[Drakelist] Drake L-7 FS/Trade

2011-04-13 Thread Kevin Nathan
Hi All,
 
I have a very nice condition L-7 that I am not using.  This amp has
performed flawlessly for me but I recently bought a new solid state amp and
it is not being used.  The ALC has not worked for me but all else is in
great condition.  I would use it on AM but it is too big to fit my available
space.
 
I'm asking $1,200 for the amp and we would need to discuss how to ship it.
I live in the Seattle metro area and would, of course, prefer pick up or a
meet somewhere within reason.  I would also consider a partial trade
including cash and a small, medium power desktop unit I can fit in the small
space I have for use with my C line on AM.  Models of possible interest in
this category might be the AEA LA-30, Amp Supply LA-1000, Dentron DTR-1200,
Heath Kit SB-200 or something similar.  Of course, a Drake L-75 would be
great if it would fit in my space.  I can't remember the dimensions on it
though.  Can anyone help with that?
 
Thanks much for reading and very 73.
 
 
Kevin :)
Amateur Radio:  K7RX
 
 
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[Drakelist] R-4B Mods (Epilogue)

2011-04-13 Thread Paul Christensen
Earlier today , I finished the last set of R-4B mods.  Those of you 
following my progress, this marks the ten week point of incremental changes. 
The last (and final, I swear!) set of modifications:


1) Added the Sherwood PD-4 active product detector; and
2) Replaced the Sherwood AMP-4 audio amp with something truly special:  a 
modified form of the SM0VPO Class AB design.  This amp is rated at 4W into 
4-ohms, so it can accommodate both headphones and an MS-4 speaker.  The 
circuit board was made by FAR Circuits, based on the artwork available on 
the SM0VPO website.  IMHO, this is the Holy Grail of "single supply" audio 
amps.


Adding the PD-4 was easy enough now that the Sherwood PS-4 board is 
delivering regulated and decoupled +12V throughout the R-4B.  Findings?  Not 
a whole lot.  AGC attack is much smoother but I notice no other changes.  An 
ancillary benefit of the active design is that In/Out isolation is better 
than that of the diode product detector and as such, there's probably less 
opportunity for audio to feed back into the AGC circuits.


I was not expecting much change between the Sherwood AMP-4 and the discrete 
SM0VPO design.  However, the new amp board elevates the R-4B audio to a new 
level of audio performance.  I searched for low-noise transistors for use in 
the high gain stage and kept the TIP-41 types in the output stage as a truly 
low-Z drive source for the headphones and MS-4 speaker.  The output coupling 
cap is a low ESR type with a whopping 2700 uF of output C.  The only way 
this amp can be improved is to utilize a bipolar supply to attain DC 
coupling between stages.  I cannot justify that level of extra effort just 
for DC-coupling "bragging rights."  Just adding the Sherwood PS-4 to the 
Drake R-4B was complicated enough (see prior message threads for details).


http://72.52.250.47/images/AMP-1.jpg

The discrete audio amp has zero residual noise, no hiss, no hum, no buzz. 
Unlike the monolithic LM3xx series, it's totally silent.  I raised the amp's 
ground buss potential above the R-4B's chassis and used a large conductor 
size between the new amp board's ground buss and a common ground point on 
the Sherwood PS-4.  Likewise, the audio input shield ties back to the same 
ground point.  I did this to avoid buzz-inducing currents on the chassis 
from the AC tube filaments and the CT high-voltage secondary of the power 
transformer.  The common point is in the corner tip of the R-4B chassis -- a 
point where AC currents are minimum.


http://72.52.250.47/images/AMP-2.jpg

I had one issue develop:  As I unplugged the headphones, I noticed 
intermittent instability.  For clues, I went to the National Semiconductor 
datasheets for the familiar LM383, LM380,and LM386 output amps.  Each uses a 
small resistor in series with a cap (e.g., 2.7 ohm in series with 0.1 uF) at 
the output to better stabilize the amp under changing loads (e.g., 
un/plugging headphones).  That worked very well with the discrete design and 
completely cured the instability without affecting performance.


When I have time in the next couple weeks, I will measure the THD and IMD of 
the new amp.  I have a Tektronix TM series test set with 
ultra-low-distortion oscillators and automated distortion analyzer. 
According to SM0VPO, typical THD at 2W is under 0.01%.


