So I lucked into a c20 for 400 bones, good deal in my eyes...sat in a basement for years so cosmetics are good but not show. I am replacing my Lafayette KT600 with it, because it just sounds fantastic! Me myself I hate hate running equipment on old caps, I ordered new cans from hayseed and the rest from just radios. I am sitting here listening to the c20 and it just sounds great! I have it on an isolation transformer to keep it from pulling to much voltage, the cans aren't getting hot. It is ful of bumble bees. I am wonder should I replace all them or just the electrolytic? I hate to change out the BB's and it alter the sound. I am not sure if anyone out there has done a before and after comparison. But I am just really curious. If they were just standard paper caps I would have no problem, but I know the whole debate that goes on with BB's...I wonder if there is truth. Whats your guys thoughts?

I've never got a complaint from any customer after ripping out BB's.

The stigma is all in the audiofools heads.

I'm sorry... but I thought you had more experience on restoring electronics ...since I've seen your posts here a long while.
But what you are saying is kinda weird!
Seems like you don't really know what needs to be done and not.

When you say "you hate to replace Bumble Bee caps because you don't want to change the sound"
OMG...
That is nonsense, silly and dangerous.

If an old (BB) cap is creating a special sound only because it is leaking and now has a certain high ESR.
THAT high esr will eventually cause the circuit to fail and must be replaced or you are asking for trouble.

Of course electrolytics NEED to be replaced (if they are bad- or VERY old) .. That's it.. Check them for leakage and replace if bad.

Here's the worst thing you said:
"I have it on an isolation transformer to keep it from pulling to much voltage, the cans aren't getting hot. "
OMG... an isolation transformer cannot reduce the current drawn!!!!!

My plan, with all equipment I keep is to do a entire recap, if it comes on with or with out hum. If it plays and I want to use it, then I want to completely recap it. If I don't want to use it I won't recap it. I either do a 360 or I don't. I don't usually going in and pinpoint the problem area if its working, and only replace that one cap or resistor. And see how long it takes for another cap to die. Its either all or none.

I am talking on this piece, not on anything I use regularly...they get tossed.

I call it an isolation transfer, it is more a variac then a transformer. It just doesn't have the range a normal variac does. Both the c20 and the trans/var are fused encase it sorts, I am also watching it as I am using it...if I see the tubes doing anything I don't I'll pull the plug.

This C20 had no visible problems(leaks/burnt items) nor any hum/buzz. All the caps have been ordered and on the way here. Once I get the parts it will be restored.

I wasn't asking my ethics on repair. I was asking about the thoughts on BB's on this c20.

The entire senseless dialogue concerning "bumblebee" caps appears to exist for one reason alone.

As a cost-cutting measure (they were relatively inexpensive caps), they were used in the tone control circuitry of certain electric guitars. Many restorers of these guitars, like many restorers of antique radios, insist on returning everything to its original appearance (which means having "bumblebee" caps in the tone control circuitry).

Guitarists, few of which have any technical literacy worth mentioning, soon discovered this. Some relatively bright spark among them decided that the "bumblebees" were being kept for their "sound" and started the word around. Now it has the force of Holy Writ among the twangers and bangers.

The truth is that these caps were relatively inexpensive molded paper caps which had no particular redeeming virtues even when new. Like wax-paper caps, they suffer from the old-age illness of leakiness almost universally. Some are prone to explode under stress. Like all overaged caps, they should be replaced, each and every one, wherever found.

Re-cap that Mac! When it's up to specs, it will have more than enough "sound" for anyone!



Larry

I'm going to take another approach. You got a screaming deal on that preamp. It's probably worth a lot more untouched than with new caps, because collectors worship those old untouched preamps for what they represent as opposed to how they sound. Recent completed sales on clean units have brought over $2000. For the profit you could get selling it, you could buy a much nicer performing and better sounding preamp. But, that said, if you really want to keep it and use it, then your best bet is to recap it. Buy some nice polypropylene film caps to replace the bumblebees, and it will sound at least as good as new, if not better.

I agree with you 100%, My Lafayette sold way under what a untouched one would go for. I have no idea why, I myself would rather have a restored unit that I wouldn't want to worry about then one, that I would have to repair monthly.

I was pondering selling it, but I really would like to use it until something better comes along. I figured since I got such a good deal, I would be able to get what I got back out of it. I have decided to go through with the restore and just save all the caps in a box and if I sell it say they are all available....Then again I've thought of selling the .22 BB's as I see those being gobs of money

That one I can answer - when it's restored you have no idea who did the restoration and whether it was done correctly. An untouched one may not work but you at least know how good the restoration is if you do it yourself.

Brett

If you put bumblebee caps on a capacitance meter after they've been pulled and replaced, you will find that they've often changed value. The change is seldom if ever in the direction of less capacitance. No, they tend toward more capacitance. For example, a .047uF will measure .062uF or similar. Now this is very disturbing. Ask this question: What makes them increase in value? Well, let's look at how they're constructed. Most tubular capacitors are rolled up like cigars -- two plates laminated on paper or plastic. My read on why they increase in value is that the cigar inside the molded case shrinks! As they shrink, the plates get closer together, and due to the laws of physics this increases the capacitance.

But consider. You have a device with, say, 300vdc across it, and the actual capacitor is shrinking, literally changing its internal geometry. Think this through a little more. Shrinking means that the cigar is undergoing a structural change. A multitude of stress gradients are invading the dialectric and the plates. These stress gradients lead to micro-structural cracks, delamination zones, etc. You can see how this can lead to leakage and shorts.

