[Heathkit] DX-60 Problem

[Chris Codella, W2PA]

Harry,,

You'll find a lot of DX-60 experts here.  But you'll need to give a 
little more information.  I'm impressed that you were able to repair the 
broken bandswitch wafers!  Don't give up.  I'm also surprised and amused 
that your DX-60 turned up at an antique mall.

Rewiring and re-capping the PS is a good start.  Are you sure about the 
other components of the power supply? 

Also, since you're getting HV on pins 6 and 2 of V4, R25 might be 
blown/shorted - it should be more like 25V.

The blown 8.2 ohm cathode resistor may indicate a bad 6146.  I had a 
brand new 6146 do this - It had been laying on its side for 30 years and 
I assume some sort of internal short occurred.  It migh also indicate 
that the bias supply wasn't operating at some point in the past. 

73,
Chris, W2PA

Harry Vaught wrote:

> I bought a DX-60 at a local antique mall a couple of weeks ago.  I 
> paid too much, but it was nearly mint, cosmetically, and I had gotten 
> a really nice HQ-170C at the same booth last year.  I should have 
> known...
>
> Both bandswitch wafers were broken and the shaft was frozen at the 
> panel bushing.  I got the shaft freed, epoxied the wafers and powered 
> up. There were fireworks from the 6DE7.  I replaced it with a 6EW7, 
> since AES was out of 6DE7's.  Since then I've rewired and recapped the 
> power supply and replaced a charcoaled R13, the 8.2 ohm resistor in 
> the 6146 cathode circuit.
>
> The voltages on the modulator tube are a mess.  I get 500-600 volts on 
> pin 6, the first section plate and on pin 2, the second section grid. 
> Same on pin 9, the second section cathode.  I've isolated the 
> modulator tube by disconnecting incoming and outgoing connections.  
> Nothing makes any difference except disconnecting the high voltage, or 
> removing the tube.  I'm lucky I haven't cooked the new tube.
>
> Screen voltage on the 6146 is ok for CW, but high for AM.  Key-down 
> bias on the driver is about -24 volts instead of -85.
>
> The documentation has no resistance chart, only voltages.  I've 
> checked voltages and connections through the various switches 'til I'm 
> exhausted, but I'm no good at deducing problems from voltages alone.
>
> Does any DX-60 guru out there have any suggestions as to where I 
> should look?  If I don't fix it pretty soon, someone's going to get a 
> nice looking bargain.  I don't like things that don't work and I can't 
> fix.
>
> Harry Vaught, KT4AE
> Maryville, Tennessee
>
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