I'm in the really OLD radio and SET clubs now.

radio, tape, stands and accessories
Coffee Phil
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Re: I'm in the really OLD radio and SET clubs now.

Post by Coffee Phil » 15 Oct 2019 00:18

Hi Big B,

Looks like you are farther along than I am with the old Radiola which I bought. Here is a bunch of stuff on the 01A including the data sheet: http://vinylsavor.blogspot.com/2013/10/ ... x201a.html

You seem not satisfied with the sound with your horn speaker. I'm not sure what can be expected, but you should be able to connect it to modern electronics to get some idea. Just keep the output low as I believe these speakers are much more sensitive than modern moving coil speakers. I have never seen inside one of those speakers but I'm guessing that they have a metal diaphragm like an earphone of the period loaded into the horn.

I found a balanced armature paper cone speaker for the Radiola. I had never seen inside or heard one of those before. I hooked it to a small amp and while it would not rival a moving coil speaker it was better than I would have expected.

Phil

Big B5515 wrote:
14 Oct 2019 08:24
I finally got around to trying out the Freed Eisemann tonight, after picking up a 6V, 5AH SLA battery for it's heater power. I had bought the 9V batteries over a year ago, which were a little weak from the start, but after 3 hours, the heater battery was about discharged, and the 10- 9V batteries in series were still at 81V. It was a bit tricky trying to find a station, I finally used the signal generator to figure out dial settings for 650 and 740, both of which I was then able to tune in. Unless listening to a weak signal, the extra gain of the last tube only made sound more distorted, the medium level output usually sounded clearer and reduces current draw, as last tube's filament only has power when speaker is plugged into loud connector. The volume level was not exactly loud either way, and sound quality is nothing to write home about. As the last tube was more sensitive to heater voltage, I suspect it may be weak, however it seems I heard 01As are only good for maybe 100mw, or so as a AF amp. I've yet to check the tubes, or do anything to it yet, but noticed that I do need to try to tighten up the center dial's variable capacitor which now turns a little too easily.
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Big B5515
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Re: I'm in the really OLD radio and SET clubs now.

Post by Big B5515 » 15 Oct 2019 17:17

A distant station such as 650 Nashville, can sound halfway decent at times, if volume (heater voltage to 2 rf tubes) is adjusted just right, the other "battery" control varies heater voltage to detector and AF tubes. The dials were easily tightened up with set screw on rear, but while all 5 tubes still tested strong and showed grid function, the only remaining 201A globe style tube was lighting the leakage\short light on my tester. Swapping this leaky tube with second AF tube that's unused with speaker plugged into medium connector made little difference in sound quality. The volume level is adequate for a quiet room, but I suspect headphones were more popular for listening to sound from a single 01a back then, it just doesn't have much extra power to overcome noise. The speaker itself seems to sound ok, but it's magnet may be a little weak as it is unrestored, I just looked for one that actually produced sound, and there were few choices. The previous owner had replaced a 1uf capacitor that is parallel across the 90V to ground, interstage transformers, and the grid leak capacitor & resistor. The distortion of stronger, louder signals is not much different than I get from that primitive 1931 Deltrola 4 tube TRF, however this earlier 3 stage radio has much better selectivity. While the previous owner had used a .00028 uf grid leak cap consistent with schematic value of .00025, he mentioned that it originally had .002 uf, schematic calls for 2 Mohm resistor. As his replacement parts are out of site under a tube socket, I have yet to confirm any values, but had read something about varying them them to suit different reception conditions. I'm just glad to confirm it still works, and suspect sound quality was the least of concerns in ~ 1924 (I'm guessing) radio, now to hunt down a good spare 01A or so. I do however think a pack made for 60 cheap Alkaline AA batteries might be the better, longer lasting choice for powering this radio, and probably my RCA short wave portable as a B power supply, especially as the price has since doubled on the 50 cent 9V batteries I was using.

circularvibes
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Re: I'm in the really OLD radio and SET clubs now.

Post by circularvibes » 15 Oct 2019 18:04

Big B, do you have any small super magnets laying around? You can see if magnetism loss in your speaker is an issue by attaching a super magnet to the original and trying the output. I have done this to improve old PM speakers in table radios and as a fix for weak magnets in phono motors with magnetic pitch control like an old Braun unit. It may also make it slightly louder or less distorted even if it isn't suffering from loss.

Big B5515
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Re: I'm in the really OLD radio and SET clubs now.

Post by Big B5515 » 16 Oct 2019 04:15

I had another look at the radio today, and located a loose screw connection on the grid of RF stage 2, which was causing signal to drop, and antenna tuning to vary slightly. Tightening this also improved the distortion issue some. I also determined that the leaky tube (6.5 Mohm heater to grid) is actually in 2nd RF position, and grid leak resistor is proper value. Reading up on detector circuits, the one used in this radio was chosen for sensitivity and gain, so distortion is to be expected with fully modulated signals. Parts of a live broadcast from Nashville did sound very clean, versus a louder, compressed signal. I also tried broadcasting a signal from the phono oscillator I built, which also sounded much better with lower modulation, however I still could not use the final AF stage without greatly amplifying the persistent hum present in both this small transmitter, and our local station which always seems worse near house wiring. I'll have to look into how to disassemble the speaker and get to it's magnet, I simply attached a wire and gave it a try. It can actually still sound decently clear and loud enough with a strong signal that isn't heavily modulated