Globe King 500C PTT trouble.

[ke7trp]

Today I atempted to get the PTT working on the Globe 500C. I am tired of bending down and flipping the Transmit switch on this beast.

With the PTT line hooked from PS deck to Modulator deck and all known wiring and plugs tight and correct, I get a LOUD BUZZ when I key the MIC.

This Buzz is the relay buzzing at what sounds like 60HZ.  If you try to key it for more then 1 second, You blow the main fuse on the rig.

I have traced this all down to the Push to talk Rectifier, SR1.  This is a solenium type that is Green or blue in color.  Is this my source of trouble?
 
What is the recomended plan of attack on this thing? Silicone diode? What type and rating?

Thanks alot guys!

Clark

[N3DRB The Derb]

get rid of any selenium rectifiers in the rig. replace em all with diodes, and any lytic caps hanging off them, replace them too. Try that first and come back if problem's still there.

[ke7trp]

In study of this schematic, You can see the SR1 Selenium rectifier hooked up after the S04 which is the PTT socket (I guess as this is a 3 pin plug).  This 3 pin plug goes down to the PS Deck and operates the relay coil directly. You can see this on the other PS schematic as S06.

Again... If I flip SW13 on the PS deck (the transmit switch) the transmitter keys up fine.  If I use the PTT on the mic, I get a LOUD BUZZ of the relay.

Clark

[ke7trp]

Ok fair enough.  What Diodes do I purchase?  The only ones I have here are 1amp/1000v.  I would guess I need a silicone diode, Just dont know what to purchase.

C

[Steve - WB3HUZ]

Since it's the PTT circuit, it will be relatively low voltage. Your 1kV/1A silicon ones should work FB. Stay away from the silicone ones. Those are fake. 

[N3DRB The Derb]

no, they look fake in photos but feel like skin covered selenium rectifiers.

[ke7trp]

Robert helped me again!

I ended up using a 3amp/1000volt diode.  The rectifier was not bad though..  Still chattered.  Then I found that some *&*&(^ installed an 80MFD at 500 volt in place of C40 which is a 500mfd at 6 volt. 80 was not enough for the half wave. I found a 1000MFD at 25 volt in the junk box. Soldered it in and now its fixed.  I guess I will get the rest of those Seleniums out of there. I see three others in the schematic.

The Globe 500 now has PTT. I can sit back in the chair and key the mic and talk. No need to get up, Lean over and Flip the transmit switch everytime Its my turn.. The simple pleasures in life.. 


Clark