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Author Topic: Heath kit SB-200 bleeder resistor temperatures  (Read 8448 times)
K6BRN
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« Reply #30 on: March 14, 2018, 09:22:12 PM »

Bryan:

It's all relative.

The SB-200 was another fun project - could I bring it back from the dead? (I've rebuilt quite a few radios, both tube and solid state over the years - but never for profit).  I did not want to kludge together a board and parts for the SB-200 power supply and wanted to concentrate on other areas.  I have limited free time and pick and choose what I want to work on for enjoyment.  The cost of the Harbach kits were just not very significant in that equation.

Had I wanted to, there are numerous surplus supply stores in L.A. that I drop in to, and the monthly TRW ham swap meet almost next door that I often buy parts for projects at.  So I could have reduced cost.  But the ready to go Harbach kits were too also too tempting.

Brian - K6BRN
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WA7PRC
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« Reply #31 on: March 14, 2018, 09:34:30 PM »

Had I wanted to, there are numerous surplus supply stores in L.A. that I drop in to, and the monthly TRW ham swap meet almost next door that I often buy parts for projects at.  So I could have reduced cost.  But the ready to go Harbach kits were too also too tempting.
Lucky you. In my area (near Seattle), we used to have several ham radio and electronics outlets. Before the late Alan Harbach started his business, that's where I found parts. Its mostly gone, now. Thankfully, there're many online sources. MOST of Jeff Weinberg's offerings are OK, if a bit (or a lot) overpriced.
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W1QJ
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« Reply #32 on: March 15, 2018, 05:45:50 AM »

Had I wanted to, there are numerous surplus supply stores in L.A. that I drop in to, and the monthly TRW ham swap meet almost next door that I often buy parts for projects at.  So I could have reduced cost.  But the ready to go Harbach kits were too also too tempting.
Lucky you. In my area (near Seattle), we used to have several ham radio and electronics outlets. Before the late Alan Harbach started his business, that's where I found parts. Its mostly gone, now. Thankfully, there're many online sources. MOST of Jeff Weinberg's offerings are OK, if a bit (or a lot) overpriced.

In defense of Jeff and his prices, this type of thing is seen throughout marketing.  All one has to do is look at a simple thing like Watermelon.  A HUGE watermelon could sell for as little as $4.00 whereas a 1/2lb of pre chunked and wrapped watermelon can cost you $5.00.  Same thing with vegetables.   You can buy a mixture of vegetables in a big say 2 pounds and it will cost you several times what you could have bought individual entire bunches and cut it yourself.  And the list goes on.

Jeff at Harbach is basically selling simplicity and THAT is what you are paying for.  There is no guess work.  You buy the kit and you assemble it and it works.  Like in the grocery store, you are paying for someone to chunk up that watermelon and that someone to clean and chop up the vegetables.  Jeff is getting paid to assemble a kit with the correct parts so it makes it easy for you. 

The next choice that can save you some money is to buy the W7RY variety.   There you buy the board and outsource your own parts.  It is nice that W7RY gives you a "ready made" order form for all parts thru Mouser.  Just submit it via email.  Most of the time the parts are in stock.

The last way is to entirely home brew your own circuits. Certainly not as neat or quick as the other two methods.   
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WA1RNE
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« Reply #33 on: March 15, 2018, 09:38:57 AM »


 If I were rebuilding my SB-200 I'd consider the following:


 1) At a nominal line of 120 Volts AC, the DC output is ~2400 Vdc no load.  At high line of +10% there will be ~ 2640 Volts DC output no load, which is approximately 440 Vdc across each of the 6 capacitors IF they balance evenly - or about 2.3% margin at worst case high line.  That's a little dangerous. Even at 5% high line or 2518 Vdc there's less than 7% margin for the capacitor voltage rating.  yes there are surge current ratings but that's not wise to rely upon for continuous duty.

