Micro CoGen.

Thanks - I finally made it back over here and downloaded it.  Grad school while working has been sucking up lots of my time...

Quote from: rcavictim on December 16, 2009, 09:09:45 PM
aqmxv 

Here is a pdf file of all you ever wanted to know (again) about the 8417 including curves.

Quote from: SHIPCHIEF on September 02, 2010, 02:57:13 PM
I have noticed that these seals wear a groove in the steel shaft.

Nope.  The seal doesn't wear anything down - rubber is much softer than the shaft..  Dirt held by the seal wears the shaft down, which is why it was such a problem with rope seals on front-engined cars (front pulley was right behind the radiator being dirt-blasted, especially on dusty roads).  The easy way around this one is to get a double-lip seal.  The outer lip is not springloaded, but touches the shaft.  Its purpose is to keep dust away from the inner lip, which has the usual spring on it.

One thing I've considered doing is reversing the seals on a listeroid.  If everything is set up right, the crankcase should have negative pressure most of the time due to the action of the reed valve.  You would want the lips of the seal facing outward to keep air and dirt from entering at the seal lips...

There's not a lot that is very critical on these engines.  Four thou is probably fine.  I don't think I'd go below about .003" just because of exhaust valve stem swelling.

Quote from: rcavictim on December 15, 2009, 09:33:24 PM
My little ignitron, the size of a 2 liter pop bottle could switch on a 20,000 amp DC current at up to several KV in micro seconds. This old tech was the perfect answer to my high current switch problem.  Unlike an SCR, I could not blow this ignitron up from reverse inductive surge and all the other things that kill solid state devices.  Tube technology rocks!

You're reminding me of my favorite mercury vapor rectifier:

Its specs (from page 4 of this paper): 630V @ 111A.  These were the alternate source of power for the London deep level shelters of WWII - they rectified the 50 Hz line current to run all the critical systems.  In the event of failure of the mains current, the supply switches could be thrown to run the systems on Underground (London Passenger Transport Board) DC power directly.

See also this page, which seems to have another of the same Hewittic rectifiers

Quote from: cgwymp on December 16, 2009, 05:22:40 AM
Let me know if you can't find yours -- I still have mine.  Same Sylvania book with the missing cover that you'd no doubt recognize.....  ;-)

I've got an RCA tube handbook that includes the 8417 curves - they're the hard-to-find part.  KT88 curves are everywhere.

Quote from: rcavictim on December 15, 2009, 10:09:20 AM
Nice to hear you have two vintage Bogen amps.  The bad news is that they use 8417's.  That tube was very failure prone because they underdesigned it for the power it is expected to run.  Add the high failure rate with very high level of scarcity in today's supply chain and expect to have to pay big bucks for any if you need some down the road.  A few years ago you could still get them occasionally on ebay for in the $60 each range.  By now most have been hoarded by dealers.

I've got a spare set of tubes - I've had the amps for 20+ years, so am familiar with their failings.  I traced their schematic out myself on my desk when I was in my 20s, because I couldn't find it published anywhere.

Quote from: rcavictim on December 15, 2009, 10:09:20 AM
Are you sure your amps are run class-B?  That makes more power at the expense of sound quality.  That would be acceptable and expected for a public address system amp  where power was more important than sound Q, but class-AB1 would be better, and class-A still better for a P-P hi-fi amplifier.

Yes, as I remember (it's been a while) the grid bias suggests it's pure class B.  I've been thinking about tweaking the grid leaks, etc to sacrifice some output for quality.  I don't think I would bother with class A, but AB1 would be a reasonable compromise.  Four 8417s should give a pretty respectable output in AB1.  I have a tube handbook somewhere with those curves, so can figure out just what voltages to run where.  I did a THD measurement on them for idle fun years ago and found that they were actually pretty good up to about 80% output if everything was in spec.

Quote from: rcavictim on December 15, 2009, 10:09:20 AM
If those amps sat unused for a long while they should be soft started with a variac which allows the electrolytic caps to form again.  Otherwise they could fail early.  They should run cool or comfortable to the touch, not hot.  If these have original capacitors under the chassis a total recap is in order.  A leaky cap could easily lead to a swift thermal runaway of your expensive and dear 8417's.

No worries.  I have three variacs around the house  -  they're so useful that I wish I had more.  Back when I was young and poor I used a ceiling fan speed controller to soft-start them.  Nowadays, I have variacs, so use those.  Among other things, I found that the Bogens are happier at about 90% of modern line voltage because the power transformers are wound for a nominal 117 V mains feed, and most of my houses have been 123-127 V at the socket.  That gets my B+ and grid voltages just where they should be, and no doubt prolongs tube life as well.  Likewise, I tend to run my tube radios around 100 VRMS, because their nominal line voltages are generally about there.  I've recapped a bunch of radios from the 20s and 30s over the years and have no fears with that.  The Bogens are so simple compared to something like my RCA 19K...

The last time I lit these up was about three years ago, so you can rest assured that they'll get a very slow start before I put music to them.

