Topics

HT-1 low output


K4LXY <k4lxy.cw@...>
 

My HT-1A is only putting out about 2.5W.  Originally it put out nearly 5W.  Any suggestions of where to start troubleshooting?
Thanks
73 Howard K4LXY


Timothy Fidler
 

Howard,
Here is the alleged main board schematic. This came from right here, Adam's site . Files section or similar

  I especially don't like how the So  called DDS signal is displayed.

I believe it comes in from the LEFT through the filter.

Suggestions.

1. See if anyone has published a list of typical voltages even DC voltages for the board when good. That's a good point to start from

OK so you don't tell us if the OP is low on both 40 and 20 or just generally low.  That makes a big difference.

If the unit has NOT gone a bit deaf too then it implies the DDS unit and its filter is good.

At that point I'd suspect  C 14 and C 26 because if they fail or partly fail you will get no power through.

Then I would look at C37 and C 44 etc... all the PI filter capacitors  depending on whether you had an issue on one band or both.  Look at means physical look and then if anything does not look bad , lifting one contact and a check with a precision LC meter to see the capacitor still looks good.

There was a case with the 50 W PA that QRPLabs sells where one power op capacitor failed or half failed and it took forever to find because it looked
like a ferrite core issue. It appears that capacitor was delivered bad. 

It is almost impossible for working low power inductors to go bad or shift value. 

If the power problem is on 40 and not on 20 , l'd be looking at R1a and R1b because if those contacts are not in can clean when they need to be
the filtering and power Xfer is going to get very messed up.

Finally and very unusually the IRF 510 then is suspect.  If you are going to replace it then make sure you use a brand name IRF  VISHAY is known
to be good. Many lower tier IRFs are utter crap...die copies that are not quite right and so on.  The IRFs from The Toroid king in the US are prolly good though
I don't know they are VISHAY.  Nearly everything from ebay Chinese vendors in that area is suspect , eg failed components from 20 years ago that should
have been dumped but were bagged and on sold etc etc. 

 

  There is no capacity to retrim the bias on the IRF once a new one is installed.  It is what it is  (it gets a bias only when the KEY signal is asserted). The bias scheme looks pretty crude.

If you get it going or at least a bit better and since you have already probed around and had an Iron in there.. I'd look at replacing the 4401 transistor with something a bit more Manly like a 2n4427 with a heatsink.  or a 2n3866 from the Toriod king.  (NB Adam may shoot this idea down as trying to push the CCT too hard )  This gives you the option to reduce the emitter resistors and give the IRF a bit more drive.  No guarantees on the  spurious emissions area if you drive the IRF a bit harder.. but you only live once.  if you try to hot rod the cct then clearly if the IRF has not heat sink previously it will now need one.  Even some clip on one at 18 deg C per watt is better than nix.

Please let me know what works and what does not.


   Tim Fidler  NZL (nth Auckland )


K4LXY <k4lxy.cw@...>
 

Thanks, Tim.  I only discovered this issue yesterday so am only beginning to look into it. This is very helpful.
BTW, I have many good memories of Auckland. I've been there many times, associated with AUT.
73 Howard K4LXY


Timothy Fidler
 

Damn.  I wrote  a l0ng reply and it went off to the bit bin.. .this is a dreadful interface by IINET and I should be rig. that I don't use it for long emails. There is a Draft back up button but it is not always vis on a Del PC screen.

  

Timothy E. Fidler : Engineer BE Mech Auckland 
Telephone Whangarei   022  691 8405
e: Engstr@...



----- Original Message -----
From:
crkits@groups.io

To:
<crkits@groups.io>
Cc:

Sent:
Thu, 19 Nov 2020 00:32:24 -0800
Subject:
Re: [crkits] HT-1 low output


Thanks, Tim.  I only discovered this issue yesterday so am only beginning to look into it. This is very helpful.
BTW, I have many good memories of Auckland. I've been there many times, associated with AUT.
73 Howard K4LXY


Timothy Fidler
 

Here's a  bit of nostalgia for you.

https://www.flying15.org.nz/

I have one of these but it is not in Auckland but further north.   The short clip shows FFs with  RAngitoto in the background and a other times, parts of Takapuna, Auckland Nz.

