[Milsurplus] [MMRCG] "Magic" 5Y3?

Tue Sep 28 15:13:17 EDT 2021

I absolutely agree: the bleeder resistor is going OC.

Ken W7EKB

On 28 Sep 2021 at 16:22, Jim Whartenby via Milsurplus wrote:

> 
> Dave 
> Two additional comments:
> How fast does the bleeder resistor get up to temperature?  About 17 watts is dissipated at 450 
> volts across 25k so I would think that it is getting pretty toasty.  It could be possible that as soon 
> as the bleeder goes above room temperature, it is open circuit.  Have a heat gun?  It is too much 
> of a coincidence that peak and measured voltages are the same.  Just saying.
> 
> Does the 500 volt supply do the same instant over voltage trick?  You could trade the 5Y3 and 
> 5R4 for the few seconds it would take for a test to see if the 5Y3 is the issue.
> Jim
> 
> Too much agreement kills a chat.  E. 
> Cleaver
> 
> 
> 
> 
> 
> 
> 
> 
> -----Original Message-----
> From: Jim Whartenby via Milsurplus <milsurplus at mailman.qth.net>
> To: milsurplus at mailman.qth.net <milsurplus at mailman.qth.net>
> Sent: Tue, Sep 28, 2021 9:58 am
> Subject: Re: [Milsurplus] [MMRCG] "Magic" 5Y3?
> 
> I don't think that you have to go that far, just load the power supply with a suitable 10k power 
> resistor to effectively lower the DVM input resistance.   
> It almost seem to me that the bleeder resistors are open.  That 25k should draw 10s of mA but it 
> seems that they are not in the circuit.  
> 325vrms X 1.414 = 460v peak which is what you read on the meter.
> Jim 
> Too much agreement kills a chat.  E. 
> Cleaver
> 
> 
> 
> 
> 
> 
> 
> -----Original Message----- From: Ray Fantini <RAFANTINI at salisbury.edu> To: 
> MMRCG at groups.io <MMRCG at groups.io>; milsurplus at mailman 
> <milsurplus at mailman.qth.net> Sent: Tue, Sep 28, 2021 9:13 am Subject: Re: [MMRCG] "Magic" 
> 5Y3? 
> When working on analog equipment use an analog meter , like a Simpson 260. See what 
> happens then? Ray F/KA3EKH 
> -----Original Message----- From: MMRCG at groups.io <MMRCG at groups.io> On Behalf Of David 
> Stinson via groups.io Sent: Tuesday, September 28, 2021 9:41 AM To: Boatanchors at mailman 
> <boatanchors at mailman.qth.net>; milsurplus at mailman < milsurplus at mailman.qth.net> Subject: 
> [MMRCG] "Magic" 5Y3? CAUTION: This email originated from outside of Salisbury University. 
> Please exercise caution when clicking links or opening attachments from external sources. Over 
> the summer, I've finally managed to refurbish a Harvey Wells APS-90 power supply. It was a 
> rusted hulk when I got it, including the inside and outside of the case, but the iron was still good: 
> https://photos.app.goo.gl/CGsPor2fGqdXpEkB9 
> https://photos.app.goo.gl/NCQHtMZ1gDPnoNHJ6 Cleaned the chassis with a Dremal tool wire 
> brush (several of them.  USE EYE PROTECTION!  I pulled wire brush bristles out of my forehead 
> :-D ) then coated the cleaned areas with Rustoleum. Took the case and front cover to a talented 
> and reasonable powder-coat shop, Misfit Powder Coating- nice work and reasonable in Wylie, 
> Texas https://misfitpc.com/ where they sand-blasted them and powder coated and my, they look 
> pretty now.  I asked for a shade darker paint. Replaced the writing on the front panel with laser-jet 
> printed decals.  I think it looks spiffy. I intend to use it to power projects, after installing a regulator 
> in the Low-B+ circuit to fix the output at 250V Regulated, at least for now. Easy to change to any 
> other voltage by just swapping a zener or two. APS-90 data sheet and diagram: 
> https://tinyurl.com/vpk53b4 Now- here's the mystery  The Low-B+ buss is speced for 300V at 100 
> Mills, using a 5Y3 rectifier. But this buss is "getting froggy" on me.  When I power the supply, the 
> Low-B+ buss, before the 5Y3 has had even a second or two to warm-up, immediately starts 
> outputting about 460V. Watch this: https://photos.app.goo.gl/SFZo7t7RM6x2hqoKA I have not 
> addressed the extra-high voltage yet. More concerned with how the thing is delivering "instant on" 
> voltage.  Is the 5Y3 gassy, so it acts like an 0Z4?  Several tests show no evidence of gas. An 
> open bleeder, so the micro-Amps sourced before the filaments heat is "spoofing" the meter? 
> Nope; the bleeder is good. So this is interesting.  Anyone got any notions? I'll obviously be 
> replacing the 450V caps I just installed with 600V, after which the FET regulator will make the 
> Low-B+ buss "nice." GL OM ES 73 DE Dave AB5S -- This email has been checked for viruses by 
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