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eHam Forums => Amplifiers => Topic started by: KM4AH on February 01, 2018, 06:28:07 PM



Title: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 01, 2018, 06:28:07 PM
What is that telling me ?  One would think it has to be under coupled. But, the power out continues to increase.

Pair of 3-500Z's on 40 meters.  75 meters tunes as usual. Haven't tried other bands.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 01, 2018, 06:35:00 PM
Check capacitor on 40m band-switch position. If not bad, increase value.   


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: AF6LJ on February 01, 2018, 06:52:18 PM
Also check your input VSWR on forty meters, bad match = low drive = not enough loading cap.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1BR on February 01, 2018, 07:01:50 PM
What model amp?


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 01, 2018, 11:57:39 PM
What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 02, 2018, 03:07:02 AM
What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 02, 2018, 04:40:31 AM
What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.

It is a 500 PF door knob. When you go to 75 meters it adds another 750 PF door knob. And, when you go to 160 there are two large red wafer caps in parallel that are added.

The only door knob I have here that will fit in that space is a 1000 PF 5 KV.

So, that is too much I assume. Would another 750 PF door knob work and not get everything else below 40 out of whack ?

I am a hell of a parts replacer. Since I am going to have to order one anyway what value would you use ?


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1QJ on February 02, 2018, 04:54:13 AM
If your problem is on 40 meters there should be no padding needed on 40 if the right tune cab was installed.  That amp was a fabrication remember.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 02, 2018, 04:57:35 AM
What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.


It is a 500 PF door knob. When you go to 75 meters it adds another 750 PF door knob. And, when you go to 160 there are two large red wafer caps in parallel that are added.

The only door knob I have here that will fit in that space is a 1000 PF 5 KV.

So, that is too much I assume. Would another 750 PF door knob work and not get everything else below 40 out of whack ?

I am a hell of a parts replacer. Since I am going to have to order one anyway what value would you use ?

You could try swapping 750 door knob used on 80 with 500 used on 40 to see what it does for 40m to give you a idea of value you might need. As far as effect on lower bands, a small change should have minimal impact


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: N8CBX on February 02, 2018, 06:09:46 AM
HV door knob caps are unnecessary for C2, only necessary for C1. Silver mica 1kv caps can easily be use for your padder C2 caps.
Jan N8CBX


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1QJ on February 02, 2018, 06:34:18 AM
No padding of load or tube is required if the right caps were used in the conversion.  I’d install the correct stuff.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: G3RZP on February 02, 2018, 06:58:42 AM
A 750pF capacitor on 7 MHz is about -j30. 1500 watts in 50 ohms is 274 volts rms on a carrier. The capacitor in that condition would have about 9 amps flowing through it, so would need to be rated for the current. 


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 02, 2018, 07:45:36 AM
What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.


It is a 500 PF door knob. When you go to 75 meters it adds another 750 PF door knob. And, when you go to 160 there are two large red wafer caps in parallel that are added.

The only door knob I have here that will fit in that space is a 1000 PF 5 KV.

So, that is too much I assume. Would another 750 PF door knob work and not get everything else below 40 out of whack ?

I am a hell of a parts replacer. Since I am going to have to order one anyway what value would you use ?

You could try swapping 750 door knob used on 80 with 500 used on 40 to see what it does for 40m to give you a idea of value you might need. As far as effect on lower bands, a small change should have minimal impact

That will be the simplest thing to try. The tuning is such that the Load Cap on 75 has little dramatic effect. I mean you can find a peak output, but 1/4 turn in either direction won't make 50 watts out difference. Matter of fact on 40 you can unmesh the cap from 0 up to 20 on the dial and won't lose 50 watts. Running about 75 watts drive and 1200 or so out.


BTW, the owner said it was blowing a fuse on 40 meters. I have not had that problem. But, when tweaking the tune and load for max out using a pulser it starts to make a clicking  noise when C2 is finally fully meshed and power out is still increasing. Doesn't sound like an arc, could be the T/R relay. But, something going on that I don't much like.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: N3QE on February 02, 2018, 07:49:42 AM
It means you aren't driving the amp hard enough when tuning.

