Heathkit HW-8 Ham Radio Modification - Hear Weak Signals Better (by WDØAKX)

[janetwinslow]

The FET in question was a bit variable in production. Replacing the MPF105 in three of my HW-8 with MPF102s made no difference. Maybe mine were later production runs of the HW-8 where Heathkit selected better FETs.

[RadioHamGuy]

That is great to hear, glad you were able to use that mod! Sure is an easy to do improment. Good listening...73..Larry

[rmachayes]

Hey Larry, just made the MPF-102 swap.  Not a huge difference in reception but definitely an improvement especially with the noise. Thanks for posting.  73, Mac W4OSD

[RadioHamGuy]

I don't have a link, I think I pulled it out of a modification book on that radio at the time. I would bet with some searching there might be info on the mod somewhere on the internet though. It may have come from the articles you are talking about, guess it has been a while now so off hand I am not sure where the info came from.

[janetwinslow]

I think it depends upon the particular MPF105 . I've changed three on HW-8s and it made no difference. Putting a 10uF cap across the zener diode supplying volts to the front end makes much more difference by removing noise.

[mggk]

Hi larry
Have you made any more videos of any more mods please?

73 Dave M0GGK

[preventum]

i just found your youtube on HW8 - I checked my transistor; it is a M417-169. The installation manual does say a MPF-105. Why would someone install the incorrect transistor. Is it another mod. Thank you for any assistance you can provide. KC6EOA

[WAQFE]

I always felt that a coupling capacitor was as good as a MPF105, swapped all of them out in my HW9 de WA8QFE

[janetwinslow]

Put 47uF across ZD1 and that will make the rig quieter.

[RadioHamGuy]

@DONSAHAM Yes, it only requires a diode, 2 resistors and a cap. I can scan in the schematic for it and where it goes and send it to you by email if you email me -- my call sign at arrl.net. It is a very simple mod and works fine. Hard to describe without showing you the diagram though. Thanks!

[RadioHamGuy]

@rhblakeman Great info thanks! I have been using over 90% alcohol for many years, that does work much much better than the 70%, that leaves a film from the other contaminants always. Thanks for the good info, I will have to try the other things you mention.

[RadioHamGuy]

@rhblakeman Thanks. Also appreciate the info on the steel brush etc, I didn't realize that or think about that I guess so I will try to keep that in mind now, I do have a brass brush also but didn't really consider the difference I guess. So I will have to use that more then. Makes sense to me. Good luck with the SB-102, I remember using those in the past.

[Ronbob]

Great little mod. I ordered a pack of MPF102's to try on an HW-8 I'm restoring to sell. Thanks for the tip...

[TheRudydog]

Hey, just installed the MPF-102 (cost less than $2) in Q-1 on my HW-8 and what a difference it made. Less noise and better sensitivity. Can't beat that for a ten minute 2 buck repair job. Thanks much for your posting. 73

[MooneyDriver]

Do you have the link to the mod? Is that the meter mod that Ade Weiss published in his 2 article series on the HW8 and making it a contesting rig?

[DONSAHAM]

Great Video. Can you describe the mod you did on the meter to make it work on receive as well as transmit?

Don k6iaa

[janetwinslow]

I think it depends on the characteristics of the particular MPF105 each rig contains as the spread is quite wide. It's not the best FET to use in that position but in the rigs I've had, changing it made no improvement. Proper alignment did improve things and all mine now have a readability of signals down to 0.05uV!

[mrkattm]

How is that transistor different? Was the gain better or was it due to the small signal parasitics? You also did not mention what mode the transistor was operating in, CE, CB, CC ? Seems like a bad practice to make mods one does not understand. Please let us know, but over all good video you have a nice way about you... thanks

[aerobob]

Soldering flux does deteriorate over time and becomes conductive. It should not be left anywhere you wouldn't want current flow, even though it is likely to be a high-impedance path it is still a path. Depending on what it has absorbed, it can also become reactive. I don't remove flux 100% but I do remove any flux that creates a bridge between components or traces.