Hi guys, i'm new to this forum. I restored a few radios in my life. Two silvertone wire recorders, a couple american fives, seeburg r jukebox,and iv'e got 3 transoceanics coming up. A couple weeks ago i bought a zenith porthole. Tested the crt (16ep4) and it tested good. I recapped the whole chassis. i powered it up for the first time on sunday. Got good picture and small sound. i have been reading other threads on here about portholes. cwmoser's thread mostly. And i used other peoples postes on powering it for the first time. i thought i would join and post some troubleshooting on mine. it's identical to cwmosers except it has the single chassis. I don't have any pics yet, but heres the craigslist ad thats still up.

http://atlanta.craigslist.org/nat/atq/2715561710.html

Now here is some of the problems i'm having with it so far. The picture I had to begin with was pretty good. I was trying to make a adjustment to the quadrature coil for the low sound. Well turned it off and removed the osc adjust for each channel so I could get to the quadrature coil easier. Well I turned it back on and the picture got brighter. The blacks in the picture got brighter, like a washed out picture. The brightness control works good but has no effect on the blacks getting brighter. So what do I need to do to fix this? The other problem i'm having with the picture is the horz. lines that are worse at the top of the screen than at the bottom. Is that these old tvs had? The sound on it is way to low. The quadrature coil i adjusted at its peak was still to low. And while i'm turning up the volume from the lowest point, the volume comes up and then while i'm still turning it up the volume drops off about half way on the dial and then comes back up as i'm still turning it. It's kind of hard to explain. I'll some pics soon.

Have you cleaned the volume control? It's my standard practice to clean all of the controls & switches & tube pins before trying out a set, but perhaps not everyone does that.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I have cleaned it. And checked it with my mutimeter. it goes from 700k down to o evenly.

Here's a few pics of it. The cabinet is in my shed. I notice the volume is great when the set is first turned on, but after its warmed up is when the volume drops off.

Here's a video of it playing:

You need to adjust the vertical linearity. The top half of your screen is stretched out in comparison to the lower half. The people's heads are too large and their legs are squashed and stumpy. If you don't have a test pattern generator, tune in something like a cable TV program listing, which will make it easier to tell when the top-to-bottom proportions are equal.

You may need to adjust the height at the same time, since the two adjustments are often interactive (changing one can affect the other).

Phil Nelson

.....And, your vol. control is definately dirty.
Have you re capped this set?
Bill Cahill

If the volume is dropping off after a while, you might want to substitute the audio output tube with another one (same type number). Sometimes, when they warm up, they get a heater to cathode short which usually is noticed by hum or even lower volume. You might also want to monitor the audio output tube voltages as this is happening...

Yes, I have recapped the set. I have adjusted the vertical linearity. i'm having problems with it. Its at the max. i turn it the other way and it crushes the screen down.

I too had a lot of trouble with horizontal centering along with vertical size.
I put up a test pattern and had to turn the horizontal center control to max to get it close.
Like you, I had to stretch the vertical size some to get the picture to fill the screen.

I wonder if there is a subsequent circuit update that addressed this problem that we need to apply?

I remember I had an issue with subdued sound on mine too. Can't remember what the fix was.

Carl

FYI, your 16EP4A picture tube is same as in my porthole - I'm told these CRTs are not "aluminiumized" and the brightness is much less than later CRTs.

One other thing, make sure you have a 1000volt capacitor in the cathode of the 6BQ6 Horizontal Output. I made the mistake and used a 630v .33uf which later resulted in the picture playing for a few minutes after powering up, and then fading to black.

Also, later a 120pf capacitor in the horizontal circuit opened. Those these mica type capacitors are normally reliable, I'm told that they put under greater stress in the horizontal circuits. I went and replaced all the 100-200pf capacitors in the horizontal circuits and the picture brightness and contrast improved.

I really like these Zenith potholes - looks like you have a good one. My porthole gets a lot of attention from visitors.

Carl

Cwmoser, my set looks just like yours, except it has the single chassis. A pain to recap. That single chassis is crammed, and I mean CRAMMED.
I went back and recleaned my vol. pot. And it helped alot on the volume being consistent. Must not have cleaned it good the first time. But the volume still dops off after a few minutes.

Did you recap using all 630v capacitors?
Sounds like something is breaking down.
Might be a marginal tube.

My chassis got a little cramped because I did not stuff the electrolytic cans.
I would look at the circuit after the 1N64 germanium diode and substitute those tubes.

Carl

Mine doesn't have a 6bq6. It has two 25bq6gt for the hor. output.

Opps ... I meant the capacitor at the cathode of the 6W4 Damper. Sorry.

Carl

BTW, how does your 4:3/round slide switch work? When I switch to 4:3, the picture size is vertically too small. I never looked into this as I planned on playing it so that it fills the screen.

Carl

Mine works great.



Mine has a 25w4gt damper and had .22 uf cap coming off of pin 3 of the cathode.

Here is a pic of mine with it on 4:3 ratio. You can till i'm a stooge fan.

I think I had to compromise the vertical position so it would fill the screen.
Here is mine with the slide switch in 4:3 mode:



Carl