If you start actually driving the amp into it's "sweet spot" for power delivery, you will find you have to advance the load control.

If you are tuning up with voice modulation it is likely it is not possible to hit the proper tune up based on average-reading meters. Solid carrier or at least a pulser at PEP power is the way to tune.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 02, 2018, 07:51:38 AM
That will be the simplest thing to try. The tuning is such that the Load Cap on 75 has little dramatic effect. I mean you can find a peak output, but 1/4 turn in either direction won't make 50 watts out difference. Matter of fact on 40 you can unmesh the cap from 0 up to 20 on the dial and won't lose 50 watts. Running about 75 watts drive and 1200 or so out.

Try swapping both, placing 80m 750 pf on 40m and 40m 500 pf cap on 80.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 02, 2018, 07:53:30 AM
It means you aren't driving the amp hard enough when tuning.

Not so sure as he is getting 1200 watts out at current drive level.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 02, 2018, 07:54:35 AM
That will be the simplest thing to try. The tuning is such that the Load Cap on 75 has little dramatic effect. I mean you can find a peak output, but 1/4 turn in either direction won't make 50 watts out difference. Matter of fact on 40 you can unmesh the cap from 0 up to 20 on the dial and won't lose 50 watts. Running about 75 watts drive and 1200 or so out.

Try swapping both, placing 80m 750 pf on 40m and 40m 500 pf cap on 80.


Well, I can drive it with 200 watts if necessary and try what QE says.

I can swap them easy enough, famous last words.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: AF6LJ on February 02, 2018, 08:31:14 AM
That will be the simplest thing to try. The tuning is such that the Load Cap on 75 has little dramatic effect. I mean you can find a peak output, but 1/4 turn in either direction won't make 50 watts out difference. Matter of fact on 40 you can unmesh the cap from 0 up to 20 on the dial and won't lose 50 watts. Running about 75 watts drive and 1200 or so out.

Try swapping both, placing 80m 750 pf on 40m and 40m 500 pf cap on 80.


Well, I can drive it with 200 watts if necessary and try what QE says.

I can swap them easy enough, famous last words.
Have you checked the input VSWR to make sure the transmitter is seeing a more, or less fifty ohm load??
That will cause the same thing to happen.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: N3QE on February 02, 2018, 08:59:13 AM
It means you aren't driving the amp hard enough when tuning.

Not so sure as he is getting 1200 watts out at current drive level.

Just because he's getting 1200 Watts PEP out under voice modulation, doesn't mean he has really tuned the amp up, especially the load control.

I was ham for 40 years before I really learned the foibles of "tuning up" using voice modulation and how this often results in a non-optimal position on the load knob.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 02, 2018, 09:46:33 AM
It means you aren't driving the amp hard enough when tuning.

Not so sure as he is getting 1200 watts out at current drive level.

Just because he's getting 1200 Watts PEP out under voice modulation, doesn't mean he has really tuned the amp up, especially the load control.

I was ham for 40 years before I really learned the foibles of "tuning up" using voice modulation and how this often results in a non-optimal position on the load knob.


A carrier/steady tone is best for tuning but depending how you use you voice tuning it can be done that way too in a pinch. 


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 02, 2018, 11:11:47 AM
It means you aren't driving the amp hard enough when tuning.

Not so sure as he is getting 1200 watts out at current drive level.

Just because he's getting 1200 Watts PEP out under voice modulation, doesn't mean he has really tuned the amp up, especially the load control.

I was ham for 40 years before I really learned the foibles of "tuning up" using voice modulation and how this often results in a non-optimal position on the load knob.


A carrier/steady tone is best for tuning but depending how you use you voice tuning it can be done that way too in a pinch. 


Actually I'm using a pulser or pecker . Not sure I want to use a higher duty cycle until I figure out a little more about what is going on.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 02, 2018, 11:13:14 AM
That will be the simplest thing to try. The tuning is such that the Load Cap on 75 has little dramatic effect. I mean you can find a peak output, but 1/4 turn in either direction won't make 50 watts out difference. Matter of fact on 40 you can unmesh the cap from 0 up to 20 on the dial and won't lose 50 watts. Running about 75 watts drive and 1200 or so out.

