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Eico 2050 - Adding Loudness switch?

mcaddie7

mcaddie7

Active Member
Hey all,

I have an Eico 2050 which I’ve gutted and installed the nicest parts with tightest tolerances I could find. This thing sounds lovely.

However, I’d like to change the hi pass filter switch on the front to be a loudness switch for lower listening volumes. Any tips or tricks? I could find an exact how to fit this model.

Any other mods are also welcome
 
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Isn't the 2050 the facelifted version of the ST-40 but same circuit? If it is, see if the ST-40 schematic has the answer you seek.
 
Thanks for the info!

Looking at the ST40, the loudness switch is here. Apologies for not being much use here, this sort of mod is new to me. Link. Would someone mind explain this loudness circuit in terms of parts, and what loops are switched on / off?
1747235871619.png

This is the eico 2050, I'm assuming I would add some sort of circuit here where the two red x's are, right before the pin 2 of the tubes? My assumption is I would then keep the Hi Pass filter switch off, keeping those wires intact that make continuity on each side to preserve the OFF function. Turn the switch on, and remove any wires connected to that position, and then from there connect my loudness circuit?
1747236176817.png
 
The loudness circuit usually requires a volume pot with the proper loudness tap on it. If your 2050 volume doesn't have the loudness tap then it won't work for you. You will need to find another volume pot with the tap.
 
yeah if the pot doesn't have the tap you're pretty much SOL. See if there is an extra tab on it that isn't connected to anything though, you may find they used the same pot in both models.
 
gadget73 said:
yeah if the pot doesn't have the tap you're pretty much SOL. See if there is an extra tab on it that isn't connected to anything though, you may find they used the same pot in both models.
Click to expand...
Is that all I'm looking for, an extra tab on the volume pot? Or are they specific to loudness circuits? I'll take a picture when I get home in a few hours.
 
Look at the schematic above for the ST-40. The volume pot has a 4th connection on the left side of the schematic symbol. Quite often it is on the opposite side of the shaft from the normal 3 connections. Here is an example.
1747243859100.jpeg
 
^^ yes, this. If its got that extra tab poking out of the opposite side with nothing on it, you're probably good to go. If the ST-40 schematic or parts list happens to say where that tap is you can measure to confirm.
 
Alas I can't seem to find one online that is the required 500k. Any other solutions / sources or are these just hard to find, even in modern equivalents.
 
Tapped volume controls are very difficult to find. Only way I can think of to "make" one is to use a stepped attenuator and wire in your connections at the appropriate tap.
 
mcaddie7 said:
Alas I can't seem to find one online that is the required 500k. Any other solutions / sources or are these just hard to find, even in modern equivalents.
Click to expand...
I went down the Eico ST70 loudness control rabbit hole several years ago and found this piece of information that you might find useful, if you manage to find a solution to tour loudness tap dilemma.

The loudness circuit used on the ST70 is the same as used on the ST40 and was not designed to be very useful.
There was a lot of discussion in the DIY audio world at the time, and I found the revision to the circuit I have shown here made it work a lot better.
 

Attachments

Here is the way it was done back in the 60s. You could buy a Centralab Compentrol for a few dollars and then just replace the volume potentiometer. The second picture is showing what the PEC contained. If you can find one of these vintage controls, you have what you need.

Compentrol2.jpgCompentrol.jpg
 
Okay so there is one for sale on ***Bay but it's 90 and an old Citation 1 volume pot.

I did find this, I know the original is 500k but would 250k work without changing the characteristics of the amp too much? If a 250k wouldn't work then I guess I'm stuck to adjusting the tone controls when listening quietly as the 500k version of this appears to be basically non existent.

1747417793226.png
 
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