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What are the chances this would happen twice?

Charles W. Powell
 

I built the Hilltoppers 20 I got at Ozarkcon and it went together well.  The transmitter puts out almost 6 watts.  But in trying to check the receiver, it acted like it was muted.  I encountered this same problem with the HT I modified for 30 meters and I found Q1 was bad.  I had sidetone audio and annunciator on the HT-20 that was just completed.  Soooooo.... with similar behavior and no test equipment, I thought I would start with removing Q1.  Q1 does the switching to mute the receiver on transmit.  Voila!  The receiver came to life.

So this raises a couple of questions.  First, did we get some bad BS170 MOSFETs in the recent batches, or am I just lucky?  Second, with my modded HT-30 only putting out about 3 watts and all my other HTs putting out over 5 watts, do I have a bad BS170 in the finals of the HT-30?  Is there any way to check the finals without simply removing and substituting?  It doesn't look to me like there is any way to check them because everything is in parallel, so no way to isolate any single MOSFET.  Comments?

Final word would be to warn folks to watch out for problems with the BS170s.  I'm thinking it's probably just dumb luck I ended up with two bad MOSFETs, and both ending up in Q1.  But there may be others as well.

72,

Chas - NK8O

Tim McDonough N9PUZ
 

Good grief. Not to wish ill fortune on you Charles but I hope you're just "lucky"!

Wonder if the group has had other reports of failures?

Tim N9PUZ

On 4/14/2019 2:41 PM, Charles W. Powell via Groups.Io wrote:
I built the Hilltoppers 20 I got at Ozarkcon and it went together well.  The transmitter puts out almost 6 watts.  But in trying to check the receiver, it acted like it was muted.  I encountered this same problem with the HT I modified for 30 meters and I found Q1 was bad.  I had sidetone audio and annunciator on the HT-20 that was just completed.  Soooooo.... with similar behavior and no test equipment, I thought I would start with removing Q1.  Q1 does the switching to mute the receiver on transmit.  Voila!  The receiver came to life.

So this raises a couple of questions.  First, did we get some bad BS170 MOSFETs in the recent batches, or am I just lucky?  Second, with my modded HT-30 only putting out about 3 watts and all my other HTs putting out over 5 watts, do I have a bad BS170 in the finals of the HT-30?  Is there any way to check the finals without simply removing and substituting?  It doesn't look to me like there is any way to check them because everything is in parallel, so no way to isolate any single MOSFET.  Comments?

Final word would be to warn folks to watch out for problems with the BS170s.  I'm thinking it's probably just dumb luck I ended up with two bad MOSFETs, and both ending up in Q1.  But there may be others as well.

72,

Chas - NK8O

Charles W. Powell
 

Well, it did happen twice.  I replaced Q1, the BS170 that switches (mutes) on transmit, and I have normal receive audio now.

I bought a few extra BS170s so I think I may look at the PA in my HT 30 as well.  There's no reason that it should only put out 3 watts when all of the other HTs I've built put out more than 5 watts.

72,

Chas - NK8O

Tim McDonough N9PUZ
 

I'm curious, were the bad BS170 parts you discovered generic, no-name parts or were they marked from a major semiconductor house?

Tim N9PUZ


On Tue, Apr 16, 2019 at 10:23 AM Charles W. Powell via Groups.Io <doctorcwp=yahoo.com@groups.io> wrote:
Well, it did happen twice.  I replaced Q1, the BS170 that switches (mutes) on transmit, and I have normal receive audio now.

I bought a few extra BS170s so I think I may look at the PA in my HT 30 as well.  There's no reason that it should only put out 3 watts when all of the other HTs I've built put out more than 5 watts.

72,

Chas - NK8O

Charles W. Powell
 

I will look Tim.  Interesting though that this HT-20 puts out 6.9 watts measured on my scope into 50 ohms, using the same lot of BS170s.  The MOSFETs were whatever was supplied with the kit, but my replacement for the HT-20 was a brand-name from DigiKey.

