DIY vacuum tube audio

[Henry W]

when you get to where you can't find that much needed tube, there is always this

http://www.youtube.com/watch?v=9S5OwqOXen8

always fascinates me how some guys won't take no for an answer!

bob g

Hello Bob,

I missed this.
It is sure an art.
I wish I had the chance to see tubes being made .

Thanks for posting it.

Henry

[Henry W]

Here are some pictures of the inside of one of my Amps.

Henry

[Henry W]

Some more.

[Henry W]

Again

[Henry W]

Last one.

[rcavictim]

Henry,

You did a fine job building those amps!  Excellent looking star ground bTW.  I do the same thing.  Your iron budget was pretty healthy I see.  Did you ever get a chance to try any other outpout iron in that amp than the amorphous core Lundahls?  Just wondering if the sonics are worth the extra $$$$.  Inotherwords, can your ear really tell?  A friend of mine has been trying to develop a better amorphous core output xfmer with Morgan Jones.  This stuff is all way over my station in life.  I have to make most everything myself out of scavenged components pilfered from inexpensive industrial surplus and occasionally amazing landfill treasures.  Fortunately I do that well.  Purchasing two brand new manufactured amplifiers from MIngDa was quite out of character for me but sometimes you have to treat yourself.  Still, I didn't sit on that big 300B-805 SET amp long before I totally rebuilt it in my own image.

I recognize that your's is a P-P amp but just FYI, I've discovered that parafeed allows me to use a cheaper and more common P-P xfmer in the output of a SET amp and with the DC out'a the core, plus no gap so L is maximized, plus any balance issues with the primary windings are now gone if you don't use the ct., that they can sound very very good.  I also like to simultaneously use a technique  called ultrapath which gets the power supply out of the signal path of the output stage.

I had a read through the info you posted on the speakers and I would love to listen to your system if that were only possible.

[Henry W]

Hello rcavictum,

Thanks for the complements.
I learned that a good star ground is more important than most people think.
The iron was not bad when the U.S. dollar was strong. Now it would be, three times the amount?
I tried tried the standard Lundahl LL1620 P-P output transformer an there is a difference. The music is not as open and detailed. The sound stage seems HUGE!!! and more refined with the Lundahl LL1620AM P-P output transformers. For what I spent back then it was well worth it.

rcavictum wrote: I recognize that your's is a P-P amp but just FYI, I've discovered that parafeed allows me to use a cheaper and more common P-P xfmer in the output of a SET amp and with the DC out'a the core, plus no gap so L is maximized, plus any balance issues with the primary windings are now gone if you don't use the ct., that they can sound very very good.  I also like to simultaneously use a technique  called ultrapath which gets the power supply out of the signal path of the output stage.

I am not to farmiliar with parafeed amps. I know we had some people at one time into parafeed line stages.
They sounded very good. This is a section that I have not had much exposure to parafeed. Sorry.

We are starting to have some people in the club building Single Ended Transformer Coupled GM70 Amps. And they sound very good!!!

I was thinking today that I don't have the money to buy new iron for a GM70 Single Ended Amp so I will be doing another upgrade on my Amps. As you see in the pictures I made them so I have plenty of room for future upgrades. I know if and when the 300B's burn out I will be changing the Amp to KT-88's 4 Tubes per amp. The modification is very easy and tubes are cheep!!! I think I can use most of the Iron that is in the Amp. I know I can use the same power supply tranformer and choke. The filiment transformers for the 300B's have to come out though. It will be a painless and fun project.

I am glad you read about the Ariel and ME2 speakers. we like them very much. I can say I would never be able to afford speakers that will compare to the music that these make.

I will open the crossover box and take pictures of them. If I remember correctly I used a 10 or 8 ga. air core inductor for the mid woofer's. and 12 ga. for the tweeter.

Well it is getting late.

Oh, you know there might be someone closer to you that has a pair of Ariel or ME2's. The Ariel Club of North America might be able to help.

Take care,

Henry

[clytle374]

It has come to my attention that I have forgotten most of what I knew about tube audio.

[Henry W]

Hello clytle374,

It is ok, I forgot lots of stuff throughout the years.
If you like Tube Audio it is never to late to get back into it. There are simple Tube Amp designs out there and a little time and patence you can build one from scratch or buy a used amp like a Dynaco ST-70 and go through it with minor up grades and you will be surprised how good music will sound out of it with a good pair of fairly efficent speakers.

Henry

[Henry W]

Here is a picture of the ME2 Crossover Network.

It is layed out so changes can be made. It took me Hundreds of hours of listening to adjust it to my liking.

Below on the very bottom of the picture you will see extra 12 watt wire wound Mills resisters. I think they are rated at 1%. These are to change the charactor of the sound.

If you like like your music to sound like right up front of your face or layed back and some distance away. You have the ability to change it by trimming the value of tweeter capacitor between 5.0 uF and 5.6 uF (I chose 5.0uF)

If you look at the cluster of the Caps just below the upper air core inductor for the tweeter you will see one cap disconnected. The reason is that little 0.10uf cap changes the sound just enough that everything sounds very detailed and at times playing some CD's may sound just a tad bright. I believe it is just the way the music was recorded on the CD. So some day I will be hooking up a switch so I can use it as needed.

Here is some good stuff to read on the crossover design. http://www.nutshellhifi.com/Arieltxt2.html#top

If you want to start building a good sounding audio system using tube amps The speakers and crossover is the most criticle piece. This is where the money should be spent. Once you get the speakers the way you like then the additional money spent on building a good Amp will not be wasted.

How do I know this? Well, after hundreds of hours of listening, testing and changing of components in the crossover I found even a Mid-Fi Tube Amplifier will sound better than most Hi-Fi  Tube or Solid State Audio systems costing upwards of $10,000.00 and more.

And about speaker cables. Save your money!!! Buy a 250 ft. roll of 12 ga. Romex wire at Home Depot.
This is what I use. I went with the Monster Cable route and many other exotic cables and it just does not make enough of a difference to justify the cost spent for them.

Romex at one time was the choice of speaker cable in Hi-End audio years ago.

Henry

[aqmxv]

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?

[rcavictim]

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?

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.

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.

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.

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.

Do you have a schematic of your Bogen amp circuit?

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 tubes.  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.

[Henry W]

I agree with rcavictum,

You can get good money for those Bogan Amps and buy a Chinese amp, or at nice kit amp with the money and you will have a better sounding Amp. Or you can always buy a Dyanco ST-70 or some other brand of vintage amp and modify it.
You have differant choices and that is a good thing. One important thing is to buy an amp that has a good avilability of tubes.

I feel that the money should be spent in good speakers and crossovers and there are good speaker kits out there that are designed for tube amps.

I will get back later,

Henry

[aqmxv]

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.

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.

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.

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.

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.

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!

[Apogee]

You guys are cracking me up!!!

What is it about the same personality type that likes antique engines also likes diy audio?

It's good!

Nice job on the amps!!!!! 

Don't forget about the diyaudio.com site.  It's pretty much the king of the diy audio sites I think.

GREAT TOPIC!!!!

Regards,

Steve