[Hammarlund] HX-500 trials

Mon Apr 25 20:08:33 EDT 2016

You guys are quick with the responses!

I'll recap for those who didn't post to the list.

Current finals are 6146As.  I swapped them out with another pair of 
6146As, and got the same results.

I checked the actual tube pin at pin 5: -50V on the tube itself.

Coax attached to the rig and into a watt meter/dummy load shows zero 
output, so if they are going to a parasitic, it's beyond my wattmeter's 
ability to see.

Finals are pulling 230 mA as measured between the output of the HV 
supply and the plate choke.  This is in standby.  When I turn the mode 
switch to CW and go to MOX, there's no change (nor output).

I don't have access to my spectrum analyzer where I am, so I can't see 
if a parasitic is out there somewhere.

Another test run: when the neutralizing capacitor is fully meshed, the 
tubes draw over 400 mA, so there seems to be some effect on the 
condition via that (if that makes anyone have a brainstorm.)

Results are the same whether or not the driver tube is in place.

OK!  Looks like we have a winner (maybe!)

 From Alan - K6RFK:

Hi Jeff,
I think that -50 on the control grid is not negative enough for the high
plate voltage and 250 on the screen.  Pin 14 on the accessory socket is
connected to the cathodes of the 6146s.  Use a milliamp meter or volt meter
on this pin and adjust the bias pot for 50 Ma or 0.5 volts from the pin to
ground.  If the current is much more, that is why the tubes are getting hot.
73, Alan

When I placed the meter on pin 14 of the accessory socket, I got a 
whopping THREE volts on it.  Dialing the Bias pot all the way back only 
got me down to about 2.5

So -- I got out my tray of resistors and started clipping in some fixed 
values. With a 22K 1 watt resistor in place, I was able to get the 
voltage on the accessory socket down to .5 volts.  Standby current was 
about 50 mA, LSB/USB current was about 60 mA, which is exactly where my 
HX-50A sits in MOX mode on those modes.

Best of all though is when I threw it into DSB, I was able to punch it 
up to a full 100 watts carrier into the dummy load!  Since I'm at a 
remote site, I don't have much of my test gear with me, so I'll have to 
leave it at that, but the finals have been TAMED!

I should have remembered this because I had to do the same thing on my 
HT-32s.  I wasn't able to get the cathode current where it was supposed 
to be, and I had to add a similar resistor.

The only thing that troubles me is that it seems like it's a fairly high 
value of resistor to have had to add in there.  I think in my HT-32 I 
only used a 6.8K, and that so I had some room to adjust the pot.  With 
22K I'm still wide open on the bias pot.  Still, at least I have output, 
so I know all the oscillators and mixers are working.  Driver and plate 
tune just fine:  250 mA or so with 100 watts on the meter on 80-40-20, 
and 80 watts at 200 mA on 15. Neutralization is probably a bit off since 
I golden screw driver'ed it win my frustration, but that'll get addressed.

For the record, the control grid voltage is now -80 vdc.

So, any thoughts on the resistor value?  I'll be able to get it on the 
scope in a week or two.

On 4/25/2016 7:06 PM, Jim Liles wrote:
> What kind of 6146's are they?
>
>
> -----Original Message----- From: Jeff Sent: Monday, April 25, 2016 
> 5:43 PM To: hammarlund at mailman.qth.net Subject: Re: [Hammarlund] 
> HX-500 trials
> Thanks to all of the great responses!  I didn't think that the socket 
> might be the problem.
>
> Alas -
>
> No.  -50 volts on the pin at the top of the socket.  Both of them. I 
> let it heat up for a minute to discover both plates on the two 6146s 
> start to get red; the "first" one in the pair just draws current faster.
>
> So -- -50 v bias on the tubes, 250 volts on the screen, about 900 v on 
> the plates.  Still the tubes draw current.
>
> Open to any other thoughts... tonight I'll put the ammeter on the 
> plate choke to see exactly what it is pulling and report back.
>
> And thanks to everybody for the manual information!
>
> Jeff
> WB3JIH
>
>
>
> On 4/24/2016 7:21 PM, Jeff wrote:
>> Oh -- and if anyone has a clean PDF of the manual, let me know.  I 
>> appreciate the one on BAMA from N9SOR, but the watermark he's put on 
>> it has washed out some of the text on the schematic and 
>> voltage/resistance tables.
>>
>> I'd be glad to trade perfect quality PDFs of the original HQ-140X or 
>> the HXL-ONE manual, or Hammarlund HT-32 if you're interested.
>>
>>
>>
>>
>> On 4/24/2016 7:17 PM, Jeff wrote:
>>> Well, been playing on and off with this rig.  Finally reversed all 
>>> the golden screwdriver "mods" to the rig and have all the specified 
>>> component values in, including the Hammarlund power supply mods now 
>>> done correctly.
>>>
>>> Still, way high voltages on the meter.  Yes, I'm running a bucking 
>>> transformer on the input, so I'm only putting about 109 VAC into it.
>>>
>>> And... now it is drawing current like crazy in standby mode. As it 
>>> warms up, you can hear the power supply start to load then the left 
>>> hand 6146 will start to get red.  Reversing the tubes has no change, 
>>> always the left one.  So, checked all the components in the power 
>>> supply again, replaced all the components in the PA section (some 
>>> drifted resistors, but not terribly off), checked wiring and 
>>> grounds.  Still the one tube takes off.  Replaced parasitic choke 
>>> resistors as the original carbon comps turned to dust in my hands 
>>> when I started working them out of the choke. Still the same. 
>>> Removed the 12BY7 driver tube, no change.
>>>
>>> Checked the bias supply -- right on the money with -90 and -50 volts 
>>> where it should be.  I do however note that I have over 3 volts on 
>>> pins 4 & 6 of the 6146s, when the voltage chart in the manual says 
>>> between point 6 and point 9.  About 250 volts at the junction of the 
>>> screen resistors.
>>>
>>> I am able to verify that the 1650 KC oscillators are working, so at 
>>> least it appears that I'll be able to get some sections going. It is 
>>> also drawing a lot of current though on the LV power supply, and I 
>>> haven't tracked that one down yet either. Enough to burn up the two 
>>> watt 15 ohm resistor in the LV supply.
>>>
>>> I also notice now the meter is totally dead.
>>>
>>> Anybody have any thoughts?  The PA current draw doesn't seem to be 
>>> related to the driver section -- the tube's out of the rig...
>>>
>>> And I thought my CE 100V was a bear to trace out...
>>>
>>> Thanks for any thoughts --
>>>
>>> Jeff
>>> WB3JIH
>>>
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