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Zenith 7H920 AM/FM set 7 tube - Printable Version

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RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-02-2018

here is my down and dirty rendition of shielding a cap.

automotive aluminum sticky back muffler patch repair tape.
a short section of de-soldering wick.


if this does not work well enough, i will move up to something i pulled from some coax cable i laid out next to the cap shown.
that coax braid is aluminum though so i would need to do a tiny crimp to transition in a copper leg.

RE: Zenith 7H920 AM/FM set 7 tube - David - 12-02-2018

Several years ago I saw a DVD on amazon with all the riders info, after nas air crashed I purchased the DVD the quality is the same but trying to find things is a PITA. I do not understand how nas air indxes works but be glad the site is up and running. Looked at your radio on my copy and they look about the same resolution.

RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-02-2018

all caps replaced and finally i moved on to demo of the filter cap can.

i removed the dual section 80/40 that was installed by the previous repair and measured it.
the aftermarket dual section cap measured as follows:
the 80uf was reading 3uf
the 40uf was initially reading about 10 then to 11 then 13.2, 14.2.... it was charging up but no where near 40

so not only was the original filter caps diagnosed in the past as bad but this aftermarket one is to.

hopefully this ends up being the source of the gargle noise i hear.

your wondering why i did not do the filter caps already... well as the previous post i did a video you can watch,, there was no audible indication that i could hear that is telling me that filter caps were bad... no steady hum or anything.

my plan is to do filter caps as follows....
the 80uf = use 2) 160uf 160v caps in series ,,, OR,,, a single 67uf 160v ---- thoughts?
the 40uf= use 2) 47uf 160v
the last 40uf= use a smaller 47uf 50v or 25v i have on hand.

RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-02-2018

thank you david!!!

RE: Zenith 7H920 AM/FM set 7 tube - David - 12-02-2018

When looking at filter caps for AC/DC sets measure your incoming line voltage (mains voltage) and divide by .707 to get the peak voltage on the line. For North Florida my line voltage runs app. 123.9 most of the time, 123.9 divide by .707 = 175.24 volts. So on AC/DC sets I will use 220-250 volt rated caps with a high ripple current temp rating of 105C. I only want to do this once

RE: Zenith 7H920 AM/FM set 7 tube - Radioroslyn - 12-02-2018

Does it do it w/o your outside ant connected?? Also try flipping your non polarized plug around.

RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-03-2018

yes to part 1

i did try that to part 2

RE: Zenith 7H920 AM/FM set 7 tube - David - 12-03-2018

On my Z set from the same time period as yours with a four section E-Cap, I used 4  47uf at 250 volts and the set is  good to go. Did you check the resistors as you were replacing the paper caps what % did you have to replace.

RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-03-2018

just got the filter cap section re-canned up.
i ended up using all 160v because of size,,,, but the 160v ones i used are all 105degC rated which should help with the possible inrush and our modern utility potentials but...... if it does not, i have it set up so that from now on i can come in from the top and replace with some of those fancy shmancy tall skinny reditions that have higher voltages.

i used 1) 160v 100pf & 3) 160v 47uf caps to fill up that short but wider can.

I have not measured resistors yet... visually there are 2 that have a more lacking appearance than others but.... that means nothing. i will make time to do resistors next but at the moment i am hot to trot to see if these filter caps rid myself of the gargle noise.... i am betting yes .

tomorrow i will be firing it back up. i had an unexpected dial string failure so i learned how that installed and discovered i and easily adjust the needle if it happens to be off., otherwise at the least an AM band alignment will be done.

if it all works ok,, then i get to polish the outside and such then put it up on its new spot on my shelf in the garage.

RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-04-2018

put it all back together and works great.
she cleans up real nice and to be honest,,, the sound out of this thing fills a room!!!!!!!!!
its hard to describe but for a single speaker it sure does sound like stereo to me.

FM works great without a rabbit ear antenna and i have no idea why. ,,, however, fm is broke from 94 on down... no biggie.

here's a pic of it all cleaned up.

RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-04-2018

here is a video of it playing with no gargle.

https://www.dropbox.com/s/4f422zs1hg2o1rk/VID_20181204_154537.mp4?dl=0

RE: Zenith 7H920 AM/FM set 7 tube - Paul Philco322 - 12-04-2018

Can't go wrong with Elton and Kiki Dee!

Looks great.

Paul

RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-04-2018

thank you!

I am at 101 vdc at pin 6 of my rectifier tube,, a lot better than what it was before.

the diagram says i should have 120... perhaps i have a few small issues remaining

RE: Zenith 7H920 AM/FM set 7 tube - jcassity - 12-05-2018

ok,, this thread would be worthless if i did not at least entertain a modification due to something i see wrong in the original design as far as looks go.

this set has an interesting feature that when the light comes on,, the yellow translucent plastic rings behind the knobs light up a warm yellow.
currently the light only illuminates "boldly" the right half of the dial indicator & the right knob.

i want to do dual bulbs, one on either side of the of the front of the chassis.

i need to measure what the voltage is to this single huge bulb and has a keyway like an 1156 automotive bulb.
the current bulb is like the old 70's christmas tree lights,, the big glass bulbs and its a single contact but dual elements inside. i think the bulb says its 45watt,, there is no pn on the bulb.

RE: Zenith 7H920 AM/FM set 7 tube - EdHolland - 12-05-2018

Nice work - and a lovely set Icon_smile