  I would upgrade the capacitors to a 150 uF, 600 Volt rated unit which provides a 34% capacitor voltage margin at nominal line and ~28% at +10% high line.

 https://www.mouser.com/ds/2/293/e-lgn-880025.pdf


 2) The present rule of thumb for balancing resistors - short of calculating capacitor leakage current is:  R (megohms) = 10/C

   Therefore an 80K or 82K balancing resistor is called for, which at high line dissipates 2.4 watts, so use a 5 watt rated device or better.


 ...WA1RNE
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WA7PRC
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« Reply #34 on: March 15, 2018, 11:02:06 AM »


 If I were rebuilding my SB-200 I'd consider the following:


 1) At a nominal line of 120 Volts AC, the DC output is ~2400 Vdc no load.  At high line of +10% there will be ~ 2640 Volts DC output no load, which is approximately 440 Vdc across each of the 6 capacitors IF they balance evenly - or about 2.3% margin at worst case high line.  That's a little dangerous. Even at 5% high line or 2518 Vdc there's less than 7% margin for the capacitor voltage rating.  yes there are surge current ratings but that's not wise to rely upon for continuous duty.

  I would upgrade the capacitors to a 150 uF, 600 Volt rated unit which provides a 34% capacitor voltage margin at nominal line and ~28% at +10% high line.

 http://www.mouser.com/ds/2/293/e-lgn-880025.pdf

 2) The present rule of thumb for balancing resistors - short of calculating capacitor leakage current is:  R (megohms) = 10/C

   Therefore an 80K or 82K balancing resistor is called for, which at high line dissipates 2.4 watts, so use a 5 watt rated device or better.

 ...WA1RNE
From that datasheet, 150uF/600V Nichicon #LGN2X151MELC40 (Mouser #647-LGN2X151MELC40) = $8.51 ea (6 ea = 51.06).
Even with buying W8CQ's bare $25 PCB, that's still less than $90 for the easy way.
Cheepest would be to reuse your OE board or, if not usable, buy one. A certain fellow in CT who does a lot of HK amplifier work probably has 'em for cheap. I've already identified suitable parts for the rest. I haven't bothered to create a Mouser BOM like Jim W7RY does.
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KM1H
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« Reply #35 on: March 15, 2018, 12:33:47 PM »

Quote
1) At a nominal line of 120 Volts AC, the DC output is ~2400 Vdc no load.  At high line of +10% there will be ~ 2640 Volts DC output no load, which is approximately 440 Vdc across each of the 6 capacitors IF they balance evenly - or about 2.3% margin at worst case high line.  That's a little dangerous. Even at 5% high line or 2518 Vdc there's less than 7% margin for the capacitor voltage rating.  yes there are surge current ratings but that's not wise to rely upon for continuous duty.

Yet, with thousands of SB-200 PS caps not failing from overvoltage, but rather from excessive leakage due to age, why bother with 600V caps.

The Harbach kit uses 450V caps for decades now and are fine.

If really worried than go to a 500V cap which are more readily available and lower cost.

Carl
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K6BRN
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« Reply #36 on: March 15, 2018, 11:36:06 PM »

Thanks, Carl.

WA1RNE really had me going.  I was just about to wrap my SB-200 in blankets,  in case it blows up.  I think I'll just put it back on the shelf, with its slightly overpriced but nicely built Harbach mods. 
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WA7PRC
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« Reply #37 on: March 16, 2018, 02:02:54 PM »

I think I'll just put it back on the shelf, with its slightly overpriced but nicely built Harbach mods. 
Even with a new PCB, more than twice the cost is a bit more than "slightly" overpriced:
Time to rebuild or replace the power supply. I used the Harbach kit and they work great.
If you don't need a PCB, the cost is a LOT more. Digi-Key has:

Capacitors C4-C9: CDE capacitors pn 381LX151M450H032 (150uF/450V) as stk no 338-3698-ND for $3.96 each.
Resistors R5-R11: TE Connectivity pn ROX3SJ100K resistors (100K/3W) as stk no A106004CT-ND for $0.46 each.
Diodes D1-D16 (1N2071/1N4005/1N5397) use 1N5408: Diodes Incorporated pn 1N5408-T (3A/1KV) as stk no 1N5408DICT-ND for $0.39 each.

