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!

https://farm5.staticflickr.com/4448/...28c3de_z_d.jpg

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.

https://farm5.staticflickr.com/4465/...ae1e3c_z_d.jpg

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

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.

I've got the suitcase version awaiting CRT check and eventual restoration.

Well, the Hallicrafters has made it to the bench and most capacitors have been replaced.

https://farm5.staticflickr.com/4466/...1a56e4_z_d.jpg

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).

https://farm5.staticflickr.com/4477/...cbc85b_z_d.jpg

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. :scratch2:

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

HV coil
 

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

I have 4 spare chassis so it was a good idea to save the Philco

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.

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

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:

https://farm5.staticflickr.com/4467/...442535_z_d.jpg

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

https://farm5.staticflickr.com/4514/...e398bb_z_d.jpg

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.

https://farm5.staticflickr.com/4493/...05d435_z_d.jpg

Perhaps there is hope yet for the old Hallicrafters!

jr

https://farm5.staticflickr.com/4448/...28c3de_z_d.jpg

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.

Very true, but a little Deoxit D5 carefully applied with a toothpick fixed ch3 and ch4 reception.

Back together, HV is only about 2.3 kV under load (supply refuses to start if set much higher), 7JP4 is quite weak, and we have some jailbar problems to fix, but the set mostly functions.

https://farm5.staticflickr.com/4477/...61ff52_z_d.jpg

Here is the HV section... any recommendations for mod to improve starting under load?

https://farm5.staticflickr.com/4466/...9362a3_z_d.jpg

jr

I've been away from this forum for a while.
That's an interesting test that uses the neon lamps.
I also have a 505 to restore sometime. I think most sections of the HV coil are wound with Litz wire. I have a spare chassis and the coil resistance on that one measures twice the other one, which measures the correct amount. I wonder if half of the strands in the Litz wire are open. Perhaps the cause of the HV problems is unequal thermal expansion between the wire and the coil varnish or coil form, that causes separation of the strands.
I too am looking to replace the rubber CRT gasket. I was eventually going to make my own. I wouldn't doubt that you may beat me to it because it is on the back burner for me.

Still working on it... hobby plastic attempt was a no-go... second idea involved left-over garage door weatherstripping shows some promise. Cross section of the weatherstripping was about correct to cushion the front of the CRT, and provide a decent outside trim.

https://farm5.staticflickr.com/4543/...9144c4_m_d.jpg

I cut the weatherstripping to the correct length, formed a circle and glued the ends together. Followed up with several thin coats of flat black rattle-can vinyl spray.

https://farm5.staticflickr.com/4577/...b1fe1f_z_d.jpg

I likely will try to fabricate the 3:4 mask out of hobby plastic and glue it to the weatherstripping. Still a work in progress, and far from ideal, but it's better than nothing.

jr

Excellent work on that mask so far. It should do fine until a replacement turns-up.