Question about Echolette Klemt NG51

[Picure]

Hello, first time posting here. I would like to ask a question about a Echolette Klemt NG51 I aquired yesterday off reverb.com. The unit I have is very clean and in full working order. However, I have noticed that when I turn all 3 record heads to their max levels, the 2nd record head is louder than the other 2. I red somewhere that there are inernal trim pots that can adjust the volume of these heads even further. I would like to make sure about this before I go noodling around inside because I know nothing about electronics.

Also, I get a 60 cycle hum as I increase the "reverb" volume. I read on this forum that there is a hum balance pot to adjust this but the poster never mentioned if this hum balance pot is for the preamp or the tape delay section because this hum is only present when the tape echo function is engaged. Otherwise it is whisper quiet.

Thanks!

[Mick Bailey]

Welcome to the forum. Some useful information in this link;

http://music-electronics-forum.com/t37002/

The schematic shows individual trim pots for each head. With these old 'skeleton' pots they can sometimes seize and forcing them can cause them to break up. I usually give them a squirt of Deoxit and leave them for a few minutes before adjustment. It's best to read up and get as much information as possible before diving in - it's easy to get old tape machines badly out of shape by making a mistake.

[Mickey]

Welcome to the forum. Some useful information in this link;

http://music-electronics-forum.com/t37002/

The schematic shows individual trim pots for each head. With these old 'skeleton' pots they can sometimes seize and forcing them can cause them to break up. I usually give them a squirt of Deoxit and leave them for a few minutes before adjustment. It's best to read up and get as much information as possible before diving in - it's easy to get old tape machines badly out of shape by making a mistake.

What will also improve the echo sound is to adjust the variable capacitors which are located near the pre-sets. These are set to 60V, 90V & 120V for heads 1,2 & 3 respectively. You will require a AC Voltmeter to do this as the voltages are all AC.

[Picure]

Thanks for the tip! But where do I measure the volts with the voltimeter?

[Mickey]

Thanks for the tip! But where do I measure the volts with the voltimeter?

Easy, use the link from oc disorder and then scroll down to the diagrams which indicate where to make the measurements. Also when adjusting those pre-set recording levels, if you don't have a CRO you can get close by carefully listening to the volume of each head's echo after setting the front control panel knobs to approximately 1/2 way mark.

[Mickey]

Hi,Guys, to those of you who have serviced/repaired these units I wonder if you can shed light on the AC voltages on the recording heads. These have been noted at 60, 90, & 120V in various posts but I wonder where, who and how these voltages came about. Folker Staedel from Germany advised me to adjust the variable caps to obtain these voltages and I would certainly not disagree with him, but I wonder how they were derived, maybe noted on a factory memorandum? Would appreciate any comments/information re these voltages. Mickey

[Picure]

Easy, use the link from oc disorder and then scroll down to the diagrams which indicate where to make the measurements. Also when adjusting those pre-set recording levels, if you don't have a CRO you can get close by carefully listening to the volume of each head's echo after setting the front control panel knobs to approximately 1/2 way mark.

Thanks a lot! Unfortunately, I personally am not an electritian and do no understand schematics. I was hoping there would be pictures or a video to show how its done. But that is a bit much to ask for I think. Haha

[oc disorder]

Hi Picure,

Firstly , "I read on this forum that there is a hum balance pot to adjust this but the poster never mentioned if this hum balance pot is for the preamp or the tape delay section ?"

The hum balance pot is for the pre-amp , it is the centre tap for the heater supply to the tubes as in some Fender amps
but when adjusted to it's optimum , the recorded signal and the play back signal benefit too !

As you say it's whisper quiet when not echoing I doubt adjustment will make any improvment.

As you look down into the unit facing you it is located between the lower two tubes on the left.

I suspect the hum you hear is cumulative from stray magnetic fields being picked up by the heads in the same way
a "guitar hum's " when standing close to an amplifiers power transformer.

However make sure all metal physical connections (chassis) are clean and secure .. I find even after all these years
the German Engineering still holds up and in my case couldnt get any better.

