Th. Lösch Phono Amp: Question about IC used & ECC808 to ECC83

[MartinR]

Hello,

1. Can I use flexible wire or am I supposed to use solid wire?

The terminals of the socket should be able to move a bit, so flexible wires are ok.

2. Should I attach a aluminium profile cooler to the voltage regulator?

Yes! The voltage regulator dissipates around 5W. It would get quite hot without it.

3. I was not able to get my hands on the Phillips NHG; may I use any other 47uF/100V-Elko or is this thing special?

You can use what ever you like.

4. I read the old thread of Kofi Annan building the Lösch Pre. The main matter of concern seems to be the grounding ...

I´m using this ground scheme:
Each triode has its own star point with the local gridleak resistor, cathode resistor, and PSU filter cap tied to it. From the local star points goes one wire to the central star point which in this case is the socket of the first tube. The B- is tied to the central star point as well as the heater supply, chassis and turntable.

There is a nice picture in this German tube forum to clarify things.

Kind regards,
Martin

[Herr Grau]

Thank you very much!
I'm already working hard, the PSU is as good as ready, the Amp will follow over the next days.

New Question:
Since the one thing I must not do is connect earth to the chassis at different points, how do you guys isolate the cinch-sockets from the chassis? They are almost completely made of ducting material.. I thought of a piece of plastic tube, a heat shrink tube or something?

[MartinR]

Hello,

Sorry, but I never had this problem because all the jacks I´ve used so far have plastic washers.

Kind regards,
Martin

[Herr Grau]

I fixed the problem with PVC tubes, works alright. Next time I won't buy the cheapest cinch jacks

One last question:
The little Wima Caps in the PSU (0,1uF / 63V) parallel to the heaters:
I thought of soldering them directly to the socket and not into the PSU. That shouldnt be a problem, is it?

It's realy progressing. I laquered the PSU case today, made half of the amp case. The most fun part is to come

[MartinR]

Hello,

I thought of soldering them directly to the socket and not into the PSU.

That´s what I did.

Kind regards,
Martin

[Herr Grau]

Hi folks,
I admit it: I have no clue, what's wrong.
I soldered everything together, checked again and .. doesnt work.
Please help me!
There seems to be a problem in the power supply somewhere already, but I'm confused:
- If I disconnect the power filter line (beginning with the 4,7uF Mcap) there ARE 320V at the output of the transformator.
- If I connect it again, the voltage drops to 170V
- If i cut the line between the MCap and the first Elko, there are 390V at the trafo output.

How is that even possible? What should I do?

Thanks in advance

[SY]

You may have a bad electrolytic or one that's wired in backward. I'd make a chart of the voltages along the power supply rail and see where the excessive current draw is coming from.

[MartinR]

Hello Herr Grau,

as SY has already pointed out something is drawing too much current. I would disconnect PSU and amplifier in front of the 1K8 filter Rs and observe what the voltage is doing. If it´s above 300V, the mistake isn´t in the PSU. Go further down the filter rail until you can identify what´s drawing the current.

Kind regards,
Martin

[Herr Grau]

Ok,
measured against mass:
1. Complete power filter line removed: 320V
2. First cap (MCap) soldered to it: 390V
3. First Resistor and second Cap (first elko) soldered to it:
At the start only 180V, at the elko only a few volts left.

There ist seems to be no short circuit though because i can not measure a low resistant from anywhere to mass.

I cannot make anything of this.

(I dont have to disconnect all the mass lines to the rest of the amp for this measurement, do i?)

All parts are brand new...

[SY]

I don't understand what you mean by "mass." Bitte, uebersetz fuer mich. Ground?

And are the rail voltage measurements made with the tubes removed?