[AMRadio] too much HV Fin.

[Bernie Doran]

811As in good condition will not be damaged by simply having higher than 
normal voltage on them.  As I recall the Viking 500 used an operating 
voltage of 2KV.

The voltage rises under low/no load conditions because the choke must have 
changing current flowing in it to develope the back EMF.   With low current 
flow the choke effectively becomes a non choke and the system becomes 
capacitor input.  This is partly due to under size bleeder resistors and a 
few other factors related to being cheap.

Now if someone want to get paranoid, consider that when replacing the vacuum 
tube rectifiers in a receiver, usually 5Y3 or 5U4 type animals, with silicon 
diodes and equilivelant series resistor. The full B+ plus more than a few 
volts will be available on the tube plates and all other components as none 
of the tubes have warmed up and have initally no current flow.  With a VT 
rectifier it also had to warm up a bit before it would conduct and it rather 
served as a slow start device.  Ideally one should probably have a time 
delay prior to turning on the B+. Does it make a differance? probably not a 
great differance, I do not do it, but I do have the cheap surge limiters in 
line. The size of a nickle and about a $1. so why not?   I also add a small 
resistor usually 10 Ohms or less to drop the line voltage to the original 
designs lower end.    Before some one yelps, this only applies to older 
receivers and other small pieces of VT equipment.


----- Original Message ----- 
From: "CL in NC" <mjcal77 at yahoo.com>
To: <amradio at mailman.qth.net>
Sent: Wednesday, October 19, 2011 9:52 AM
Subject: Re: [AMRadio] too much HV Fin.


> 08:57 PM 10/18/2011, you wrote:
>>I think the silly part comes fundamentally from blaming the HV
>>increase on the SS diodes.
>
> Well, as I said, always have found this to be true and realize that the 
> lower voltage drop across silicon diodes versus a HV rectifier is the 
> reason, but the theory of how much it should change never seemed to work 
> out.  In the winding down tube era, every mod kit I put in a commercial 
> tube receiver came with a resistor in the 560ohm 10 watt range, current 
> draw dependent of course, to offset this higher voltage.  In the HA10, the 
> real culprit that I overlooked is the missing swinging choke, so all I 
> have is a cap input filter where the cap is charging towards the peak of 
> the DC from the rectifier while under the bleeder resistor and 811 idle 
> current draw which apparently is not enough to limit the HV to something 
> more comfortable for standby 811's.  In Bill's case, as noted, he just may 
> have a shorted choke.  We'll check that out.
>
> Charlie in NC
> ______________________________________________________________
> Our Main Website: http://www.amfone.net
> AMRadio mailing list
> Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/
> List Rules (must read!): http://w5ami.net/amradiofaq.html
> List Home: http://mailman.qth.net/mailman/listinfo/amradio
> Post: AMRadio at mailman.qth.net
> To unsubscribe, send an email to amradio-request at mailman.qth.net with
> the word unsubscribe in the message body.
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html