Author Topic: Lafayette Superheterodyne Radio - 1935  (Read 2462 times)

Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #15 on: August 23, 2020, 08:38:45 AM »
So I myself have done very little on this.  @charles  has very kindly offered to test the valves, and I still need to get them through to him.

But what has happened is that my friend took the cabinet to a furniture restorer he has used, and the results are absolutely stunning. It probably looks better than when it left the factory floor!






Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #16 on: August 23, 2020, 08:41:55 AM »
Very interesting re field coil drivers . Those 6L6's (?) also look good . CV1917 perhaps ? ( the 6L6's I mean )

The valves are: 2 x 47 output pentodes, 1 x 80 rectifier, 1 x 55 double diode, 4 x 56/57/58 RF amps. So the type 47 are the power amp stage

Online Trompie67

Re: Lafayette Superheterodyne Radio - 1935
« Reply #17 on: August 23, 2020, 08:43:23 AM »
So I myself have done very little on this.  @charles  has very kindly offered to test the valves, and I still need to get them through to him.

But what has happened is that my friend took the cabinet to a furniture restorer he has used, and the results are absolutely stunning. It probably looks better than when it left the factory floor!







Oh my. That looks absolutely beautiful!  :thumbs:
"Trumpets are a bit more adventurous; they're drunk! Trumpeters are generally drunk. It wets their whistle."
Paul McCartney

With thanks to F_D for this pearl of wisdom!

Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #18 on: August 23, 2020, 08:47:12 AM »
Oh my. That looks absolutely beautiful!  :thumbs:

It does! But now the pressure's on me to restore the electronics to the same standard.....

Offline Family_Dog

Re: Lafayette Superheterodyne Radio - 1935
« Reply #19 on: August 23, 2020, 10:06:04 AM »
The Furniture Restorer certainly knows his stuff, that is absolutely brilliant! Now Mr. Sid, the electronics are up to you and I suggest you get down to it with puhlentee of pics along the way.


-F_D



-Eric

That Guy in South Africa...
*************************************
http://groups.yahoo.com/group/vintage_tube/
*************************************

Offline fredeb

Re: Lafayette Superheterodyne Radio - 1935
« Reply #20 on: August 23, 2020, 12:21:48 PM »
That does look amazing , I'm sure this unit will sound even better than new when you're done with it El Sid .

Can you , for interests sake , post the schematic please ?
« Last Edit: August 23, 2020, 12:23:53 PM by fredeb »
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #21 on: August 23, 2020, 04:45:34 PM »
Hi Fred - this schematic from reply #1 is the closest I've managed to find:




Offline kubusi

Re: Lafayette Superheterodyne Radio - 1935
« Reply #22 on: November 22, 2020, 05:57:03 PM »
If you need any of those valves and 2.5 volt pilot bulbs give me a shout, have them all
FIRST LAW OF VALVE AMPLIFIERS
Hot glass looks exactly the same as cold glass.

Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #23 on: November 22, 2020, 08:35:07 PM »
If you need any of those valves and 2.5 volt pilot bulbs give me a shout, have them all

Wow - thanks kubusi! Charles has also very kindly offered to help, also with testing the existing valves to see which need replacing. I will be in touch.

Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #24 on: November 23, 2021, 08:33:19 PM »
Finally getting going a bit here.

First up I took out all the valves and tested the transformer. No problems - it is making the 2 x 380V AC for the B+, 2.5V AC for the heaters, and 5v AC for the rectifer heater.

Then checking components. The caps are very old - even the replacement caps are ancient! I tested a few out of interest, but they were all way out of spec. The exception is the 2 micas I tested which are OK. So there's a lot of recapping to be done. I had heard that those old dog-bone resistors were quite good, so was very disappointed when I started testing them. They are almost all way out - at least 50%. Only 2 were within 20%. So I will have to replace all of those too, which is very sad because they look so cool.

I have started with components I have lying around, and the others are on order.

The filter caps have been replaced with 3 x 10uf on a terminal strip. The wire, although braid insulated, is still pretty good so I have not had to replace it. Stripping it is a pain in the bum though - I have found a razor blade is the only way to not end up with a bunch of fluff on the end.



Here's a pic the modern 10uF 450V cap next to the 8uF 450V cap it is replacing!






Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #25 on: November 23, 2021, 08:36:20 PM »
Started removing caps and lifting resistors to test


Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #26 on: November 23, 2021, 08:41:15 PM »
The deisgn of this thing is quite tricky - it took me a while to work out how the power supply works. All DC current is returned via the speaker field coil and the 21H choke to the centre tap of the transformer. Usually those are on the positive side.

It seems to me that the negative bias for the two output pentodes (top right) is set by the 2 x 500k resistors (500MΩ on the old schematic) to the right of the choke in the form of a divider between the voltage after the field coil and ground. Now since the speaker is missing, I think the simplest would be to put a resistor in place of the field coil. But i have no idea what a typical resistance of a field coil is - any suggestions? A choke would also probably work, but cost and also have no idea what the inductance of the field coil is.


Offline Family_Dog

Re: Lafayette Superheterodyne Radio - 1935
« Reply #27 on: November 23, 2021, 08:44:49 PM »
I feel so guilty looking at this... I have a 1930s RCA Cathedral AM/SW radio with a cabinet in beautiful condition, I really need to restore it to its former glory with caps/whatever replacement. It still worked fine when I last tested it but that was some years ago. Maybe a job for the December holidays - we'll see!


-F_D



-Eric

That Guy in South Africa...
*************************************
http://groups.yahoo.com/group/vintage_tube/
*************************************

Offline Family_Dog

Re: Lafayette Superheterodyne Radio - 1935
« Reply #28 on: November 23, 2021, 08:49:20 PM »
The resistance in place of the choke should not be very big, I would start with a 100-ohm resistor of about 3w and play around with that. This is a thumb-sucking value, I have no idea how much current is drawn from the rectifier but you probably only want to drop some 20-30v across the resistor.



-Eric

That Guy in South Africa...
*************************************
http://groups.yahoo.com/group/vintage_tube/
*************************************

Offline El Sid

Re: Lafayette Superheterodyne Radio - 1935
« Reply #29 on: November 26, 2021, 06:50:58 PM »
The replacement component count is 22 caps and 30 resistors.  :sd: 

It went up somewhat because i checked the caps and resistors inside the RF and IF  transformer cans. Normally these are highly accurate components, e.g. mica caps, but in these old cans (pic below), they are pretty much the same as the others in the radio, hence crap. If you look closely you will see the cores of those transformers are wood! No wonder they are so massive.

It's also a bit tricky because some of the components need to be very close to the design values (particularly in the RF and IF sections), which are not the same as modern components (e.g. a bunch of 5k and 500k resistors) , so I'll have to buy some pricier 5% or 2% components, or cobble together equivalents.