Klemt Echolette E-51 trim pots and tubes location

[nisios]

Hi everyone.

This is my first post here. Very nice forum. I have a little analog gear repair shop, i started thsi year.

I've had an old KLEMT Echolette E51 for many years that needs a bit os love!

It needs replacement of the filter capacitors and a tune up, but acctually it is in pretty good shape for such an old beast.

Its a complete pain in the ass to work on this unit because it it almost impossible to disassemble. I honestely dont have a clue how they were able to make it like this.

The thing is that the pots and tubes are completely unlabeled in my unit, i dont know if this is the case for other units. The tubes are easy acctualy, as i have the schematic. But the pots arent that easy.

Also is there a specific way to bias the recording heads?

Another thing that bothers me is the way my record head number 1 pot behaves, if i go CCW all the way the unit starts to self oscillate really fast instead of shuting off the echoes. I see in the schematic that this pot is different than the others and that it is somehow connected to the regeneration circuit. What was the point of this? I solved this annoying problem (or not) by unsoldering one of the pot lugs. But i wonder what was the purpose of this in the first place.

Thanks and sorry for such a long post (and my bad english).

[oc disorder]

No need to apologise for the post and welcome by the way.. Your English is good and I don't have a second language so who am I to judge !! :-)
Wow You almost need to speak German to deal with the Klempt.
I am just giving you a link as I am not an expert on this.
I hope this is some help.

Echolette NG51 Tape Loop Echo | ReVamp Blog

[nisios]

Thanks very much, very helpfull.
I thing i got all that i was missing from that link.

[dmeek]

http://music-electronics-forum.com/i...attach/gif.gif


R76 is the hum balance pot. It was very sensitive on the Echolette I looked at recently.

Doug

[Kazooman]

Hi everyone.



Also is there a specific way to bias the recording heads?

.

You bias the heads by adjusting the variable capacitors located on the end of the chassis. You really should use an oscilloscope to do this since the oscillator runs at about 60 KHz. Heads 1, 2, and 3 should be set to 60, 90 and 120 volts respectively.

[nisios]

Hi,

Thanks for the info.
Looking at the schematic i can only see a reference for the specified capacitance in the bias and not a specific voltage as you indicate. Is there some sort of service manual for these units im missing?

[Kazooman]

Hi,

Thanks for the info.
Looking at the schematic i can only see a reference for the specified capacitance in the bias and not a specific voltage as you indicate. Is there some sort of service manual for these units im missing?

I do not know of any service manual. I got my information from Bobby Staedel. He is the world's expert on these echos. He runs a repair business in Germany. You can Google his name to get to his website.

When you adjust the bias you should use a fairly long non-conducting screwdriver. The capacitors will sense the proximity of your hand and you get a slightly wrong setting.

There is an owners manual, but it is not a lot of help as far as repairs are concerned. If you send me a personal message with an email address I can send you a PDF of the manual.

Also, think you mentioned replacing the filter caps in your original post. I do not know of any source for the required caps in a size that will fit in the space of the original caps. I had to replace the caps on one of my Echolettes because the solder terminal broke off. The only suitable cans I could find were larger in diameter. I was able to locate on in the original place, but had to mount to other one at the far end of the chassis and connect it with wiring. It worked fine, but is certainly far from original.

[nisios]

I already sent you a PM, thanks!

I already replaced the filtering caps, although i didi it with 47uF ones and i think i will increse it to 68uF just to get a bit less ripple.
They are just regular electrolytics connected under the metal chassis. I left the old metal ones in place, just disconnected them.

I got rig of a lot of noise with the new caps (and i also substituted the old diode bridge). I also changed a couple more electrolytics i had "easy" access and a couple of paper capacitors. In the end i got the unit runnig pretty smooth, no more crackeling noises and excessive hum. Im trying to make some new tape now as the old one is pretty screwed now. That will further bring general noise down.

I had to change the input gain pots, unfortunately for some regular alpha ones, wich are not like the originals, but thats ok.

I'm tempted to change the "Original Signal" trim pot for a regular pot i can more easily ajust while playing.

[Kazooman]

The manual is on its way.

[nisios]

Thanks!

[Audiotexan]

I've had an old KLEMT Echolette E51 for many years...

[ATTACH=CONFIG]29654[/ATTACH]

So future passers-by are aware, the schematic posted is for the NG-51, and not the E-51.
But it's at least close and something to work with!

PS: No offence to OC, since I was going to put the same thing up, only his copy is cleaner!

[oc disorder]

How about this one Mr Texan ...?



'cept there's no reference to Klempt but I assume it can be a genetic term these days..

I presume the coils are tweaked for max resonance using one of those nylon/plastic slug adjusters

Can anyone banish my ignorance re why the record heads have different value tunable caps there ?
Seems like 60pF, 120pF and a 200pF with a fixed 100 in parallel ?

I've seen hams using grid dip meters to "tune their slugs" (almost sounds like barnyard talk..) when I was about 12.
I presume it's related to that path...
and one more question anyone how can you tell the correct polarity of the heads as the two coil wires are independent of the shield which is just connected to the heads metalwork... like a balanced mic. the wires on the one I have seen look the same colour...

[Audiotexan]

How about this one Mr Texan ...?
-ATTACH-

Tha's puuurrty right thar!!
Nice find =)

Can anyone banish my ignorance re why the record heads have different value tunable caps there ?
Seems like 60pF, 120pF and a 200pF with a fixed 100 in parallel ?

Only a guess here, but I'm curious too.

From the looks of it, it strikes me as a way to tune the carrier (modulation) frequency of the record heads. I have my suspicions as to why, but I'll stop there so I don't derail (both myself and the thread lol).

I also noticed that the figures you inquire about appear to be alternate values (with the primary spec being 150pf at each one so that all 3 are the same on one unit, and perhaps different on another). Perhaps there was an optional 'factory mod' version of this unit available as well with the 200pf/120pf/60pf?

(Assuming that the R73/R72/R71 in that part of the schem correspond to the "1st head, 2nd head, 3rd head" and are simple 'level' controls on the pic of the front panel from the "ReVamp Blog" link that you kindly shared earlier)

*Waits for someone far more experienced to chime in*

[nisios]

I dont know but i believe one obvious adavantage of using tuneable capacitors instead of variable resistors is that, first of all, at bias frequencies you have tunable capacitors with a value of interest, second this way you are able to change the ammount of bias voltage to the head without affecting impedance at audio frequencies.

You get two almost independent ajustments, one for audio signals and other for high frequency bias. I believe this makes the job of tuning both bias and audio signal strength to the head much more easy and stable.

Im saying this but im not very familiar with head bias schemes, im not the expert, just my opinion looking at the schematic.

[nisios]

hum....

I will need to have a look at mine, apparentely it doesnt do a thing, and you are telling me yours was very sensitive....
These pots are very fragile, maybe i have a broken pot...