Klemt Echolette S...(cont.)

[oc disorder]

This is a continuation of a thread originally posted by Translucid titled "Klemt Echolette S"
re Noteas Klemt Echolette E51 S (the gold one!).

Nick (notea) is in France and despite my inability to speak French (I knew those French lessons were useless way back at school ..not much help to me now!!! ) he is testing the components around the ECC82/12AT7 and measuring the voltages while we try to determine why the bias oscillator is not working.
Any contributions welcomed !

notea wrote-
"I'm back to this beast, and I did the reading anti-clockwise this time of the ECC82, and it's seems that we've got the proper values here except that there is no DC at pins 3 & 8.
Pin 1= 300V, Pin2= 100K, Pin3= 470 ohms+ 0 DC, Pin 4&5= 5V AC, Pin6 = 305V, Pin7= 100K, Pin8= 470 ohms+ 0 DC, Pin9= 0 AC
can't explain why there is no DC at pins 3 & 8?
"If there is no DC at pin3&8 of the Ecc82 it's because of the osc coil that doesn't work properly."
- So I checked the lug of the 0.1 uf cap and there is no voltage at all,
- So no voltage on L2 and 300 VDC on L1, that's mean the cap is dead right?
- I don't know where the test point is on the osc coil for the 270V AC so i checked each lug and I got nothing except
where there is the DC coming (I read 600-650 AC)
Cheers, Nick"

Hello again, we just had a long weekend celebrating the 8 hour day in Aust. but the way things are looking "dunno" (translation = don't know) if we will be celebrating this for much longer !!

"the cap is dead right?"

Wish I could give quick answers ... well I'll try... maybe.. if you are referring to C18 the 0.1 (500v?)
that taps off the secondary of the oscillator coil L1 and supplies the Erase head with a high freq
AC signal that normally erases the tape.

If it is shorted the resistance of the erase head may drag down the secondary voltage although
it may be too much for the erase head and it too could short (inside wires melted together) or go open circuit (internal wire melts/breaks) meaning there is no resistance reading from the head.

Try unsoldering one end and see if a voltage appears at the ECC82 cathode pins 3 & 8.

We now know that the 2 x 100k resistors on the grids are ok and the cathode resistor 470Ω
is also ok.

That leaves the tube/valve, the Oscillator Coil (transformer) and the capacitors that could be broken.

The tube is easy to test , just put in one that is known to work or a new one that works.

The Oscillator Coil is a difficult one... would have to get a second hand (used) one or have some expert rewind it at great cost ..I don't know of anything suitable at the moment so we will keep our fingers crossed and hope it is ok.

The capacitors we can change fairly easily.
They can change their value , and this upsets the circuit as it wants to resonate vibrate ... um oscillate !

I think it's more likely the 3 capacitors connected to L2 have drifted from their value.
From your photos the capacitors look "old waxy style" and after heat and many many years
their capacitance in farads may have changed.

So lets replace all four which should not be expensive.
From the NG51S schematic
C18 = 100000pF = 100nF = 0.10uF Check the voltage on the old one above 350vDC should be ok.
C19 and C21 = 200 pF = 0.20nF = 0.00020uF silver mica 500v?
C20 = 1000pF = 1nF = 0.001uF 500v good here too.

"I don't know where the test point is on the osc coil for the 270V AC so i checked each lug and I got nothing except where there is the DC coming (I read 600-650 AC)"

We wont get the AC as it is produced by the oscillator which is not oscillating.
E.g. Our power outlets in the home ..110vac or 230vac at 50 or 60 HZ (Hertz = cycles per second)
The oscillator is probably about 60,000HZ or 60KHZ very high vibration !!
With some multimeters they can give strange readings where oscillators are involved.
It's almost transmitting as it is vibrating at a very high rate when it is working :-) !!!

