Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Feb Sat 22, 2020 7:58 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 12 posts ] 
Author Message
 Post subject: iPod Amplifier built from 1920's components.
PostPosted: Jan Mon 20, 2020 9:10 am 
Member

Joined: Jan Thu 16, 2020 12:29 am
Posts: 172
A while ago I came across some Samson brand 1920's vintage audio transformers. They inspired me, so I decided to craft them into an amplifier, see attached picture.

The physical construction consists of a pre-painted steel Hammond chassis, the front panel material came from the Luthier's suppliers. I tried to keep it as simple as possible, yet with the art & styling of 1920's electronics.

I was very interested to investigate the the calculations for the ideal plate to plate resistance for a class AB1 push pull amplifier, rather than just the graphical approach.

I found after researching the topic that a lot of the work in this area was done by the staff at MIT.

Very early in the piece, the benefits of push pull in terms of reducing the tube's dissipation and generating more power at the same time were not recognized, in fact RCA initially recommended running valves in push pull in class A mode, making it look somewhat unattractive to a designer. I have explained a lot of the technicalities in this article:

http://worldphaco.com/uploads/UX-171-A_ ... ifier..pdf

Of note it is important when working with pre-painted steel chassis to smooth & paint the cut hole edges, or of course they will rust later.


Attachments:
UX171.jpg
UX171.jpg [ 441.23 KiB | Viewed 541 times ]
ux171b.jpg
ux171b.jpg [ 578.24 KiB | Viewed 541 times ]
Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Mon 20, 2020 2:49 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 7647
Location: Minneapolis, MN USA
I like the styling and application. I built a tube based amp for my ipod but it is not vintage style and not near as attractive as yours.
You do good work. We love functional eye candy.


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Mon 20, 2020 2:50 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8550
Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
Nice work !!


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Mon 20, 2020 3:59 pm 
Member
User avatar

Joined: Dec Sun 21, 2014 6:37 am
Posts: 2067
Location: Portland, TN, USA
Very nicely done!

Your attention to detail, both technical and mechanical, is inspiring.

_________________
73, de Chuck K4CCW

If talk is cheap, it's because the supply usually exceeds the demand.


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Mon 20, 2020 4:44 pm 
Member
User avatar

Joined: Jul Tue 15, 2008 6:13 pm
Posts: 7336
Location: Gretna, Nebraska
That is a very attractive project. What did you do to the back of the speaker? Is that a cover you added?

_________________
http://www.vintagerestorationservices.com
Paul
...... how hard can it be?


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Tue 21, 2020 12:21 am 
Member

Joined: Jan Thu 16, 2020 12:29 am
Posts: 172
processhead wrote:
That is a very attractive project. What did you do to the back of the speaker? Is that a cover you added?


It was a shielded speaker magnet type, I found a piece off copper water pipe that was almost the same internal diameter as the magnet. I had to machine it out (the inside) about 0.3mm to get a short section of it to just slip over the magnet. I made it long enough to just house the impedance matching transformer that I designed and wound to go in that space. The end of the pipe then had a thick machined phenolic disc which is retained by small screws and has the thumb nuts/connections on it, to sort of give the speaker an older look.

(It is quite tricky to machine copper and it requires a lot of lubrication)


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Tue 21, 2020 12:30 am 
Member
User avatar

Joined: Jul Tue 15, 2008 6:13 pm
Posts: 7336
Location: Gretna, Nebraska
ACORNVALVE wrote:
processhead wrote:
That is a very attractive project. What did you do to the back of the speaker? Is that a cover you added?


It was a shielded speaker magnet type, I found a piece off copper water pipe that was almost the same internal diameter as the magnet. I had to machine it out (the inside) about 0.3mm to get a short section of it to just slip over the magnet. I made it long enough to just house the impedance matching transformer that I designed and wound to go in that space. The end of the pipe then had a thick machined phenolic disc which is retained by small screws and has the thumb nuts/connections on it, to sort of give the speaker an older look.

(It is quite tricky to machine copper and it requires a lot of lubrication)


Very nice look. You obviously have skill and patience.

_________________
http://www.vintagerestorationservices.com
Paul
...... how hard can it be?


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Tue 21, 2020 1:28 am 
Member

Joined: Jan Thu 16, 2020 12:29 am
Posts: 172
Dale Saukerson wrote:
I like the styling and application. I built a tube based amp for my ipod but it is not vintage style and not near as attractive as yours.
You do good work. We love functional eye candy.


Thank you for the kind remarks.

Of course it is always possible to go over ornate. A good example would be the design of the Time Machine from the movie in the 1960's with Rod Taylor. It had a lot of plush velvet like material and gold domed studs etc. The best description I ever heard of it was: "It looks like something Elton John would have driven through the Everglades ".

The Time Machine from the second movie (with Australian Actor Guy Pearce) was better, it looked like it was made with Fresnel lenses from a lighthouse and had what looked like a Babbage Analytical Engine as the control console. Lots of Brass and Crystal.


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Fri 31, 2020 4:42 pm 
Member

Joined: Feb Sat 08, 2014 7:43 pm
Posts: 76
Location: Denver, CO
Very pretty, Acorn.


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Jan Fri 31, 2020 5:10 pm 
Member
User avatar

Joined: Jan Fri 02, 2009 11:32 pm
Posts: 641
Location: Equinunk PA 18417
I am envious of your visual style and building skills. Beautiful workmanship! It cannot be compared to my own, which seems to be stuck in a childhood cigar box phase.

_________________
-Richard


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Feb Sat 01, 2020 12:15 am 
Member

Joined: Jan Thu 16, 2020 12:29 am
Posts: 172
Thanks for the kind remarks about this amplifier.

In the article about this iPod amp I put a link to, on the original post, there is a real gem hiding in it, for audio enthusiasts.

I wondered if anyone would pick up on it. It is a remark about second harmonic distortion in class A amplifiers (based on pentode tubes) where there is a function available not possible with a Class A transistor amplifier stage, though the knowledge of this is not common in the Audiophile industry I have found, as it appeared in very few textbooks in the tube era:

"It is possible run a single pentode in class A operation with the correct load
resistance for zero second harmonic distortion. This is not physically possible with a
class A transistor. The method of how to do this is outlined on page 553, Sec 18-5,
Electronics Devices & Circuits, Millman & Halkias 1967, McGraw-Hill".

Actually it is an excellent book and worth buying, just for the section that explains this, but also for anyone interested in tube or solid state design.


Top
 Profile  
 
 Post subject: Re: iPod Amplifier built from 1920's components.
PostPosted: Feb Mon 03, 2020 5:07 am 
Member
User avatar

Joined: Dec Sat 24, 2011 9:17 pm
Posts: 5460
Location: Vancouver Island, Canada
Those transformers found a good home where they'll be admired for years to come. Good job!

_________________
Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
[:l>)


Top
 Profile  
 
Post New Topic Post Reply  [ 12 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 7 guests



Search for:
Jump to:  






























-->


Privacy Policy :: Powered by phpBB