[Central-Electronics] Fwd: Re: 6550

Jim Candela jcandela at prodigy.net
Thu Jul 25 17:18:22 EDT 2013 

Gordon,

    I wonder if you have an impedance meter? Something like an Autek RF1?

http://www.autekresearch.com/rf1.htm



   These will measure RF components at whatever frequency you choose. Lots of folks miss the point that at RF, a part that is rated at 1 Khz is likely to be way different. For example, a .01 uf disc capacitor wrapped around my grid dip meter coil with the leads twisted together in a loop, will go through series resonance at around 7 Mhz. So above the resonant point (series resonance) this thing looks like an inductor. For a parallel resonance situation an inductor looks like a capacitor when above the resonant frequency.

Another possibility is a grid dip meter. With a grid dipper you can wind an air core coil, and with a known capacitance make a parallel L-C circuit. Then use the Grid dipper to find the resonant point(s). For example a 22 uh inductor should resonant with a 100 pf capacitor at about 3.4 Mhz. 

  As to the size, the 100V puts out 100 watts into 50 ohms, so that would be 71 volts RMS. This inductor therefore should not be tiny. Perhaps wind the coil as several smaller coils in series to minimize the turn to turn capacitance that will cause a coil self resonance at a higher frequency. Maybe try 10 turns #28, 1/4" dia, then move over 1/8" or 1/4" and do it again two or three times. Then see where you are. You could get more scientific of course, but with a little instrumentation, and sweat you can likely get there without puling out the credit card.

Jim
WD5JKO


________________________________
 From: Gordon <gordon at n6wk.com>
To: "central-electronics at mailman.qth.net" <central-electronics at mailman.qth.net> 
Sent: Thursday, July 25, 2013 3:27 PM
Subject: Re: [Central-Electronics] Fwd: Re:  6550
 

Hmm, I also see that the different chokes have different Q's and also different Resonant Frequencies.. Now I'm lost as to which one to 0rder.... :-(

HELP !!!  PLEASE !!


