Hans Summers <hans.summers@...> wrote:

Note that the BS170 is rated 500mW continuous current. There are four of
them. Granted they probably don't share the load equally but you have to be
really badly mismatched to get to over-current situation.

It makes me wonder... do you think it would be a good idea to swap them
with more powerful transistors? Not to get more power, but to get more
protection in case of mismatch.

American hams/former CBers will understand this.

When 4 watts isn't enough, GET AN AMPLIFIER.

FWIW there are still loads of CB amps floating around, and some of
them still work. Even if you get one for a dollar that doesn't work,
you can still get replacement finals ... not for cheap like "back in
the day" but if you compare 1980 finals prices to 2022 prices, they're
cheaper than they seem. According to this calculator
<>
a $15 final (e.g., MRF454 or MRF455) in 1980 would cost $54 and change
today.

RF Parts has them for a little less (around $48), although they appear
to be M/Acom (as in "MAY come on") instead of batwing.

I still haven't started on my QDX -- logistics issues with getting an
RPi 4 and some shack rearrangement, but at least I have a 40M NVIS
antenna ready to use now.

73
Jim N6OTQ

On 10/08/2022 17:20, WA1EDJ wrote:

I know QDX is not a 6M rig ( yet ).? ?Would 1X BS170 be better than 3 (at 50Mhz) to lower gate capacitance?

Bob

It is push-pull so 2 would probably be better.

But the LPF switching would have to be changed or removed, 1N4007s are unlikely to be loss- free at 60MHz.

73 Alan G4ZFQ

Limiting the current is in excellent and efficient way to protect the finals. TenTec did this for years with their power supplies.? A 20 amp power supply would trip out at 20.2 amps and super fast.? When you ran a 10-tech rig in the car you had to have a special airpax magnetic circuit breaker that was rated for fast Trip.? This was their only SWR protection.? If someone out there with more time than I have would design a small electronic fuse with an adjustable trip between 1/2 and 1 1/2 amps this could solve the blown final issue.? Anyone up to the challenge?
--
Thank you,
Randy?AB9GO

开云体育

Some kind of foldback solid state (fast) current limit?

开云体育

Could a TT PSU schematic serve as a template?
My Model 979?? (5A adjustable)? still works fine with my Century 22.

Michael UK
2E0IHW


TenTec did this for years with their power supplies.?
A 20 amp power supply would trip out at 20.2 amps and super fast.
...
If someone ... would design a small electronic fuse with an adjustable trip
between 1/2 and 1 1/2 amps this could solve the blown final issue.?
Anyone up to the challenge?

TI and others make eFuse ICs which can trip in microseconds and whose trip current is set with a single resistor.? Some have under- and/or over-voltage inhibit and soft start capabilities.? I use them in SATCOM power supplies where fuses are no-go.
73, Don N2VGU?

p.s.? At the same time a 9 volt regulator could be implemented on the PCB for a desirable one board solution.? The qdx running at 9 volts would be much cooler overall.

Hans anything you would be interested in as a new product?? There should be a good demand for a product like this.
--
Thank you,
Randy?AB9GO

--
73, Dan? NM3A

Randy,
Problem with that approach is heat. Putting the regulator on the PCB foes not allow for much heat diffusion to environment.?

But here's a solution for you. Look at msg #79293 where I explained my solution to this problem. Also, here are a couple of pictures. ?

--
73, Dan? NM3A

开云体育

Hi Dan & Randy,

I copied Dan's Solution with a 7809. However, as the rig still got quite hot, I added a heatsink on top of the case (see pic) ... But still I do develop Temperatures around 50°C in continous FT8 operation ... It seems that the 7809 radiats a lot of heat, especially with a 13.8V shack power supply. If I run the QDX on 12V batteries, it's more relaxed. - But I'm still not 100% happy with this ...

Vy73

STefan.

Randy,
Problem with that approach is heat. Putting the regulator on the PCB foes not allow for much heat diffusion to environment.?

But here's a solution for you. Look at msg #79293 where I explained my solution to this problem. Also, here are a couple of pictures. ?

--
73, Dan? NM3A

-- 
Stefan U. Hegner    <db4st@...>
              * * *
DB4ST --- German Ham Radio Station
D-32584 L?hne ----- Locator JO42IE 
              * * *
GPG-Key | C3CC 23A4 FBA8 622B 48AE
F-Print | 4F19 D0EE E39E ABDC 2BCE

I am using a DROKK switching buck/boost DC to DC converter.? It seems to work well, and I can adjust the voltage easily to allow for lower power output for things like the WA2EBY amp that I use to boost the power out.

Here is what I am using:


You could use a fixed, smaller converter if you wanted to mount it in the case.

73
Evan
AC9TU