So, perhaps now is a good time to summarize all my R-4B mods:

1) Eliminated all power-hungry voltage dividers and substituted with a 
Sherwood PS-4 board;
2) Replaced power transformer with an R-4C NOS unit thanks to the generosity 
of a list member.  This R-4B runs super cool to the touch;
3) Replaced the multi-section power supply cap with a multi-section type 
from Tom at hayseedhamfest.com;
4) Removed the entire R-4B audio section and replaced with a modified SM0VPO 
Class AB audio amp board;
5) Changed H/P jack to TRS so newer stereo phones can be used without 
hunting for an adapter;
6) Replaced all 12.6V tubes to their 6.3V equivalents (e.g., 12AX7 is now 
6AX7).  This, because the R-4C transformer only uses a 6.3V filament 
secondary since the R-4C uses all 6.3V tubes.  From the factory, the R-4B 
has a mix of 12.6V and 6.3V tubes -- and a CT 12V filament secondary;
7) Using an outboard inrush surge limiter on the AC line cord:  Two CL-90 
thermistors in series.  In addition to inrush limiting to the filaments, the 
filaments now see 6.3V instead of 6.8V from my high AC  mains line voltage 
(runs about 125VAC);
8) Replaced all paper caps with "yellow-jacket" metalized Polypropylene 
types;

9) Replaced the diode product detector with the Sherwood PD-4;
10) Replaced both dial lamps with blue LEDs from N9OO.   Love the new look 
against the orange neon dial indicator;
11) Was going to replace a tired NE-2 bulb.  For whatever reason, reversing 
the neon lamp leads has given it new life;

12) Changed AC line cord to 3-wire for safety;
13) Changed AGC "Slow" time constant;
14) Changed several audio coupling and bypass caps to extend the

Re: [Drakelist] TR-7A SHUTDOWN

2011-04-13 Thread Nigel Gunn G8IFF/W8IFF

This is getting confusing.
Is it the RADIO or the POWER SUPPLY that is closing down?
Nobody has said.


On 13-Apr-11 22:17, Gary Poland wrote:

Check the PIN diodes 
73, Gary



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--
Nigel A. Gunn,  1865 El Camino Drive, Xenia, OH 45385-1115, USA.  tel +1 937 
825 5032
Amateur Radio G8IFF W8IFF (was KC8NHF 9H3GN),  e-mail ni...@ngunn.net   www 
 http://www.ngunn.net
Member of  ARRL, GQRP #11396, QRPARCI #11644, SOC #548,  Flying Pigs QRP Club 
International #385,
   Dayton ARA #2128, AMSAT-NA LM-1691,  AMSAT-UK 0182, MKARS,  ALC, 
GCARES, XWARN, EAA382.


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Re: [Drakelist] TR-7A SHUTDOWN

2011-04-13 Thread Gary Poland
Check the PIN diodes 

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Re: [Drakelist] TR-7A Shutting Down At High Power

2011-04-13 Thread Ron
Lee is very correct about the PS7 and a little bit of stray RF.  If you have 
any accessories on the 12 volt line (RCA jack) of the PS7, make sure that there 
is a .01uf cap across that line inside the PS7.  I believe that was a factory 
upgrade/mod fairly early in the PS7 history.

Usually this show most often on 40 meters becasue it is the peak gain of the 
original final RF brick.  If you fix it there, you then usually have a stable 
PS7.  

BTW if you are not currently using a switched AC power socket, I would 
recommend that you look into one (computer switch deck is a good solution).  
The TR7 power switch/pot combo is put under quite a bit of stress with on/off 
cycles.  I have not tried to locate a duel pot, duel switch combo, but my guess 
is that it is non-existent.

73,
Ron WD8SBB


--- On Wed, 4/13/11, leecra...@aol.com  wrote:

From: leecra...@aol.com 
Subject: Re: [Drakelist] TR-7A Shutting Down At High Power
To: rfch...@verizon.net, drakelist@zerobeat.net
Date: Wednesday, April 13, 2011, 4:16 PM



 

Also have your friend check his grounding.  Stray RF getting into the 
PS-7 will also shut it down.
 
73
Lee WB6SSW
-Inline Attachment Follows-

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Re: [Drakelist] TR-7A Shutting Down At High Power

2011-04-13 Thread LeeCraner
Also have your friend check his grounding.  Stray RF getting into the  PS-7 
will also shut it down.
 
