[AMRadio] SP600 Question

Ray Smith rrs4 at sti.net
Tue Sep 15 03:00:38 EDT 2009


Thanks for your graciousness when you said, "it is your radio to do as you 
wish and one thing we try to do as operators of AM equipment is preserve the 
equipment and mode."  I greatly appreciate your comment.  Fields like that 
of the electronic technician represent a very small selection of the 
population, and I believe it includes a smarter than average group of 
people.  I find that this also concentrates the percentage of Prima Dona's. 
A Prima Dona is the grand old lady of the opera who demands it be done her 
way, or not at all.  I find a statistically higher average of these people 
in my chosen field of employment.

I hope that nobody will hate me as I admit that while a teen in the 1960's, 
I stripped everything except the tuned circuits and their associated 
hardware, and the HF local oscillator circuitry from a BC-348.  I then used 
circuits from the ARRL ham manual and rebuilt my own radio using miniature 
tubes.  Some of these had multiple tubes in one glass envelope, giving me 
more total circuits than the WWII radio I had so little appearent respect 
for.  I even gave my radio a product detector.

I learned a lot building up that homebrew radio in a BC-348 shell.  By use, 
I learned that the local oscillator had too much drift, and to copy RTTY on 
my homebrew Terminal Unit and retired teletype printer, I had to ride the 
tuning control constantly.  The TU used 88 mH toroids from Ma Bell, and I 
put these on frequency using a homebrew tuning fork oscillator.  Those were 
some hours of real pleasure, indulging my love affair with communication 

I read quite insulting things today from some Hams who write and talk like 
it is a sin to modify old tube equipment.  Don't get me wrong, I would not 
lie and palm-off a modified radio as a classic or pristine collector's item. 
I understand the difference.  I just prefer homebrew, even on a commercial 
platform.  Some people talk like I should be ashamed of what I've done.  I 
guess a few will forgive me for completely reworking my TCS-12 receiver, as 
the wiring was destroyed by a mouse in 1982.  Does that make it OK for me to 
gut it and replace the 12SK7 RF stages with 6LQ8's, using the triode as a 
high impedance cathode-follower driving the very high-mu pentode side with a 
choke fed, capacitor coupled output tank, all with the goal of higher Q by 
removing the DC current from the coils?  (It is all to overcome the Miller 
Effect.)  Different things excite different people.

I have a TCS-12 transmitter that I gutted back in the '60's.  I stripped out 
the modulator back then and put it on CW at 100 Watts.  Nobody was using AM, 
that I knew of.  When I do get it back on the air as a 100 Watt AM rig 
(different modulation transformer of course), and I figure out how to get 
some sort of 160 Meter inverted-V in the air, I hope somebody will hear me, 
and give me a report.  It would be nice to be told the rig sounds good. 
I've lugged that box around all these decades through all those moves, and I 
would like it to look and sound good.

Ham radio is a collection of related hobbies.  For me, the pleasure is in 
building something that looks as good as I can make it, and that works as 
well as possible.  I guess I'll never be a real operator like most of you, 
and I am a little envious.  But, please, all who read these confessions of 
mine, realize that some of us actually love the electronics and the theory 
more that operations.  I hope that what gives me great pleasure will not be 
seen as a sin, because it has entailed the destruction of these three boat 
anchors over the 60 years of my life.

I enjoy reading all of the technical comments shared here.  It helps me 
enjoy the humble clamp tube as a fellow ham points out the problem of 
grid-conduction it both excitation and the plate voltage are removed.  Those 
early radio guys sure were smart, weren't they.  Or maybe they burned out a 
few clamp tubes before they figured out how to stop doing that!

