[Hallicrafters] Re: [Boatanchors]Replacing recttubeswithdiodesquestion

[jeremy-ca]

----- Original Message ----- 
From: "Rodger" <wq9e at dtnspeed.net>
To: <Boatanchors at mailman.qth.net>
Cc: "Hallicrafters List" <hallicrafters at mailman.qth.net>
Sent: Wednesday, February 13, 2008 3:10 PM
Subject: Re: [Hallicrafters] Re: [Boatanchors]Replacing 
recttubeswithdiodesquestion


> These threads have a way of quickly degenerating and these will be my last 
> comments.
>


Hmmmmmm



> I add a dropping resistor because with increased plate and screen voltage 
> most of the tubes are going to be operating at a higher temperature.  If 
> there is a large safety factor in the original design then no problem with 
> higher voltage.  Perhaps Henry Van Cleef is still reading these lists and 
> he can repost his experiences with some vintage gear in which the original 
> design was operating some of the tubes at the "ragged edge".   The 
> suggestion by Bob WA2UEH to consider changing to a choke input filter can 
> also be used in some cases, I did this with an SX-42 I bought years ago 
> which had a replacement transformer with too much secondary voltage.  The 
> choke input filter will result in substantially less output voltage which 
> may be too low in some cases and hum reduction is going to be more 
> difficult with this filter configuration but if these are not "deal 
> breakers" in your application then it is worth trying.


The choke input configuration will yield about 0.9  of the RMS secondary 
versus 1.4 for capacitor input. An additional section can be added by using 
a resistor with a value approximating the choke followed by another 
capacitor. This is a common configuration in vintage audio amps designed 
with cost in mind.



>
> The NTC inrush limiters I use have a fairly high cold resistance which 
> drops quickly as they warm up due to current draw.  The ramp up in voltage 
> can be easily measured.


As I stated, they operate at the zero crossing and provide minimal 
protection. In a high power amp they provide even less protection. Granted, 
something is better than nothing.



Are they necessary for vintage gear?
> Perhaps not but a reduction in component stress is certainly not a bad 
> thing.  I have within my personal collection over 150 pieces of restored 
> gear ranging in size from an S-38 through a Desk KW and Gates BC-250GY and 
> I have repaired and restored many pieces for others.



I have about as many receivers and 5 transmitters but I build my own amps 
and modulators.


The use of
> inrush current limiters has removed that wonderful starting "bong" that 
> the Halli SX-42 and 62 transformers often like to make


Never noticed any bong with mine but I never turn vintage gear on without a 
Variac for the first time and never beyond 105V. Then its recap time if the 
xfmr is OK.


but more
> importantly it has allowed the use of fuses sized to carry the running 
> load of several of my transmitters instead of sized to carry the load due 
> to current inrush.  A great practical article on the use of these limiters 
> appears in the July 97 issue of Electric Radio.  It was written by Jim 
> Garland (W8ZR) who was at that time still the university president at 
> Miami of Ohio and he has great writing skills.  I recently purchased an 
> older 1980's era Orr Radio Handbook and it has an interesting receiver 
> construction article also by Jim.


Ive known Jim personally for decades. I provided parts for several of his 
projects.



>
> I build the SS replacements as plug ins simply to make the gear easy to 
> put back to "factory stock".
> These lists are always going to bring forth a variety of viewpoints and 
> they are useful in that they allow us to examine a number of differing 
> points of view.  I am simply sharing my experience and reasons; I have no 
> psychological need to convert anyone to my way of thinking.  My advice on 
> vintage gear is free so take it for what you think it is worth.  I only 
> charge for business advice because that is the area of  my doctorate and 
> that is where I do my consulting work (which has paid for most of my 
> vintage gear acquisition).
>
> Rodger WQ9E


Im impressed. My advise is also free and I only hold an inferior MSEE backed 
by 53 years of ham radio experience and a lifelong career in RF engineering 
with a side trip into serious high voltage engineering, 100KV to 1MV.

Now happily retired and spend all day in a well equipped home RF lab playing 
with "toys" or doing microwave/millimeterwave consulting work/prototyping 
for past employers.

Carl
KM1H