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 Post subject: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Sat 01, 2019 7:21 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: wisconsin
I have 3 of the Hallicrafters T54 Sets, one is an early one with metal tubes, and the other 2 have the 6AU6 in the I.F strip
all have a tag date of 1948, one of the later ones is pretty much a parts set.
I have Recapped the other 2 and the Early one has the typical Sagging HV when it gets warm the other one is fine
I wanted to test the parts chassis HV supply to see if it was any good but didn't want to Tear out the bad one from the good chassis just to install another bad one.
so here is what I did and don't know if anyone else has done this:

I rebuilt the parts HV supply and decided why not power it up on external power supplies ? so that Exactly what I did
B+ in is suppose to be around 230VDC so I used my adjustable HV supply for that and Gave it 6.3V for the OSC filament
shown below in picture, this one works well, I was able to get a little over 6.5KV and I adjusted it down to 5KV shown below
the Top meter has the HV probe on it, the bottom meter is to monitor B+ because I don't trust the old meters on the power supply
I have left this on for a few hours and took a hair dry to heat up and this one does not sage at all.
the last pic is it back in it's cage running for some time now
so next is to install it in the Set with the Bad HV Xformer
anyone else tried this method ? :)

Terry


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Sat 01, 2019 10:26 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 1795
Location: Dallas, TX
I was planning on doing that sometime. I have a set that I have yet to work on, but I know the H.V. can be a problem. When I look at the schematic however it seems that the B+ rides on top of the 120 VAC line voltage, I don't see why they did it this way or if it would make any difference.
I've been reading anything that has to do with the H.V. sagging with temperature cause and the best idea is that the primary and secondary resonances don't track with temperature. The standard cure has been a small fan. Maybe the H.V. load is a factor.
One coil I have has a secondary with twice the normal resistance, I think that that may be because they used Litz wire and half of the strands are broken.

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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Sun 02, 2019 3:53 am 
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Location: Long Island, N.Y.
Notimetolooz wrote:
….. The standard cure has been a small fan..


Yes. Although you might feel it's "unorthodox" to give-up and have a fan running inside a TV, it does do the job. I took off the HV boxes top (which really helped to keep the heat in!), placed a good size old computer fan facing downward), and secured it neatly with a band of elec. tape. I have the set on for an hour now and there's almost no percievable fading. Out of all the 7" electro. TV's, it's been my experience that the Hallicrafters models were the most troublesome. My 505 not only had the picture fade, but it's super-sensitive with white on the screen. If there's a nearly full white screen - it screams! I've had many of the popular 7 inchers over the years and none had these issues. I stayed away from the Philco 7 inchers because they fade quickly too.


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Sun 02, 2019 9:08 pm 
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Location: wisconsin
I know there is a proper way to set HV in these, but who has those Value Resistor to place across the HV filter cap under the HV Cage
and peaking it for 5 kV I don't think is proper but for test purposes to see how things work
I found that if I peak C32 for max HV I can back off in one direction and the 6C4 has higher current draw
and back off in opposite direction there is less current draw and HV slowly comes back
so I adjusted this one for lower current @ around 4.8kv and its very stable
if I run C32 in the opposite direction of the peak then it draws more current and HV drops slowly


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Mon 03, 2019 8:26 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
Some time ago I found a short article in the December 1951 Radio & Television News.
It says that the maximum output voltage point may cause the oscillator to quit under
load. It recommends finding that maximum point but if drawing an arc with a screwdriver
causes the oscillator to stop then backing off the adjustment cap until it does not quit.
It does not mention current draw. The article indicates this is useful for all similar 7" power
supplies.

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It's not the Destination, It's the Journey.


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Tue 04, 2019 10:37 am 
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Location: wisconsin
Notimetolooz wrote:
Some time ago I found a short article in the December 1951 Radio & Television News.
It says that the maximum output voltage point may cause the oscillator to quit under
load. It recommends finding that maximum point but if drawing an arc with a screwdriver
causes the oscillator to stop then backing off the adjustment cap until it does not quit.
It does not mention current draw. The article indicates this is useful for all similar 7" power
supplies.


you can easily kill the Osc in a few ways but the adjustment below is what the manual says and what I experienced

Terry


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Tue 04, 2019 3:41 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
Right, 95 microamps through 50 Megohms is 4750 volts.
It sounds like they want the cap adjustment on the high side of peak voltage.
That article seems to recommend the low side.

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It's not the Destination, It's the Journey.


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Thu 06, 2019 8:38 pm 
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Location: wisconsin
Here is the Early T54 playing with the HV supply I did a bit of work on
this is in a sort of bright room and using the Weak 7JP4 of the 4 that I have
I have not tested it with the 2 Really good 7Jp4's yet
after playing for 4-5 hours Every Day after work for the past week maybe longer it maintains it's HV and Size as it should

what I did to this HV coil that I didn't tell yet was
I sprayed it in alcohol ( a really good wash ) then let it dry in hot sun
then I Sprayed it down with FLux Remover the kind in a large can from GC
then I Carefully Scraped away the Varnish between the lead connections- Very Carefully
then let it dry in the sun outside off and on for a few Warm days
then Resoldered all the Wire leads to the terminals
then slowly powered it up on an External power supply and monitored HV shown above
HV at first power up on the power supply was a bit low as it was drawing more current at first
but I let it run at a lower voltage for several hours and it got better and better HV with lower current
then I installed it in the Early chassis, my other chassis later model seems fine

I am going to do this next to the HV supply I removed from this chassis

I am happy with the results


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Fri 07, 2019 1:05 am 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
I'll have to keep this in mind when I get around to working on my set.

