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 Post subject: 120 vac transfore for b+ 180-200 vac
PostPosted: Sep Fri 27, 2019 12:10 am 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
looking for 120 volt transformer that will provide 180 to 200 for plate voltage. the original was for plate and 6 volt heaters.

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Sep Fri 27, 2019 12:38 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 5384
Location: Rochester NY USA
How much current / how big can it be? I may have one from an FM tuner that has 6.3 and 120V, would need to use a half-wave rectifier since the two windings share a common ground terminal.

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Sep Fri 27, 2019 4:21 am 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3256
Location: Lexington, KY USA
The B+ current, the rectifier circuit, and whether a heater winding is needed, are all things that matter for a replacement.

If the transformer is to have a heater winding, the current required from that is also important.

Could this be a continuation of another thread on the same radio?

https://www.antiqueradios.com/forums/viewtopic.php?f=6&t=361063&start=0

At least some of the information needed is over there.

As soon as additional threads are started, people start asking the same questions again.

Ted


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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Sep Fri 27, 2019 11:21 am 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
yes you and i have discussed this radio before and your help was appreciated. I don't know or understand how to measure current current on a radio where transformer is open the only info on the schematic is basic with no voltages listed it is 7 tube at 6v.heater assuming b+ has got to be around 160 vdc. trying to series 2 transformer to provide b+ and already have 6.3 trans for heater, this way the entire power supply can be bypassed. originally provided 6volt dc with vibrator or 115 volt ac. would run dc through full wave rectifier to eliminate rectifier tube. Maybe i am over thinking this.

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Sep Fri 27, 2019 5:51 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3256
Location: Lexington, KY USA
Adding up the tube manual B+ current for each tube gives around 50mA total. It is likely the set draws less, but this would be a reasonable design value for the supply.

Hammond and others do make power transformers with suitable high voltage windings. Some have 6.3V windings, too.

The low cost solution might be to use a 115V : 115V transformer with a voltage doubler to get your B+.

Ted


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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Oct Sat 19, 2019 10:44 pm 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
found a motorola that fits the bill and some success radio plays but volume leaves a lot to be desired tone cont is working and volume cont is also working. This has been in the works for 6 months so to hear it speak to me is rewarding now to figure out getting volume up, the schematic i have is really hard to read need more education i guess.

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Oct Wed 23, 2019 3:00 pm 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
lowered b+ to 135 vdc getting arcing in band switch tried cleaning contacts but no help.showing B+ in band switch going to ck cap and resistors in that section

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Oct Thu 24, 2019 7:00 pm 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
got B+ to 170 but arcing in band switch continues is there a way to by pass band switch or repair, tried cleaning contacts but not helping. set worked on all bands but volume low, this was when B+ was at 240 to 275 vdc oscillator working at that time and tuning caps were right on the money, however at that high voltage, caps started failing and a couple of dog bone resistors cooked. in the swamp on this one. seems the more i do the further i slip.

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Oct Fri 25, 2019 1:39 am 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3256
Location: Lexington, KY USA
Is this schematic correct for this radio? (Credit to egg!)

[url]file:///media/sdd1/Knoppix%202018/Electronics/Antique%20Radio/ARF%20Post%20Truetone%20D716%20%20060219/Rider-1941-VWXYZ-OCR-Page-0073.pdf[/url]

If not, can you link a correct one?

Have you found any service information that provides expected voltage measurements for this chassis?

Are you still using the 6X5 rectifier? If you have made any changes to the power supply, perhaps you can provide a sketch of what is there now.

B+ must normally be pretty low for this set, since the filter caps are only rated for 200V.

Perhaps excessive B+ voltage has started arcing in the switch, which then damaged the switch, so arcing now occurs at normal B+ voltage.

The above schematic shows B+ only on one pair of bandswitch contacts. These contacts bridge across the MW primary of the oscillator coil.

You can try disconnecting the two bandswitch contacts that connect to the oscillator coil prmary (and to B+). Be sure the coil itself still connects to B+.

This will allow MW reception only.

If this stops the arcing, SW operation might be restored by coupling the coil to the switch contacts through a capacitor, while grounding the other side of the switch. If the switch is badly damaged by arcing, this may not work.

Ted


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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Oct Fri 25, 2019 11:48 am 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
Ted this is what i have. trying to find sams photofact with voltage ect.


Attachments:
schematic d716.pdf [118.66 KiB]
Downloaded 17 times

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Last edited by mountain man on Oct Sat 26, 2019 12:44 am, edited 1 time in total.
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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Oct Fri 25, 2019 7:54 pm 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
just found out sams did not cover anything until mid 40's

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Nov Sat 02, 2019 1:34 am 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
replaced all electrolytic caps and paper caps at 90 to 98 vdc it starts to receive stations on am but starting to increase voltage starts the arcing in the band switch, it seems also that some component, once the arcing happens , in the front end is heating up and killing the signal . getting there but terribly frustrating.

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Nov Sat 02, 2019 3:12 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 13944
The arcing band switch will probably require replacement, likely arcs due to a burned wafer in the switch. If exact area of arc is found, then the burned area will have to be cut or scraped out. Think of this condition as a cancer. Cleaning with anything that contains lubricant will only worsen condition.

Dependent on voltage drop of rectifier(IE, 6X5 22v @ 70MA), you'd use a transformer with slightly higher AC output than the B+ specification. In reality something around 150v@50ma should be fine, as original 6ZY5 is only rated at 40 ma. For heaters total current of all tubes and add maybe ┬ŻA for headroom.

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Nov Sat 02, 2019 4:25 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3256
Location: Lexington, KY USA
Yes, don't keep powering the radio with the switch arcing. More arcing just makes it worse, and may damage something else.

Disconnect the part of the switch that has failed. Pending work on the switch, you can continue work on the radio while the single band is operational.

Ted


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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Nov Sat 02, 2019 8:21 pm 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
i put a jumper across the culprit contacts at the switch will test tonite when stations are available

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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Nov Sat 02, 2019 8:52 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3256
Location: Lexington, KY USA
i put a jumper across the culprit contacts at the switch

This is not what I suggested above.

Jumpering the contacts at the switch won't help, unless the arcing was between a contact pair that is supposed to be making contact but is not. In this case you have an open coil winding, as well. If you fix the coil, the arcing will stop, but the selected band will still not work.

If the contacts are disconnected from the circuit, the jumper won't matter.

If the contacts are not disconnected from the circuit, you still have B+ arcing to wherever, and the jumper still doesn't matter.

It would help to know exactly what is arcing to what.

Ted


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 Post subject: Re: 120 vac transfore for b+ 180-200 vac
PostPosted: Nov Tue 12, 2019 12:56 am 
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Joined: Feb Mon 18, 2013 1:50 am
Posts: 109
Location: NW Arkansas in the Ozarks 72641
removed switch, cleaned contacts and tightened rivets on contact arms. arcing cured. still it seems to have a mind of it's own one time when i power up radio works at low volume next time, nothing. some thing in the ft end has problems that cause it to intermittently operate also noted over heating of components using infrared temp sensor. still checking on problem trying to track down cause. as long as i keep b+ below 90 vdc no overheating.

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