73
Lee WB6SSW
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Re: [Drakelist] TR-7A Shutting Down At High Power

2011-04-13 Thread K9sqg
As a side note, "full power" means different things to different people.  If 
the final brick is adjusted for max output, then yes more current will be drawn 
but so also the instability might rear its ugly head.  Best to keep things at a 
"manageable" level...





-Original Message-
From: rfch...@verizon.net
To: drakelist@zerobeat.net
Sent: Wed, Apr 13, 2011 2:24 pm
Subject: [Drakelist] TR-7A Shutting Down At High Power


I have a friend who remarked that his TR-7A shuts down when he tries to run 
full rf output.  Otherwise the rig runs fine.
 
Is this problem related to the current adjust pot in the PS-7 power supply?
 
Any suggestions would be appreciated
 
Tnx & 73EdK2ZE

 
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[Drakelist] TR-7A SHUTDOWN

2011-04-13 Thread W4AWM
 
Hi Ed,
 
I am no expert in this but the PS adjustment could be the problem.   Also, 
I have found that low input line voltage can cause the same  problem.  This 
I discovered on field day when I was at the end of a  long power cable.  All 
was fine until I started tuning up with the antenna  tuner.  As I 
approached max power, the rig would shut down and I had to  turn it off and 
then back 
on to "re-boot" .  After I discovered that the  line voltage was dropping 
to 105V under maximum load and ran a separate, heavier  and dedicated power 
cable from the generator, the problem was totally  eliminated.
 
I'm sure you will hear from Garey shortly who is the consummate expert in  
Drake gear.
 
73,
 
John,  W4AWM
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Re: [Drakelist] TR-7A Shutting Down At High Power

2011-04-13 Thread Don Cunningham
Ed,
>From my limited experience, that is indeed the problem, the PS-7 is current 
>limiting due to a need to adjust it.  I think that instructions for adjustment 
>are in the PS-7 manual.  One friend's rig had a bad pass transistor and 
>exhibited this same symptom, however.  I would still try the adjustment first.
73,
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[Drakelist] TR-7A Shutting Down At High Power

2011-04-13 Thread rfchoke


I have a friend who remarked that his TR-7A shuts down when he tries to run full rf output.  Otherwise the rig runs fine.
 
Is this problem related to the current adjust pot in the PS-7 power supply?
 
Any suggestions would be appreciated
 
Tnx & 73    Ed    K2ZE

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Re: [Drakelist] TR-3 S Meter

2011-04-13 Thread Garey Barrell

Tom -

What happens if you turn the RF GAIN full CCW??

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs



pony...@aol.com wrote:

  Hi Gang,
  I have a nice TR-3 that looks, and works well with one caveat. I 
can't get the S Meter to deflect past S2.
  So far I have swapped all the tubes involved??? Removed the meter, 
and it tests OK, so far, I haven't found any resistors out of spec. 
Tried changing the value of the shunt resistor, which is connected to 
the zeroing pot. Not much help there. I don't see much change in the 
voltage at either the receive IF, or the transmit IF. I understand 
that the TR-4 has a meter sensitivity pot, whereas the TR-3 has only 
the zero pot.

  Does anyone have any other ideas?
  Thanks for reading this  Tom, WD8JPP
   


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Re: [Drakelist] TR-3 S Meter

2011-04-13 Thread PonyTom
Hi Gang,
 
  I have a nice TR-3 that looks, and works well with one caveat. I  can't 
get the S Meter to deflect past S2.
 
  So far I have swapped all the tubes involved??? Removed the meter,  and 
it tests OK, so far, I haven't found any resistors out of spec. Tried  
changing the value of the shunt resistor, which is connected to the zeroing 
pot.  
Not much help there. I don't see much change in the voltage at either the  
receive IF, or the transmit IF. I understand that the TR-4 has a meter  
sensitivity pot, whereas the TR-3 has only the zero pot.
  Does anyone have any other ideas?
 
  Thanks for reading  this  Tom,  WD8JPP 
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[Drakelist] 2C & 2CQ

2011-04-13 Thread John Boyle
The 2NT has been sold.  The 2C & 2CQ are still available.  Photos on request.

2C excellent condition $175 w/manual

2CQ excellent condition $225 w/instructions

Postage from eastern Ontario is about $30, probably less for 2CQ.

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[Drakelist] WANTED 4 NB

2011-04-13 Thread Old Cowboy
 
Hi all...
 
Looking for a 4 NB board with cable. Or possibly a R 4 C with an NB board
installed.
 
Thanks,
 
Bud, W7CWY
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