01-29-2018, 04:34 PM
I often take a break from the internet in January (some may have observed this in the past), but I have spent some time in the radio room. A few years ago I scored a Parker McCrory (Parmak) console from a local antique store. I liked the looks of it due to the large dial and eye tube. We had it in out living room and I got tired of people asking 'Does it work?" So, I flopped it up on the bench and started some checks. The initial tests revealed the power trans and speaker field may be ok. Open primary on the output transformer. Next I tested the tubes. I found a weak IF tube (6K7) and a dead 6F5 and 6E5. All others tested good, even the 80! I started the recap. It seems to have gone well overall. You can see that I decided to use discrete e-cap instead of messing with restuffing. I connected to the output transformer on the signal tracer for testing purposes.
Upon a slow power up, I was amazed to find it was picking up stations! It wasn't real strong, but showed me that everything was working. I started doing some fine tuning (not the alignment) and here was what I have found: Upon powering up it would sometimes make shrieking and popping noises. I noted that it had an (undersized) universal output transformer. It had been replaced at some point. It went dead on the 3rd power up, some some quick observations noted the tuning eye tube was showing it was tuning in stations. Ok, onward. A finger test on the 6F5 grid cap produced nothing. I poke with a meter probe on the 6F6 grid produced a hum. The 6F5 died, so I rummaged around and found a fairly decent replacement. This brought the radio back to life. I suspect this is what killed the output transformer, and probably the one prior. It plays fairly well, but is weak on volume. Tuning seems sensitive. This may be due to the mismatched output test transformer.
Now, I havent been able to find any schematic in riders for this, so I dont know if this was an odd one run make or was bought out by another company. The model number is 105212 as far as I can tell. I am having to use my instincts on this one, but any help would be appreciated as far as a diagram, experience, or history.
The 6F6G output tube appears to need a transformer with a 7000 ohm or so plate load according to the RCA tube manual. Judging from the size of the speaker (about 12"), I am guessing the trans to need to be about a 5w. It has around 200v on the plate. I have no idea what the impedence of the speaker is. It does work, but again, very weak.
Here are a few pictures of things before I started the recap:
More to come...
Upon a slow power up, I was amazed to find it was picking up stations! It wasn't real strong, but showed me that everything was working. I started doing some fine tuning (not the alignment) and here was what I have found: Upon powering up it would sometimes make shrieking and popping noises. I noted that it had an (undersized) universal output transformer. It had been replaced at some point. It went dead on the 3rd power up, some some quick observations noted the tuning eye tube was showing it was tuning in stations. Ok, onward. A finger test on the 6F5 grid cap produced nothing. I poke with a meter probe on the 6F6 grid produced a hum. The 6F5 died, so I rummaged around and found a fairly decent replacement. This brought the radio back to life. I suspect this is what killed the output transformer, and probably the one prior. It plays fairly well, but is weak on volume. Tuning seems sensitive. This may be due to the mismatched output test transformer.
Now, I havent been able to find any schematic in riders for this, so I dont know if this was an odd one run make or was bought out by another company. The model number is 105212 as far as I can tell. I am having to use my instincts on this one, but any help would be appreciated as far as a diagram, experience, or history.
The 6F6G output tube appears to need a transformer with a 7000 ohm or so plate load according to the RCA tube manual. Judging from the size of the speaker (about 12"), I am guessing the trans to need to be about a 5w. It has around 200v on the plate. I have no idea what the impedence of the speaker is. It does work, but again, very weak.
Here are a few pictures of things before I started the recap:
More to come...
If I could find the place called "Somewhere", I could find "Anything"
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44