So you have some shopping to do . You may like to trace the erase head connection and see if it still
measures resistance like you did with the record heads.
It may be a bit different to the 1.??K .
I'm fairly sure its wire connects to that 0.1 on top of the coil.

| Farnell element14
http://fr.rs-online.com/web/c/?sra=o...EUR+200pF+500v


Further reading on things that flip back and forth (oscillator)
https://www.youtube.com/watch?v=WkipSDmoOHU
Astable Multivibrator (Oscillator)

[Mickey]

Hi, back from my trip down south and have just read the responses to your issue. Can you borrow, beg or steal an oscilloscope? If so you can quickly check the waveform from the oscillator on the erase head, it should be approx 60Khz at a AC voltage of approx 80V. The oscillator transformer is a very robust device and will most likely be alright. Have you checked the 1uf capacitor on the 470 ohm feed resistor? Also have you measured (from either pin 3 or 8 of the 12AT7) to ground, this should measure 470 ohm. Replace the capacitor that goes across the anodes with a .001 uf 630v capacitor, make sure this is a high voltage capacitor as there is a large AC component across the anode windings. My advice is to replace one component at a time then check for a result, as often when a blanket component change is made chances for a wrong connection are multiplied. Good luck.

[notea]

Hi and thanks both of you,

- Oc, i've unsoldered on lug of the C18 cap to check if there was DC on pin3&8 and there is not.
- i've checked the resistance first directly on the erase head at the top of the unit, then on the c18 lugs and i get an infinite reading so i guess the head is open, i hope it's not broken though? otherwise i may have to order one..
- Mickey, i don't have an oscilloscope but i'm thinking of stealing one somewhere as you suggested me.. I did the AC measurement on the erase head and i don't have any voltage.
-"Have you checked the 1uf capacitor on the 470 ohm feed resistor?"> sorry i don't know where it is, could you label it for me?

Next step is ordering components, as soon as i get them i'll do the cap job.Hope i don't have to order a new erase head..
I might need some advices for the osc coil before i bugger it (i try aussie slang!), i'll unscrew it from the top of the unit, label the wires, but do i have to unscrew the bias screw in the middle of this square tagstrip or leave it alone?

Cheers Nick

[Mickey]

Hi Nick, with the valve removed you should measure 470 ohm from either pins 3 or 8 to ground. C18 is the feed to the erase head and would have no effect re R37 (470 0hm). R37 is the cathode resistor for 12AT7 (Rohr 5). An open erase head will not stop the unit from working, you would end up with infinite echos.
The 1uf filter (bypass) capacitor is wired directly to the bias oscillator transformer where a 470 ohm resistor feeds the HT to the primary coil. It's value is not critical as I usually replace it with a 10uf 350V capacitor. On some schematics this capacitor is not shown near the oscillator coil. I believe it is C47.
Leave the oscillator coil ALONE!!!!!! To check the erase head just measure across it, should measure about 3 ohms. Again your problem will NOT be in this area of the circuit.
Good luck and keep us posted, Mike

[notea]

Hi Mike,
i doubled check the readings on pin3&8 of the ECC82 and i've got 470ohms so i guess it's a good news,
my worry is, to access those caps i might need to remove the osc coil as suggested Oc in previous posts?
but i'd like to do this this in a proper way,
it looks like it is held just by one screw on the top of the unit and i suppose i don't have to touch the bias screw to pull out the osc coil?
What could be another way to replace those caps without removing the osc coil?
I'm ordering the parts tonight, can't wait to have them!

Cheers Nick

[oc disorder]

Hi again.... I cannot see how a tech can get to the base of the Osc. tube without removing or moving the osc. coil.
To undo the chassis to gain access seems like a nightmare to me. Perhaps a can opener? or as a friend did once.. used a nibbler
to cut a big hole and then made a plate to cover the mess !!! (not an echolette I might add !)
Nick , with the erase head if you have good eyesight or in my case use a jewelers eyeglass ( for magnification ) gently check
the fine/tiny wires under the solder blobs ...

