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Author Topic: Heathkit HB-200 renovation  (Read 51372 times)
W8JI
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« Reply #15 on: September 16, 2011, 10:06:14 AM »

You don't ever really want to use a MOF (metal oxide film) or a modern carbon for suppression.

The proper resistors are either an Ohmmite OX or OY series metal COMPOSITION...... or a special order Allen-Bradley carbon composition. Many carbons look exactly like a carbon comp, but are carbon film.
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K4TLJ
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« Reply #16 on: September 16, 2011, 11:18:50 AM »

I bought a SB200 a couple of years ago that had been unused for many years. It worked as received;
But I became leery of the 40 year old filter caps and replaced all of them with snap in types. Holes were drilled in the PC board for the leads. I replaced the bleeder resistors as well.
I also replaced the metering resistors, added a glitch resistor and replaced the electrolytic in the bias circuit.
After acquiring a 'modern' solid state transceiver, I added a soft key circuit of my own design that uses a FOD852 optoisolator.
I don't think a soft start is necessary.
The amp output is 600 watts on most bands with a bit less on ten.
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5B4AET
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« Reply #17 on: September 16, 2011, 12:48:14 PM »

The amp is in the original state (no mods) exept the new power supply.........wirred it for 240v.
Made all possible checks - valves unpluged and powered it up few hours ago!!!
And YES............2250volts!!! No suspicious sounds or smells  Grin
 
Is the 2.2kv considered good voltage bearing in mind that there is NO load yet ?

http://i1099.photobucket.com/albums/g399/5B4AET/P1020427.jpg
http://i1099.photobucket.com/albums/g399/5B4AET/P1020438.jpg
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KA5N
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« Reply #18 on: September 16, 2011, 03:31:52 PM »

Re the soft start from Harbach if you use it for 220 Volts, the resistors are 20 Ohms and for 115 volts 10 Ohms. 
You must have some kind of soft key for use with modern transceivers.  The soft key from Harbach works just fine.  An external unit from Ameritron is fine as is the
one put out by the Heath Store. 
Your HV should be 2400 volts with no load.  With low line voltage it may be lower.
With the new power supply board (with new meter resistors) it should be OK.
However,,,  have you checked to make sure that all the resistors on the power supply board are the correct values???  The previous owner selected parts, plugged
them into holes and soldered them.  He could have made a mistake!!!
Take nothing for granted.
Allen
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5B4AET
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« Reply #19 on: September 17, 2011, 03:09:14 PM »

Checked the Harbach power supply parts and appear to be placed in the correcet palces. AC supply is 240v, still the meter shows 2200volts. Noticed that the meter needle is not going back to zero always and also it gives 2.2kv and other times 2.25kv. Could this mean that there is a meter problem? I use the calibration but does not fix the variation between 2.2kv and 2.25kv, can it be fixed? The Harbach ps panel is not the one advertised on their site now. The caps are attached with screws. Could this be the reason for the lower voltage? Any ideas any one ?

Already replaced the antenna relay and the output plug, few caps and resistors. I will replace/remake the anode parasitic filter and Im still working on replacing the fan with a modern computer type one. Probably will be quiter and more efficient.

Soft key kit arrived and will connect this one (throw away the old one).

 

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KA5N
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« Reply #20 on: September 17, 2011, 03:50:14 PM »

Checked the Harbach power supply parts and appear to be placed in the correcet palces. AC supply is 240v, still the meter shows 2200volts. Noticed that the meter needle is not going back to zero always and also it gives 2.2kv and other times 2.25kv. Could this mean that there is a meter problem? I use the calibration but does not fix the variation between 2.2kv and 2.25kv, can it be fixed? The Harbach ps panel is not the one advertised on their site now. The caps are attached with screws. Could this be the reason for the lower voltage? Any ideas any one ?

Already replaced the antenna relay and the output plug, few caps and resistors. I will replace/remake the anode parasitic filter and Im still working on replacing the fan with a modern computer type one. Probably will be quiter and more efficient.

Soft key kit arrived and will connect this one (throw away the old one).

I wouldn't worry about the meter circuit too much.  The slightly low HV won't make much difference.
The screw mounts on the capacitors is because the kit for the power supply is an early type.
Harbach says they can't get that style capacitor and went to a snap in type.  One style works as
well as the other.  With the soft key installed you should be close to check out of the amp.

Good deal.
73  Allen
 


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W8FU
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« Reply #21 on: September 19, 2011, 03:10:03 PM »

I would leave the fan alone.  If it is working I see no reason to change it. If your amplifier has the Harbach power supply board  all of the components should be new style and should be good unless the previous owner did something bad, which would probably be evident upon inspection.  I wouldn't worry too much about replacing the soft start as there seems to be considerable opinion that is not needed in this amplifier. However, the soft key is definitely needed as others have mentioned. If you carefully inspect  how it was wired and there appears to be no error then I see no reason to replace it.   Unless the relay is not functioning I would not bother replacing it. The soft key mod takes care of the high-voltage keying problem. 2 or 3 years ago I installed all of the Harbach mods in my SB 200  and was very pleased with the result. Although I did buy the fan I have not installed it because the old one is working well and is quiet.  I will keep the new fan as a possible replacement should that be needed later.  As Tom mentioned, it's probably not a good idea to change things simply for the purpose of changing.  I suppose it would do no harm to check some of the resistors for value changes and replace any that have moved out of tolerance. But beyond that, I would simply enjoy the amplifier. It should serve you well.
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K8AXW
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« Reply #22 on: September 20, 2011, 09:34:50 AM »

Panicos: I wouldn't go to the extra work of replacing the SB-200 fan if it is running good...no bearing noise.  I would put a drop of light oil into each bearing though.  You will have to probably remove the fan to do that but replace it.... no.  Most SB-200 fans continue to cool the tubes adequately.