Try swapping both, placing 80m 750 pf on 40m and 40m 500 pf cap on 80.


Well, I can drive it with 200 watts if necessary and try what QE says.

I can swap them easy enough, famous last words.
Have you checked the input VSWR to make sure the transmitter is seeing a more, or less fifty ohm load??
That will cause the same thing to happen.

I will. Just finished putting a floor pan in my 81 F150. Worn out right now.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1QJ on February 02, 2018, 03:19:32 PM
What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.

What capacitor are you talking about?????


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 02, 2018, 04:00:16 PM
What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.

What capacitor are you talking about?????

Its explained in thread


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 02, 2018, 04:51:04 PM
What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.

What capacitor are you talking about?????

Its explained in thread


OK JX .   I swapped the 40 meter 500PF with the 75 meter 750PF and now it loads at about 39 instead of 0  on 40 meters. 75 loads about the same.

You can only creep up drive a few watts at a time because if it is even slightly out of tune something starts chattering. Not sure what that is all about. Seems to be 60 cycle whatever it is.

As long as it is in tune seems to play OK

Incidentally, tuning with a pulser and RTTY tunes at exactly the same place.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1QJ on February 02, 2018, 07:14:25 PM
That amp with a proper load cap does not need any padding on 40 meters.  It obviously has the wrong load cap when someone made the conversion.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 02, 2018, 11:44:03 PM
That amp with a proper load cap does not need any padding on 40 meters.  It obviously has the wrong load cap when someone made the conversion.

I don't doubt it. But, he did the project for free for a friend. Didn't charge for parts, shipping, or anything. Looking a gift horse in the mouth sort of thing I suppose.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1QJ on February 03, 2018, 01:59:17 AM
All right then fine but if you are called upon to make repairs why not do it right?  The correct load cap is about $35.  Cheap is dear.  You get what you pay for. 


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 03, 2018, 05:18:01 AM
All right then fine but if you are called upon to make repairs why not do it right?  The correct load cap is about $35.  Cheap is dear.  You get what you pay for. 

Well, If it can be explained to me why it will play one bit better with the correct loading cap than it will having to add another pad for 40 meters maybe I will.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1BR on February 03, 2018, 06:27:58 AM
All right then fine but if you are called upon to make repairs why not do it right?  The correct load cap is about $35.  Cheap is dear.  You get what you pay for. 

Well, If it can be explained to me why it will play one bit better with the correct loading cap than it will having to add another pad for 40 meters maybe I will.


It will increase the tuning and impedance matching range.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 03, 2018, 01:35:57 PM
All right then fine but if you are called upon to make repairs why not do it right?  The correct load cap is about $35.  Cheap is dear.  You get what you pay for. 

Well, If it can be explained to me why it will play one bit better with the correct loading cap than it will having to add another pad for 40 meters maybe I will.


It will increase the tuning and impedance matching range.


I understand. But, it tunes fine where it is going to be used.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: K9AXN on February 03, 2018, 02:12:04 PM
What is the difference in the tuning range capacity of the stock and what is in the radio?


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 03, 2018, 07:29:15 PM
All right then fine but if you are called upon to make repairs why not do it right?  The correct load cap is about $35.  Cheap is dear.  You get what you pay for. 

Not sure why he needs to buy a cap if after he swapped 40m and 80m caps he said 40 tunes better and 80 about same as before.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1QJ on February 04, 2018, 07:25:30 AM
All right then fine but if you are called upon to make repairs why not do it right?  The correct load cap is about $35.  Cheap is dear.  You get what you pay for. 

Not sure why he needs to buy a cap if after he swapped 40m and 80m caps he said 40 tunes better and 80 about same as before.

Ok then, end of thread problem solved.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: AF6LJ on February 04, 2018, 09:56:52 AM
That will be the simplest thing to try. The tuning is such that the Load Cap on 75 has little dramatic effect. I mean you can find a peak output, but 1/4 turn in either direction won't make 50 watts out difference. Matter of fact on 40 you can unmesh the cap from 0 up to 20 on the dial and won't lose 50 watts. Running about 75 watts drive and 1200 or so out.