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It's not the Destination, It's the Journey.


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Fri 07, 2019 3:23 pm 
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Location: Pewaukee, WI
Yeah this is worth looking at when I get to the metal cabinet version I just picked up for a song, and when I revisit the portable I recapped last year that has HV sag after a few minutes.


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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Sun 23, 2019 7:46 pm 
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Location: Martha's Vineyard, Mass.
Working on one now. In the midst of recapping, replacing way out of spec meg resistors in the sweep section, adding a 1N4007 diode and a 50 ohm resistor to replace the selenium rectifier, cleaning and testing controls, cleaning pin sockets, etc. Everything's coming along fine.

Waiting on those 500pF 6kV caps, some ,25 tubulars, and a few electrolytic caps.

The HV Coil in mine looks clean inside and out. The chassis was completely original. It's a T-506 model with the mahogany cabinet and the cosmetics are pretty good, but I sent the cabinet out to be sanded and resprayed. I'll handle the front panel cosmetic restoration myself.

I hope on power up I don't have this voltage fade. Keeping my fingers crossed. 8)

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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Sun 23, 2019 8:04 pm 
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M3-SRT8 wrote:
Working on one now. In the midst of recapping, replacing way out of spec meg resistors in the sweep section, adding a 1N4007 diode and a 50 ohm resistor to replace the selenium rectifier, cleaning and testing controls, cleaning pin sockets, etc. Everything's coming along fine.

Waiting on those 500pF 6kV caps, some ,25 tubulars, and a few electrolytic caps.

The HV Coil in mine looks clean inside and out. The chassis was completely original. It's a T-506 model with the mahogany cabinet and the cosmetics are pretty good, but I sent the cabinet out to be sanded and resprayed. I'll handle the front panel cosmetic restoration myself.

I hope on power up I don't have this voltage fade. Keeping my fingers crossed. 8)


don't know if you know this yet, but one of those HV filter caps and some.25uf caps are under the HV coil in the cage
I replaced everything under mine, including wiring, its not hard but getting the wiring thru the chassis holes can be a pain
and more of a pain to feed thru
mine still is Rock solid after all I did
also a good way to tell if your HV is lowering or saging would be the Size, if you place marks on the CRT face you can tell easily
if it sags you will get an over scanned Raster slowly but you prob already know all this
I also installed a NOS selenium because I didn't want to mess with adding diodes and Resistors, the old one was fine but I found a new one
Also the 7JP4 Filament surge at power up is high, both my T54's do this no matter how I Rearrange tubes with various Filament ratings.
can make a weak 7JP4 look good at first power up till things get stable, I swapped various condition tubes for this test

Terry


Last edited by wiseguy on Jun Sun 23, 2019 11:59 pm, edited 1 time in total.

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 Post subject: Re: Testing Hallicrafters T54 HV transformer
PostPosted: Jun Sun 23, 2019 11:40 pm 
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Joined: Nov Thu 08, 2007 2:44 am
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Location: Martha's Vineyard, Mass.
wiseguy wrote:
M3-SRT8 wrote:
Working on one now. In the midst of recapping, replacing way out of spec meg resistors in the sweep section, adding a 1N4007 diode and a 50 ohm resistor to replace the selenium rectifier, cleaning and testing controls, cleaning pin sockets, etc. Everything's coming along fine.

Waiting on those 500pF 6kV caps, some ,25 tubulars, and a few electrolytic caps.

The HV Coil in mine looks clean inside and out. The chassis was completely original. It's a T-506 model with the mahogany cabinet and the cosmetics are pretty good, but I sent the cabinet out to be sanded and resprayed. I'll handle the front panel cosmetic restoration myself.

I hope on power up I don't have this voltage fade. Keeping my fingers crossed. 8)


don't know if you know this yet, but one of those HV filter caps and some.25uf caps are under the HV coil in the cage
I replaced everything under mine, including wiring, its not hard but getting the wiring thru the chassis holes can be a pain
and more of a pain to feed thru
mine still is Rock solid after all I did
also a good way to tell if your HV is lowering or saging would be the Size, if you place marks on the CRT face you can tell easily


if it sags you will get an over scanned Raster slowly but you prob already know all this
I also installed a NOS selenium because I didn't want to mess with adding diodes and Resistors, the old one was fine but I found a new one


Terry


Yup. I know about dat. Going to tack on extra lengths of wire before I pull the HV Chassis out. Will probably replace the wire anyways.

I've already bypassed the Selenium Rectifier with a diode and the dropping resistors. I figure better safe than sorry. I'm shooting for a trouble-free power up. I read everything I could on this chassis before I approached it. Saw Buzz'z videos on it as well. Very entertaining... 8)

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