Ray Smith

----- Original Message ----- 
From: "Jim Wilhite" <w5jo at brightok.net>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Monday, September 14, 2009 10:41 AM
Subject: Re: [AMRadio] SP600 Question

> In line with your message, some time back  maybe a year or more,
> John/K5PRO found a DX 100 in stock state.  He began to read and look
> for modifications for the transmitter.  And as most of you know,
> there are many that have been published so he gathered them together
> and, one at a time, made those modifications.  They even included
> changing the modulation transformer and almost all were to increase
> the audio range and gain additional headroom.  The simple mod was to
> parallel the coupling caps in the audio section only.  I wish John
> would join this discussion to explain what all happened.
> Some of them actually made the audio worse than the stock
> configuration in terms of distortion.  I am not sure where John left
> the DX 100 but from what I remember, the mods did not provide much,
> if any, gain.    So after all that you have a piece of equipment
> that is not like the manual.  And as most of us know, the paperwork
> done when mods are made is not kept and transferred with the radio.
> This leads to hours of tracing the circuit then deciding if we
> should  keep the mod in place.
> This is amateur radio at its finest.  People actually working on
> something to improve it and we are one of the only groups that is
> allowed to make modifications and use the radio on the air.
> Everyone else must get approval from the FCC.  Where we go wrong is
> failure to properly access and prove our work.  Most of us rely on
> the ear of another ham or their S meter readings.  These two topics
> are for a long discussion at another time, but my message is think
> about what you are doing before taking the clippers to a radio.  You
> actually may be doing more harm than good and you will definitely
> reduce the value of the equipment if either of these two things are
> important.  To me, removing a unit of a radio that I will not use
> does not make sense.  However, that said, it is your radio to do as
> you wish and one thing we try to do as operators of AM equipment is
> preserve the equipment and mode.
> Jim/W5JO
> ----- Original Message ----- 
>> Hi Don,
>> How about those vintage Johnson Ranger & Viking transmitters with
>> all of the
>> "classic" hi-fi audio mods done on them by the latest & greatest
>> AM
>> ghuru(s)...?
>> ...And I do NOT mean mods that might entail a simple increase in
>> capacitor
>> value here, the removal of a bypass capacitor there, etc. etc.---I
>> mean the
>> whole enchelada, where some current "expert" corrected the
>> "faults" of the
>> original Johnson engineer by (literally) completely gutting &
>> re-building
>> the entire audio section, from beginning to end...!
>> ...And then they peddle these abominations as "classic" rigs...
>> It's like dropping a Chevy V-8 into a '32 Ford, & selling it as a
>> "vintage /
>> classic" car---hardly! And you are right-on: such butchery DOES
>> (IMHO,
>> anyway) detract from any possible re-sale value of something that
>> has
>> morphed into someone else's "ideal" personal creation...
>> ~73~ Eddy VE3CUI - VE3xZ
>> **************************************
>> You know the mods I meanAU
>>> >  I have started replacing caps in an SP-600 JX-17. I removed
>>> > the crystal
>>> > unit and was wondering if there is a need for it other than
>>> > using
>>> > crystals. In other words can I leave it out and if so what
>>> > connections
>>> > need to be made to bypass it.
>>> >
>>> If you are not using the crystal unit, but it is not impairing
>>> the
>> function
>>> of the receiver, what is the point of removing it?  You might
>>> find it
>> useful
>>> sometime in the future, or if you eventually sell or swap the
>>> receiver, a
>>> subsequent owner might want it in original condition.  Besides,
>>> you will
>>> either have a useless function control on the front panel or some
>>> empty
>>> holes.
>>> IMO it decreases the value of a piece of equipment to butcher it
>>> with a
>>> "modification" that serves no useful purpose.
>>> That reminds me of AM transmitters that sometimes appear at
>>> hamfests that
>>> have had all the components in the speech amp and  modulator
>>> removed to
>> make
>>> "CW transmitters" out of them after SSB came along.  Or a
>>> Hallicrafters
>>> receiver I saw once in which a CB'er had removed all the coils
>>> except for
>>> the band that had 11m.
>>> Don k4kyv
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