Try swapping both, placing 80m 750 pf on 40m and 40m 500 pf cap on 80.


Well, I can drive it with 200 watts if necessary and try what QE says.

I can swap them easy enough, famous last words.
Have you checked the input VSWR to make sure the transmitter is seeing a more, or less fifty ohm load??
That will cause the same thing to happen.

I will. Just finished putting a floor pan in my 81 F150. Worn out right now.
After a job like that I wouldn't want to do much ether. :)


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 04, 2018, 10:19:45 AM
I will. Just finished putting a floor pan in my 81 F150. Worn out right now.
After a job like that I wouldn't want to do much ether. :)

Want to try some fun? Yesterday I changed the fuel pump on a friends Volvo AWD in a parking lot in cold in wind. You have to remove rear seats and access plates under then to get to fuel pump in tank. But, to make matters worse the AWD tank is one piece tank split into two chambers connected with a runner over rear drive shaft and pump and sending unit installs on one side and then you have to fish a remote pickup for pump to other side which also has its own sending unit. (so you get to play in gas with hands in cold too.  Top that off with a bastard 4 inch plastic nut that holds units in that needs a special wrench. Fixing a floorboard by comparison would be a piece of cake. 


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: AF6LJ on February 04, 2018, 10:37:55 AM
I will. Just finished putting a floor pan in my 81 F150. Worn out right now.
After a job like that I wouldn't want to do much ether. :)

Want to try some fun? Yesterday I changed the fuel pump on a friends Volvo AWD in a parking lot in cold in wind. You have to remove rear seats and access plates under then to get to fuel pump in tank. But, to make matters worse the AWD tank is one piece tank split into two chambers connected with a runner over rear drive shaft and pump and sending unit installs on one side and then you have to fish a remote pickup for pump to other side which also has its own sending unit. (so you get to play in gas with hands in cold too.  Top that off with a bastard 4 inch plastic nut that holds units in that needs a special wrench. Fixing a floorboard by comparison would be a piece of cake. 

Glad you got it done, the only car I ever owned was a Mopar (77 dodge charger) Like that Valvo they are a little different. :)


I spent yesterday reassembling the resolution bandwidth / span width switch in my HP-8569B spectrum analyzer.
Broken contacts needed repaired. The rotary switch is made from an etched circuit board with the pattern of the stationary contacts, the rotor is a plastic disk with metal contact fingers hot staked to the plastic rotor. The contacts fall due to fatigue after about 25 years. Lots of small pieces and everything has to be clocked right for both switches to work, they are driven off a common shaft that can be disengaged to allow each control to work independently.
The hard one is next, that being the course and fine IF gain control which shares a shaft with the input atten....

The last time I did one of these (last year) rebuilding the IF gain / input atten. control stack took four tries to get it right ... I didn't have the rotors and their coupling hubs clocked right. This time I shall make lots of witness marks, and take even more photographs.

When I am not rehabbing amateur radio boat anchors, I am rehabbing HP and Tek Iron. :)

Won't be doing ether for a while, I injured my wrist yesterday wrangling an 8569 parts queen...



Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 04, 2018, 10:55:31 AM

When I am not rehabbing amateur radio boat anchors, I am rehabbing HP and Tek Iron. :)


I used to repair rigs for others some times ago but do not anymore. I sometimes struggle to keep up with own needs. (motivation)


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: AF6LJ on February 04, 2018, 11:34:36 AM

When I am not rehabbing amateur radio boat anchors, I am rehabbing HP and Tek Iron. :)


I used to repair rigs for others some times ago but do not anymore. I sometimes struggle to keep up with own needs. (motivation)
I understand; sometimes a long walk in the woods is a better alternative.
I still enjoy it a lot though, been into electronics as a hobby since about 1968, a job from 1972-1994...
Always a hobby and my first love.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: K9AXN on February 04, 2018, 11:52:43 AM

When I am not rehabbing amateur radio boat anchors, I am rehabbing HP and Tek Iron. :)


I used to repair rigs for others some times ago but do not anymore. I sometimes struggle to keep up with own needs. (motivation)
I understand; sometimes a long walk in the woods is a better alternative.
I still enjoy it a lot though, been into electronics as a hobby since about 1968, a job from 1972-1994...
Always a hobby and my first love.