It is just possible that the IRF mounting system used does not give enough HT away  from the Mosfet,  leading to degradation over time. I used to have a nomograph that I picked up in Israel (Eldar Elecctronica , now gone) which showed heat xfer coeff for any Alum square plate of varying thickness and in various posn's I know it went missing during a move. .. but of a bummer.   TEF


K4LXY <k4lxy.cw@...>
 

I have good memories of being on a friend's yaht in Auckland.  He had a house at Mahurangi that he often loaned to my wife and me.

I found the problem - my fault.  I've been using the H-T1a to drive a QCX amp in my pickup truck.  I installed a reed relay in the H-T1, using the circuit for the Xmit LED to trigger the relay.  Apparently the draw is too much, probably drawing down the control voltage.  The 2.5W was fine for driving the amp (at 25W), so I hadn't noticed the problem.  

I had meant to find a more elegant solution instead of a relay but hadn't gotten down to it.  Guess now I should.

Thanks
Howard


Timothy Fidler
 

Indications are that the IRF may be highly stressed under long term use-  Basis  55% efficiency of the MOS ( a bit of a punt ).

https://www.heatsinkcalculator.com/free-resources/flat-plate-heat-sink-calculator.html

199 °C
Source Temperature
41.4 °C/W
Thermal Resistance
Dimensions
Length:
60mm
Width:
40mm
Thickness:
1.5mm
Thermal Conductivity:
237W/(m⋅K)
Air Flow
Ambient Temperature:
20°C
Orientation:
Vertical
Power Source
Ws:
15mm
Ls:
15mm
Power:
4W
Rth-jc:
3.5°C/W

Do you need more functionality?


K4LXY <k4lxy.cw@...>
 

2.5W is fine for driving the amp, but I don't want to stress the IRF.  Also, when using the HT-1 barefoot, I'd want the 5W.
The control circuit I'm using puts out 4.5v without additional load.  The reed relay drops it to 3.5v.  I tried an optical relay but that didn't work.
Any suggestions of what I might replace the relay with?  A P-type MOSFET or 74ACT00 logic chip was suggested to me for another similar application.
Alternately, if the reduced power doesn't stress the IRF, I could add a switch to allow me to switch the relay out of the circuit when not using the amp.  Driving the amp with only 2.5W isn't a bad idea.
Howard


Timothy Fidler
 

I take it you want power out when you have a logic low - without seeing the circuit you are trying to achieve it is difficult to be sure what is going
on.

if you want power out on low and you want to use logic level drive signals then the BS-250 is the ONLY  mosfet to use because it is a wired device and it is a logic level Mosfet .  Unfort is now  OO Production . You can get them from 
Futurlec.com which is an on line place. I don't think he has min orders.  It is run out of Oz but looks as if it is a US outfit (AKA "passing off ") 

You may also be able to get them from US suppliers.  It is basically a compliment to the  BS 170 and it has been used as a complimentary pair with lousy symmetry up to about 25 Mhz.  with just one pair you can get abt 2.5 W out  CW only  for what it is worth.  Obviously you don't need an output transformer in that case. you could use three pairs for nearly 8 W out for very little power in (perhaps 400mW) Off topic though. 


You need to ensure that the MOS is pulled fully high on turn off - this  may not be as easily done as you think.

The amp from QRP labs is designed to have  4-5 w at the input and has a -3dB power input Pi circuit.  you can change hat circuit to give whatever dB loss you desire and still  present a 50 R load.

regards


Timothy E. Fidler : Engineer BE Mech Auckland 
Telephone Whangarei   022  691 8405
e: Engstr@...



----- Original Message -----
From:
crkits@groups.io

To:
<crkits@groups.io>
Cc:

Sent:
Thu, 19 Nov 2020 06:11:36 -0800
Subject:
Re: [crkits] HT-1 low output


2.5W is fine for driving the amp, but I don't want to stress the IRF.  Also, when using the HT-1 barefoot, I'd want the 5W.
The control circuit I'm using puts out 4.5v without additional load.  The reed relay drops it to 3.5v.  I tried an optical relay but that didn't work.
Any suggestions of what I might replace the relay with?  A P-type MOSFET or 74ACT00 logic chip was suggested to me for another similar application.
Alternately, if the reduced power doesn't stress the IRF, I could add a switch to allow me to switch the relay out of the circuit when not using the amp.  Driving the amp with only 2.5W isn't a bad idea.
Howard