Quote from: rcavictim on December 15, 2009, 10:09:20 AM
Just thinking out loud. Maybe you'd be well off to have an experienced tubehead modify your Bogens to operate at half output power on a single pair of KT88's.  This would require some socket and circuit rewiring.  I'd have to look at some impedance and other specs before being certain about the success of such a modification however.  The 8417 was touted as a low distortion tube as well as high power.  Any deviation in optimum transformer load and other parameters will likely add some distortion.  That may or may not be tolerable.

I've thought about going to different tubes, but I have so seldom used these to a major proportion of their output that I figured I'd worry about it when it became a necessity.  I'm quite capable of doing any such mods myself as long as I have the curves for the desired tube.

Quote from: rcavictim on December 15, 2009, 10:09:20 AM
Do you have a schematic of your Bogen amp circuit?

yes; two.  One I drew, and another that Bogen kindly sent me years ago when I sent them a letter with a SASE asking for any lit they had on the beast - MO-100s were apparently common, and the MO-100A quite rare.  They're interesting beasts - really Swiss-army-knives of an amplifier with many output options and switchable audio filtering.

Quote from: rcavictim on December 15, 2009, 10:09:20 AM
Maybe you could sell the Bogens and buy something lower powered that is high quality from modern Chinese offerings, or another quality vintage amp that uses more practical tunes.  If you have a budget and room for big speaker cabinets I'd lean in that direction because the efficiency can be high and the distortion low.  Tricks that make the cabinet of modern speakers also increase distortion and make them inneficient so that big amplifiers are needed to drive them.  My philosophy is the opposite.  I like large efficient, low distortion speakers and very high quality low power tube amps (i.e. generally less than 50 watts/ch. and more like 3 to 20 watts).

As for recommending a modern quality speaker?  I have little knowledge of asuch things but I have a good idea what is pretty super from the golden age.  You can't go wrong with a pair of Altec Model 19 for example.  $2000 on ebay give or take.  Twenty tube watts would be plenty for a pair of those if you like it loud once in a while.  They are very efficient.  There are other very nice vintage speakers.  Klipsh corner horns also in the $2000-2500/pair ballpark if you have the proper room and corners for them.  They are also highly efficient.

Where about's is this 'man cave' located?  I could keep an eye out for suitable speakers in your area.

The man cave is in northwestern VA.  I see that you're tending toward the sort of speakers I generally choose as well.  My father has a set of the Altecs and I like the sound very well.  They have superb treble and midrange presence, which is (along with the effortless bass muscle of a tube amp) is something I've grown happily accustomed to.  I'm embarrassed to say that I have never actually heard a pair of the Klipsch corner horns.  I'm guessing they have similar qualities.

The man cave will be mostly for my enjoyment.  The vast majority of family listening is to a class AB/class B surround receiver upstairs hooked to the multimedia system.  The good news is that the new house (unlike the last two) has room for both!

There are uses for vegetable oils with machinery in applications where gumming is a feature, not a bug.  Castor bean oil (that's where Castrol's name comes from - not that there's any castor oil in their current products) forms a film on metal that has to be machined off to remove it - very useful if you need to preserve metal in contact with moisture.  Likewise, it's the best two-stroke engine lube I've ever used.  Even if you overheat and seize the engine it will usually not score the bore because of the plastic-like coating from the gummed oil.

The downside, obviously, is that it can seize the insides of equipment up if you don't use it carefully.  I tend to use it once a season or so on two-strokes at 20:1, and the rest of the time I use a modern synthetic two-stroke lube at 30:1 or 50:1.  If you run castor oil all the time it will carbon up the ring lands (especially at at 20:1).

I used to use it (or Klotz lube formulated with it) at 20:1 in racing snowmobiles.  Worked great, but you had to warm the gasoline up to room temp first, because the castor oil would just sit there in a gelatinous blob and not mix with the fuel below freezing.  If you look at history - racing oils for cars and airplanes were generally castor oil based until petrochemicals offered better lubricity and lifespan.

So it's worth considering using a vegetable oil like jojoba or castor in machinery, but you don't generally want to leave it there without a coating of something that doesn't gum on top.  Put it in for heavy-duty use, get the equipment hot once, then switch to a plain old hydrocarbon oil so that it won't gum up.

We're moving house this week (rental -> real house).  One of the boxes I put my hand on last night contained one of my two Bogen MO-100A monoblocs.  (4x8417 finals in class B push-pull).  I was smiling at the thought of hooking them up to my new (to me - not new at all) pair of walnut-cased Advents - a gift from my father in law.

Which leads me to my question - What's a good current-technology speaker?  As you can probably guess, I have 100 W/channel to play with, so power requirement (within reason) isn't an issue.  That said, I'd like to keep avg max demand at 70% or less of that where THD is low on the amps.  I don't like my music deafeningly loud, but I do like clear and even reproduction.  The Bogens are perfectly happy 18Hz-30KHz (tested them myself), and I hear pretty well for an old guy.  compact size is not a concern - the system will probably be going into my man cave/listening room.

Suggestions?

FWIW, the Indians set mine up knife-edge on at the factory.  I'm going with a XYZER dipper, so orientation becomes pretty obvious...