Sue,

The HP 8568B is one of the most used instruments on the bench here.  A real tribute to a time when excellence was a way of life.

Regards Jim


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: AF6LJ on February 05, 2018, 11:49:06 AM

When I am not rehabbing amateur radio boat anchors, I am rehabbing HP and Tek Iron. :)


I used to repair rigs for others some times ago but do not anymore. I sometimes struggle to keep up with own needs. (motivation)
I understand; sometimes a long walk in the woods is a better alternative.
I still enjoy it a lot though, been into electronics as a hobby since about 1968, a job from 1972-1994...
Always a hobby and my first love.

Sue,

The HP 8568B is one of the most used instruments on the bench here.  A real tribute to a time when excellence was a way of life.

Regards Jim
Indeed...
To many who pride themselves in repairing test gear this falls in the intimidating category.

65 LBS of love. :)


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 05, 2018, 01:50:48 PM
I will. Just finished putting a floor pan in my 81 F150. Worn out right now.
After a job like that I wouldn't want to do much ether. :)

Want to try some fun? Yesterday I changed the fuel pump on a friends Volvo AWD in a parking lot in cold in wind. You have to remove rear seats and access plates under then to get to fuel pump in tank. But, to make matters worse the AWD tank is one piece tank split into two chambers connected with a runner over rear drive shaft and pump and sending unit installs on one side and then you have to fish a remote pickup for pump to other side which also has its own sending unit. (so you get to play in gas with hands in cold too.  Top that off with a bastard 4 inch plastic nut that holds units in that needs a special wrench. Fixing a floorboard by comparison would be a piece of cake. 


My own stupidity I admit. But, I frost bit my thumb and index finger cutting out the old pan with a die grinder. Had a pair of gloves on the bench. Sore as the dickens for a couple of days. So, not so much sympathy for your cold hands.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 06, 2018, 05:05:48 AM
My own stupidity I admit. But, I frost bit my thumb and index finger cutting out the old pan with a die grinder. Had a pair of gloves on the bench. Sore as the dickens for a couple of days. So, not so much sympathy for your cold hands.

I have repaired several floorboards in my life time. I do not use metal though. I remove loose rusted metal and then I sandwich the damage area between fiberglass mats. (mat has random weave pattern vs fiber glass cloth and it molds and bonds better for this kind of repair)  If a support is needed due to a large hole to can use a board covered with a garbage bag to support it as it can be removed when it sets up. I also drill 3/8 inch holes through good metal around repaired area so that mat coated with fiberglass resin can bond through holes and make reliable patch. You can use fiberglass resin with a cheap throw away paint brush to apply it or fiber glass gel wit a nylon putty knife that it it easy to remove hardened gel from.When finished I coat underside of repair with spray on undercoat.  Never had to redo a repair and patch itself is rust proof.   


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 06, 2018, 10:13:08 AM
My own stupidity I admit. But, I frost bit my thumb and index finger cutting out the old pan with a die grinder. Had a pair of gloves on the bench. Sore as the dickens for a couple of days. So, not so much sympathy for your cold hands.

I have repaired several floorboards in my life time. I do not use metal though. I remove loose rusted metal and then I sandwich the damage area between fiberglass mats. (mat has random weave pattern vs fiber glass cloth and it molds and bonds better for this kind of repair)  If a support is needed due to a large hole to can use a board covered with a garbage bag to support it as it can be removed when it sets up. I also drill 3/8 inch holes through good metal around repaired area so that mat coated with fiberglass resin can bond through holes and make reliable patch. You can use fiberglass resin with a cheap throw away paint brush to apply it or fiber glass gel wit a nylon putty knife that it it easy to remove hardened gel from.When finished I coat underside of repair with spray on undercoat.  Never had to redo a repair and patch itself is rust proof.  


Yeah, I thought about that. I have a roll of 1708 and maybe a gallon of West Systems 105 left over from rebuilding a 1960 Glasspar G3 . Plus a big bag of cabosil.

