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What is this? Valve Amp?

soulshoes

Member
2016-04-17 10:45 pm
Hi All,

I have acquired what appears to be a valve amp but neither the controls or the outputs seem obvious. I don't want to blow any speakers by doing the wrong thing so I'd like to have some expert guidance on this please.

I have to admit that I am a beginner when it comes to valves so please be gentle.

When I got this it had no plug on it so I put one on with a 3amp fuse. It works in as far as the light comes on and the valve glows but from there I am stumped.

There are a couple of screws on the back that don't look like they would be speaker connectors or else they would be conductivity between them. The other section looks like banana plug sockets and have the markings AE and E. I have no idea what these mean but due to the fact there is a 1/4" socket I was assuming this is some kind of guitar amp head. I could be wrong.

The front ratio pot knobs turn independently of the display ring and for each turn of the black knob the indicator moves about 30 notches. 25 for the smaller one on the bottom. The one on the right seems like a volume control but unfortunately has no stop and turns infinitely.

There were 2 extra "miniature dual purpose coil" by Denco supplied with this so not sure what these do. Whether they have different ratings etc. They have original datasheets with them. The stickers which appear to have come off of these say MAXI-Q Denco(Clacton)LTD RANGE 4 DP and another one says RANGE 5 DP

The valve is a Mullard ECF82.

Any ideas. I am hoping someone knows what these controls are. It cost me £4 so I've not lost anything(yet). Would prefer not to loose my life by doing stupid things hence why I need your help.

Here are the images.
https://drive.google.com/folderview?id=0B78LtjC_hXFYZFV5bHdhUkF5SlU&usp=sharing
 
have the markings AE and E

Aerial and earth....otherwise called antenna and ground.

a superhet receiver....

Not enough parts for a superhet. The coils were obviously sold with that in mind, but superhet requires a minimum of 3 stages, usually 4 or 5. At least 3 tuned circuits would also be required.

Looks like a simple diy short wave receiver or similar. Band changing by swapping coils.

I agree, probably a superegenerative receiver with different plug in coils for different frequency bands. These were common DIY devices in the post WWII era. It's probably designed for use with headphones.

Two knobs, the one attached to the variable capacitor is tuning, the other probably the "regen" control or maybe just a simple volume control. Regeneration was a method of employing positive feedback to increase gain and improve selectivity.
 

TonyTecson

diyAudio Moderator Emeritus
2003-05-29 2:57 am
Maybunga, Pasig City
Hey George, the thing that got me into tubes in the first place was that article from a Grolier encyclopedia, The Book of Knowledge" sometime in 1964.....a 6sn7 super-regen build for a ham, one tube, and coils and variable caps....

yes, that was a super-regen receiver, my bad....

I recall my first ever project was a crystal receiver set....lifted from "Electronics Made Easy" by Lothar Stern....wonder if copies of that book still exists...

OMG, my age is showing...:D
 
The 1/4in jack is probably for headphones. With just a single (two-section) valve there probably won't be enough volume to drive a loudspeaker.

Denco coils were popular in the UK. They covered both TRF and superhet designs. The 'Range' showed what frequency range the coil was designed for; the 'Colour' showed what position in the circuit the coil was intended for - the leaflet you have shows all this. There were coils for RF amp (i.e. antenna input), regenerative detector (for TRF), local oscillator (for superhet: two sets, for 465kHz or 1.6MHz IF). One ingenious technique was that the connection for oscillator padder capacitor appeared on different pins on different ranges, so you could plug in different coils and get the right padder. All use B9A bases, but could also be permanently mounted in a small chassis hole - that is why they are called Dual Purpose (DP).