SB-401

[John P.]

Hi,

  A while back I upoaded a mod to the files section.  It dealt with this "floating screen circuit" problem that affected the AVC (AVC Hang).

  I anyone needs a copy of this mod I'll be happy to send a copy of it directly

John - WA2HIP

--- On Tue, 8/17/10, Kenneth G. Gordon <kgordon2006 at VERIZON.NET> wrote:

> From: Kenneth G. Gordon <kgordon2006 at VERIZON.NET>
> Subject: Re: SB-401
> To: HEATH at LISTS.TEMPE.GOV
> Date: Tuesday, August 17, 2010, 9:09 PM
> On 17 Aug 2010 at 18:43, Jim Schnurr
> wrote:
> 
> > I have an SB-401 that has been working perfectly. It
> recently decided
> > that after about an hour it would suddenly key itself
> up.
> 
> As I remember it, something very similar occurs in the
> SB/HW transceivers 
> when the final amp tubes get gassy or exhibit grid emission
> (or something 
> like that). This is caused in THAT case by something weird
> in the screen 
> circuitry. It can be fixed by adding one wire to the
> switching relay which 
> grounds the final amp screens when in the receive mode.
> 
> I know this sounds strange, but it is mentioned in a
> Heathkit service bulletin.
> 
> > I replaced
> > the 6D10 , 6EA8, 6AV11 and 6J11 with new stock I had
> on hand. It still
> > does the same thing after about an hour warmup. I
> wonder if anyone
> > else has experienced the same problem. It is probably
> a component that
> > is getting hot in the vox-keying circuit.
> 
> That may be, all right, but I would first either remove the
> final amp tubes 
> (6146s), or replace them, and see if the problem no longer
> occurs. If it 
> doesn't, then there may be a service bulletin that mentions
> the fix.
> 
> Ken Gordon W7EKB
> 
> -----------------------------------------------------------
> Products bought, sold or traded here is the responsibility
> of the
> parties involved.  This list and the City of Tempe are
> not responsible
> for losses or misrepresentations of any kind.  Buyer
> beware!
> 
> -----------------------------------------------------------
> This list is a public service of the City of Tempe,
> Arizona
> -----------------------------------------------------------
> 
> Subscription control - http://www.tempe.gov/lists/control.aspx?list=HEATH
> To post - HEATH at LISTS.TEMPE.GOV
> Archives - http://lists.tempe.gov/archives/HEATH.html
> 


      

-----------------------------------------------------------
Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.aspx?list=HEATH
To post - HEATH at LISTS.TEMPE.GOV
Archives - http://lists.tempe.gov/archives/HEATH.html