20's neutrodyne valve radio

[unrealdave]

Here’s an interesting radio.  It’s a bit grubby but I am going to see if I can get it working.

Here’s my take on it (please join in with anything to add or correct)

• There’s a primary and secondary aerial coil
  
• 4 valves – the first 2 are rf amplifiers, the 3rd is the detector and the final one an af amplifier stage which can be bypassed if using headphones. 
  
• The 2 rf amp stages use Neutrodyne Condenser’s to keep the valves stable.
  
• There are 3 Ohm resistors in the LT line – I guess to drop the voltage down to 5 volts from a 6 volt supply for the original der valves
  
• The grid leak is missing.
  
• The af coupling transformer is o/c
  
• Corrosion and flaky joints are all over the place.
  
• One of the LW coils will not fit.
  

Should be easy?

Are there rules re attachments on post's?

[Mark Hennessy]

Looks like an interesting project - quite a bit to do!

Are there rules re attachments on post's?

Not really, within the usual bounds of decency

See http://golbornevintageradio.co.uk/forum/...p?tid=4835 for information about maximum file sizes, but beyond that, just go for it

Good luck,

Mark

[Crackle]

Hi Dave
It looks home made, or at least the wiring does. There is a neutrodyne condenser listed in the radio museum. http://www.radiomuseum.org/r/collinsons_...enser.html and from the description it seems the term "neutrodyne" was a type of radio.
Mike

   

[unrealdave]

from the description it seems the term "neutrodyne" was a type of radio.

Hiya Mike - fancy seeing you here

neutrodyne was just a method of using triodes to amplify rf before the screen grid came in.  The inter electrode capacitance in a triode (between the plate and grid) caused oscillation but the neutrodyne cap (usually just a small air spaced var cap) cancelled it out.  The SG valve was far better so the neutrodyne bit the dust.

[tiv48]

I have never attempted any thing like this so will find it interesting,
Good luck
Rob T

[Terry]

neutrodyne was just a method of using triodes to amplify rf before the screen grid came in ...

I would call that a neutralising capacitor (or condenser, as it would have been known). So it is quite possible that, as Mike hinted in his post, that 'Neutrodyne' may have been one manufacturer's trademark rather than a generic name.

[Alan Douglas]

Neutrodynes are common enough here but I've never seen a British one. Is there a name on the coils?

There were "licensed" Neutrodynes made by 14 manufacturers under Hazeltine's patent, and there were kits of parts sold. The trademark was aggressively defended but there were some off-brand sets with the coils fixed at the "correct" angle (which however varied with the coil spacing) of 55 degrees.

[pwdrive]

Any makers name(s) on the coils, interstage transformer, neutralising capacitors etc might give a clue as to its origins.

Lawrence.

[unrealdave]

In the Brown Brothers catalogue from 25/26 there are a lot of neutralising / stabilizing / micrometer etc  condensers for neutrodyne circuits. 

I guess you guys are to young to remember them

 I have attached some pic's

[unrealdave]

The coils are marked Peto Scott Co LTD.  Again I have put some pic's up