Playing with 2 Volt valves

[Mike Watterson]

Here, the cheap alkaline PP3 work out 50% more expensive than Zinc biscuit ones per hour; Duracell & Energizer packs about x2 more expensive per hour use.

Maybe you've poor quality zinc biscuit ones (too old) or they are too dear, or the Alkaline ones are much cheaper there than here. Certainly the shelf life is about x5 more.

The 6.5 mA seems high for two valve regen at 56V. About 8mA for a superhet off 90V.

[Murphyv310]

The output don't forget is driving a speaker and the bias is set for a bit more quiescent current to give less distortion, I can reduce it to 4ma overall but audio level is less and distortion higher.
So far it's run around 100 hours with no problems, on the second set of PP3s now.
I use GP batteries from CPC, The alkaline work out cheaper in the long run.

Addendum..... Sorry its 63 volts using 7 PP3

[Mike Watterson]

I was assuming earphones! Certainly 6 mA to 7 mA with a speaker pretty good.

[Mike Watterson]

All these Gilbert Davy's Radios will work with rod tubes:
http://www.daveysradios.org.uk/index.html
I have the 2nd edition of his book somewhere.
Many designs to download.

Obviously the mains ones may need adapted and HT for g2 should be via an HT tap or voltage divider if a lower than HT volts needed for g2, though will work with a single resistor. AGC to g1 won't work because sharp cutoff. Either use a 1 M pot with 2 resistors to give 15V to 60V on g2 for RF gain (or IF gain) or use the anode of a DM70/DM71 magic eye as AGC amp to drive g2.

Replace heptodes and octodes with two rod tubes, they'll work in the existing circuits with one tube as osc triode with its anode driving RF input pentode g2 direct. Signal to g1. I've replaced DK91, DK92, 1L6, DK96 with pair of 1j24b. A triode-hexode ECH81 / UCH81 etc can be replaced with same pair of devices and wiring as the DK92 replacement.

The Rod tubes have a similar upper frequency limit to an EF80 so will work at VHF.

[AdrianPH]

I know the past few posts have been regarding Rod valves, but current drain and supply voltage have been mentioned. Now at my end I have minimum fixed voltage of 150 Volts so was driving the one valver with that, so I decided to just use a resistive dropper to get down to the 90 Volt range that I could do with PP3 batteries or a small stack and I am still getting good results down at 90 Volts and the current has dropped to 2.3 mA so around 200 milliwatts consumption and still a reasonable volume in the headphones.

These simple circuits are really impressing me. Will try lower voltages tomorrow.

Adrian

[BusyBee]

Hi Adrian. That's a nice looking set with neat layout.

For anyone interested there are probably thousands of articles on the World Radio History site as there are many of the old mags and articles from those days. They inspired me and I have one I constructed, inspired more in the era of the 1930's.
It is two valve, roughly looking period (but not accurate) as I used a 6K7 for the RF amp and 6н8с (Russian double triode) for the detector and audio. I used the 60V suppy I use for rod pentodes for the supply, which works well. Many of the designs of the period state that the detector voltage is best around that anyway. My coil former is home made, using 40mm water pipe with the ribs made from right angle plastic strip (obtained from a model shop) glued on. It has three coils, input main and reaction , the design of which was a popular one obtained online. I was lucky to get some very period looking chokes from John Birkett in Lincoln (sadly no longer I understand). Working on lower voltages and currents enabled me to use one of those miniature transformers more intended for transistor equipment for headphone output. I worked out impedances somewhat at the time but don't remember the details. I can provide the transformer type though if anyone is interested. It seems to work Ok but is obviously not period. One of those little RS ones designed for valves may be better but I had several of the little transistor ones of different types / ratios.

I did start on a rod pentode version but have done little with it recently, currently looking at superhet ideas. For me, there is something about a period looking layout though. I do have a fairly ancient looking variable capacitor with SM drive and another pair of the same valves so an update after learning from the first beckons lol.

[AdrianPH]

That Internet site is generally my main reference for articles, the likes of the old Popular Wireless that was around in the 1920's for this one.

I have changed the audio transformer around at the moment and used one from a Vidor picnic radio to provide the headphones and I the plan is to use the previous one (ECL86 type) for output to a speaker. The idea is that the second ale is just an audio amp, I have a couple to play with such as an Osram LP2 or Cossor 230XP. The speaker will be a major part of it hopefully. If it works in practice then I will remake it in another enclosure and try to get it a bit more period style.

I find this all so much more satisfying than modern electronics.

Adrian

[AdrianPH]

I added the second valve stage, at the moment it is using a HL210 which seems to have a quite high Ra between 18500 and 23,000 ohms depending on who made it.

as per another thread still awaiting to see if I win a better audio transformer, but it works in principle, here is a video.

https://youtu.be/gn8A07HbqYM

Things to consider if I get the xfmr would be a speaker and a new cabinet if I feel like taking it that far.

Adrian

[AdrianPH]

The RS economy O/P transformer arrived today and has been fitted, I think a perceptible difference, but not much, had little difference between the 8K and 15K settings so left it at 15K.

I have also been playing with the reaction coil and changed it from the large coil previously to a 10 turn coil on the former and find it a bit easier to control, small improvements. I also won some Colvern R2R coils from Ebay so will see how they can be used at some stage.

Adrian

[AdrianPH]

Continuing to play with the two valve receiver.

As I am limited at present with a 150 Volt psu, I am just trying a few serial resistors in line with the HT.

With a 47 K Ohm in series from the psu the main HT is at 89 volts, then I have another 68 k Ohm to drop the HT down to 50 - 51 Volts for the first reaction and detector valve. What is surprising is that audio level is still listenable in the speaker. OK I need a better speaker, it is a 4 Watt speaker it's driving, so base is low, but not bad.

Overall the radio is drawing 1.3 mA. Approx 0.75 mA in the audio amp and 0.55 mA in the first stage.

What gets me is what low output one can still listen on a speaker? I have over 2 volts peak to peak of audio from the detector valve and approx 18 volts pk - pk on the LF valve, probably driving the speaker at around 5 milliwatts of audio.

Adrian