Another famous passive EQ

[opacheco]

So these pots are HONKERS and I don't know how I found replace them.
But the protective lids do come right off and I see the issue...now I just need to find a way to straighten out these suckers.

Edit: bent and back in business!
View attachment 145047

I have severals controls units like this in the pic and I suggest to you buy a couple used units like this (by the way, what model is this attenuator switch, T, Lader, Pot????) and replace each contact!….I can be almost secure that contacts are very common in antiques units attenuators!

opacheco

 

[egroys]

delete

 

[MidnightArrakis]

Replace the bad pot....

JR

[Replace the bad pot] -- With some "Acapulco Gold"???.....

/

 

[egroys]

I have severals controls units like this in the pic and I suggest to you buy a couple used units like this (by the way, what model is this attenuator switch, T, Lader, Pot????) and replace each contact!….I can be almost secure that contacts are very common in antiques units attenuators!

opacheco

I wish I could! They go for four figure$ and I got mine for $100 from my old friend and mentor!!

 

[egroys]

Those attenuators don’t tend to straighten out once bent AND it looks like some are outright snapped off. Measure it and see if it’s a standard or custom value. Possibly replaceable if standard.

Forgive my lack of knowledge, but are you suggesting that if not all of the contacts are touching, the unit doesn't work as intended? Where would I be able to get replacements? And what would be the correct way for me to measure? Thank you in advance!!

 

[egroys]

Also, should I strap a 600ohm resistor across the output terminals?

 

[emrr]

oh duh, it's one of these. if it measures as working correctly then it is. it's a custom value, the schematic for the Langevin 251 is sorta right but not quite, but close enough if you have to make another one by gutting another attenuator with the same contact arrangement. Don't gut a useful value like 600/500, find an oddball, there are plenty. Go read the other threads on 251's about loading and response, I've said plenty about them.

 

[egroys]

oh duh, it's one of these. if it measures as working correctly then it is. it's a custom value, the schematic for the Langevin 251 is sorta right but not quite, but close enough if you have to make another one by gutting another attenuator with the same contact arrangement. Don't gut a useful value like 600/500, find an oddball, there are plenty. Go read the other threads on 251's about loading and response, I've said plenty about them.

Much appreciated! The low freq pot was the one that was busted. Seems to be fine now!

The 5 and 10kc measure correctly, however, the 3kc doesn't appear to be correct. I intend to clean and de-oxit the unit, but curious where you might suggest I start inspecting for the wonky 3k? It appears to boost above 10k where 5 and 10 have a clear bell at their respective frequencies...

 

[emrr]

if it's just a high boost the inductor section for that frequency isn't connected or is open. Can't tell you where to look other than it's a terminal on the square can.