R1084 not....

[Herald1360]

I've won what was described as a R1084, but clearly isn't (see pics). I'm not worried, it looks like an interesting box of spares and I won't have any particular qualms about breaking it. I'm sure if even one of those TXs is useful I'll get my money back easily enough.

It looks like a homebrew TX in a R1084 case- anyone any better ideas or even remember a '50s design that might fit?

[Herald1360]

It's a big brute! As a battery operated receiver it's huge. In its present format it's still definitely boat anchor class and all the iron weighs a fair bit.

Can't examine it closely at the moment , it'll take two people to get it out of the car, but there's at least a fair sized 500-0-500 HT transformer in there plus a couple of PA bottles and other assorted goodies.

[Nickthedentist]

Intriguing. Do post a better pic when you can.

[Herald1360]

Had a peek this morning (still in the car)......

2- 807s nice ceramic sockets
1- 1613 Pentode for class c RF amp
1- 6N7 Double triode for class b push-pull audio- interesting.....
various rectifiers and a 130V regulator.

500-0-500 and 400-0-400 HT TXs plus a heater TX

Not a lot of turns on the PA coil- maybe a monobander for 20m?

A wide spaced variable capacitor

Couple of vernier drive knobs (look like R1084 originals)

Various unidentified TXs and Ls

I reckon I got my £6 worth

I'll try for some pics tonight if it's not raining.

[Herald1360]

Pics

[HamishBoxer]

That was indeed a good (very) buy at that price.

[G6Tanuki]

Definitely a nice collection of parts! I'm guessing immediate-post-WWII homebrew.

I'm intrigued about the valve lineup: if the two 807s are in either push-pull or parallel, a single 6N7 won't provide enough audio [from memory it can manage about 17 Watts] to fully anode-and-screen modulate the 807s.

[Herald1360]

The 807s are in parallel. I don't think I'll be reverse engineering it, but I'll try to figure out the modulation scheme when I get a chance to look at it more closely.

It's got its marching orders from the car, SWMBO was just a tadge unimpressed when she saw it this morning All I've got to do is find some grunt to help.....

[Keith]

The boxed transformer at the rear right looks like it might be a modulation transformer and the under chassis view shows two holes that could have accommodated a pair of modulator valves. Maybe the original owner went back to CW!

[G6Tanuki]

The 6N7 would be a good valve to transformer drive a modulator pair of 807s in zero-bias push-pull (1200V on the anodes, 100-odd mA standing current). I used something similar for 100-watt 'indestructible' guitar-amps in the late-1970s.

[Herald1360]

I really hope the standing current wasn't 100mA. I reckon an 807 would melt trying to cope with 120W!

That arrangement was class B with the screen and control grids transformer driven with 0V bias on both. The standing current in class B would be near to zero (literally class B amps only conduct over half of the signal cycle).

http://www.google.com.ar/patents/US2494317

[G6Tanuki]

Sorry, I meant peak current 100mA. I experimented with a degree of negative-bias too, in order to satisfy the guitarists' need for distortion. Would that be described as "Class BC1" perhaps?

[Herald1360]

Not sure.... if there was grid current maybe BC2?

[Herald1360]

Spent an enjoyable time today poking round the museum at RAF Henlow. Lots of interesting stuff and very helpful staff.

Here's some pictures I took of the real deal. Interestingly I think some of the surviving bits of my unit are in better condition than theirs.

The calibration charts in the lid are splendid examples of draughtsman's calligraphy on individually drawn plots of dial readings vs frequency for each band covered by the plugin coils.