Quote Originally Posted by Kazooman
"I believe that Bobby Staedel rewinds Echolette heads.
I have no idea what this would cost and you need to figure shipping to and from Germany."
bobbysreparaturen.de
I think he does a swap providing yours is in good condition well ... apart from the broken wire - which he can rewind later.

Does anyone know if a changed load on the secondary winding would stop it oscillating ? i.e. lack of a low ohm load as in open erase head?
Reflected impedances and all that..

Nick .. when the parts arrive just try replacing the 1000pF across the coil first as Mickey suggested.
The cheesehead straight slot screw (about 1cm) on the top is just a mounting screw, there is no bias adjustment at the coil.

[Mickey]

Hi again, many years ago I had valve extensions ( both home made and professional) these allow me to measure voltages and waveforms without having to dig deep into the innards of a repair item.
As for reflected impedance I would think that the oscillator circuit used in an Echolette would not be affected by O/Cs or S/Cs. Many of the better quality tape recorders used the multi-vibrator circuitry as it is far more stable and can supply higher bias/erase currents.
I'm concerned that Nick is in to deep already and that he should stop digging the hole which may end up with another Echolette on the scrap heap.
Maybe he should re-iterate what his initial problem is and what he has found so far. As they say "make haste slowly"
Cheers, Mike

[Mickey]

Hi Nick, I wouldn't replace those caps which are located hidden behind the coil. These are styroseal low value caps and unlikely to be faulty, even the .001uf one. Fit a ECC82/12AU7 and check for 11V DC at the cathodes of this 12AU7. If you are adventurous solder a piece of thin wire to the positive test lead and then if you pry the valve up a little you should be able to measure the voltages on the pins of the valve with the power switched on. The anodes of this 12AU7 should read approximately 290V and you should have no voltage at the grids, if you do have voltage at the grid you either have a faulty valve or the coupling capacitor is faulty (leaky!)
Having a 12AT7 in Rohr position 5 makes me wonder if a previous owner tampered with this unit. Have a close look for any obvious mistakes such as incorrectly connected replacement resistors or capacitors.
Cheers, Mike

[oc disorder]

Whoops had a mental block my apologies

ECC82 = 12AU7


Think I picked it up here

http://music-electronics-forum.com/t...6708/#poststop

[notea]

Hi, i checked the tiny wires of the erase head, there was a bit of dust that i cleaned but they seem fine.

- I put the ECC82 in place, let a tiny space to see the pins and measured pin1,Pin3&8,
it was a bit tricky and i hope the fact that the tube was not completly pushed down doesn't effect the readings too much..
-anyway, i hardly measured 260VDC on pin 1 and from time to time the meter went crazy (perhaps the fact that the tube is not completly pushed?)
- On pin 3&8 i measured 5VDC (by the way sorry for this learner question but i don't know why without tube i should have read 11V and 0 V with the tube in place?)

So i will order a new ECC82, and may be 'll try to replace C18 as soon as i receive the parts, cause it's easy to change
i'll be away this w-e but early next week i'll do a recap of my problem with all the readings i made on each tube and tapeheads,
including a recap of your advices for this step by step troubleshooting since the begining.

Cheers Nick

[oc disorder]

Yes Nick the 11 volts DC is only there when the tube is conducting. Sorry I just assume that.
When the ECC82 is not plugged in , there is nothing connected to that 470 ohm cathode resistor
(R79) except ground and 2 empty pin sockets :-(

It does seem to be partially working.

[Mickey]

Hi Nick, did you measure the voltage at pin 6? This should be the same as pin 1. Your erratic metr readings are most likely caused by the pins on the valve being slightly oxidised so a good contact is a matter of perseverance.
If you are measuring 5V at pins 3&8 that may suggest that the oscillator isn't working as it should, that is why you should also measure pin 6 which is the other anode.
If you are still having problems identifying the connections to the oscillator transformer, they are as follows: Looking from the top with the back of the NG51 away from you,
pin1 top LHS goes to ground, pin2 (next one down and it is only a connection point) goes to the erase head, pin 3 has capacitor feeding erase head connected, pin4 goes to record heads. On the RHS pin1 (at the top) is the B+ input, pin2 goes to ECC82 anode, pin3 goes to other ECC82 anode. The LHS windings are the secondary while the RHS windings are the primary.

