Binson Echorec 2: Need to figure out specs for choke replacement

[Anchorman]

Hi all!
I have an Echorec 2 tube model which I want to get up and running. I have come to the conclusion the choke is not working (I think it's open), so I need a new one, but I don't know how to figure out the specs of it. There are 5 ECC83 and 1 ECC82 tubes. Immediately after the transformer (250V output) there is a bridge rectifier, then a 40uF cap to ground, then the choke. How do I know what inductance and resistance etc. the choke should have? Can I just use a choke with the best possible specs as long as it fits? Any guidance is very much appreciated!

Cheers!
/Carl

[JasonG]

There are some really good websites dedicated to those Echorecs those things have a cult following and for good reason. I wish I had one.
My guess is someone on one of those websites would be able to help you out.
                  http://en.wikipedia.org/wiki/Binson

[Anchorman]

Thanks for the quick reply! I have tried Google but can't find any info on choke specs, maybe my only chance is to get in contact with a person who knows. No one on the plexipalace seems to know. Binson.com/ESE, though very knowledgable, sells replacement chokes so they have no interest in giving me the specs to buy one much cheaper. Maybe I should just buy one from them anyway.

[Anchorman]

According to http://www.aikenamps.com/Chokes.html, it seems it is a "capacitor input supply", with a "cap-inductor-cap" network, commonly called a "Pi filter".
Hmm, maybe I can figure this out by myself, that link is really good, gives good directions on choosing specs.

[JasonG]

It sounds like your on the right track. And I honestly can't say I know too much about how they work. But like I said it might not be a bad idea to contact some one who as restored one. I saw a page ages ago that show one being restored it looked like a big job but well worth the time.
Good luck and keep us updated. like I said I am a fan.

[Anchorman]

I spoke to binson.com (ESE), and even though they sell replacements, they also were kind enough to tell me approximate specs. I might order from them now because of the kind service

[sean k]

I got a bunch of chokes years ago and used them ocassionally on tube amps in variations to acheive the Dc voltage I wanted in the amp. The beauty of a choke is it's ability to give you an RMS output as opposed to a peak output given the inductance is great enough to acheive this. One of my favourite tricks was using a cap input followed by a choke but the cap would be 100- 470 nano so what I was doing was using the small cap to store a portion between peak and RMS so I could get the voltage I wanted. Chokes are kinda like caps in that the inductance will work just like a cap. If theres not enough for the voltage then it will output above RMS and if its above it'll smooth things right down and even be quite good at holding back voltage under duress.

So a choke is choosen firstly on it's current capability then on it's ability to smooth things out. If you know the voltage at the AC side and then whats required on the circuit you can then work out how the choke is used  and whether or not the input is the choke or a cap will help. If its cap input in the micro farad range then just about any choke over 2 henries will do but if its choke input and the DC voltage is the RMS AC then 5 - 10 henries is more usual... if not bigger.

Current rating is the most important but after that dickering about with cap sizes in relation to the choke and amount of load will get you what you want.

[Anchorman]

sean k, thanks a lot for your input! The input cap is 40uF, so any choke with specs over 2H, and with sufficient DC current spec will do?

[sean k]

Well. given the input cap is 40uf anything will do including a resistor! The choke then just adds tons of smoothing so anything will do. Common  are 5, 10, 20 Henries etc.

I gotta old gulbransen organ and it was missing a choke and I was told to just put a resistor in there and I can now see the reasoning. Chokes really were the best way to do things in the olden times  because the bigger filter caps were expensive but now bigger caps are more affordable and chokes are expensive  , well I do know why actually, because they are basically obsolete... simply because they are expensive to produce and other things do what they used to do alone... Get a choke or just get bigger caps... it's only smoothing.

[Anchorman]

Thanks again, I haven't been able to read that somewhere else, so I really appreciate the information. So basically, I can try with larger caps, a choke with sufficient current and voltage specs, or just place a high wattage resistor between the two '+'-sides of the 40uF+40uF cap ('-' goes to ground)? Also, I could just ignore  the choke and bypass it and still use the 40uF cap, and the Echorec will still work, only with more hum maybe? Again, Thanks!

