[TenTec] Power Supply temperature

[Bob McGraw - K4TAX]

The power supply of the late 80's worked just fine while I was living in S. 
FL.   Heat and humidity and all.   Yes they do run hot but the heat sink is 
adequate to keep the pass devices within the required temperature range. 
In running RTTY at 100 watts with the Omni VI Plus, the PS heat sink would 
get too hot to touch.  Nothing wrong with that.  I did find that allowing 
the heat sink to hang off of the back of the table did allow for better 
convection cooling.

The most common issue with these supplies has to do with the bridge 
rectifier using the power supply base plate for cooling.   I've found more 
than one that adequate heat sink grease or thermal compound was not used. 
This caused failure of the bridge rectifier device.  Also, be sure the 
mounting screw is very tight proving good thermal conduction to the base 
plate.

On the Omni VI Plus S meter, proper calibration is the answer.  After the 
receiver alignment is completed, with the input terminated into 50 ohms and 
the RF gain at maximum, adjust R29 for a S meter value of 0.  Be sure that 
you do not set the pot such that the meter offset is depressed but to a 
point where the meter just starts to move upscale by less than the width of 
the meter pointer.  Then with 50uV applied at the antenna input on 14 MHz, 
adjust R25 for a S-9 indication. Then apply 1.60 uV at 14 MHz and adjust R19 
for a S-3 reading.  Repeat these two steps several times as there is 
interaction between the adjustments.  Having done this on many radios, I 
find the S meter to be reasonable accurate.

73
Bob, K4TAX


----- Original Message ----- 
From: "Bry Carling" <bcarling at cfl.rr.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Tuesday, February 18, 2014 8:20 PM
Subject: Re: [TenTec] Power Supply temperature


Thank you Clayton,

It sounds like this is a very common thing with Tentec Radios / Power 
supplies of the 1980s.
Maybe into the 1990s as well. I am sure the engineers just expected you to 
keep things from
touching the super hot heatsink back there, and also never to live in 
Florida (grin!) A fan is
definitely going to get added.

I have been loving this OMNI VI Plus though. The S meter is a terrible liar, 
and my noise level
can be anywhere from S2 to S6 here on most bands. It hovers around S4 
usually which is
annoying, and it rarely ever reaches S9 even on the striongest signals.

I still manage to have a lot of contacts, especially with the SKCC Group. 
This afternoon I
worked a guy up in the northeast who was using a Heathkit HW8 and running 8 
watts out. He
hit S5 on my S meter which is an actual S7. Not bad for 2 watts.

73 de AF4K, Bry

On 18 Feb 2014 at 17:25, Clayton Brantley wrote:

> Brian: Might want to measure the voltage at the large cap and then
> deduct the output
> voltage from that first measurement. That will tell you how much is
> dropped across the
> pass transistor. If you have more than a few volts difference then
> all that has to be
> dissipated as heat. It's the old I squared R thing.
>
> 73 Clayton N4EV
>
>
>
>
>
> On Tuesday, February 18, 2014 8:00 PM, Brian Carling
> <bcarling at cfl.rr.com> wrote:
>
> I will do the same and report results.
>
> Best regards - Bry Carling
>
>
>
> > On Feb 18, 2014, at 4:16 PM, Dave Edwards <kd2e at comcast.net>
> wrote:
> >
> > I'll go turn it on now.
> > 20 meters, medium volume.
> >
> >> On 2/18/14 4:12 PM, Brian Carling wrote:
> >> Thank you Dave. I think it does get hot just on receive only. I
> will try it that way for a while this afternoon. If you could do the
> same and tell me what you find I would appreciate it.
> >>
> >> Best regards - Bry Carling
> >>
> >>
> >>
> >>> On Feb 18, 2014, at 3:33 PM, Dave Edwards <kd2e at comcast.net>
> wrote:
> >>>
> >>> What happens on receive only?
> >>> I can turn my OMNI VI Plus on, let it sit for a while and see
> how hot it gets if that will help.
> >>> ...Dave
> >>>
> >>>
> >>>> On 2/18/14 1:27 PM, Bry Carling wrote:
> >>>> I have noticed that the power suply with my OMNI VI Plus seems
> to get extremely hot, even
> >>>> wit hcasual CW operation.
> >>>>
> >>>> Has anyone else noticed the same? I can barely touch the fins
> on th eback.
> >>>>
> >>>> Thanks for any insights.
> >>>>
> >>>> Bry AF4K
> >>>>
> >>>> _______________________________________________
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