But, I just bought a pan from LMC and went that way.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KH2BR on February 11, 2018, 10:59:34 PM
When we get older, we take shortcuts and at times miss simple things while working/ troubleshooting circuits.
One big one that got me a couple of times is that I could not measure voltage in a circuit, and started tracing backwards and found I did not have power hooked up to the circuit even though the power supply was turned on.
Another problem is changing out parts and finding out the load was wrong.
I just bet a dummy load was not used to isolate the antenna system. I also expect the use of a  antenna analyzer was overlooked.
Changing out parts needlessly is a bummer if you overlook the obvious. 


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 13, 2018, 03:38:15 AM
When we get older, we take shortcuts and at times miss simple things while working/ troubleshooting circuits.
One big one that got me a couple of times is that I could not measure voltage in a circuit, and started tracing backwards and found I did not have power hooked up to the circuit even though the power supply was turned on.
Another problem is changing out parts and finding out the load was wrong.
I just bet a dummy load was not used to isolate the antenna system. I also expect the use of a  antenna analyzer was overlooked.
Changing out parts needlessly is a bummer if you overlook the obvious. 

It sure is good you checked in. None of us would have ever thought of that.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1QJ on February 13, 2018, 05:18:40 AM
I think all hams should read a generic "troubleshooting" book.  Better yet, if you are working on amplifiers perhaps reading a book on basic "amplifier troubleshooting" is more appropriate.  I honestly don't suspect that we should have to ask the question to someone seeking the help of the group if he has his amp plugged in or if he has his coax cables switched or even if he has a bad jumper coax cable.  Basic bare bones troubleshooting should go a long way and catch 50% of the simple fixes that come down the pike. 

I would also suggest in the case where a ham will be doing several upgrades to a vintage amplifier like an SB-220 or an SB-200 or whatever, that if they are not seasoned at doing such work on amps that they only complete on upgrade at a time and after each one go back and make sure that the mod they just did works and the amp functions properly before moving on to the next one.

All too many times someone will come along and says, I installed all the Harbach mods on my amp and now the amp does not show any HV and the amp will not keep into transmit and there is no reading on the HV meter  and when I switch to grid the meter goes negative and the meter lights are very dim.  That would seem to indicate that just about every mod done has a problem with it.  This person will spend a month getting his amp straightened himself, even if he does.  One mod at a time and check progress after each one.

Because I have been doing these mods for 40+ years I can go through all of them without instructions and complete them all at one time and when finished turn the amp on and go.  I could not do that in the beginning but at some point I was able to.  Do one at a time and make sure you are good before you move on.



Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W8JX on February 13, 2018, 05:46:36 AM

One mod at a time and check progress after each one. 

Do one at a time and make sure you are good before you move on.


Very good advise


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 13, 2018, 01:43:00 PM
With this amp the guy took a no tune amp which basically has a C1 and C2 for each band padded appropriately for space considerations and converted it to a standard tune. It really didn't matter where the 500 and 750 were for 75 meters because they were added. It worked better with the 750 on the 40 meter band switch position instead of the other way around.

Now, could you change it to an air variable with more range ?  Of course.  But, it is not my amp, I won't charge anything , and it loads pretty much in the middle of the range on 40 and 75 didn't change to amount to anything.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W1BR on February 13, 2018, 01:56:17 PM
Without knowing the grid current readings  and just how heavily loaded the amp really is this is all idle speculation...


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: KM4AH on February 13, 2018, 03:33:55 PM
Without knowing the grid current readings  and just how heavily loaded the amp really is this is all idle speculation...


The amp would not tune to peak output with an appropriate conservative drive for 2 3-500Z's  without running out of the range of C2 .

If you can't tune to peak output I'm not sure how you know where to tweak the load for grid current.


Title: RE: Power out increases until the load cap is 100 % meshed
Post by: W4BOH on February 24, 2018, 04:32:42 PM
What is Z of antenna?
If it's quite low, you'll need more load cap.
What does the amp do into a dummy load?
Low Z loads take a LOT of loading cap to match properly.
Wilson