Klemt Echolette S...(cont.)

[Sin1949]

I already asked several times: What is your source? And are these Vpp or Vrms values, as the difference would be almost a factor of 3?

The source or the information for the value of the heads HF bias Voltage (60Volt at H1, 90Volt at H2 and 120Volt measured at H3 and the erase head around 70Volt.)
I believe it came from somebody who know an expert for the vintage German equipment (Dynacord, Echolette, Schaller, etc) his name is Mr. Bobby Staedel.

The values are Vpp

Following your request I measured the voltage on the Oscillator tube #5 (ECC82)

Without tube measured directly from the tube socket.

Pin 1 (Anode) = 318 Volt / DC
Pin 2 (Greed) = 0 Volt
Pin 3 (Cathode) = 0 Volt

Pin4 and Pin5 (heathers) 3.97 Volt/AC

Pin 6 (Anode) = 318 Volt / DC
Pin 7 (Greed) = 0 Volt
Pin 8 (Cathode) = 0 Volt

Pin 9 (heather) =1.9 Volt/AC

Voltage measured with the tube (ECC82) being in the socket

Pin 1(Anode) = 302 Volt / DC
Pin 2 (Greed) = (Negative) - 42,5 Volt / DC
Pin 3 (Cathode) = 3.48 Volt / DC

Pin 4 and Pin 5 (Heathers) = 3.8 Volt / AC

Pin 6 (Anode) = 301 Volt / DC
Pin 7 (Greed) = (Negative) - 41.4 Volt / DC
Pin 8 ( Cathode) = 3.45 V / DC

Pin 9 (Heather) = 1.86 Volt / Ac

I hope those values will help to tell if the Oscillator is working properly?

Thanks in advance,

[Helmholtz]

Nothing conspicuous here.

Heater voltage is measured between pin 9 and pins 4/5 - not wrt ground.
What are the supply (B+) voltages at points A1, A2, A3?
I recommend to follow Mickey's instructions from post #17 of this thread.

Here's some more info on HF bias (by Mickey):
https://music-electronics-forum.com/...044#post693044

It seems that exact HF voltages are not really critical, but have some influence on echo sound.
A new oscillator tube might increase the HF voltages, but as said the oscillator works and your real problem must be elsewhere.

Failure history might give some clue: Did the unit work fine before and what happened/changed before failure? E.g. new tape loop etc.?

[Sin1949]

Nothing conspicuous here.

Heater voltage is measured between pin 9 and pins 4/5 - not wrt ground.
What are the supply (B+) voltages at points A1, A2, A3?
I recommend to follow Mickey's instructions from post #17 of this thread.

Here's some more info on HF bias (by Mickey):
https://music-electronics-forum.com/...044#post693044

It seems that exact HF voltages are not really critical, but have some influence on echo sound.
A new oscillator tube might increase the HF voltages, but as said the oscillator works and your real problem must be elsewhere.

Failure history might give some clue: Did the unit work fine before and what happened/changed before failure? E.g. new tape loop etc.?

Hi Helmholtz,

I was busy today with some other thinks but I managed to spent some time with my Echolette NG51S and I found something interesting which may lead as to the problem.

By using my tone generator and applying 200Hz signal to the input jack of my echo unit I checked the Voltages on the three variable pots (R26, R27 and R28). Those three variable pots are located on the top row of the face plate.

The pot R26 is a double pot coupled with a pot R51. This pot is controlling the volume of the Head 1.
The pot R27 is a single pot and this one is controlling the volume of the Head 2.
The pot R28 is also a single pot and is controlling the volume of the Head 3.

So here what I discovered:

By using my digital Scope I measured the Voltage on all three pots (R26, R27 and R28)

On the Pot 28 (H3) the Frequency was 58KHz

The Vpp minimum was 259 mili Volts.
Vpp max was 11.4 Volt when I put the Pot 26 on Minimum!
Vpp max was 8.4 Volts when I put the Pot 26 on Maximum!

On the Pot 27 (H2) the Frequency was 58KHz.

The Vpp minimum was 216 miliVolts
The Vpp max was 11.2 Volts when I put the Pot 26 on Minimum!
The Vpp max was 3.6 Volts when the Pot 26 was on Maximum!


On the Pot 26 (H1) the Frequency was 58 Khz

But Thisis INTERESTING!

The Vpp minimum was 302 miliVolts!
The Vpp maximum was 305 miliVolts!

So it looks that the double pot (26) is not working properly. It looks that there must be some problem where I should pay attention. I am not sure exactly where to start my investigation, do you have any idea?
What would you recommend?

Thanks!

[Helmholtz]

Let me get the above clear:

You applied a 200Hz signal to the input and scoped the AC voltages "on" the pots R26/27/28.
Now what does "on" the pots mean, as they have 3 terminal (lower ones grounded)?
Did you scope at the wipers?

The signal at the record heads should be a mix of high HF voltage and low NF (200Hz) voltage, the small 200Hz signal riding on top of the HF.
To see only the 200Hz signal you should pull the oscillator tube and scope the pot wipers as well as directly at the rec.heads.
This will also tell if the pots are working

BTW, as there is only one HF oscillator, there is only one HF frequency.
I guess it might change slightly if you alter the settings of the variable caps, which are used as HF voltage droppers.
But HF frequency at all heads must be the same.

[Mickey]

A little short on response but how did this repair end, did you accomplish a good repair? Interested because I'm reparing a gold unit at the moment.

[Mickey]

Apart from the usual issues such as faulty "small" signal capacitors, HT filter capacitors, tape heads and valves/tubes, the record level pot for Record Head 1 has been known to become faulty.
This pot is easily replaced with a dual 1Meg pot of the nut fixing variety which can be easily bought on Ebay and other selling sites.
Heads are becoming a seious issue although play-back heads can be substituted with various tape recorder heads, the record heads are a problematic issue.
The early NG51 versions are probably the easiest ones to repair as the later printed circuit board varieties require due care and diligence as well as lots of patience when refurbishing these.
As with all vintage gear the cost of repairs is becoming prohibitive and I wonder how many of these great Echolettes are now on the "too hard" shelf?