[AMRadio] Screwiest Elmac problem ever

Sun May 16 00:00:14 EDT 2021

Hello

Looking at the schematic here ,I'm not sure 300 v pk to pk is enough if you have 500 volts on the plates from the power supply and 220 vdc on the screens. 300 volts pk to pk is only around 110 volts rms The modulator should be able to put out 40 watts ,not going to get there with the pk to pk that low across a 5 k .

Don't know what kind of test equipment you have ,but if you can check the input output of v6 and v7 and then check the screen voltage on the v8 and v9 ,they were notorious for causing problems in the 5881 , once we get those readings then we can go from there. Anxious to see if you have 500 volts on the plates of 5881 .
If you have some spare tubes you can do what Jim suggested ,if not lets see what we can do to narrow the problem down. 300 volts pk to pk is not alot ,if you have 300 rms or avg then we have different ball game here,but I'm going on the 300v pk to pk in your previous email. Keep the faith the old girl will eventually get fixed ,just takes some time.

John ac7xh

> On May 15, 2021 at 12:29 PM sparky52 at cox.net mailto:sparky52 at cox.net wrote:
> 
> 
>     Good Point Jim
> 
>     John ac7xh
> 
>         > > On May 15, 2021 at 12:20 PM JAMES HANLON <knjhanlon at msn.com mailto:knjhanlon at msn.com > wrote:
> > 
> >         While you're checking switches, make sure that the rotary switch in the rear is on the AM position.
> > 
> >         Jim, W8KGI
> > 
> > 
> >         ---------------------------------------------
> >         From: sparky52 at cox.net mailto:sparky52 at cox.net <sparky52 at cox.net mailto:sparky52 at cox.net >
> >         Sent: Saturday, May 15, 2021 1:09 PM
> >         To: w5jo at brightok.net mailto:w5jo at brightok.net <w5jo at brightok.net mailto:w5jo at brightok.net >; CL in NC <mjcal77 at yahoo.com mailto:mjcal77 at yahoo.com >; amphone <amradio at mailman.qth.net mailto:amradio at mailman.qth.net >
> >         Subject: Re: [AMRadio] Screwiest Elmac problem ever
> > 
> >         hello
> > 
> >         One more thing ,you might check the switch in the back that changes the type of mic ,from carbon to xtal may have been accidently thrown.
> > 
> >         john ac7xh
> >         > On May 15, 2021 at 8:30 AM w5jo at brightok.net mailto:w5jo at brightok.net mailto:w5jo at brightok.net mailto:w5jo at brightok.net mailto:w5jo at brightok.net mailto:w5jo at brightok.net wrote:
> >         >
> >         > > Hummmm! maybe a microphone, cord or connector for a start?
> >         > > Jim > W5JO
> >         >
> >         >
> >         > > -----Original Message-----
> >         >
> >         > > Maybe a couple of you follow the Elmac emails, but Gary, K3OS has had is > AF67 do something weird. He is a regular check in on the Old Friends group > that meets on 75 meter 3 times a week here in the Upstate SC area. It was > working just fine, then the mod fell off to a very low level. It does have > a new modulator interstage transformer from Hammond, which was installed > long prior to this problem, the rest original. He is getting 40 watts out > in CW and AM, the modulator has been checked end to end, including > terminating the output transformer with a 5K load where he read 300 volts P > to P across the secondary. When you hook it all back up, you get 10-20% mod > max. Voltages, components, all check good, she just won't modulate. Any > ideas?
> >         > > Charlie, W4MEC in NC
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