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  #1  
Old 10-06-2017, 07:51 PM
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Hallicrafters 505 Soon to hit the Bench

From the darkest corner of the garage, I braved the spider webs and dug out this Hallicrafters that has been awaiting restoration far too long. It appears that there has been no under-chassis repair at all. Look at all those ugly paper caps!



Cabinet had been stripped for refinishing and all knobs and push-buttons were found in a plastic bag. Speaker is missing. HV cover is missing. I have already re-populated the empty tube sockets.



The biggest problem (so far) is the missing rubber boot that holds the CRT and safety glass... anybody making reproductions or have a spare?

Wish me luck, its going to the bench soon,
jr
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Old 10-06-2017, 10:21 PM
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decojoe67 decojoe67 is offline
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Good luck with the resto. I have a 505 too and it's great looking set designed by Raymond Loewy. The one negative about them is picture darkening as the set heats-up. Mine has the HV cover missing too and likely the reason is to keep the coil cooler. After having mine repaired twice the only sure way to prevent the darkening was to install a small fan atop the HV box blowing down. I can watch my set for a full movie and there's practically no darkening.
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Old 10-06-2017, 10:27 PM
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I've got the suitcase version awaiting CRT check and eventual restoration.
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Old 10-11-2017, 03:01 PM
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Well, the Hallicrafters has made it to the bench and most capacitors have been replaced. I have an order in to replenish my stock.



I noticed a serious error in the Sams 91-6 folder... the polarities of c-4 a & b are backwards... negative ground is indicated but both of thes caps must be wired with positive ground, for the circuit to make sense.

I have re-capped the HV supply and have it operating on the bench (most of the time).



Most of the time it is well behaved, delivering around 4.2 kV with 220 volts input, drawing about 13 mA, but once in a while the HV drops to zero and the current drawn by the poor little 6c4 shoots up to more than 60mA! This does note bode well, I suspect an intermittent shorted turn in the HV coil.

I may have to get serious about finding a replacment for the HV supply in these electrostatic sets, as I also have the typical slumping HV problem in my Philco 7 incher.

So far, a fun project... I may try fabricate the CRT boot from hobby plastic, if one does not turn up.

jr
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Old 10-11-2017, 09:01 PM
tvdude1 tvdude1 is offline
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HV coil

I mounted Motorola coil from a vt71 in my 7 inch philco and works great. Just use the vt71 circuit.
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Old 10-12-2017, 01:00 AM
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Quote:
Originally Posted by tvdude1 View Post
I mounted Motorola coil from a vt71 in my 7 inch philco and works great. Just use the vt71 circuit.
Nice! But I would hate to scrap out an early Motorola, though it may come to that... right now, I am leaning more toward harvesting the flyback out of a cheapo thrift store Bentley (or similar) 5 inch set and driving it with a 555/power transistor circuit to make 4 to 5 kV... I suspect that something like that could work.

Or perhaps something like this:

http://www.ebay.com/itm/EMCO-F40-Hig....c100033.m2042

not affiliated,
jr
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Old 10-12-2017, 06:45 AM
tvdude1 tvdude1 is offline
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I have 4 spare chassis so it was a good idea to save the Philco
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Old 10-12-2017, 11:18 AM
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The VT-71 IS the most common electrostatic set, and probably the most common set pre-1950. I've seen some swap meets where 3-4 sets missing CRTs were stacked like cord wood for ~$20 a pop....If I found a VT-71 with a dud CRT or a cabinet beyond help I'd probably be harvesting parts from it if I needed any.
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Old 10-12-2017, 12:22 PM
tom.j.fla tom.j.fla is offline
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On the few electrostatic sets I have converted to solidstate H.V. supply i have used the F80 unit gives plenty of over head for high voltage. You just need a 0-20 volt at 1 amp supply to give it its' juice to run. All the best, Tom.J
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Old 10-15-2017, 06:21 PM
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Some HV experiments

I put the HV supply back in its enclosure to observe behavior... no better, HV continues to come and go. When it is working ok, neon indicators show voltage on all coils:



When it quits, the neon indicators next to the higher voltage coils do not light:



Suspecting that the problem might be in the highest coil, I removed it and built a simple voltage doubler to recover the lost voltage. This approach seems to be working, as I can easily get 5.5 kV or more, with only about 10 mA being drawn by the 6C4. I have to be careful in adjusting the trimmer cap, to not exceed the 6kV rating of the multiplier caps.



Perhaps there is hope yet for the old Hallicrafters!

jr
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Old 10-15-2017, 07:20 PM
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Those switches like the channel selector in your set are very prone to getting dirty, making for flakey operation. That will probably the last item you'll deal with in your restoration.
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