[Hammarlund] HX-500 trials

Wed Apr 27 17:19:09 EDT 2016

     I think line voltage was more like 117V but the receiver label or 
handbook will say.  The excessive voltages listed would require the line 
to be on the order of 126V. That is quite possible these days but 
depends on where you are. I still think he needs to check his meter 
against a known good one.
     FWIW, local voltage (metropolitan Los Angeles)is around 120V but 
varies around somewhat.

On 4/27/2016 1:57 PM, Richard W. Solomon 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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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL