[Heathkit] DX-40 question

[wb8jkr@juno.com]

 That's a pretty good idea, but it wouldn't leave much reserve voltage
for regulation. The wiring change in the DX40 I have in mind isn't really
needed, but I'm going to move the 15K resistor from the B+ to the
center point in the HV doubler in the DX40. I don't need all that
voltage and doing so will reduce the power heating the zener
dropping resistor in the VF1. 
 In this particular circuit I use a regulated 20 volts to feed the
oscillator and buffer stages in order to get the same high level output
obtained from the original VF1 circuit, I know it sounds high, but
stability is really quite good.

Mark  WB8JKR

On Fri, 26 Dec 2003 12:05:21 -0800 k6uuz@juno.com writes:
> How about powering it from the filament supply via a diode and 
> filter.
> You could use 2 diodes in a voltage doubler circuit if required?
> 
> Ed Richards K6UUZ
> 
> 
> On Fri, 26 Dec 2003 09:36:43 -0600 "Ed Worst" <edworst@att.net> 
> writes:
> > Hello Mark,
> > 
> > Did you say you just did a solid state conversion for a VF-1?  
> > That's on my
> > winter to-do list.  Do you have an article you can point me to for 
> a
> > reference?  I have an article from Dec 72 QST that I was going to 
> > use, but
> > if you have something newer it would probably be a better mod.
> > 
> > I have a DX-35, and in the manual it says, "Pin 4 supplies B+ 
> > voltage
> > through a 20k 10w resistor.  This provides approximately 250 volts 
> 
> > at 20
> > milliamperes." {for a VF-1}
> > 
> > So that means there's a 400v (20k x .02A) drop across the 20k / 
> 10w
> > resistor.  That would put the 6146 plate voltage at 650v (250v at 
> > pin 4 plus
> > 400v across the dropping resistor).
> > 
> > If you're planning on powering the solid state VF-1 from that, 
> WATCH 
> > OUT!
> > That's a 650 volt source with a 20k impedance.  I don't know what 
> > voltage
> > you need for the VF-1, but the voltage you will get from pin 4 is: 
>  
> > 650v -
> > (20,000 x I), where I is the current in Amps drawn by your 
> modified 
> > VF-1.
> > 
> > If your mod is from that Dec 72 article, you'll be OK because the 
> > mod
> > includes two additional 15k / 5w dropping resistors and a 20v 
> zener.
> > 
> > Hope this helps, and if you have any questions send me an email.  
> As 
> > I said,
> > the VF-1 mod has been on my list for years, and ... this is the 
> > year.
> > 
> > 73,
> > ed - k9ew
> > 
> > ----- Original Message -----
> > From: <wb8jkr@juno.com>
> > To: <heathkit@mailman.qth.net>; <Heath@listserv.tempe.gov>
> > Sent: Friday, December 26, 2003 8:12 AM
> > Subject: [Heathkit] DX-40 question
> > 
> > 
> > >
> > >   Does anyone know the typical no-load/load plate
> > > voltage is on the 6146?  I have a schematic, but I can't
> > > read the printing, looks like 380 volts no load, and
> > > this seems low.
> > >  What I really want to do is determine the rated voltage
> > > at the acc. socket pin 4. I converted a couple of VF-1's to
> > > all solid state for a friend and I need to make a small
> > > change in the DX-40.
> > >
> > >
> > >
> > > Mark  WB8JKR
>