72,

Chas

On Apr 16, 2019, at 10:34 AM, Tim McDonough N9PUZ <tim.n9puz@...> wrote:

I'm curious, were the bad BS170 parts you discovered generic, no-name parts or were they marked from a major semiconductor house?

Tim N9PUZ

On Tue, Apr 16, 2019 at 10:23 AM Charles W. Powell via Groups.Io <doctorcwp=yahoo.com@groups.io> wrote:
Well, it did happen twice.  I replaced Q1, the BS170 that switches (mutes) on transmit, and I have normal receive audio now.

I bought a few extra BS170s so I think I may look at the PA in my HT 30 as well.  There's no reason that it should only put out 3 watts when all of the other HTs I've built put out more than 5 watts.

72,

Chas - NK8O


Jim Pruitt
 

The BS170's that I am putting in the Hilltopper kits was purchased from Digikey and in one order so the lot number should be the same for all of the BS170's being supplied in the Hilltopper kits.  I have not had any other reports of bad BS170's in the kits.

Thank you.

Jim Pruitt
WA7DUY


On 4/16/2019 9:08 AM, Charles W. Powell via Groups.Io wrote:
I will look Tim.  Interesting though that this HT-20 puts out 6.9 watts measured on my scope into 50 ohms, using the same lot of BS170s.  The MOSFETs were whatever was supplied with the kit, but my replacement for the HT-20 was a brand-name from DigiKey.

72,

Chas

On Apr 16, 2019, at 10:34 AM, Tim McDonough N9PUZ <tim.n9puz@...> wrote:

I'm curious, were the bad BS170 parts you discovered generic, no-name parts or were they marked from a major semiconductor house?

Tim N9PUZ

On Tue, Apr 16, 2019 at 10:23 AM Charles W. Powell via Groups.Io <doctorcwp=yahoo.com@groups.io> wrote:
Well, it did happen twice.  I replaced Q1, the BS170 that switches (mutes) on transmit, and I have normal receive audio now.

I bought a few extra BS170s so I think I may look at the PA in my HT 30 as well.  There's no reason that it should only put out 3 watts when all of the other HTs I've built put out more than 5 watts.

72,

Chas - NK8O

Charles W. Powell
 

Just lucky, I guess!

Chas

On Apr 16, 2019, at 11:28 AM, Jim Pruitt <jpruitt67@...> wrote:

The BS170's that I am putting in the Hilltopper kits was purchased from Digikey and in one order so the lot number should be the same for all of the BS170's being supplied in the Hilltopper kits. I have not had any other reports of bad BS170's in the kits.

Thank you.

Jim Pruitt
WA7DUY

Curt
 

Am curious whether the BS170 is as prone to damage from static as have heard the 2N7000 is. Somehow had the impression it was more rugged, but not sure where that impression came from,

  Understanding that cumulative static damage happens before we receive parts, am paranoid assembling with FETs of any variety.  The assembly is done in an aluminum tray, the FET goes immediately from the antistatic bag into the board.  I use a grounded wrist strap, if the humidity is very low then assemble other components and wait for another day.

Curt KB5JO

Charles W. Powell
 

That’s a difficult question. Where I live (near Kansas City) static discharge is rarely an issue. We have fairly high humidity, and I typically work in my basement. Static damage is always a possibility, but the BS170 is supposed to be pretty tough.

Chas - NK8O

On Apr 18, 2019, at 8:22 AM, Curt via Groups.Io <rhulett1=consolidated.net@groups.io> wrote:

Am curious whether the BS170 is as prone to damage from static as have heard the 2N7000 is. Somehow had the impression it was more rugged, but not sure where that impression came from,

Understanding that cumulative static damage happens before we receive parts, am paranoid assembling with FETs of any variety. The assembly is done in an aluminum tray, the FET goes immediately from the antistatic bag into the board. I use a grounded wrist strap, if the humidity is very low then assemble other components and wait for another day.

Curt KB5JO