Another 7G605 Zenith TO - Printable Version
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+--- Thread: Another 7G605 Zenith TO (/showthread.php?tid=19764)
RE: Another 7G605 Zenith TO - morzh - 05-06-2019
Mike
Yep, I've been buying thing from Mark, mostly in person in Kutztown where he always comes; I bought dial covers for several radios, some grill cloth etc.
I have to see first how it looks with the existing one; after all this is the second radio and I don't know if I am going to keep both.
Plus it is missing the front door which I was never able to find; but this was the first one I bought.
RE: Another 7G605 Zenith TO - morzh - 05-15-2019
I have extracted the tuning cap and am giving it a bath.
Then upon drying I want to zap it with high voltage to see if anything burns out.
I am not sure why I am having those crackles on BC, but even though I don't think it is dirt, I'd like to exhaust all possibilities.
RE: Another 7G605 Zenith TO - jake wells - 05-15-2019
be on the look out for nickle hydride batteries for the A section of the battery pack they tend to last longer than D batteries and are rechargeable.
RE: Another 7G605 Zenith TO - morzh - 05-16-2019
I have already put alkaline in mine. They last decent time.
RE: Another 7G605 Zenith TO - morzh - 05-16-2019
Yesterday I decided to investigate the issue of the crackles while tuning. To remind, it only showed on BC band and only between 1200 to 1600 kHz.
I took the tuning cap out and gave it a good bubble bath with soft long brush between the vanes, then dried with heat gun on low.
Then left overnight and today I connected it to a doubling rectifier via resistor 30K.
I put the voltmeter across the plates and turned it on. I did all three sections one by one while turning the rotor.
No sparks or jumping voltmeter value, meaning no shorts and no burning debris.
I also didn't expect the crackles to be the result of the bad wipers contact to the rotor as there are 4 of them - no chance of such repeatability.
So....put it back, turned it on......no crackles anymore.
Put the dial back, then the pointer....same, no more crackles.
I will have to realign the bands.
Mystery.
RE: Another 7G605 Zenith TO - rfeenstra - 05-16-2019
I used to service Hammond tone wheel generator organs where the vibrato was generated with a variable cap turning at a specific speed. it was common to develop a very choppy vibrato because of the metal growing hairs that would short out the plates. The easy solution was to zap each section of the cap with high voltage from the rectifier, burning off the hairs. Perhaps your cap decided to be a long haired hippie?
RE: Another 7G605 Zenith TO - Eliot Ness - 05-17-2019
Maybe the cleaning did the trick. Sometimes removing an assembly like that and redoing all the connections will clear up some issues, but in your case I suspect there was some dirt too small to see, or perhaps a few hairs like rfeenstra mentioned. How high was the voltage you had hooked to it?
RE: Another 7G605 Zenith TO - morzh - 05-17-2019
There was no hair, I am sure of that.
I am also sure the washing took care of whatever was there. I have very soft paintbrush with very long bristles, which get inside most capacitors' spaces between the vanes, so couple with soapy water that I am sure did the trick.
Metal hair would produce sparkles.
Again, there was no electrical reaction whatsoever that could register on the meter, before or after washing.
The voltage was 300V.
RE: Another 7G605 Zenith TO - morzh - 05-24-2019
I don't remember if I said that I found this set to be less sensitive than the other, especially when using the battery.
So after clearing up the crackles problem I decided to see what gives.
Yesterday after realizing that touching the loop antenna input did not result in anything while on any band (though connecting the rod has effect on SW) I extracted the 1st RF tube, bypassed the filament with a 30 ohm resistor and found out that this did not affect the reception at all.
Further investigation showed the primary of the RF transformer is OK (and so is the plate voltage) so I suspect it is the secondary winding that might be bad.
However the radio tunes correctly (it did pass the alignment).
Will poke more tonight. I want this to perform at least as good as the other one.
RE: Another 7G605 Zenith TO - morzh - 05-25-2019
Well...a wire from the secondary of the mentioned RF transformer coming to the BC band switch was inconspicuously broken. Once reattached, the sensitivity went way up.
Now I think I should re-align the set, just in case.
RE: Another 7G605 Zenith TO - morzh - 05-26-2019
Assembled it back, works fine, sensitivity is the same as that one of the other set.
Finita l'avventura.
RE: Another 7G605 Zenith TO - Eliot Ness - 05-26-2019
You need a door, but you already know how hard they are to find. Maybe someday you'll find a trashed 7G605 you can rob the door from. I think there might be two different style doors with slight differences, so you've got to watch out for that too. Mine is only missing the handle and I've finally found a donor for that already.
RE: Another 7G605 Zenith TO - morzh - 05-26-2019
Yeah.....not likely I ever find one but then it's still a working Bomber TO.
I might at some point sell one. Not sure I need two.
So far it is on my display shelf.
RE: Another 7G605 Zenith TO - morzh - 05-27-2019
My tube portables (some transistor ones are on the right)
RE: Another 7G605 Zenith TO - KCMike - 05-27-2019
You got a nice collection there Mike.