Lash up Direct Conversion Receiver

[pwdrive]

Just a quick listening update on this test bed receiver, about 5 mins ago I tuned the 7 mhz amature band and picked up ON7TQ (Roger in Belgium) I normally try and listen out for him when I am doing any SWLing at night as he usually pulls in some good contacts, tonight was no exception he made contact with PR8RF (Brazil) I managed to resolve PR8RF on this receiver although as expected the transmission from Brazil was weak on my short length of wire, but his call sign was made out ok, unfortunately for me is he was talking in Spanish, ON7TQ was acting as an intermediary between various Spanish and other European stations who wanted to copy PR8RF.
If any members are new to SWLing then listen out for Roger (ON7TQ) and try and follow him with his contacts, he's a real gent (excuse pun)

Lawrence.

[pwdrive]

Forgot to add obsevations when using my sig. gen. as local osc feed to mixer:
The output from the sig. gen. is connected via a blocking capacitor direct to the cathode of the 6AC7 pentode I am using as a mixer, initially I set the coarse and fine attenuator controls for maximum output on my AVO CT378A this gives 25 mv at the output if terminated with a 75 ohm load, the cathode resistor is 390 ohm, reception was possible but rather week, I checked the sig. gen. specs for the "force" output and it quoted 200 mv into a 200 to 300 ohm load so I used that facility, I set the RF out to the red line on the gens. thermo couple, the receiver works well but I noticed that advancing the RF out a bit further to FSD the received signals increased in strength proportionatly, I am not sure what the optimim injection voltage is as just over 200 mv is all I can push, even at the level it gives some hope of using the harmonic generator idea as originally discussed, we will have to see.

Lawrence.

[pwdrive]

I found a 6SC7 valve (Double Triode) which tested ok so I have used one of the triode sections to now drive the 6F6 sound output valve, there is plenty of volume now with more to spare, the final design will probably use an ECL82/3 or ECL86.
Had a go today at winding my own regen tuning coil with feedback winding and coupling winding, I found an old paxolin former approx 1.5" O.D. x 4" long, I wound the tuning coil to give an approx tuning range of 550 khz which equates to approx 275 khz either side of the converter frequency.
This frequency has now been changed from my original attempt which was 3.25 mhz, I've wound the new coil to give a center frequency of 2.25 mhz so that the tuning capacitor I have will (with padder and trimmer) tune from 1.975 mhz to 2.525 mhz.
The reason for this change was because although my original attempt tuned ok it would only tune 200 khz of the 550 khz with enough regen to occur for SSB/CW reception even with the feedback winding very closely coupled, this was due to the low L/C ratio approach which I wanted to use to increase frequency stability when regen just comes into oscillation (this is needed for SSB/CW)
With the new lower frequency I have still managed to maintain a reasonable low L/C ratio while maintaining a reasonable image distance of 4 to 5 mhz.
With the home made coil and the extra audio valve in place, I switched the receiver on, the results were good, the regen feedback winding had to be slid 1.5" up the former from the tuned winding to get the most sensitive reception (the least loading)
The primary winding which was connected in the mixer anode circuit worked ok but when tuning the grid circuit of the
mixer out of band some spurious oscillations were heard at the top end of the RF tuning range, I tried altering the coupling of this winding by sliding it towards and away from the tuned regen but still the spurious oscillations occured also tried the usual such as grid stopper/decoupling etc but no joy, the 6AC7 valve used in that stage is quite a high gain one and as such I think maybe inter electrode capacitances might be part of the problem, it's the only spare valve I have though.
So a different approach was required, I changed the mixer anode coupling to the regen det from inductive coupling to choke and capacitor coupling, this works extremely well and gives an increased level of signal to the regen det. with no "pulling" of the regen when tuning the mixer grid circuit.
The anode end of the choke is coupled to the top end of the regen tuning coil by a 22pf capacitor and thence from there to the grid of the det by another 22pf, the grid leak is 2.2 m ohm.
The variable capacitor I am using for the regen tuning is approx 15 to 400pf this is connected across the tuning coil via a 180 pf, the coil in addition to the tuning capacitor has a 220 pf in parallel fitted across it and also an old BFO trimmer in series with a 22pf as an extra fine tuning for SSB/CW.
Eventually the main tuning capacitor will have a reduction drive fitted, I am hoping to obtain a second hand PW Drive from an old HRO scrapper, this drive gives a 10 to 1 reduction and the vernier scale can be read down to 1 khz or less over a 500 khz tuning range.
Anway as said I tried it all out tonight after the revamp both on the 20 meter and 40 meter amature bands and I have to say it's the best regen I have built even though it is still in the "testbed" stage. The fine tuning trimmer has just the right "action" so that when any part of a particular SSB's transmission spectrum is located with the main tuning capacitor resolving it is very quick and easy with the fine tuning trimmer arrangement I have used. The band conditions at our location were very clear tonight (little mush)and reception was excellent
So far so good. Coil details on the former described above: Main regen tuning winding: 20 turns close wound, regen feedback winding 10 turns in same direction but on a sliding paper former, bottom end of main coil to chassis, top end to tuning capacitors, regen winding: bottom end (nearest top end of main winding) to anode of det top end to HT via choke/decouplers etc. I am not sure what gauge the wire I used was but I salvaged it from the speaker winding of a typical valve single ended sound output transformer.
Hope these observations/comments are of some use.

