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Bell 2122 restoration project (long)

H2s04

H2s04

auralmicitisis
Hello all,

I've been trying to find the gumption to post about this for a few months now. It started in March, telling myself that when summer came, I could finally get to work on a restoration project, and actually finish it. Well, summer has come, and I've procrastinated until the end of July by telling myself "I'm not ready yet" and other excuses of the like. Anyway, I thought I'd just get that out of the way first :yes:

I'll be honest; my history with restoration has been very spotty, filled with mediocre successes and poor refinishing jobs, mostly due to misinterpreted advice from other forums, and poor planning on my part. So, with the acquisition of a Bell 2122 tube amp last october, I decided that I couldn't live with it in a non-functional state sitting atop a RTR deck. I also have a strong desire to experience tube audio in a personal setting, so this little amp is a great start for someone on my budget.

To continue, I've never been very good at finishing projects I start, mostly because I always seem to hit a wall when things get complicated, and I feel like I'm just too young to be working on such old pieces. With that in mind, I want to set out VERY SLOWLY on this project, trying to gather as much information and help as I can along the way. I know that you guys are VERY understanding about such things, and some of you should receive medals for what you've had to put up with on this board in the past :lmao:. I realise I should I have started this earlier, but lets face it, I'm a little shy :scratch2:

Okay! Now, on to the technical stuff.

My restoration experience includes the following: replacing capacitors in several vintage radios, replacing electrolytic capacitors in an early 60's RCA table-top television set, and a complete tube replacement in an already-working Eico HFT-90 FM tuner. The FM tuner works perfectly, but needs a new volume potentiometer because the integral on/off switch broke in the on-position (luckily) during operation recently.

Eletrolytic replacement went OK, but the picture was poor, and I decided that I just didn't know enough yet to pursue the matter any further.

And now, the major issue: paper capacitor replacement. After replacing capacitors in each radio (both slightly worked prior to the application of my "expertise") both exhibited the same symptoms: a loud 60 Hz humming noise, and one would continue blowing tubes. No responce to tuning; nothing. I took extreme caution when working on each set, making sure each solder joint was done perfectly, and solidly. I also checked each resistor prior to the post-operative first run. So, I'm in a fog here now :dunno:

You can probably see now why I'm taking so much precaution before I set out to restore my Bell 2122 amp. I want to go at it as if I were completely new to the scene, making sure I triple check each direction, and ask as many questions as possible. I just hope you guys (and gals) will be able to put up with me :sigh:

Now, I want to go every thing that I should do before ordering the capacitors I need, and also, what type of capacitors do I really need?. I've seen people using metalized polypropylene, polyester film, orange drop, and the like. I have no idea what capacitor is right for which job, and which capacitor is which beneath the chassis (except for eletrolytics, I'm comfortable with those by now :thmbsp: ). To note, I used metalized polypropylene film capacitors in both radios that failed; was that an incorrect move?

I'm planning on purchasing a tube tester on ebay, and I'm in a bit of a fog as to which one I should get, so if anyone could help instruct me with that as well, it would be a great help :yes:

If anyone has a schematic for this particular amp, it would prove to be a great asset while working on this project, I'm sure. Can someone tell me the bulb voltage as well for the indicator lamp? It just needs to be replaced :)

Again, I would just like to thank everyone on AK for the help they have given me in the past, and I hope that this project will work out better than ones in the past :yes:
 
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The Bell 2122 is a fine little amplifier. I have found that the way Bell constructed their tube era equipment made them the least fun to work on. Taking the old capacitors out is made difficult because of the tight spacing and the sound mechanical connection they used when installing them. The reward for all the effort is you will have a very musical amplifier to listen to once you finish the refurbishment. The chassis tends to polish up well also.

When I replace capacitors I do it one at a time. That is, I remove a capacitor I want to replace and then install the replacement. Then on to the next one. That makes it more difficult to get one in the wrong place.

Capacitor type: On an amplifier like the Bell 2122, I would replace the current paper capacitors with Mylar type capacitors. Make sure the capacitance and voltage ratings are equivalent to the ones you are replacing.

Tube testers: Hickok

Good luck on your project.
 
Your 60 cycle hum would be from the power supply electrolytics, not the caps you put in there as coupling filters. Before you buy a tube tester, buy a variac since even new caps should be warmed up. You can buy a whole new set of tubes for much less than a mediocre tester, so make sure it is a part of the hobby you want to pursue.
I buy lots of caps and cool toys at a place called Tanner's and last time I was in there asked if they sold on line. Jim told me no, but there is a place called BG Micro (Dallas local) that does, so you might Google them up.
You should be able to buy all resisters, coupling caps and things like that for a good price, but not replacement multi section electrolytic cans. Maybe some short snap ins for monitors that have the voltage capacity that can go under the chassis if there is room.
At Tanner's I picked up a handful of .047/1000 WIMAs for .39 ea because you just never know when you will need one. It is a good thing they are 30 miles away going through downtown Dallas or I would be in there all the time.
 