[Nasse]

Was that if you have tube rectifier don´t put bigger caps or the rectifier might die

[Anchorman]

Nasse, thank you for the heads up! Fortunately, the rectifier is solid state.

Just to see if the unit works okay or if I need to order new parts, will it be okay to just bypass the choke, connecting the two '+'-sides of the cap to each other? Is there any risks with this, except I might get more hum in the signal due to the lesser filtering?

[Mick Bailey]

Before doing anything, think why the choke has gone O/C. This may be due to excessive current consumption, in which case the windings may have acted like a fuse. You could have a shorted tube. I would first investigate the supply lead connected nearest the choke output side and look at the resistance to ground. Because of the high-ish resistance values in the following RC filter stages (the schematic shows 4.7k then 10k) any fault that would burn out a choke would most likely be before the 4.7k resistor. A shorted capacitor could also be the problem - check them out.

To be on the safe side, if you want to power up the unit, replace the choke with (say) a 470R resistor, preferably 5w. You still need to investigate the fault prior to doing this. If you think a tube is shorted, remove it and check out the pin-to-pin resistances. Only the heater connections should read low resistance.

If you just replace the choke, you may end up with another O/C choke to add to your collection.

[Anchorman]

Thanks for the input Mick, very good information! I will investigate all the tubes and the resistance to ground from the choke output. I recently changed the 40uF+40uF cap, so it should be good. However, the reason the choke is bad is probably because I accidentally drilled into it when I was drilling a hole to mount a new bridge rectifier. It's hard to say if the choke was working properly before my stupid mistake. I'll order some 5W resistors and try it. Thanks!

[sean k]

Yup, drilling into transformers isn't so good for them. I did it recently myself into a small 9.5V power box transformer and even though it still sends out 9V it ended up getting very hot so even if I didn't actually cut through any wires I'm pretty sure I took off enough of the coating on the wires to create a hot spot where the current was jumping. Not a good idea drilling enclosures where stuff is mounted...

Nows your chance to learn all about chokes... if you only cut a few wires on the outer layer it might not hurt to unwind those layers and start again from the uncut or unnicked wire. You would lose a little inductance and the resistance would drop ever so slightly but it seems a waste to throw something that might still have 95% of it's windings intact. Don't do this though if you aren't up on the ramifications of doing it wrongly. If the drill went right through to the other side I'd say its not repairable, unless it's rewound and all the E's and I's are intact but if it was just a nick then...

[Mick Bailey]

I've also rescued chokes where the damage is in the outer windings. Sadly, when they fail electrically this is rarely the case. I've found that you can remove quite a few windings and the choke will function perfectly well so long as it was conservatively rated for current handling in the first place.

After A/B-ing choke and resistor smoothing, I would go for choke every time - it's so much quieter. A small Hammond choke may even fit the original hole centres and these aren't too expensive (even here in the UK). If you get the Binson working OK with a resistor in place of the choke you might consider restoring it to its original spec and refitting a choke.

[Anchorman]

Thanks again for your insights! I might try to repair it, but first I need to learn more about chokes, so that I know what to do. I think it's just one thin wire (or very few) that's cut, the drill didn't go deep. I guess I need to study it to understand how to fix it, I might upload some pics, but I won't be able to until next weekend. I'll try replacing it with 5W resistors first though.

[Anchorman]

Okay, I have replaced the choke with a 5W resistor, , making it an RC-filter instead of LC-filter. What's strange though, is that before I replaced the choke the transformer output voltage was around 250V , now I read 30-40V between them. What might explain this? Cheers!

[Mick Bailey]

Where are you taking the reading for the voltage?

[Lurco]

Okay, I have replaced the choke with a 5W resistor, , making it an RC-filter instead of LC-filter. What's strange though, is that before I replaced the choke the transformer output voltage was around 250V , now I read 30-40V between them. What might explain this? Cheers!

you write: "5W". Q: what value of resistance? You write: "30-40V between them". Q:  between what?