[Hammarlund] HX-500 trials

Thu Apr 28 07:37:56 EDT 2016

Hi,

I recall something about a bucking transformer to get the input voltage 
down. I could have been in a different thread on a different list.

73,

Bill  KU8H

On 04/27/2016 08:44 PM, Brian Harris via Hammarlund wrote:
> 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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