From the Revampblog (scroll down to the bottom) :-
Echolette NG51 Tape Loop Echo | ReVamp Blog

On this last pic you’ll see a heavy twisted black and white cable. There’s a good reason for this, but you can improve matter just by tightening down bolts. The transformer is bolted to the main chassis and the main earth (ground) is connected to that. As the heaters have a centre tap to ground (via hum balance ) any problems with the chassis connection between the transformer (that’s the big brown thing on the left of the pic, with wires all over it) is big bad news for hum and background noise. The heavy black/white cable actually straps the main and the sub chasis’s together, so the electrical connection of the frames isn’t really important. If that’s not done, slacken the screws off to the transformer chasis, and then tighten them down again. It will shift any claggy accumulations and refresh the ground connection.

Again I doubt this will help as you say:- "this hum is only present when the tape echo function is engaged. Otherwise it is whisper quiet."

Secondly :- "I have noticed that when I turn all 3 record heads to their max levels, the 2nd record head is louder than the other 2."

'Spose the attractive young lady in the third row came up to you after the gig and commented that your second head was a bit loud?

Seriously , it's a bit hard to conduct here a crash course in '50s electronics just for this .. can you live with this?
or must you leave no stone unturned ?

It's possible you may make it worse .. eg = the control is stuck and breaks when you try to turn it

Pre-set pot R30 adjusts the pre set level for head no 2.



Make sure you observe and mark exactly where it is before you break the seal and turn it.

On the diagram you will notice the audio/sound comes in from the left to get to the head and the bias comes from the right
just like politics ! (sick joke)

Sound or audio has to go through the front panel volume R27 the the preset vol R30 and a resistor before it makes it to the head where it kinda wobbles the bias to leave a magnetic imprint on the tape.

Good luck and don't say we didn't warn you !

And Micky I don't know how they arrived at those figures my half arsed guess is the first magnetic "Hit" has to be 120v with the 90v and 60v following to try to not submerge the former with the latter.. The Germans did have a flying saucer of sorts too !

[Mickey]

Having just completed an overhaul of an early NG51S Klemt Echolette Tape Echo, I decided to do some checking of the bias circuitry of my Dynacord E51 Tape Echo, these units are possibly the last of the valve units and my example is in quite decent condition and sounds great.
Perusing all the information that I have collected over the years I was rather surprised that the last schematic that I received from Folker Staedel shows that the bias voltages to the heads are reversed to what is usually noted. On this latest schematic Head 1 has 160V AC, Head 2 has 120V AC and Head 3 has 90V AC. On other schematics and images I have these shown as 60V, 90V & 120V on one schematic while another shows these as 15V, 30V & 45V for Heads 1, 2 & 3 respectively, the former as provided by Folker Staedel.
As head No 1 is nearest to the playback heads I would think that this head would require the strongest signal to over-ride the signals recorded by heads 2 & 3, with head 3 requiring the least amount of recording signal, this is my assumption. Possibly the last schematic forwarded to me by Folker may actually have the correct adjusted bias voltages.
If only one head is used for recording the bias voltage level will have little effect on the playback signal but when 2 or 3 recording heads are used simultaneously then these differing bias levels come into play.
To check my assumptions, I increased the bias voltage to all heads to approximately 200V, this increased the output of the recorded signal but also it's distortion. I wouldn't bias the heads with such a high AC voltage.
Then I set the voltages to 120, 90 & 60 V for heads 1, 2, & 3 respectively and noted that the tone was very clear but the levels had dropped.
Finally I adjusted all the head bias voltages to approximately 140 - 160 V and this to my ears provided the best overall tone with the least distortion.
Hopefully a reader will respond with a more scientific explanation to my findings

[Souleyman]

What is a properly resistance of record heads guys? Can't find the information. I have the one dead others shows me about 1k-1.2k but I've met the same heads with about 500 Ohm. Is it possible?

[Mickey]

The heads should measure approximately 1.2K. If you are measuring 500 Ohms you'll find that these heads belong to tape recorders, they are OK for playback but you should replace both heads to keep the right balance.

[Souleyman]

Thank you for the answer
I'm already installed the one 0.5k as a record head and it works fine and easy adjusting with stock resistor and cap trims. And it looks like identical with the original heads.