06-13-2006, 06:20 PM
Longer antenna than 20 ft. will be much better. The early non-AVC version may not be as sensitive as the later Model 70 with AVC.
Interesting. This seems very variable from one early brand of non-AVC superhet to another. Some in my collection don't suffer as much from this as others, though they're from the same superhet era. It may, indeed, be a design factor with the Philco 70 early series (below s/n 22,000).
I _did_ hook it up to a homebrew BCB tuned loop, and that sure helped, of course...problem is, the only space for the 70 in the house is a very tiny room...looks like I'll be building some more tuned loops!
Clean the mica wafers in the tuning gang and conpensation trimmers. Grundge and crud can impair them.
Done when I overhauled the tuning capacitors; completely diassembled and (very gently!) cleaned them. I may have missed the low freq oscillator trimmer...I'll go back and check.
Weak tube or tubes. Check tubes with a good transconductance tube tester.
As per previous post, tested all on a Hickok 539B.
There may be moisture absorption (fairly common) in one or more RF or osc coil form that needs to be gently "baked" out if it possible.
This may prove a bit difficult, as I live near the ocean... conditions that regularly run 75-90% humidity. But I'll give it a go.
Check for poor electrical contacts (very common) in all parts of the tuning gang assy., especially the grounding and rotor contacts.
Cleaned all that up when I overhauled the tuning capapcitor assy', but will look again... basic assumptions should often be tested!
All in all, I think the idea that this is a design and longer/better antenna issue is probably correct. But I will go back and see if any more bugs need swatting.
Thanks to all who have responded for your kind input! It's deeply appreciated. This is a great group of people.
73 DE Lin/KJ6EF
Interesting. This seems very variable from one early brand of non-AVC superhet to another. Some in my collection don't suffer as much from this as others, though they're from the same superhet era. It may, indeed, be a design factor with the Philco 70 early series (below s/n 22,000).
I _did_ hook it up to a homebrew BCB tuned loop, and that sure helped, of course...problem is, the only space for the 70 in the house is a very tiny room...looks like I'll be building some more tuned loops!
Clean the mica wafers in the tuning gang and conpensation trimmers. Grundge and crud can impair them.
Done when I overhauled the tuning capacitors; completely diassembled and (very gently!) cleaned them. I may have missed the low freq oscillator trimmer...I'll go back and check.
Weak tube or tubes. Check tubes with a good transconductance tube tester.
As per previous post, tested all on a Hickok 539B.
There may be moisture absorption (fairly common) in one or more RF or osc coil form that needs to be gently "baked" out if it possible.
This may prove a bit difficult, as I live near the ocean... conditions that regularly run 75-90% humidity. But I'll give it a go.
Check for poor electrical contacts (very common) in all parts of the tuning gang assy., especially the grounding and rotor contacts.
Cleaned all that up when I overhauled the tuning capapcitor assy', but will look again... basic assumptions should often be tested!
All in all, I think the idea that this is a design and longer/better antenna issue is probably correct. But I will go back and see if any more bugs need swatting.
Thanks to all who have responded for your kind input! It's deeply appreciated. This is a great group of people.
73 DE Lin/KJ6EF
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