Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Audio Transformers Die? R-390 / R-390A




 
The AM Forum
November 21, 2017, 03:15:48 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Audio Transformers Die? R-390 / R-390A  (Read 286 times)
0 Members and 1 Guest are viewing this topic.
WBear2GCR
Member

Offline Offline

Posts: 3414


Brrrr- it's cold in the shack! Fire up the BIG RIG


WWW
« on: October 26, 2017, 09:30:44 PM »

The recently acquired, de-moused, made to run R-390 was up and running and suddenly the audio went
stone cold silent. Troubleshooting led to a dead 12AU7 section and an open primary on one of the
three 10k:600ohm transformers... the one that drives the other two output sections. This is the R-390, not
the 390A, but they both use the same transformers.

On-the-air today WA1HLR and K1QAR both said that this is a reasonably common failure. Sad

I was able to effect a repair by making the PS regulator from another audio module work again.
(see pics). But I still have a module with a dead transformer that I definitely need.

Thinking of re-stuffing on of these cans with another suitable transformer. Anyone got some dead ones
around? Or a good one? Extra audio module, working or not?  Cheesy

The big question is, is there any experience on this matter? Don't think I have run across it in my online
and hardcopy reading so far...

                     _-_-bear

Pic shows a dramatic looking shot of the bench (forgot to turn off some lights and it looked good) and
the pointer looking at the bad 2.7k resistor that provides the connection to ground at the bottom of the
two VR tubes - aka the voltage reference for the regulator, without it the voltage soars up.


* R390 AF MODULE ON BENCH.JPG (520.5 KB, 1480x1027 - viewed 98 times.)

* R-390 AF MODULE RESISTOR.JPG (514.26 KB, 1480x1110 - viewed 84 times.)
Logged

_-_- bear WB2GCR                   http://www.bearlabs.com
w4bfs
W4 Beans For Supper
Contributing
Member
*
Offline Offline

Posts: 1183


more inpoot often yields more outpoot


« Reply #1 on: October 30, 2017, 04:29:23 AM »

hi Bear ... nice workbench .... reminds me of what a busy one looks like.... like the exam light .... looks like a dentists office got hyjacked ...73
Logged

Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
WBear2GCR
Member

Offline Offline

Posts: 3414


Brrrr- it's cold in the shack! Fire up the BIG RIG


WWW
« Reply #2 on: October 30, 2017, 02:59:17 PM »

hi Bear ... nice workbench .... reminds me of what a busy one looks like.... like the exam light .... looks like a dentists office got hyjacked ...73

Yeah, he put up quite a fight too! :p

Actually an epay purchase, selected carefully for non-functional status electrically, but ok mechanically.
Turned out to be a fried on/off switch connection. Soldered it. Very tight light, good for getting into a small
area - maybe tighter light than i had hoped for... but has been useful.

the bench?
I am hopeless.
Absolutely hopeless.

Can't STICK to doing JUST ONE project. Ever.

Start one... another comes along, then another, then another, then just a quick one, then one more,
then some more...  pathetic.

                  _-_-
Logged

_-_- bear WB2GCR                   http://www.bearlabs.com
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.056 seconds with 18 queries.