I have scanned the Sams folders for the 2122 and the 2122C. Email me and I'll send a copy - tbavis(at)rochester(dot)rr(dot)com
 
hello all,

To answer a few things first, I bought a variac last summer to work on several TV's, but as I said earlier, decided I didn't know enough at that juncture to start working on them. Regarding tube testers, I'm fine with buying new sets of tubes and such in place of a tester, but I also need to test about 30+ tubes that have some value, so I want to make sure they rate pretty well, say, if I were to sell them. I can't really afford one of those Hickok testers, although I've heard they're the best from people in the past. I'm looking for a tube tester that can test 12AX7 tubes, as well as earlier tubes like 01A tubes, etc. Could someone suggest a good contender?

I'm still unsure as to how I should go about "warming up" vintage electronics; I posted about this very same topic last summer, and everyone seems to have their own "style" of variac use. I also hear something about how some tubes need to be removed during the warming phase because the plates can overheat due to a frequency problem, or something-or-other (I don't really understand it, do if anyone knows what I'm talking about, please, help out :yes: ) so is that something I need to worry about here with my Bell 2122? I know that with vintage TV's, you need to remove the H. out tube or else some plates will melt (!!!). What voltage should I start at? 60? 70? I'm in the dark here :lmao:.

Now, capacitors...

I know capacitors relatively well by now by looks, but when someone says "use mylar capcitors" I'm sort of stumped ( ;) ). By mylar, do you mean orange drop capacitors, or those yellow cylindrical capacitors? With the past projects I mentioned, I used yellow cylindrical capacitors that were a mixture of polyester and mylar film. What is the difference between these two? Why are some better than others for certain applications?

Also, who is the best online source for capacitors? As for tubes, I usually just get them from antique electronic supply. When I was first getting into this hobby, I looked there for capacitors, but wasn't impressed with their selection; maybe they've changed since :dunno:.

Regarding the schematic that Tom nicely sent me, I have one question: it seems that in the diagram on page 2, the unit has three electrolytic capacitors (power capacitors) and my unit only has two. I'm refering to the cardboard-wrapped one between the right-hand 6V6GT output tube and the 6SC7 tube, or for people with the schematic, "C3". Why is this?; why is my unit built without this capacitor?

Thanks :)
 
Also, why does the 6V6GT tube require that dark coating on the inside? Are there 6V6GT tubes that don't have this coating? My question is purely out of aesthetics, as this amp really only has *one* tube that actually glows to the point where you can see it (the others are either metal or coated, and the 5Y3GT is obstructed by the power xfmr.

And on another note, does anyone know when this amp was made?
 
There should be a date on the Sam's to give you an idea of when it was made.

Different caps can change the sound of the amp depending on where they are. The use of electrolytics is to save space and money, for coupling caps it is a matter of taste and, or availability. Did you try a search on the name of the company I gave you? Orange Drops are typically good, liked by most, disliked by few but I use old paper in oil if I can find them.

Most 6V6s do not have a carbon coating inside the glass. I know RCA did it in the US and Brimar in England. I am sure there are more, but most are clear glass.

There is a small paper on variac use for warming up caps in a sticky post at the top of the page of the Tube Forum. This is how I was taught to do it. It works for me and the guy that taught me can design an amp with a RCA tube manual, a piece of paper, a pencil and a calculator. I've seen him do it.
 
I have some reservations about this baking-in-the-oven proceedure that you recomend; what if the unit, like mine, is painted? Wouldn't exposing paint this old to such a high temperature cause alot of damage to the paint? Also, what about the bakelite (i think?) tube sockets? And any other integral plastic parts of the chassis?

And still, what about frail under-chassis wires? They seem brittle enough without first baking in an oven for several hours.

However, I totally understand your point about drying out the power transformer; its an issue i'm sure few of us would think about when working on something like this, and I want to commend you for that. Maybe I'm just too paranoid? I believe that paranoia in this hobby is an advantage :P

So, on the restoration front, is safe to say that I can go ahead and replace the wax/paper capacitors with orange drop capacitors? Are those "mylar" capacitors? Speaking of which, I looked on google for awhile about Tanner's electronics, and I couldn't find anything more than a few references on different forums.

I'm worried about replacing the capacitors in this unit because of the sheer "compactness" of the connections; there are several places in which I will have to remove one capacitor just to get to another, and I'm concerned about breaking any connections in the same area.

On another note, it seems as if there was some sort of modification made to it, as there is a large plastic label above one of the inputs that says "TAPE OUT" and underneath the chassis, it looks like a resistor was un-soldered from the central prong, but it wasn't removed, which is odd to me. I'm not sure what this modification did, but I guess it just must convert the input into an output.

I'm going to go ahead and order a new set of tubes from antique electronic supply, and maybe get the capacitors I need if I'm correct, eh?