[notea]

Hi,i'm back to the "gold cage"
First i wanna Thank you guys again for all your advices,and guiding a beginner like me trough this piece of machinary..

This is a recap of our work since the begining:
troubleshooting the Echolette NG51s with no echo.

The visual indicator does respond when the signal is applied

TUBE READINGS:

Tube n°1:
Pin1&6=230V
no ohms readings on the other pins
Tube n°2:
Pin1=199V,Pin2=162K,Pin3=992ohms,Pin6=290V
Pin7=990ohms,Pin8=343ohms
Tube n°3:
Pin1&6=136V, no ohms readings on the other pins
Tube n°4:
Pin1=202V,Pin2=1000k,Pin3=988ohms,Pin6=227V
Pin7=1000k,Pin8=2k20
Tube n°5(ECC82):
-without tube: Pin1&6=300V,Pin2=100k,Pin3=470ohms
Pin6=300V,Pin7=100k,Pin8=470ohms
-with tube pluged in:
Pin1&6=230V,Pin2=100k,Pin3=470ohms+7V,
Pin7=100k,Pin8= 470ohms+7V

TAPEHEADS
-I measured 1k14 ohms for each except the erasehead that seems open

* with the reverb control fully clockwise i touched the head gap of the replayheads with a screwdriver as suggested Mickey
and i can hear no sound coming from the amp

-I measured the trim caps
"The voltages you measured are for record head 3 & 2. You only need to measure where
the head connects to the variable capacitor.For head 3 you measured 45 volts .. (according to Kazooman) this should be 120 volts AC @ aprox 60kHZ.
For head 2 you measured 30 volts this should be 90 volts AC @ aprox 60kHZ.I suspect head 1 ('s) reading (which is hard to get to under the rectifier) would be lower 10 or 15 volts so
I guess the oscillator is low on the output.Oc Disorder"


-stange thing is i got AC on trim caps but i can't find any 270V AC on the osc coil..
-i Have 7VDC at pin3&8 of the ECC82 with the tube pluged in.

I'm still waiting for the parts and the new ECC82, i will replace the 0.1uf (C18) but we're not sure it's gonna solve the problem.

Cheers Nick

[oc disorder]

Hi Nick , that C18 (0.1uf) is in series with the erase head so if the erase head is open you won't get any change by fitting the new cap as only one end is connected.
To satisfy my curiosity while you are waiting could you solder a say 10 ohm resistor across the erase head (this places a load on the coil's secondary) and try measuring the 270vAC again ..could also check the ~30 and ~40 volts AC at the trim-caps.
This is sticking my neck out (well you are in France) ... that C18 may be faulty and have contributed to the erase heads demise!
We haven't checked the playback heads yet for continuity. They terminate in the bowels of the machine unfortunately.
Anyhow first hopefully you can get the osc. working.

One possible problem we haven't dealt with is the possibility your multimeter is not capable of measuring AC which is oscillating
at a high frequency.

This is why suggestions have been made to borrow an oscilloscope.

A more expensive meter with a large bandwidth may solve this too if you could borrow one.

Some further reading:-
Post #15 here

http://forum.allaboutcircuits.com/th...-voltage.7607/

and

https://groups.google.com/forum/?hl=...cs/hX73zE2f0nM

[notea]

Hi Oc, ok that makes sense.. But i feel a bit lost right now, don't know what to do except replacing C19/20/21 but as Mickey said "These are styroseal low value caps and unlikely to be faulty"
and i have this 7V on the ECC82 so that means there not dead?