nc-183d hot and low negative bias

[kb3rdt]

my NC-300 runs 24-7 and it runs hot been on 8 months now but i use turn it off now i just leave in on but even if i turn it it on bout 40 min. the tranny gets really warm almost can't touch very long!

                                                                                                      Carl KB3RDT

[The Slab Bacon]

There is nothing wrong with the 183D as designed and there were incremental minor changes in each run.

How uncanny! ! ! ! !  That looks exactly like the transfoma in my 183D!

That is because it is a factory original as used in later production and as a replacement for the earlier one.

I dint knooooooo dat!! I just assumed that it was some mil surplus transfoma that someone stuck in there after the original one crapped out. I would have expected a non potted unit like the one in a 183. the other 183Ds I have repaired had the more conventional looking transfoma in them.

Velly intelesting.......  

[K3ZS]

My NC-183 (not D) had many resistors that changed in value.  Especially screen dropping resistors and all the ones in the phase inverter, and as you have done, change all paper caps.   I learned all this after replacing the power transformer three times.

[KM1H]

PS,  Don't make any of the HAMMY HAMBONE mods that I did to my 183D even though it made the receiver work better than designed.

Thats debatable.

[KA2DZT]

PS,  Don't make any of the HAMMY HAMBONE mods that I did to my 183D even though it made the receiver work better than designed.

That's debatable.

Carl,

Probably is debatable,  I put a VR 105 in there for the screens on the RF and IF stages.  Had to add 2200ohm decoupling resistors and .01uf bypass caps.  I thought it seemed to work better, but who knows.  I thought the S-meter worked better, seemed to give more accurate readings.  The mods I did to the power supply brought the xfmr temperature way down.  I didn't want to lose the xfmr as I had heard that they were prone to failure, even though I have probably a dozen xfmrs that could replace the original xfmr.

Fred

[KC2TAU]

Hey Tom, do you need a pair of 6V6's? I'd be more than happy to send you a pair of good testing old stock for the price of postage.

[AB3FL]

KC2TAU: Yes, the only 6v6s I have are in the nc-183D

All:  I bucked my nc-183d and it likes it...hihi.  It runs much cooler now and has around 108V on the primary of the power transformer. 

thanks

Tom - AB3FL

[Opcom]

Thanks!   I will try new 6V6s and maybe lower the resistors from 500 ohm to maybe 400 ohm and see what I get.

Here is the transformer

Tom - AB3FL

sacreligiously.. maybe using thermal epoxy and gluing an aluminum heatsink on the side might help (some TV sets had a heatsink built onto the transformer core)? 
Or just using a small fan to cool the iron. I've used fans on several transformers and it really does work to carry the heat away.

As an example, the NCL-2000 iron will run pretty darn hot if the unit is keyed down for a couple hours at a time which I was doing using it for a source of 200-500W RF power.

One concern for that style is that transformer there looks potted, so that's a heat issue right there. Perhaps the core actually touches the outer case on a couple sides which would be helpful if you direct airflow at it. There's no need to drill holes, any airflow will help. Must be taboo though because no one seems to want to do it, or admit to doing it.

I don't subscribe to the belief that a very hot transformer is normal, no matter what the rating. I'll try to cool it if possible to increase life.

[K1ZJH]

It is still a lot easier, and much less intrusive, to add an external
bucking transformer on the AC line voltage. Redesigning the power supply
seems to be a rather extreme approach to a problem with a simple cure.
None of these mods address the issue that many manufacturers may have
used xformers that are bit shy in iron/inductance and that may be going
into saturation when run at higher AC line voltages.

I'm not arguing that choke or resistive input is easier on any transformer,
but there are other considerations that need to made.

Pete

[K6JEK]

I have used Weber Copper Top SS replacement rectifiers on occasion. They're just a convenient way to use solid state rectifiers and add an appropriate dropping resistor with no mods to the equipment. The dropping resistor is built into the plug-in. That would at least take the 5V filament load off the transformer.  The B+ should work out the same and the dropping resistor helps with inrush current somewhat like a real tube rectifier does.  A big part of inrush current comes from the filaments which have low resistance when cold and, of course, this is one less filament.

I run all boat anchors at 115V.

[Jim, W5JO]

None of these mods address the issue that many manufacturers may have
used xformers that are bit shy in iron/inductance and that may be going
into saturation when run at higher AC line voltages.
Pete

Interesting but I wonder.  I have owned 3 NC 183D receivers and run them by plugging into the line socket for years and never had a failure.  Yes they get hot and yes heat will hurt them, but if you replace out of spec components, tubes and be sure the ventilation is good then it should last.  All the old design criteria was 115 volts +/- 10%.  That would equal to +11.5 added to 115 so it should work ok.  Don't block the vents and if something in the audio section or power supply doesn' short, the transformer should be ok.  I always put a thread of RG 58 shield wire in the HV lead right where it comes out of the rectifier to prevent a short from ruining the transformer.

[The Slab Bacon]

Interesting but I wonder.  I have owned 3 NC 183D receivers and run them by plugging into the line socket for years and never had a failure.  Yes they get hot and yes heat will hurt them, but if you replace out of spec components, tubes and be sure the ventilation is good then it should last.  All the old design criteria was 115 volts +/- 10%.  That would equal to +11.5 added to 115 so it should work ok.  Don't block the vents and if something in the audio section or power supply doesn' short, the transformer should be ok.  I always put a thread of RG 58 shield wire in the HV lead right where it comes out of the rectifier to prevent a short from ruining the transformer.

I have to agree with Jim, Although nice, a bucking transfoma, is it really necessary? ?
I run EVERYTHING right out of the wall socket. My line voltage varies from 115 to 125v, depending on the time of year. My stuff, especially the recievers will easily run sometimes for 12 or more hours at a clip. Yea, they get a little warm at times. but it helps bake the moisture out of everything.  As long as you dont have leaky caps, to overload it, it shouldn't be a problem. I also have never had a power transformer failure in my low power stuff. Plate transformers in high powered stuff is another story.

Class-A P/P 6V6s do get brutally hot, and that is just the way it is. As long as the plates arent showing any color, they're prolly OK-Fine. I have gotten some nasty burns off of class-A audio outpoot tubes over the years.

When someone on here describes something as "getting hot" you really don't know what to think. Especially if they describe the voltages as being way off, you start to expect to find a problem..