my address but it's on the About page, accessible from the Home page. Cheers

Posted by Steve L.

March 11, 2022 - 03:09 pm

Hi Walt, I've been trying to find a manual for the RP100 today but couldn't. You've done some good troubleshooting in the mean time and it does seem likely that the RP100 is the problem. By the way, I did find specs in the 1964 catalog and the input sensitivity is 100mV. So it should work well with the Cortina. One caveat: you shouldn't use the Mono setting on the Mono/Stereo switch on the Cortina--it's not implemented properly and could cause distortion or reduced level. About the problem in the RP100 (assuming it is indeed the culprit): Are you seeing the issue on both channels? If so, that suggests a common cause, which points to the power supply of the RP100. If you have a manual, there may be a voltage reading which could confirm a power supply-related problem. You mentioned, "I tried the one I have (fixed), but it just overloaded the RP-100 internal pre-amp and caused distortion." That's with the external phono preamp and you were using it with the turntable and driving the line input, of the RP100, right? In that case, it should not have overloaded the input. However, if the supply voltage in the RP100 were low, that behavior would be consistent. Please let me know how it goes.

Posted by Walt N.

March 11, 2022 - 01:14 pm

I replaced the Shure cartridge with the original Pioneer cartridge in my turntable. No difference. At this point, I'm pretty convinced that the ancient 2N407 germanium transistors in the RP-100 are getting pretty tired. I once tried what I thought was a possible match from the Russians, but it was a no go. My only thought now is to get an external VARIABLE pre-amp and bump the input to the RP-100 a little. I tried the one I have (fixed), but it just overloaded the RP-100 internal pre-amp and caused distortion. I'm not smart enough to replace the germanium transistors.

Posted by Walt N.

March 11, 2022 - 10:16 am

Little more info from testing. I have an external phono pre-amp that I used with line-in on my computer. It worked there. According to the Cortina schematic, it will just bypass the phono pre-amp for Tuner or Aux settings. So, I hooked up the external pre-amp to the tuner inputs and the turntable to the pre-amp. Results were about the same. I'm now starting to believe that the Shure V-15 cartridge in the turntable is just not making enough signal? In any case, I now have two phone pre-amps that are not giving me enough signal. Frustrating.

Posted by Walt N.

March 10, 2022 - 07:54 pm

I have rearranged my stuff for various reasons. Now, the Cortina is connected to my EICO RP-100 tape deck that I restored. The RP was working just fine getting its signal from my BD player. However, I find now that I barely have enough signal coming from the Cortina to move the meters unless I jack them way up. The record level pots in the RP-100 are not perfect, but they were working fine before, so I suspect that for some reason I'm not getting enough signal from the RP-100. Signal is clean. This is from an LP so is coming from the Phono pre-amp. The amp seems to work just fine playing LPs, though. Any thoughts? Maybe I need to work on the pre-amp after all?