&3,
Gordon


On 7/25/2013 1:22 PM, Gordon wrote:
> In agree Jim,
>  I am getting ready to order a new Choke to replace RFC-1 but not sure of what Current rating I should order.
> Any of the Guru's on the 100V have a clue? I have found sources for 22uH, so that doesn't seem to be an issue.
>   Jim, I have done the Carrier Null and I can get it down almost nothing on the meter.
> Right Now I am replacing everything under the Tube Sockets for the Finals section. I am about half done.
> I did discover an unsoldered connection on one of the tube terminals for the ground of C412.
> 
> 73,
> Gordon
> N6WK
> 
> On 7/25/2013 12:55 PM, Jim Candela wrote:
>> 
>> Gordon,
>> 
>>    I see you were up late tinkering. So getting zilch to 75 watts is a big deal! You might want to enjoy the moment before proceeding. I bet that RF choke, RFC1 is damaged, and a vital part of the circuitry since it seems odd to me to use a choke that low in inductance. A quick scribble suggests that 23uh on 80M has about 550 ohms inductive reactance. Perhaps that amount of reactance compensates for something that the broadband couplers need.
>> 
>>    Maybe you can build up something with similar characteristics? A DC short in that output circuit might be required to make the power meter behave. Or possibly, the power you see with no drive could be the carrier null being a little off?
>> 
>>    I was hoping the 100V/200V guru's would jump in here...This 20A guy is getting out of his element..
>> 
>> Jim
>> WD5JKO
>> 
>> 
>> ________________________________
>>   From: Gordon <gordon at n6wk.com>
>> To: central-electronics at mailman.qth.net
>> Sent: Thursday, July 25, 2013 12:04 AM
>> Subject: [Central-Electronics] Fwd: Re:  6550
>> 
>> 
>> 
>> Jim,
>>    I removed RFC-1 and now I get 75 watts out on 75 meters. but as I go
>> higher, each band puts out a little less.
>> I think I should be looking for a bad Cap at this point, as removing the
>> inductance made more power.
>> Another Question, What is up with the little Coax Capacitor thing coming
>> off the Band coupler Wafer?
>>      I think Tomorrow, I am going to strip everything out from below the
>> Finals cage and replace each and every part.
>> Another clue might be that my Watts meter shows a reading in transmit,
>> even with the Carrier and Power control at fully counterclockwise, and
>> the Pot for the Watts turned down as far as it will go.
>> I should not be showing anything when there is No output and all
>> controls at minimum. I even get a Watts reading in SSB with No carrier
>> and no Mic connected...
>> 
>> 73,
>> Gordon
>> N6WK
>> 
>> On 7/24/2013 7:23 PM, Jim Candela wrote:
>>> Gordon,
>>> 
>>> "At first I thought it might be the RFC-1,  mine shows 2.3uH when measured out of circuit"
>>> 
>>>      Looking at the schematic, RFC-1 says .022mh. This converted to uh is 22uh. I'd remove that part temporally and run up the drive. This might explain why you have more power output with increasing frequency.
>>> 
>>> Jim
>>> WD5JKO
>>> 
>>> 
>>> ________________________________
>>>     From: Gordon <gordon at n6wk.com>
>>> To: central-electronics at mailman.qth.net
>>> Sent: Wednesday, July 24, 2013 6:25 PM
>>> Subject: Re: [Central-Electronics] 6550
>>> 
>>> 
>>> Hi George and the Group,
>>> George, I have double checked everything you mentioned..Same results.
>>>      I tried the new tubes, and as everyone said,  They are NOT the problem.
>>> I do have a question though. If I disconnect the Coax from the last
>>> wafer that goes to the RF Sampling circuit and the SO-239 connector,
>>> Connect my MFJ-259 to the loose end of the Coax  , with a 50 Ohm load in
>>> the SO-239, shouldn't the MFJ-259 show 50 ohms? Mine is no where near 50
>>> ohms. If I check the dummy load by itself, it is exactly 50 ohms.
>>> The only thing on that Coax is the Amps Sampler for the RF output and
>>> the SO-239. At first I thought it might be the RFC-1,  mine shows 2.3uH
>>> when measured out of circuit, So it appears to be good.
>>> I also noticed that the Neutralizing Cap is NOT shown on the 100V
>>> Schematic I have in front of me.
>>> 
>>> Gordon
>>> N6WK
>>> 
>>> 
>>> 
>>> On 7/24/2013 9:48 AM, George Maier wrote:
>>>> Hi Gordon:
>>>> 
>>>> Great job on the 100V; glad to see so much enthusiasm for such a worthwhile
>>>> project.   Not sure why you are having the RF O/P problems, but your coupler
>>>> sequence is correct, and the voltages all seem within limits.  Not sure what
>>>> you've done electrically, but here are a few simple things you may want to
>>>> consider, if you have not already addressed them.  If you have, please
>>>> ignore my drivel:
>>>> 
>>>> 1 - Remove each coupler and apply a high quality contact cleaner to the base
>>>> pins and the tap connectors; i.e. - Caig Pro-Gol applied with a q-tip or
>>>> Caig pen.
>>>> 2 - Same exercise for all of the of the lower stage coil banks, which are
>>>> all removable.
>>>> 3 - Be sure to replace the 100 mf - 15V cap (C418) across the PA screen over
>>>> current relay; they're almost always bad. Also, burnish the relay contacts.
>>>> 4 - Check the 10 Ohm resistor (R450) that is in series with the power
>>>> control,  to make sure it's not open., and also the rest of the surrounding
>>>> connections and circuitry.
>>>> 5 - Remove all of the chassis interconnecting plugs (carefully) and clean
>>>> them with Pro-gold also.
>>>> 
>>>> Those steps should help to eliminate any flaky stuff, unless of course you
>>>> do have bad tubes along the line.  Generally, I agree with the other folks
>>>> here, that the PA tubes do not usually fail totally, but hey, it's certainly
>>>> possible.
>>>> 
>>>> Keep chugging, Gordon; you'll get there!
>>>> 
>>>> 73, George - W1LSB
>>>> 
>>>> 
>>>> -----Original Message-----
>>>> From: central-electronics-bounces at mailman.qth.net
>>>> [mailto:central-electronics-bounces at mailman.qth.net] On Behalf Of Gordon
>>>> Sent: Tuesday, July 23, 2013 9:02 PM
>>>> To: central-electronics at mailman.qth.net
>>>> Subject: Re: [Central-Electronics] 6550
>>>> 
>>>> I am still fighting the no to Low output on my CE-100V.
>>>> I have ordered new 6550 tubes, but now I am thinking they are nt the
>>>> problem. The tube tester shows both as very strong I am now wondering if
>>>> someone has mixed up the Broadband output Coils.
>>>> Can anyone tell me what color is correct for each band?
>>>> I have Red for 80, yellow for 40, green for 20, blue for 15 and slate for 10
>>>> 
>>>> Is this correct?
>>>> I have now discovered that I get more output as I move up in bands. I get a
>>>> whole 12 watts out on 20 and 15 meters..LOL Is there a way to test the
>>>> center Frequency of each of these broadband output coils?
>>>> 
>>>> Thanks,
>>>> Gordon
>>>> N6WK
>>>> 
>>>> 
>>>> 
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>> 
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