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Blue Hawaii BJT Build thread


joehpj

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  • 4 months later...

I am finally getting around to this build and had a couple questions about the BOM.

 - The 470R resistor in the BOM is 2W.  Is 1/2W OK?  2W won't fit in holes

 - The 100V diode in the BOM is 5W.  That also will not fit in the holes.  Can I use a 1W diode?  

 -  The BOM lists 2 R2k Trim pots, but pair of boards requires 4.  Is that right?    

Edited by Blueman2
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470R was connected direct to the tube structure so it will get hot easily. You can either lift the resistor or use higher power rating ones.

I forgot why I used 5w. and the number of the trim pots. Please follow the silk screen. I will check the BOM later.

 

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470R resistor, isn’t that the grid resistor? If so, is 2 W really necessary? From simulation I get some 2 – 4 mA through  the resistor. In my Grounded Grid with mostly surface mounted devices I use 0805 chip as 470R - 1/8W and they seem to work.

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My experience echo with JoaMat's. Kevin's original Blue Hawaii schematic on Headwize stated 1/4 W resistor is fine with this part. I've used 1/2W 470R resistor in this position on my Blue Hawaii (FET version) for the past few years with no issue.

This is the 100V zener I use on my Blue Hawaii. https://www.mouser.com/ProductDetail/78-BZX85B100-TAP 1.3W rated and works fine. 

 

Edited by mwl168
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I found the answer to my question on GG thread because I had 1/2w resistor and then I changed to 2w for this:

On ‎19‎/‎03‎/‎2017 at 7:01 AM, joehpj said:
On ‎18‎/‎03‎/‎2017 at 9:27 PM, jose said:

Please, What kind of resistor do you use for grid?

I used a KOA metal film (10K, 1 / 2w) but I can see that you used a different type (Carbon maybe???) . I'm in time to be able to change them and I would like be sure before pluging my GG.

If you use my BOM, that would be 10k/.5w as you used. A experienced builder told me grid resistors were super hot because it was connected to the internal structure of tube. I later changed to 470R/3w, just because I have them in stock.  KG said the value doesn't really matter. T2 used 20k. BH used 470R.

Now, what else? if 1/4w is fine... 

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Thanks, everyone!  I put in 1/2W for the 470R and will test the temperature once I get it running.  And I have handfuls of the 1.3W 100V zener, so glad that will work!  All I need to do is order another couple R2k trimpots.  

mwl168, earlier in your build notes, you mentioned: 

Quote

 The 360R KSA1156 emitter resistors set the current to the 3rd stage. The original BH ran 10mA, the 360R resistors in current version set it to be about 3mA to reduce heat.  If you decide to raise the current, make sure you compensate for it by lower initial value in offset adjustment.

Does the 3ma vs 10ma have much sonic impact?  I am going to be driving a set of -007s and they tend to want <JeremyClarkson>More Power!</JeremyClarkson>.   Just curious if this makes any real difference beyond heating up the room more.  

Edited by Blueman2
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6 hours ago, Blueman2 said:

Does the 3ma vs 10ma have much sonic impact?  I am going to be driving a set of -007s and they tend to want <JeremyClarkson>More Power!</JeremyClarkson>.   Just curious if this makes any real difference beyond heating up the room more.  

I started out using 150R instead of the 360R for the KSA1156 emitter resistors to set the current to the 3rd stage and never tried the 360R on my build so cannot comment on the sonic difference. I believe the original BH ran 10mA current to the 3rd stage and was later reduced to 3mA to reduce the heat. I decided to go half way based on a similar adjustment I made on my KGSSHV and in that case I like the sound of the raised current much better. 

Do note though that if you raise the current to the third stage you need to make compensation to the offset-setting resistor and trim pot. I would suggest using 1.2K or so trim pot instead of the 2K and preset it to 600R or so. You'll need to measure and do some calculation so you do not have too much voltage drop across the offset trim pot. 

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2 hours ago, joehpj said:

updated the BOM. 2K trimpot changed to 4pcs. 470R changed to 1/2w. 5W zener simply because it's slightly cheaper than 1/3w :D.

