[Hammarlund] HX-500 trials

Wed Apr 27 20:44:17 EDT 2016

I think he said he was running 109vac in. I think he may have a few shorted primary turns so I will measure the primary resistance of mine for a reference point when I get back to Arkansas next week. Perhaps other owners might do the same.  
Wa5uek
Sent from my iPhone

> On Apr 27, 2016, at 3:57 PM, Richard W. Solomon <w1ksz at earthlink.net> wrote:
> 
> Don't forget that when the HX-500 was designed, the nominal AC Line Voltage 
> was 110 to 115 VAC. Todays Line Voltage is more like 120 VAC and in some 
> places higher. Here in the Tucson area I even see voltages as high as 124
> VAC.
> 
> If you use Solid State rectifiers, you can use the unused Rectifier Filament
> 
> winding to "Buck" down the AC Line. It's done on most Collins 516F-2 Power 
> Supplies.
> 
> 73, Dick, W1KSZ
> 
> 73, Dick, W1KSZ 
> 
> -----Original Message-----
> From: Hammarlund [mailto:hammarlund-bounces at mailman.qth.net] On Behalf Of
> Richard Knoppow
> Sent: Tuesday, April 26, 2016 8:13 PM
> To: Kenneth G. Gordon
> Cc: Hammarlund at mailman.qth.net
> Subject: Re: [Hammarlund] HX-500 trials
> 
>     The rectifiers are vacuum tube diodes with an indirectly heated
> cathode.  The voltage on the plates according to the voltage chart in the
> handbook is 845V, voltage on the cathodes, and input to the filter is 790V,
> voltage to the final plates (filter output) is 780V but that is a voltage
> marked on the schematic.  Normally, the output voltage a rectifier with a
> choke input filter is lower than the voltage on the plates but is better
> regulated with load. If the filter is a capacitor input filter the voltage
> is higher with no or low load but goes down faster with load.  The handbook
> specifies a 20K ohm/V meter for the voltage charts but in the alignment
> procedure specifies a Hewlett-Packard 410-B. While the 410-B has much higher
> input resistance
> (122 megohm) it should not make much difference for the DC voltages except
> possibly at the grids of low level tubes. I think it is specified mostly for
> RF measurements.
>    The voltages are so much higher than specified and are so consistently
> high that it makes me suspicious of the meter. The meter may read high on
> all ranges but differently on some.  If it is a VOM at least an approximate
> test is to measure a couple of fresh batteries. 
> Although alkaline batteries will read higher than their specified voltage it
> won't be that much higher and zinc-air cells of the sort sold for hearing
> aids will be very close to their rated voltage and are steady.  While these
> are not precision standards by any means they will show up a global error in
> the meter. The voltages given by the OP are on the order of 7% high, more in
> some cases.  I would certainly check the meter as well as repeating the
> measurements with another meter, even a cheap one from Harbor Freight will
> do. If they do not read sensibly the same I would not trust the meter.
>     I have not gone over the adjustment and calibration procedure but it
> seems complex and I would undertake it without trustworthy tools.
>     FWIW, the mention of solid state rectifiers is a good one to follow up.
> Tubes have a definite voltage drop, it is not linear for vacuum tubes.
> Solid state rectifiers have a constant drop per diode, maybe 1.5 volts where
> the tube may have a drop of 20 to 100 volts. Mercury arc and gas type
> rectifiers also have a constant drop, about 15V in the case of mercury
> tubes, so they can be replaced by a string of diodes where vacuum tubes
> really can't be unless the load (and therefore the voltage
> drop) is pretty constant. However, the substitution of solid state diodes
> would not explain the high filament voltage. Unless something extraordinary
> has happened to the power transformer (and I can't imagine what it could be)
> the high AC voltages suggest the measuring instrument is out of whack.
> Certainly something to eliminate before doing a lot of tail chasing.
> 
>> On 4/26/2016 7:17 PM, Kenneth G. Gordon wrote:
>>> On 26 Apr 2016 at 18:38, Richard Knoppow wrote:
>>> 
>>>      There is something strange about this.
>> Boy! I certainly agree with you, Richard! :-(
>> 
>>> The ratios of correct to
>>> measured voltages vary.
>> Yes. Odd.
>> 
>>> Of course, if the voltages are wrong the currents will be wrong too 
>>> which may account for it.  I found a handbook and schematic at 
>>> Rigpix. The instruction book states the voltages are to be measured 
>>> with a 20K ohm/V meter so I don't think using the wrong sort of meter 
>>> will account for it.
>> No.
>> 
>>> However, if you do have another meter or can borrow one it would be 
>>> worth checking just to make sure the meter itself is reading 
>>> correctly.
>> Agreed.
>> 
>>>     It would be interesting to know what your line voltage is. If 
>>> you said I missed it.
>> So did I. What is it?
>> 
>>>     The difference in DC resistance of the chokes is probably normal 
>>> tolerance.
>> Yes, it is.
>> 
>>> Also note the HV choke is a swinging one intended to provide some 
>>> regulation to the supply.
>> Yes, again.
>> 
>> Now, there are several things about the stuff below that makes me wonder:
>> 
>>>> AC voltages out of the transformer are 900 VAC, 350 vac, 6.8 vac.
>> OK. Here is one: the AC voltage is 900 VAC, yet the DC voltage is also 
>> 900 VDC? Unless things are exactly "correct", this cannot be so. There 
>> MUST be some differences between these two voltages.
>> 
>>>> Filter chokes test OK -- although I don't have my LCR bridge.
>> Don't need one: an ohm-meter will do for this purpose.
>> 
>>>> According to the schematics, the HV choke should have a resistance 
>>>> of
>>>> 160 ohms, mine is 172.  LV choke should be 250 ohms, mine is 271.
>> Those are within tolerances. However, here is a problem: Assuming that 
>> 900VAC output is connected to a full-wave rectifier, the DC output 
>> voltage at the rectifier, before it ever reaches a filter will be 
>> 1.414 X 900 or 1272.6 VDC. 230 mA drawn through your choke of
>> 170 oms would mean a drop of only 29.2 VDC. THis is still over 1200 VDC.
>> 
>> Are the rectifiers solid-state diodes? If so there is very little 
>> voltage drop with those. If it is a tube or tubes, then there is 
>> significant voltage drop across those, unless they are mercury vapor
> rectifiers or argon types (3B28).
>> 
>>>> LV circuit is a CLC filter.  At the output of the LV rectifier, 
>>>> voltage is 380 vdc, should be 270.
>> 350 X 1.414 = 494.9 VDC, 320 X 1.414 = 450 VDC plus
>> 
>> The whole thing is weird...
>> 
>> Ken
> 
> --
> Richard Knoppow
> 1oldlens1 at ix.netcom.com
> WB6KBL
> 
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