RE: [drakelist] R7 audio

[DW Harms]

DW Harms [EMAIL PROTECTED] made an utterance to the drakelist gang
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Hi Garey,

Here are some answers:

1. It has the MC1496 version detector. I am not sure about Evert's R7, it is
a lower s/n...

2. Switching the preamp on/off does not influence the problem.

3. Backing off the RF-gain DOES reduce the problem significantly!

4. The signals, both weak or strong, are not so much affected. The only
bother is that the crackling noise comes along with it.

From all other reactions I got, I conclude that the issue has to do with the
attack-time of the AGC. In position fast it is very (!) fast, never seen
anything like it in any receiver. In position slow the receiver sounds
much better, but the recovery time after TX/RX is very long...

VY 73, Dick PA2DW


-Oorspronkelijk bericht-
Van: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Namens Garey Barrell
Verzonden: dinsdag 30 mei 2006 4:45
Aan: DW Harms; Drakelist
Onderwerp: Re: [drakelist] R7 audio


Garey Barrell [EMAIL PROTECTED] made an utterance to the drakelist gang
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Dick -

Questions, question, questions..

I haven't noticed what I think you are describing on either of my R-7s.

1. Does your TR-7 have the discrete Product Detector or the (later 
TR-7 and all R-7) MC1496 version?

2. Does the Preamp affect the problem?

3. Does backing off the RF Gain affect the problem?

4. Strong signals, weak signals, both?

I have the R-7 Service Manual, but it is very similar to the TR-7 
Service manual, i.e., lots of oversize foldouts and MANY pages. I can 
certainly scan specific areas, but don't really have the time to scan 
the whole thing! Trying to find time to finish up the 2-B / 2-BQ Service CD.

73, Garey - K4OAH
Atlanta

Drake B  C-Line Service CDs
http://www.k4oah.com



DW Harms wrote:

 Drakelist de PA2DW,

 I am using a R7 in combination with my TR7 for some time now, with 
 utmost satisfaction. What I do notice though, is the difference in the 
 way the R7 sounds in comparison with the TR7 receiver.

 Especially with the AGC in position fast, the audio sounds very much 
 like it is saturated in some way and there is a kind of crackling 
 noise coming along with the received signal. I always thought it was 
 my R7 that did that and it was something on the list to fix. But today 
 I visited Evert PA2KW and his R7 did sound very much the same like 
 mine! We went over it and tried tweaking the AGC but with no success.

 Now I wonder if others experience the same and if there is a fix for 
 it. It surely must have something to do with the AGC circuit.

 Evert and I decided to go and search for the service manual of the R7 
 which we don't have, so any source for that will also be highly 
 appreciated!

 VY 73, Dick PA2DW

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[drakelist] Neutralising T-4X

[kbgluxford]

kbgluxford [EMAIL PROTECTED] made an utterance to the drakelist gang
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Things are moving along smoothly, if slowly, with refreshing an old 
T-4X.  Final tubes have been replaced, screen and anode voltages 
disconnected at the feed thru capacitors on the wall into the final cage 
(just lifted the RF chokes and taped up the loose leads).  Connected a 
short coax lead with a PL259 plug into the antenna socket and the other 
end with bare braid and centre conductor to enable connection to the 
oscilloscope.  Fired up the transmitter and tuned the anode capacitor 
for a maximum signal on the scope, then tuned the neutralising capacitor 
for a minimum signal.


So far so good.

However, this is the first neutralisation I have done in 50 years and I 
think I need a bit of help, please.


Should I have terminated the coax with a 50 ohm carbon resistor where I 
have attached the scope?


There is a mains hum signal on the trace.  Is this likely to be caused 
by an earth loop between the scope connection to mains earth, the AC4 
connection to mains earth and the probe earth connected to the T4-X 
chassis?  Should I simply omit connecting the probe earth to the 
transmitter chassis or the coax braid?


Yes I could experiment, but I don't want to risk misaligning the set.

73 and thanks in advance
Kevin
VK3DAP / ZL2DAP
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