Zenith H2438R "Aldrich" restoration

[bandersen]

Let's keep the porthole part rolling. Next up an H2438R "Aldrich" from the same estate sales as the blonde I started earlier.



Also, picked up a Muntz I'll talk about in a separate thread.


It is good condition and it's all there back, knobs etc. There are remains of a felt pad in each corner of the top so I assume it had a glass top at some point.



It also came with the original owner's and service manual.



Appears to have a rebuilt (red cone) 16GP4 picture tube and it tests good.




Built in June of 1950.

[bandersen]

Here's the beast up on the workbench.
They switch the tuner to the opposition side and rotated it 90 degrees as compared to earlier models. Probably to make room for the larger picture tube.




Dual 6BQ6 horitzontal output tubes wired in parallel.


Very clean underneath. A bit more refined and simplified compared to older models. Looks like they dropped the phone-vision socket


I only see one old repair. Someone tacked in an electrolytic can cap near the front.


Finally, here's the power supply and audio amp.

[kvflyer]

Originally Posted by bandersen

Here's the beast up on the workbench....
Finally, here's the power supply and audio amp.

...

Good to see the metal heat shield next to the electrolytic capacitor. Someone was thinking!

Bob, I have three sets in queue and maybe this will be inspiration to do the Zenith that I have, albeit a 12" set. But mine is about 99% original with the flyback below deck and looking "Well Done" crispy.

Thanks for the pictures.

[bandersen]

You're welcome. I'll be doing one of the crispy, under the chassis flyback portholes soon as well

[Electronic M]

Originally Posted by kvflyer

Good to see the metal heat shield next to the electrolytic capacitor. Someone was thinking!

Bob, I have three sets in queue and maybe this will be inspiration to do the Zenith that I have, albeit a 12" set. But mine is about 99% original with the flyback below deck and looking "Well Done" crispy.

Thanks for the pictures.

That power supply was also used in table models like mine, and that cut corner on the supply heat shield is for clearing the bell of the CRT. On the table models they bolted that supply to a piece of sheet metal that slid into grooves in the wood cabinet that made it sit in the empty space above the main chassis opposite side from the tuner....A LOT of thought had to go into packaging the table model version.

I got lucky and was able to make a console supply work (didn't know my set was missing a supply) by replicating the bottom sheet metal....Now if I could find a replacement for the missing volume knob I'd be set.

[bandersen]

Starting with the power resistors. These are all bad including the candohm mounted to the chassis

[Yamamaya42]

I have not even started to address the candohm resistors in my Brittany yet, but they seem to be OK, as power seems to be fine, but I will most likely change them anyway as I don't like where they are placed, inside the HV cage seems a poor place for the bleeder network, the FBT gets hot enough w/o any help from power resistors near it!

[bandersen]

Emerson did that too in the 571 model. Sure, let's cook the poor wax coated flyback!

[timmy]

Hey bandersen you had told me how to add a10volt bias to a crt tester was that series or parallel? Was it g1 or g2 because I’m not certain I did it correctly.

[bandersen]

Are yo usure tht was me? What are you testing? I believe the Sencore CR70 adds 10 volts to the G1 bias when in electrostatic CRT test mode.

[timmy]

Yes was you but was like a year ago and you did say 10 volts but not sure . if it’s g1 do I break g1 wire and place the 10 volts In series ? Testing 7jp4 with bk 440. Is it negative to g1 and positive to g2 of the 10 volts ?

[bandersen]

A better question might be why are you trying to test a 7JP4? The phosphor on these usually wears out long before the emissions go bad.

All I know is the only tester I have that supports a 7JP4 has a switch that says (Scope -10V bias). I would think that adds negative 10 volts to the grid with respect to the cathode, but have never measured it.

I would try the 440 as is before modifying it.

[timmy]

Originally Posted by bandersen

A better question might be why are you trying to test a 7JP4? The phosphor on these usually wears out long before the emissions go bad.

All I know is the only tester I have that supports a 7JP4 has a switch that says (Scope -10V bias). I would think that adds negative 10 volts to the grid with respect to the cathode, but have never measured it.

I would try the 440 as is before modifying it.

I’m not modifying the 440 I made an adapter and it does give a reading but they all seem to be the same so I thought this may have given me a more truthful reading. I know the cr70 does these tubes. I applied 10 volts in series with g1 and g2 and just raises the needle alittle bit so I left it in series with g2

[bandersen]

It should lower the needle, not raise it during the cutoff test.

Not sure what you mean by truthful. Don't think I've ever found a 7JP4 with bad emissions - it's the phosphor that wear out first. Probably why Sencore dropped the 7JP4 from the tube chart in later versions.

[bandersen]

Got burned a bit by ordering parts based on the parts list rather than observing the actual chassis. Zenith listed some of these sand coated power resistors as only 2 or 3 watts and I got undersized parts. Just ordered up some 7 watters.
Also, the white cap is a 0.47uF in series with the horizontal yoke windings. I used a Mallory M150 polyester film cap for now but ordered up a more robust polypropylene cap rated for pulse applications.

Leason learned, review the chassis before ordering parts!