Lawrence.

[Skywave]

Hi Lawrence,

Hope these observations / comments are of some use.
Lawrence.

"Use": maybe; "interesting": certainly!

Yes, I'm interested and indeed fascinated by your progress with this project, of course. When you're finally happy with it, please provide a summary listing of its specs., performance and cct. description. One of us can then draw the cct. diag. to complete this project's documentation - then we can all build one!

Al.

[Skywave]

I am hoping to obtain a second hand PW Drive from an old HRO scrapper . . .
Lawrence.

There's a 'pw drive' on the Golborne Vintage Radio site if that's of any use!  
No, but seriously, I'd never heard of a 'pw drive' until you joined this forum . . . and it seems that it has some association with the H.R.O. receiver (shows his ignorance  ). Yes, I have owned a few of those receivers in my time, but never met that name . . . so what, exactly, does the 'pw' refer to? (I've deduced that it isn't Practical Wireless!   )

Al.

[pwdrive]

I am hoping to obtain a second hand PW Drive from an old HRO scrapper . . .
Lawrence.

There's a 'pw drive' on the Golborne Vintage Radio site if that's of any use!  
No, but seriously, I'd never heard of a 'pw drive' until you joined this forum . . . and it seems that it has some association with the H.R.O. receiver (shows his ignorance  ). Yes, I have owned a few of those receivers in my time, but never met that name . . . so what, exactly, does the 'pw' refer to? (I've deduced that it isn't Practical Wireless!   )

Al.

Hello Al, "PW Drive" Precision Worm Drive.....The worm drive that is on the end of the main tuning knob shaft that engages with the two anti back lash gears, the whole assy including the micrometer style read out is very efficient and simple as you probably know.
Although using a different approach the RA1155 tuning drive is also very efficient and simple.
Beats yer drive cord any day...

Lawrence.

[AlanBeckett]

The B40 uses a chain and gearboxes
Alan

[pwdrive]

The B40 uses a chain and gearboxes
Alan

Hello Alan, I always thought the B40D gearbox was a pit piddly for such a beast, mine has excessive wear resulting in backlash, which is a real pain for SSB/CW listening.

Lawrence

[Skywave]

Ah - Ha!  PW = Precision Worm (drive) . . . . I see; thank you Lawrence. 

When I read your reply, at first it sounded like someone's address:

H.R.O. esq.,
National House,
PW Drive,
Somewhere Stateside.

. . . . or something like that!

Al.

[Skywave]

The B40 uses a chain and gearboxes
Alan

And I know that that's the sort of arrangement that you'd be happy with, Alan. 

Al.