Added up, it's:
$3.96 x 6 =  $23.76
$0.46 x 6 =  $ 2.76
$0.35 x 16 = $ 6.24

Assuming R14 (3.6K/1%/0.5W) and R15 are needed, those can be added:
Ohmite pn WHE1R0FET, (1 Ohm/1%/5W), stk no WHE1R0FETCT-ND for $1.50 each
Vishay/BC Components pn MBB02070C3601FCT00 (3600 Ohm/1%/0.6W), stk no BC4467CT-ND for $0.29 each.

Total = $34.55
OTOH, the Harbach pn PM-200 runs $95.00.

≥ 3A meter protection diode(s) such as 1N540x or 6A10 should be added between -B & chassis. W8JI s'plains it here: http://www.w8ji.com/metering_amplifier.htm

Better HV meter multiplier resistors (R3 = 3 x 4M7/1W) should be used. Digi-Key has Vishay/BC Components pn VR68000004704JAC00 stk no VR68J4.7MCT-ND for $0.78 each. Unlike OE carbon composition resistors, these are rated to withstand the HV, and won't soar in value.
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K6BRN
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« Reply #38 on: March 16, 2018, 05:08:06 PM »

Bryan:

I understand your perspective, but it's not one I share.

I'm very happy that the folks over at Harbach are offering a high quality set of parts and kits I can build, install and operate with some satisfaction and no worry.  Never heard any complaints from hams who use them.  I pay for the quality, the convenience and proven track record of performance - that equation closes for me.

Same with Alan at Wavenode.  His products are great and he himself is a stellar engineer and fun to talk to.

Same with Danny at Myantennas.  See Alan above.  His products just work.  I like that.

The amateur radio market is tiny, with little opportunity for large financial gain, and I appreciate small companies that bring quality, well thought out products to market.  Note that MFJ is NOT on my "Happy List".  Too many problematic offerings.

I do like scrounging, as many of us do, and custom design and build, in select areas, but its not a necessity for me, and a lot of other hams.  Or Elecraft, Flexradio, Telepost, etc., etc. would have gone under long ago. 



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WA7PRC
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« Reply #39 on: March 16, 2018, 06:44:49 PM »

I understand your perspective, but it's not one I share.
You disagree that there's not a yuuge difference in cost?
[bigly snip]
Total = $34.55
OTOH, the Harbach pn PM-200 runs $95.00.
And, at $95, it comes unassembled.
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K6BRN
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« Reply #40 on: March 16, 2018, 11:05:41 PM »

No.  I disagree that the cost difference is significant, given the value received.  To me and many others.
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WA7PRC
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« Reply #41 on: March 16, 2018, 11:13:39 PM »

No.  I disagree that the cost difference is significant, given the value received.  To me and many others.
Similar parts, significant cost difference.
It didn't take much time to locate parts at a fraction of the cost.
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K6BRN
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« Reply #42 on: March 17, 2018, 12:18:42 AM »

Hmmm.  Let me understand.  You are irate because I did not rebuild MY SB-200 with the cheapest possible parts, in the cheapest possible way, knowing that I don't enjoy doing that, and I was rebuilding it for enjoyment, and like shiny new pre-made parts kits, and if YOU were to rebuild an SB-200, which you don't have, you'd use the cheap parts you have not bought, but claim to have found, but have no use for, because you don't have a broken SB-200?

I see.  Why do you care?  I'm happy.  Harbach is happy.  My SB-200 is happy.  The U.S economy is happy.  And my wallet didn't even notice.

On a more positive note... here is the cleanest SB-200 rebuild I've EVER seen, on ebay right now.  The insides are almost beautiful in execution.  Too bad the voltage doubler compartment is not shown.

https://www.ebay.com/itm/Professionally-Rebuilt-Heathkit-SB-200-Linear-Amplifier-with-Brand-N-E-W-Tubes-/273096407835
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