Thanks, joehpj!  Only issue with 5W zener is that the leads to not fit in the board I had.  I could have drilled it, but decided path of least resistance was to use a 1.3W version I had on hand.  One can never have enough zener diodes!!

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1 hour ago, Blueman2 said:

So is this BH to be run at 20ma, so that the R50 test resistor will read 1V? Assuming I have really good heat sinks, of course.  

I think you meant the "50R" resistor in series with the 50R trim pot in the plate CCA. If so, yes, adjust the 50R trim pot so there is 1V drop across the 50R resistor will set the CCS current at 20mA. I run mine between 18mA - 20mA at different time. I know there are others that run as high as 25mA. Make sure you have plenty of heatsink - the BH runs much hotter than the Grounded Grid does. 

Edited by mwl168
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I need some advice on modifying a GRHV board that does not have the delay circuit (no CPC1117N).  I want to add the delay circuit to it for use with the BH BJT I am building. 

It appears from looking at the attached diagram (for the board with the CPC1117N) that the delay circuit effectively puts a 600R resistor across the 12V (or 10V on my older board) zener D1 to shut down high voltage output.  Is that all that is needed to shut the board down? 

I plan to make an off board circuit using a 600R resistor on the output of a CPC1117N, and tie that output across the D1 using about 6" of 20awg wire.  The CPC will be driven by a timer circuit I got off of eBay.   It seems pretty straightforward, but I wanted to see if my thinking was valid.  

goldenreferencehvsic.PDF

Edited by Blueman2
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35 minutes ago, Blueman2 said:

I need some advice on modifying an early GRHV board that does not have the delay circuit (no CPC1117N).  I want to add the delay circuit to it for use with the BH BJT I am building. 

It appears from looking at the attached diagram (for the board with the CPC1117N) that the delay circuit effectively puts a 600R resistor across the 12V (or 10V on my older board) zener D1 to shut down high voltage output.  Is that all that is needed to shut the board down? 

I plan to make an off board circuit using a 600R resistor on the output of a CPC1117N, and tie that output across the D1 using about 6" of 20awg wire.  The CPC will be driven by a timer circuit I got off of eBay.   It seems pretty straightforward, but I wanted to see if my thinking was valid.  

goldenreferencehvsic.PDF

Yep - you might mount D1 on the separate board and use it's legs for connection to the main pcb

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Thanks, sorenb!  I also noticed 2 part value changes.  Older board without the relay used D1 zener of 10V, whereas new board is 12V.  Also, old board used R6 value of 30K, whereas new board uses 50K.  I am guessing I am fine using the 12V zener and 50K resistor on the old board?  Since nothing else changed, I assume it was just some tweaking done during board revs.  

Oh, and brilliant idea using D1 legs to mount the tiny board on the main board.  I am going to do just that!  Plenty of vertical room since the Caps are so high.  

Edited by Blueman2
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Sorry for the number of questions here, but I was researching soft on for the BH and wanted to confirm my understanding.  I plan to use a 45 second delay  between

  •  the time the 6.3V filament and +/-15V LV start
  • to the time the  +/-400V starts. 

Based on my experience with the SRX-Plus, this seems reasonable time to allow the voltages to settle a bit.  But I also notice on the SRX that the offset spikes to around 300V when turning off as well.  Not a problem since the spike is equal across O+ and O-, but still it is a spike.  I was considering a soft-off option, which the CPC1117N opto relay should allow.  I had 2 questions about that: 

1) Is it necessary or common to have soft stop on the BH?  I am hoping I do not need this.

2) How the heck to implement it, if needed?  Soft on is easy.  But soft off will require an always on LV power supply so that when I press a momentary switch (I think momenary would be the way to go), it triggers the right action on relays.   Anyone done this?  I prefer not to have a soft off if not needed, but just was not sure.  

3) I also suppose if needed, I could drop the timer device and just have a 3 position rotary switch, with Off/WarmUp/On and just manually do the warm up and cool down cycle.  

Thanks for everyone's patience with my learning curve.  

Bob

Edited by Blueman2
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