So, on garden-variety recaps of tube gear I go to the Mallory section of the Mouser catalog (well, actually I don't because I already have them in stock, but you get the point) and I order up a handful of 400v and 630v devices. I replace every bumblebee in the machine.

* * * * *

If my customer will let me, I'll keep the bumblebees and stash them away. Sooner or later some fellow will show up at my counter with a grin on his face like a five-year-old in a candy store ogling the lollypop display. He'll beg me to sell him the bumblebee "pulls." And like the evil capitalist that I am, I'll sell him the whole bag of goodies.

Fred
owner
Classic Audio Repair
San Diego

I guess I'm not as capitolistic/greedy, Fred.
Once I pull any old cap from a set, it goes in the trashcan.
It's done, gone, history.

Same goes for any other defective part I remove.... tossed.

I'm not really that greedy, RT, but the caps are often still useable, and people seem to be in love with them. I don't charge much. If I find one that's actually defective, I'll toss it just like you will.

I do the same with phonograph cartridges. A guy brings in a turntable with a bottom-of-the-line ADC cartridge on it, and I sell him an Ortofon 2M Blue. He's happy with the blue, and I recycle the cartridge body. Someone will come in who only wants to spend about $25.00 on a cartridge-and-stylus. He's happy to get the ADC with a low-budget generic stylus.

On the other hand, shorted output transistors practically climb into the trashcan on their own.

Fred

So the Mac is a low quality unit? What tube preamps do you recommend?

I didn't say it was a "low quality" unit. It was, in fact, one of the better preamps in its day. But its day was in the late 50's, and that means it's full of old capacitors, carbon composition resistors, etc. Its basic circuit design is in line with what you see in almost all preamps of the day, which means It also doesn't come close to performing as well as a modern preamp in the areas of noise and distortion. In fact, other than a phase inverter stage and a cathode follower, it's not much different electronically from a Dyna PAS 3. It's not sonically transparent like you would find in a sub $1000 solid state preamp today, but it does sound pleasant. I wasn't limiting my choice to tube preamps, but you could find any number of more modern (used) tube units from the likes of Audio Research, Conrad Johnson, etc. that will sound considerably better at well under the $1500-$2000, which is what he could conceivably get selling the C20. A solid state Mac preamp like a C28 would also outperform it, and a clean one of these can be found for $600-$800.

See my problem is I don't want solid state. I have never tired a modern tube setup, but I would imagine that would be up there with modern solid state. I like the looks of the 50's units and I like the period sound, yes its not the greatest quality etc. I didn't start off to have a audiophile setup with platinum speaker wires, gold plated transistor and western electric wire. I myself was look for a vintage system with period sound. I admit modern systems can for sure sound better. But thats not what I am looking for. The Lafayette KT600 was a setup from the eico hf85 I was using, the hf85 was a setup from the pas2 I had previously and now the c20 is a setup from the Lafayette. Another thing that I have found over and over again that really annoys me about solid state/modern tube stuff is the bass output...newer stuff just produces soooo much bass.

I bought my C20 in 1963, near the end of it's manufacture. The C22 would have probably been a wiser choice, since most of my records used the RIAA recording equalization curve.

The C20 had separate bass turnover and treble roll-off for equalizing nearly all early records as well as RIAA. A very flexible pre-amp.

I did some tests on mine in the 1980's? and found that when the rear panel "LOW FREQUENCY TRIM" controls were set to mid point, there was a few db peak around 100 or 200 hz.

Replacing some of the associated caps fixed the problem.

I plan to re-cap etc. the C20 and two Mc 40's sometime.

I am toying with the idea of carefully removing the tag boards "as-is" and replacing them with new tag boards with new caps and resistors or making a PC board loaded with same.

The old tag boards will be intact and can be returned if some some future owner wants it done.

Charlie

Jason, you have some really great audio equipment there. Do the recap and enjoy it. That Lafayette is no slouch either, it is a very well made unit and has great specs. You don't need a $7000 preamp, that Mac is a real find as you know and after a recap it will be as good as new.

Fair enough. When I was heavily into audio gear in my earlier days (mid 70's), I felt the same way. I had a pristine Marantz 7 preamp and a pair of Model 9 amps. Today, those would be worth a fortune. Early solid state was, to my ears, a step backward. Harsh and very fatiguing to listen to. Lots has changed since then, though, and today's better solid state stuff, especially well designed FET based amps, give you the best of both worlds.

I remember some of the tube vs, transistor debates and discussions printed in Hi HI Stereo Review and High Fidelity, etc. magazines in the early sixties.

At that time Transistor amps had much worse distortion specifications than the better tube amps. "However, there was some undefinable reason that tube amplifiers sounded better" (unquote). Perhaps, they thought, it was because transistor amps clip with sharp corners at the point of clipping.

The reason I bring this up is because of the (today) obvious hype always towards marketing the new stuff.

I wish I could find some of those old magazines, perhaps in my mother's attic, to compare the various explanations given for justifying buying the new stuff.

On the McIntosh C 20, Listening to records, using the "Magnetic" input, taking the audio out of the "Tape Output" into the power amp, bypassing the C 20's tone controls, seem to my ears, back then, to be slightly better. (Using the gain controls on the power amps). I doubt if I could hear any difference today or if any difference was worth the trouble.---Charlie

hey maybe you can re-stuff bum-bees
maybe add a resistor in series with a normal capacitor until you recreate 'The Sound'
I have never known anyone to take apart their guitar or amp for that matter and say 'hey look at my bumblebees'
normal reaction: what are you nuts ? take the next bus outa here
maybe after jammin all day and totally trahsed from sour mash or whatever someone might undo their guitar and show off the electronic components and wow the croud but I have never witnessed it

Mox nix!



L