RE: [drakelist] T-4XC current problem and others

Wed, 07 Sep 2005 18:56:13 -0700

Well gang the T4XC is starting to sing nicely. A few little things still to sort out but good for 100+ watts on all bands except 20. Looks like somebody replaced the meter shunt resistor R59. The value fitted is 3.9 but the schematic I have looks like 3.3 but not clear, can anyone confirm?
 
The 20m crystal really does seem to be dead. I have tried it in two R4C's and a simple transistor oscillator breadboard circuit but nothing seems to work. It doesn't rattle but just does not want to oscillate.
 
I have three other questions at the moment.
 
On power up the T/R relay seems to pull in within a few seconds. This causes idle current to flow. After about a minute the relay drops out and normal service is resumed, a soft tube?
 
Maybe related to this. After keying, PTT, Tune, or spot, when returning to receive position the relay seems to take a good half second or more to drop out. VOX is off. Is this connected with the question above or something else?
 
As an example on 15m with the Tx in Tune, gain at 50% gives 110 watts out, about the maximum. Switching to CW with no key inserted the power drops to almost zero at the same setting of the gain control but can be increased to about 125 watts at 75%V setting of the gain control. Is this normal? 
 
73 es thanks for all the help so far.
Martin HS0ZED
 
p.s. Eric, I can come to NC pretty much anytime. Just send me the tickets, return from Bangkok for me and the xyl, hi hi.

From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Eric Webner
Sent: 07 September 2005 08:44
To: Martin Sole
Cc: Drakelist
Subject: RE: [drakelist] T-4XC permanent current problem

Hi Martin,
 
Glad you are making progress. When you are done, please come to North Carolina and finish my C-line for me HI.
 
I learned a while ago that you may be able to get the crystal oscillator going again by simply replacing the oscillator transistor. This is certainly a lot less expensive than replacing the crystals.
 
Give it a try, and let us know how it works.
 
73,
 
Eric KA8FAN


Martin Sole <[EMAIL PROTECTED]> wrote:

"Martin Sole" <[EMAIL PROTECTED]>made an utterance to the drakelist gang
----------------------------------------------------------------------
Found it.

A short inside the meter. I never did like the way those meter studs were
not fixed like others. Obviously in dismantling everything and re-assembling
the lug on the inside got rotated and was touching the inside of the meter
case.

Note to self: Don't unscrew the meter nuts to remove next time, unsolder the
wires.

All is good now but looks like the 20m and maybe the 80m crystals are dead.
They will not oscillate in the transmitter nor in the receiver. Any crystals
from a dead radio out there?

73
Martin HS0ZED




-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Garey Barrell
Sent: 07 September 2005 04:13
To: Martin Sole
Cc: 'drakelist'
Subject: Re: [drakelist] T-4XC permanent current problem


Garey Barrell <[EMAIL PROTECTED]>made an utterance to the drakelist gang
----------------------------------------------------------------------
Martin -

Something is shorting the final cathodes to ground, "South" of the meter
shunt, R59.

There are a limited number of paths that can get the cathodes to ground,
especially when that path has to handle the idle current you are seeing in
the "key-up" condition.

Heater-cathode short in V7, (6AU6 AM Mod tube). ?

I've never measured the key-up Final cathode voltage, but I think it could
rise as high as the screen voltage if the cathodes are "open" to ground?

73, Garey - K4OAH
Atlanta

Drake C-Line Service Manual



Martin Sole wrote:

>"Martin Sole" <[EMAIL PROTECTED]>made an u! tterance to the drakelist
>gang
>----------------------------------------------------------------------
>I checked the bias voltage at the tube bases. The AC4 pot varies it
>between about -44 volts and -85 volts. If I key the radio in SSB (No
>Mic gain) and advance the bias pot until the meter shows 0.1A, bias
>voltage measures about
>-55 volts,then release the PTT the current increases to approximately
0.12A.
>
>Same problem with different PA tubes that were known good last time
>they were tried in another radio.
>
>Looking at the cathode line it seems this is taken to ground by a
>contact on
>K1 but when unkeyed should rise up to cut off the tubes. How many volts
>should be on the cathode line in the unkeyed state? On this radio the
>point at L5 sits around 0.38 volts in the unkeyed state and drops to
>0.34 volts in the keyed state. Voltages are the same with K1 removed.
>
>Ideas appreciated.
>
>73
>Martin HS0ZED
>
>
>-----Original Message-----
>From: Gary Poland [mailto:[EMAIL PROTECTED]
>Sent: 06 September 2005 10:22
>To: Martin Sole
>Subject: Re: [drakelist] T-4XC permanent current problem
>
>Martin,
> Sounds like you have lost a capacitor in the AC-4 bias supply. The
>voltage is too positive causing constant plate current.
>
>73, Gary
>
>
>
>
>
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