leak Trough line 3 (a tale of silly mistakes

[tiv48]

this should of been easy ,i hade onebut sold it 2 years ago and regreted it ever since.
a tatty one came up on ebay wich i won for £12.50. when it arived i started it up with a variac, only sighn of life wasvalve heaters glowing,
nexed i checked the ht at the filter block, 156 volts.
locking at the circuit the em84 should of had 160 volt at pin 6 this was zero the feed comes from the afc switch, it turns off the magic eye when afc is turned off. i shorted the swich out and now had a loverly green glow from the em84.
next step was to connect it to the hifi and an arieal ,oh dear afew very low level distorted stations .
there are only 2 electrolitics apart from the smothing block ,a 4mf 400 volt smothing in the anode of the cathode follower output stage.the volts at its povitive was only112 volts should of been 140 volts,its 10k anonde load had also risen to 16.4 k so that was changed as well. the only other bit changedwas a 1mf feed to top of volume control
back to the hifi,oh dear nothing at all.
back on the bench. with a bit of wire feeding the arieal and using a crystal earphone as a signal tracer found ther was audio at the multiplex output sometimes ,nothing at the output .the local distance swich caused the intermitent signal , another switch tep shorted out after spending about an hor cheching everything around the output stage i found that i had bent the tag on the volume control and it was touching the body. oh well another on down to failing eye sight, but at least it was now working .
back to the hifi , i dont belive it only hiss . more of my fault all the messing about i had pulled the other end of the arieal from its wall socket.
not as sensitive as it should be but sounds wonderfull . next is a paint job on the black . clean or change the two slide switches and try a new ecc 84.
rob t

[Paula A]

I used to have one of these back in the day (mid 80's) and remember that low sensitivity was often caused by a very strange trimmer underneath.. what looks like a ceramic resistor with a copper sleeve around it with a wire (was it green) soldered to a tag.. generally a prod will produce amazing results

[tiv48]

thanks for that will give it a try any ideas on changing the slide switches wont clean up so still shorted out
cheers rob t

[Paula A]

They can be dismantled carefully.. and the little inserts within replaced.. I once had to do 32 of them on the backside of an HH mixing desk. Chances are they have lost their "spring" over the years and rather than being dirty are either actually physically broken or the plating worn away. A decent supplies shop should stock similar switches so you may be able to mix and match bits to get something working... The fallback total bodge is to use some of the thick copper "foil" for 20's style baseboard screening and make new inserts. You can harden it up somewhat by burnishing it between steel edges.

[tiv48]

i have some replacment swiches, the problem is the way thay are fixed to the front panel.it seams to have
studes that are part of the panel that are used as rivets, may have to resort to epoxy resin! because the fm signal here is poor i may leave local distance wired to distant
rob t

[Paula A]

strange.. must be a later version.. mine were held on with threaded studs. sensitivity was never that fantastic to start with.. experience from elsewhere says to try a few new valves in the front end until one works well.

[AlanBeckett]

Rob,
Just noticed; change the title so it makes sense.
It's Trough not Through. HJL would be turning in his grave
Alan

[tiv48]

thanks alan old age again.
rob t

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paula A
yeswill thry a new ecc82 on saterday but must sort my aerial out first ,
cheers rob t

[Paula A]

Try a few.. they are very variable.. think mine had an 85 in it.. because apart from the 83 which has too much interelectrode capacitance the others 82/4/5 I just used to use at random.. if I needed an 83 I just used any of them.. in my book (as a guitar amp jockey) I found them to be 100% interchangable... at a push a pcc85 from a tv tuner sometimes does the job too.. can't remember.. it's 25+ years ago. Think my laney has an 82 and an 85 in it along with an 83.. any old valve would do me on the road.. as long as it worked...

I gathered the "try a few until one works well" info from the "other" forum.. where people seem to think thats the best way rather than messing about with testers and whatnot.. after years being banged about the mutual conductance and capacitances are likely to be all over the place even between identical NOS examples.

Don't forget the waxies either.. there are a few lurking in there.

[tiv48]

ha ha just dug out the circuit valve one should be ecc84 i wondererd why it had an audio valve as an rf amp im amazed it worked at all .so much for buying something as untouched (was working fine when stored) oh well welive but dont learn
rob t