Thanks :)
 
Also, if you would like any pictures of the chassis, modification, or anything else, I'd be glad to submit some if it would help.
 
The name is BG Micro, not Tanner's.
Don't bake if you don't want to, but chances are at 100-125* you won't get close to the heat tolerances of any of the parts and if it does cause any insulation to crack and crumble it better to find out now before touching something hot and having your eyes pop out your skull. Just kidding but I got zapped with 350V of B+ through the chest and my heart clenched so tight I could hear the blood squirting through the little capallaries in my ears and it hurt like hell.
The power and rectifier tubes will reach much higher temps than that and if you run it long enough the transformers are liable to get hot too, thus the steam, condensation, possible short and hope you are not touching the chassis while well grounded.
Most people do not bother with the baking, but nobody that has, has reported a problem.
 
Mylar Capacitors

H2s04 said:
So, on the restoration front, is safe to say that I can go ahead and replace the wax/paper capacitors with orange drop capacitors? Are those "Mylar" capacitors? Speaking of which, I looked on google for awhile about Tanner's electronics, and I couldn't find anything more than a few references on different forums.
Click to expand...

H2s04,

Many of the "orange drop" capacitors are Mylar or Polyester. The 715P series are Polypropylene capacitors and I have used hundreds as replacements in tube audio equipment. The advantage of Polypropylene is the lower dissipation factor and dialectic absorption. The disadvantage is that for a given capacitance value and voltage rating they are a larger physical size. That is the reason I recommended Mylar or Polyester. If you cannot find them anywhere else, look in the Digi-Key catalog for the Panasonic E-Series Metalized Polyester Capacitors. They are inexpensive and there is a good selection at either 400V or 600V.

H2s04 said:
I'm worried about replacing the capacitors in this unit because of the sheer "compactness" of the connections; there are several places in which I will have to remove one capacitor just to get to another, and I'm concerned about breaking any connections in the same area.
Click to expand...

That is exactly why I consider the Bell's to be such a pain to work on. Go slow, work carefully and you will be rewarded. Good luck.

Tcdriver
 
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quick question:

I can't find a 25 mfd@ 450V power capacitor that I need, is it safe to replace it with a 22 mfd@ 450V one?
 
in addition to question above: I've found a newly re-formed multi section capacitor at 20/20mfd @ 450V (the one thats actually used in the Bell 2122 that appears in the sams photofact) but the capacitor in my Bell 2122 uses a 20/25mfd @ 450V power capacitor; would it be alright if I were to use the 20/20 capacitor in place of the 20/25?
 
2122

Either the 20/20mfd @ 450V or the 22 mfd @ 450V would be fine to use as a replacement. The downside of the slightly lower capacitance would be a small increase in ripple voltage in the power supply. It is unlikely that the increased ripple would be audible.
 
Now, tube questions :scratch2:

can I replace the 6V6GT output tubes with just 6V6 tubes? or are they essentially the same thing? JJ makes a very attractive 6V6 (both visually and technically), but I don't know the difference between the two.

Thanks,

Jeff
 
6v6 Vs 6v6gt

The "G" in 6V6GT means glass. The 6V6 was a tube with a metal outer case. If the JJ tube has a glass shell then it should be called a 6V6GT. So the short answer is: yes, you may use the JJ 6V6 to replace the original 6V6GT tubes in your Bell 2122.
 
heh, thank you :)

I'm sorry for all the ancillary questions; I'm just trying to clear up as many things as I can before I go ahead.

once again, thanks for being so patient :)
 
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another question :):

I need to replace a 100mfd @ 25VDC capacitor, but I can only find capacitors at 50mfd @ 25VDC. So at the moment, I'm planning to buy two 50mfd capacitors, and solder them together in parallel in place of the original. However, they (justradios.com) have a 100mfd @ 50VDC electrolytic capacitor; can I use this in place? I realise that the voltage ratings are different, but somehwere along the line, I hear that it really doesn't matter, but I have a hard time believing this. Should I stick to my plan, or get the 100mfd @ 50VDC capacitor?

PS: I decided to buy the 20/20 capacitor, so we'll see how things work out when it arrives.
 
Check out www.digikey.com for caps. They are a big outfit and have many, many values...and many other goodies too like resistors, diodes, rectifiers, etc.,

Higher voltage is OK. You just need to meet or exceed the voltage rating of the cap that you are replacing.

As far as the capacitance value - often the old caps were +-20% when they were new so if you are within that then you are usually OK. I try not to go outside of that guideline. Sometimes the caps are marked with the tolerance and/or the schematic will tell you what it is - then I try to stay within that.
 
Update: All the capacitors have arrived, and I just finished installing them about an hour ago, making sure every single connection was conductive. So, hopefully, I can start the big warm up stage tomorrow if things work out :)

I'll post some photos of my work soon, so sit tight :)
 
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