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Old 28th Dec 2011, 5:21 am   #1
kalee99
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Question One valve regenerative set

Hi all,

Having been taken off restoring "big', sets due to my recent ill health. Going to have a go at building this circuit I found in a very old magazine. I have a few of the 6C8 valves so thought I would put one in and see what happens? The one on the drawing was a 6BF6 which I have never come across

Collecting the bits together from my junk box and will lash it up rough first.
Any thoughts will be most welcome.

Paul.
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Old 28th Dec 2011, 9:37 am   #2
Brian R Pateman
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Default Re: One valve regenerative set

Looks an interesting project.

The 6BF6 is certainly an oddball. I have dug up some conflicting information about it. According to WW Radio Valve Data (7th edition) it's a double diode.

Babani lists it (correctly?) as a double diode/triode. Neither list an equivalent simply referring to it as an "American Type."

In this case I suspect that Babani is correct.
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Old 28th Dec 2011, 9:51 am   #3
MichaelR
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Default Re: One valve regenerative set

I would be careful with that Anode circuit, you have full HT on the phones .The RFC in the Anode circuit I presume should read 2.5mh.

Mike
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Old 28th Dec 2011, 11:13 am   #4
kalee99
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Smile Re: One valve regenerative set

Hi,
Yes I read that 2.5mOhm on the drawing in the book! It is a typo from years ago. You are correct, on the parts list it is 2.5Mh.
Yes full HT across the phones, no health & safety back then
Paul.
Quote:
Originally Posted by MichaelR View Post
I would be careful with that Anode circuit, you have full HT on the phones .The RFC in the Anode circuit I presume should read 2.5mh.

Mike
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Old 28th Dec 2011, 11:54 am   #5
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Default Re: One valve regenerative set

Hi,

Just curious as to suggested HT for this circuit. When I built a similar design using an EBC33 triode (with the two diodes strapped to cathode) the optimum HT voltage was found to be in the region of 60 to 90 volts.

When HT was above 90 volts, the reaction control (regen) was extremely fierce and below 60 volts reaction was weak. Adjusting the coupling between coils helps, but for smooth operation over the tuning range adjusting the HT makes a great deal of difference as does selection of a valve with modest gm.

In this type of circuit Mazda HL2 works perfectly gm = 1.5mA/V.

Cheers

Rich

Last edited by Marconi_MPT4; 28th Dec 2011 at 11:57 am. Reason: units
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Old 28th Dec 2011, 1:18 pm   #6
kalee99
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Smile Re: One valve regenerative set

Hi, Just as it happens I have an HL2 as well so will give it a try on the lash up as well before I decide on the optimum components.
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Old 28th Dec 2011, 4:05 pm   #7
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Arrow Re: One valve regenerative set

The 6BF6 is listed in the 1956 Sylvania receiving tubes booklet.
Double-diode triode; heater 6.3 v. @ 0.3 A; gm 1.9 mA/v.

Al.
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Old 28th Dec 2011, 5:01 pm   #8
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Default Re: One valve regenerative set

Would that circuit have originated in Australia perchance?
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Old 28th Dec 2011, 5:47 pm   #9
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Default Re: One valve regenerative set

I wondered about that, I didn't recognise what sort of valve it was until I stood on my head

Peter
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Old 28th Dec 2011, 9:03 pm   #10
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Default Re: One valve regenerative set

Hi,
Headphones at HT and earthed tuning controls may be a problem. Attached circuit permits the headphones to be at HT- potential. You could also wire a 1 or 2M resistor across the headphone jack to avoid a poke when connecting up.

Cheers

Rich
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Old 28th Dec 2011, 9:52 pm   #11
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Default Re: One valve regenerative set

I should imagine it will work ok, the diag remids me of a H.A.C (Hear All Continents) British kit I built as a kid, though it even in the 1960's used a battery valve from the 1920/1930 era.

Regards,

val33vo
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Old 28th Dec 2011, 10:31 pm   #12
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Default Re: One valve regenerative set

You could use low impedance phones and an output transformer!
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Old 28th Dec 2011, 11:47 pm   #13
kalee99
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Smile Re: One valve regenerative set

Well it's working as a lash up on the bench and as the 6C8 I am using is a double triode (separate Cathodes), then I will shove an inter valve transformer in and bring the disused triode into use as an amplifier to boost the signal a bit (waste not want not)?
Paul.
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Old 30th Dec 2011, 11:50 pm   #14
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Smile Re: One valve regenerative set

Got it working very well now but decided to keep it single stage as it comes through on the headphones very well (I may well isolate the phones on final build). Working with 120 Volts on the HT. Also I have found that great care is needed to wire up the "tickler", coil just right or the set works but is very poor coverage although you can get it to oscillate?

Once wired up right it can be set up to pull in loads of stations with good gain, clarity and very sharp tuning. I am going to wind some short wave coils soon and build the set up in a nice box so will make the coils plug in ones.

Set is still a "heap", on the bench just now so will photograph as is and as finished in the case I am going to use. Photos to follow soon. Have some interesting ideas for the PSU so will be busy a while yet. I am finding the whole thing fun to do and a nice little project I can pick up as and when I get bored or thrown out of the sitting room by "her indoors",
Have not done any "home constructing", since I was a teenager!

Paul.
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Old 31st Dec 2011, 10:38 am   #15
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Default Re: One valve regenerative set

I used to find that they worked better as a lash up than when assembled neatly.

Peter
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Old 31st Dec 2011, 11:46 am   #16
kalee99
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Default Re: One valve regenerative set

Hi Peter,

Yes that did cross my mind! Certainly as it is (a heap on the bench), you can move certain wires into odd shapes and get loads more sensitivity out of it for no apparent reason I put that down to the fact that there is no chassis just now to tie everything down to ground? But then again these 20s sets did not have one & were just knocked up on a plank of wood. I guess that is why they eventually got round to fixing a copper sheet onto the breadboard before assembly?

Paul.

Last edited by kalee99; 31st Dec 2011 at 11:47 am. Reason: typo
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Old 2nd Feb 2012, 11:43 am   #17
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Default Re: One valve regenerative set

Quote:
Originally Posted by val33vo View Post
I should imagine it will work ok, the diag remids me of a H.A.C (Hear All Continents) British kit I built as a kid, though it even in the 1960's used a battery valve from the 1920/1930 era

Regards

val33vo
I've just completed a replica HAC Model DX with an extra stage of audio amplification using a PEN25 Pentode and it works very well for what it is.

I always wanted one of these sets when I was a kid but on my pocket money could never afford one. Now 40 odd years later I have my set

Kev.
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Old 2nd Feb 2012, 5:57 pm   #18
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Default Re: One valve regenerative set

As Trevor says, you could use a transformer and low resistance phones. Nothing unusual about having 'live' phones, though, but I'd only use them with battery-powered circuits. This circuit is fairly conventional, a leaky-grid detector, in spite of the upside-down drawing in the American style.
-Tony
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