[radiorich]

Hello morzh,
I have been using Nichicon 200 volt electrolytes for sets .

Sincerely Richard

[morzh]

Rich

I use 450-500V Panasonics for the transformer sets.
I usually use at least 200V for AC/DC without doubling rectifiers and 450-500V with those.

This time, I had only these, 47uF 160V Nichicons Hi-rel/Hi-ripple I bought to redo Zenith 5G500 many years ago, having spent 47uF 200V from Panasonic.
And I could not use anything else as I needed to fit 4 of these (80uF+40uF+40uF / 150V) inside plus the 40uF 50V (smaller but still using space) into that twistlock.
I decided they were safe to use as their rating of 160V exceeds the original 150V rating.

But I also noticed that the Nichicon 47uF 200V cap from the same USC series is of exact same size and exact same ripple current rating. Why I haven't bought it...perhaps it was not Mouser stock. Or perhaps I simply haven't noticed it.
But I used up the last four 47uF caps of a suitable rating I had.
Any other combination would simply not fit into the cap.

So. I think I am OK, as with he new resistor I will not even exceed the 160V, plus, again, the surge is allowed up to 1000 times for 30 seconds at 184V, which I am not even close to now.

Comromises, compromises.

[morzh]

"Goop" is truly a miracle cleaner.

I will shortly finish cleaning it up and put out some photos, but the most pronounced result is on the plexiglas dial arc segments.
They were pretty yellow.
I tried IP alcohol, no effect at all.
Same exact result I got from trying mineral spirits.

Then I put some Goop (in the olden times I'd use GoJo) on a small segment with a Q-tip; the swab came dark brown and the arc became nice and pristine-transparent-colorless.
So I cleaned it all.

When I come back, I will hopefully have photos of the case after total wiping and with some brown shoe polish application (tried it in the past with a 38-12, worked well).

[morzh]

So, after the resistors had come, I installed the 150 Ohm resistor and the initial voltage went  down to 155VDC. Consequently the rectified voltage became almost 118VDC. The plate voltage that were supposed to be 91V became 82-85V. Much bettertthan it was with the selenium rectifier but just a tad low. I wanted a bit more and I had some headroom now, so I took twlo 249 Ohms 5W resistors in parallel, made 125 Ohm 10W one, and the voltages became 123V and 91V respectively. I am OK with it.

   
   

Then I installed the 6.8uF cap in series with the filament string (convenient place was between the GND and the pin 4 of the 19T8, the discriminator-detector).
The voltage came down from 128V to 114V, which is almost ideal.
   


The diode/resistor mod looks like this:
   
   



The chassis underside now looks like this:
   

[Vlad95]

Can you post a photo of the Goop bottle?
And where can I buy it?

[morzh]

Now, cleaning.

This is what Goop took off in one swipe.
   

Now this is the plexiglass before Goop.
   

This one has one smaller arc cleaned one time, and the rest are still dirty. Clear difference.
   

So I applied Goop to all of'em.
   

Now, after cleaning the dial looks like this:

   
   
   

And the cabinet (not properly buffed yet. There are some scuffs and some substance I am not going to be removing). No it is not this glossy. Just the residual Goop hasn't dried out yet.
   

[radiorich]

Hello morzh,
yes, I hear you about the goop It is great stuff and I know what you mean about those nichicons I too have ran into spots like yours where you just need the smaller package !
I hope my zenith turns as nice as yours .

Sincerely Richard

[morzh]

Rich

Earlier you indicated yours is 7H820 and you said it is 3-band.
Is this for the old FM, New FM, and the BC?

The 820 and 920 are nearly identical. They use the same cabinet, and the sole difference is, they used a Heptode 12BE6 for the converter in 820, and in 920 they used 12AT7 dual triode instead, having a separate oscillator and a mixer.

You will be surprised by the sound. I clearly have been; I never expected this full booming high quality sound out of this backelite All American 7 AC/DC set.

[morzh]

Now, the last touch: I am soaking the knobs in Goop. They are dirty and, as one would expect, knurled. A session with rubber gloves, sharp toothpicks and rags I had with Philco 620 3 weeks ago is going to repeat itself. In a worse version: the knobs are hemi-spherical, so running a toothpick along a hemispherical groove is gonna be fu-uhn.


That is, it is one before the last touch. I realized I do not have the brackets that hold the back cover to the case. Nor do I have the screws.
Will have to find them. Brackets can be manufactured. But I would not like to do it. Bending aluminum, drilling...not my cup'o'tea. I am a circuit man.

[morzh]

I have been able successfully align the IF and discriminator curcuits.

What I haven't achieved yet is the oscillator vs dial alignment.
I used unmodulated 98MHz as they suggested; when I had trouble seeing peaks I made it modulated, peaked it at 98MHz.
But my stations are way up. 101.5 is somewhat closer to the very upper end. Where the 101 should be there is some other lower station.

Oh well, I figured others, will figure this one too.

[MrFixr55]

You WILL do that Mike. Re the knobs, I use a toothbrush and a variety of cleaners on knobs. Toothpaste, Windex and dish soap work well depending on what the dirt actually is.

I think that the sound that comes out of this set is due to the higher B+ that comes from a solid state rectifier as opposed to a 35W4, a decent output transformer and that sweet 8" speaker. The Foster Seeley discriminator helps.

Years ago, we had a V-M (Voice of Music) "suitcase" Stereo phono. The amp was rather simple. Single ended 50L6 for each channel and a 12AX7. Astatic ceramic cartridge. Open back detachable speaker cabinet. Each cabinet had 2 6" speakers of different type, in series. What gave this thing performance was the amount of metal in the output transformers and the voltage doubler power supply which put out about 160V. Lost when the house was being cleaned out before I could get it. No KLH Model 20 or even Model 11 but a good performer, all things considered.

Some of the Philco end table AM / Phono sets like the 53-1750 used a similar scheme. 35L6 output, 50Y7 voltage doubler and 8" speaker.

[morzh]

To align the radio I need dial markers. Someone put some of them on the speaker rim. But not all.

So I made a template. For this I needed a compass.
And then I remembered I have my drafting kit.
Last time I used it was in 9th grade of school. That is 1975-1976.
   


All the tools are intact. When I owned it, I was very proud of it and kept it in tip-top shape. I did like drafting.
   

The leds in the compasses (all three) are from that very 1976. I haven't used it since.
   

So I made a template.
   


On the other topics:
The resulting dirt from cleaning the knobs.
   

[radiorich]

Hello mike,
Yes, it is old FM, New FM, and the BC!
one issue with my cabinet is I forget what thou there is a small crack in the bakelite near the bottom right near the back I will glue it and no one will notice .

That set is fairly heavy and far as knobs the woset ones I ever cleaned was for my Philco 610b someone used white latex paint to pain over bakelt knobs .

Sincerely richard

[morzh]

The set is heavy...considering yours and mine are the same, it is heavy compared to a typical mid-to-end 40s AC/DC set.

I think what makes it heavier is:
- A large speaker. It is an 8" speaker. They are heavier than your typical 4-6" one used in those radios.
- A separate RF plate.
- A tuning assembly. There is a heavy top plate that is controlled by a cam attached to the tuning knob that pulls the slugs of the FM antenna, detector and the FM oscillator coils. The tuning gear and the cam also weigh something.

But then again...3 lbs altogether, maybe...

[radiorich]

Hello Mike,
Yes, zenith really went all out on our set putting a 8inch woofer .
I have both a Am and Fm transmitter so I can stream some great programs old radio shows on CD plus I can play music .
I too have a drafting kit mine I think was made in germany looks alot like yours.
Sincerely Richard