The 200V differential is nothing to concern yourself about.  I'd go ahead and try the amp.  The lower voltage could be the meter dropping resistors or even the meter itself. 

Crank it up and see what power you get out of it.  Note the HV drop.  Sounds like you're good to go.
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A Pessimist is Never Disappointed!
5B4AET
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« Reply #23 on: September 20, 2011, 10:09:31 AM »

So ...... replaced the antenna relay and added the soft key.
Pluged the tubes and swiched it on.
Tubes light up (heaters) HV ok 2200 volts but NO Grid and NO Plate current (meter dont move).

Here we go again !!!!

Help... Huh...what should i check ?

Panicos
 
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5B4AET
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« Reply #24 on: September 20, 2011, 11:16:34 AM »

Read the manual again and did some more research and found same topic:

KA5N said : "The idling PLATE current should be 90 ma, not the grid current.  With no input, the grid current should be almost zero"

So now I narrowed the problem to No plate current.
Im sure I checked and found the two resistors very close to the 33 ohm.
 Angry Will have to go and do some more checking !!



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KA5N
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« Reply #25 on: September 20, 2011, 11:42:44 AM »

If the bias voltage is too high when keyed then there will be no plate current.
When keyed the bias should be about - 2 volts and unkeyed it will rise to
about -120 volts to -130 volts.  The relay and the relay dropping resistor are
part of the bias circuit.  If you installed a new relay and you got it from Harbach then the resistor is a different value than the original and things won't work without the relay and the resistor matching.  The original resistor was 2K 7 Watts the new one is 4.7K 7 watts  If you got the relay from somewhere else then the resistor will probably be different from the original or the Harbach.  Of course something else could be amiss in this circuit.
The plate choke could also be bad and the plate voltage won't reach the plates.  Something else could be wired wrong or some connection missing.
Hard to say, but since you have been into the relay/bias circuit I would start checking there.
When working on electronic equipment it is much better to tackle one thing at a time instead
of wholescale replacement of parts.  As you can see you can't tell whether a problem is an
old one or a new problem you caused.
Good Luck
Allen
« Last Edit: September 20, 2011, 11:52:01 AM by KA5N » Logged
N4NYY
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Posts: 5224




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« Reply #26 on: September 20, 2011, 12:00:53 PM »

Quote
I need to work on that, but I've been waiting to get an SB200 in.

I can send you mine for testing after I work on it. It need major cleaning. And the only mods I do are tech service bulletins from the manufacturer. Granted, I do not know if there are any mods on mine. But judging on age and smell, it was from the pre-internet days, which would keep the hacking to a minimum.
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5B4AET
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« Reply #27 on: September 21, 2011, 01:27:55 PM »


This is one of those times that you hope to find something wrong - correct it and at last its WORKING!!!
Well, in my case I did not "manage"  Undecided to find the anything wrong.

The facts:

1. R18 on relay is replaced to 4.7km
2. Meter swich is correctly connected
3. All resistors either ok or replaced
4. Anode connectivity to HV checked - voltage not mesured
5. SB-200 meter shows 2.2kv
6. Grid voltage found 26.5v
7. Still no plate current.

Is the grid voltage (26.5v) normal? If yes then should I assume that the amp came with two dead 572b?

Any more ideas ?

Panicos
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KA5N
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« Reply #28 on: September 21, 2011, 01:48:57 PM »

Is the grid voltage (26.5v) normal? If yes then should I assume that the amp came with two dead 572b?
Any more ideas ?
Panicos

Grid voltage of -26.5V is ok when not keyed.  The grid voltage when keyed (relay
in transmit mode) should be -2v or the tubes will not conduct when a signal is
applied.  So is the relay clicking?  What is the grid voltage when the relay clicks in?
I suppose both tubes could be bad, but usually even a bad tube will show a little
plate current when the circuit is keyed.  But you have got to have the grid voltage
at a correctl level to get the correct plate current.

Allen
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5B4AET
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« Reply #29 on: September 21, 2011, 02:26:24 PM »

Allen....
thanks for your help!!

I havent connected the rig on yet since there is no plate current reading so I dont know the voltage on transmit and if the relay is clicking.
But since the grid voltage (26.5v) is ok on idle, according to the SB-200 manual there should be a 90ma plate current. So my idea is to get this 90ma on the meter before applying any input power.
Could the meter work ok on voltage but not on current? (wiring checked and is correct) And by the way, power supply electr. caps do get warm after 5 - 10 mins. Is this a sign that there is a plate current or could it mean that the ps is not operating correctly?

Panicos

   

[/quote]
Grid voltage of -26.5V is ok when not keyed.  The grid voltage when keyed (relay
in transmit mode) should be -2v or the tubes will not conduct when a signal is
applied.  So is the relay clicking?  What is the grid voltage when the relay clicks in?
I suppose both tubes could be bad, but usually even a bad tube will show a little
plate current when the circuit is keyed.  But you have got to have the grid voltage
at a correctl level to get the correct plate current.

Allen
[/quote]
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