[AMRadio] Too much HV

Wed Nov 16 07:35:42 EST 2011

There is another reason to switch over to 3B28 and that is that mercury 
vapor tubes generate noise in the receiver.  There were plate chokes that 
helped dampen this noise.

David Knepper, W3CRA/W3ST
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----- Original Message ----- 
From: "James Liles" <james.liles at comcast.net>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Tuesday, November 15, 2011 9:53 PM
Subject: Re: [AMRadio] Too much HV

> Hi Todd:
> The 866 needs to be warmed up to vaporize the mercury or they will ARC 
> over.
> Maybe too fast on the HV switch.
>
> Kindest regards Jim K9AXN
>
> -----Original Message----- 
> From: wb3fau at att.net
> Sent: Tuesday, November 15, 2011 8:04 PM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Too much HV
>
> I  agree  with you Todd. Some  years  back, i  had  silicon in  my t-368F.
> one shorted out and the other opened.  i  put in 3B28s and never had any
> trouble after that.  Russ.
>
> --- On Tue, 10/18/11, Todd, KA1KAQ <ka1kaq at gmail.com> wrote:
>
>> From: Todd, KA1KAQ <ka1kaq at gmail.com>
>> Subject: Re: [AMRadio] Too much HV
>> To: "Discussion of AM Radio in the Amateur Service"
>> <amradio at mailman.qth.net>
>> Date: Tuesday, October 18, 2011, 10:58 AM
>> On Tue, Oct 18, 2011 at 10:47 AM, CL
>> in NC <mjcal77 at yahoo.com>
>> wrote:
>> > Other than using a variac or a boost buck xfmr, does
>> anybody have a solid cure for the problem of excessive high
>> voltage when 866's are removed and replaced with a solid
>> state diode string?  I do not remember having this problem
>> when I replaced 866's or 3B28's with the commercially made
>>  direct plug in equivalent SS replacements, but only when
>> modifying ham gear.  Bill, W4TYQ in Asheville, NC and
>> myself are both working over a couple HA10 amps, and having
>> to deal with 2500VDC on the plates of 4 811's instead of
>> 1500 or so.  Both our amps came with the 866's already
>> replaced, and we are toying with the idea of just putting
>> 866's back in.
>>
>> That's a pretty big spike! Sounds like something else is
>> going on. I'd
>> be digging into those rigs and checking other things, like
>> voltage
>> taps on transformers and such. An elevated line voltage
>> will add to
>> it, but.......1000V difference??
>>
>> The bigger issue beyond what should be a slight elevation
>> in HV is
>> slamming the rig with full B+ without the built in soft
>> start of using
>> tubes. MV tubes like the 866 and 872 have a habit of arcing
>> as they
>> age, but the equivalent 3B28 and 4B32 don't have this
>> issue, and only
>> change the voltage drop slightly. I've changed all my rigs
>> using MV to
>> the Xenon equivalents and never had a HV problem since.
>>
>> ~ Todd,  KA1KAQ/4
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