Philco Roundie Hybrid

[peverett]

Swapping is the best if you have the spare tubes. Recently, I was working on a couple AA5 radios from the 1940s. Once I powered them up, they both had horrible hum even though I had changed the filters. I had checked the 50L6 output tubes on a late 1940s Hickock GM tester that uses a neon light for shorts test. They both looked ok. However, if I used a different 50L6, the hum went away. I then tested the humming 50L6s on my more modern Eico tester that applies 70 volts between the heater and cathode. They humming 50L6s leaked horribly. Goes to show that the old Hickock is not the best in at testing all possible issues.

[DaveWM]

what bugged me was I had some NOS radio shack lifetime tubes (the 6gh8's) that seemed to cause the problem.

Now that I got a pic I will do a one at a time swap and see if its a particular tube.

another issue vert centering off, there is a pot that is labled vert centering. I figure is just bias the yoke, but have not traced the wiring yet. I will need to get a schematic of this chassis. if its a bias then I need to see what the B+ that feeds it should be.

Just for fun I will put the set on a variac, I have one that can handle the load. See what happens when changing the line voltage.

I has the orig can caps, maybe a weak one in the B+ doubler (again I am assuming it uses a doubler, there are a couple diodes in the PS, guess it could be a centertaped PT and a full wave rectifier). This set does not use a HV regulater either, almost a muntz color tv (I wonder if muntz ever did color?).

[marty59]

About that vertical centering...many times I would see it way off, as well as height and linearity being misadjusted. I believe most of us understand the relationship between the vertical pots and how the top or bottom of the raster moves with it, how they interact with each other.

What I'm getting at is take the normal-service switch and put in the service position and establish your center line. Can be tricky if the convergence is off though. Now you can adjust the other pots for a good, (more) centered and linear picture.

B+, B+ Boost, and High Voltage can affect just about everything so good to check voltages...as you mentioned.

These Old Philco's are fun!!

[sampson159]

yes,muntz did color.we saw a scant few back in the day.muntz also was a pioneer in the big screen early projection sets.philco s are well known to have electrolytic problems.those cans leak like like a sieve.as in an earlier post,our families first color set was a philco ford roundie.pretty good set with a nice picture.much better than the higher level rca s in the store.good luck with yours

[DaveWM]

did the service switch, did not note the center position, will do later tonight.

in service even with brightness all the way down and the red drive all the way down I had a red line, could not make it just go away. The green and blue I was able to make just go away but since I was stuck with the red, I just adj the green and blue to the same approx brightness.

after the above adj the overall brightness in the norm position seems about right and grey scale seems good.

it did not converge either on the center line in the service postion. The pic looks fine in normal viewing. I will put a dot and cross hatch on it later to see how that shows up.

[DaveWM]

it was the lineraity that was off, touched it up and vert height and center ok now but...

Vert is a little jumpy, not rolling but just shaky, seems to collape a bit and then back, fairly rapidly too.

I am going to set it up and see if just running it for a while will fix. I did try a different 6LU8. No change.

if that does not do it then I will look into some of the vert osc caps, there is a .0082 1000v that I is a brown dip, 5%. that will be a special order, my tester can't go that high to check for leakage.

[DaveWM]

another thing I will try is to just clean the vert ht and vert lin adj pots.

[DaveWM]

that helped, a little spritz of tuner cleaner and wipe them thru a few times.

Its a little on the fuzzy side, not sure how sharp it should be. I have an extra focus rectifier I may try with it.

Need to hook the speaker up, I had to cut the wires as the old plugs were hopelessly stuck to the tranny. I wil just put on some new plugs to make it removable. then I will button it up for an extended play, after that I will try the dot/cross hatch for a convertgence touch up. Purity looks fine.