I'm new to vacuum tubes. The tubes I found were out of an old surplus hardware store. The tubes I have are 2- 12V6GT, 1-6J5GT, 1-6U8A, 1-12AT7, 1-12AU7A, 2-12BA6, 1-12BE6, 1-12BF6. I built a 12AT7 Regen with the 12AT7 with the schematic from www.mines.uidaho.edu/~glowbugs/12at7_regen.html I've been having trouble with low volume. I have tried different head phones and a speaker. The speaker with an audio transformer works the best. primary is 39.2 ohms secondary is .25 ohms. The speaker is 3.2ohms. Is there anything I can do to fix this, or is there a simple amplifier I can build.

The resistances you measure are DC values. The speaker is 3.2 ohms "impedance" or AC resistance. The ratio of resistances sounds about right and obviously, it works! Are you trying to use high impedance headphones connected to the transformer secondary? That won't work well. The headphones can be connected to the primary side of the transformer, but be careful. You will probably have the plate voltage applied to the headphones and that can be a shock hazard. If you can find a schematic for an old Knight "Ocean Hopper" or "Space Spanner" kit radio, you will get some tips on how the headphones were connected. Also check out Dave Schmarder's web site for good ideas on regen radio circuits. www.schmarder.com/radios/

Good luck.... Rich

:I'm new to vacuum tubes. The tubes I found were out of an old surplus hardware store. The tubes I have are 2- 12V6GT, 1-6J5GT, 1-6U8A, 1-12AT7, 1-12AU7A, 2-12BA6, 1-12BE6, 1-12BF6. I built a 12AT7 Regen with the 12AT7 with the schematic from www.mines.uidaho.edu/~glowbugs/12at7_regen.html I've been having trouble with low volume. I have tried different head phones and a speaker. The speaker with an audio transformer works the best. primary is 39.2 ohms secondary is .25 ohms. The speaker is 3.2ohms. Is there anything I can do to fix this, or is there a simple amplifier I can build.

Thank Rich, your suggestions really helped.

:The resistances you measure are DC values. The speaker is 3.2 ohms "impedance" or AC resistance. The ratio of resistances sounds about right and obviously, it works! Are you trying to use high impedance headphones connected to the transformer secondary? That won't work well. The headphones can be connected to the primary side of the transformer, but be careful. You will probably have the plate voltage applied to the headphones and that can be a shock hazard. If you can find a schematic for an old Knight "Ocean Hopper" or "Space Spanner" kit radio, you will get some tips on how the headphones were connected. Also check out Dave Schmarder's web site for good ideas on regen radio circuits. www.schmarder.com/radios/
:
:Good luck.... Rich
:
:
::I'm new to vacuum tubes. The tubes I found were out of an old surplus hardware store. The tubes I have are 2- 12V6GT, 1-6J5GT, 1-6U8A, 1-12AT7, 1-12AU7A, 2-12BA6, 1-12BE6, 1-12BF6. I built a 12AT7 Regen with the 12AT7 with the schematic from www.mines.uidaho.edu/~glowbugs/12at7_regen.html I've been having trouble with low volume. I have tried different head phones and a speaker. The speaker with an audio transformer works the best. primary is 39.2 ohms secondary is .25 ohms. The speaker is 3.2ohms. Is there anything I can do to fix this, or is there a simple amplifier I can build.

2000 ohm (or 1000 ohm or even as low as 100 ohm) headphones should be connected directly to the plate circuit of a 1 tube regenerative receiver. One lead should be connected to B+ and the other should be connected to the plate (or to one side of the tickler coil if the tickler coil is in series with the plate). If you are using voltages of 90 or lower, there is a shock hazard, but not too much. Just try not to touch the phone leads and the B- at the same time. This is how those radios were originally wired. If you just remember not to touch B+ and B- at the same time, you won't die. Lots of people used the radios, and there wasn't much report of death. Most 1920s TRF receivers put B+ right at the phones output as well.

Sometimes you can get a 1:1 matching transformer for those headphones. It will eliminate the shock hazard, but is not necessary if you are just cautious.

As for driving a speaker, you must use an output transformer like the one you have in order to drive a speaker. You cannot connect the low impedance voice coil of a modern speaker directly to the plate circuit. The speaker requires low voltage high amperage. The plate circuit is high voltage low amperage. 600 ohms primary at the transformer is more appropriate. www.tubesandmore.com sells transformers of this nature.

Since you are using a 12AT7, you can use one section for the regeneration and one section for a 1st audio amplifier. Using another tube of the same design can serve as two more amplifiers, or the two sections may be wired in parallel for a more powerful output tube. At 90 volts, a 6V6 serves as a fairly good output tube. It will supply around 1 watt at this voltage.

You can really use a lot of different tubes to make a regenerative receiver. There are those that work best, but experimentation with different tubes can be fun. As long as they have at least one grid, they may work. I've made a very elaborate regenerative receiver using a 6A7 tube, and I used a #47 tube, which really isn't fitting, but it was at hand. I've used a 6L6 tube. Using a tube with such a high amperage filament is overkill. Still, it worked well. 6BF6 or 12AT7 is more appropriate. Filamentary #26 and 01A tubes work well. High amperage 24 and 27 tubes work well, though they are not practical unless a filament transformer is used (I always use a filament transformer, which is why I've been able to use such strange tubes). A 6V6 will likely work, too, since a 6L6 worked.

Thanks for the info Thomas. This is very useful.

Hi Jeremy

Your matching transformer seems low in primary resistance. Maybe it was made for transistor circuits? I would expect the primary to have a DC resistance around 300-500 ohms. Try to find an output transformer from an old tube radio.

Norm

:Thanks for the info Thomas. This is very useful.

.....yeah...I was thinking that it sounded more like a filament transformer. The secondary of a filament transformer is often close to that of an output transformer, but the primary is down around 30 ohms or so. Filament transformers can often look like output transformers. I bet that if you put that transformer primary across 120 volts AC, you'd get a standard filament voltage out the secondary (say 6.3 volts or 5 volts).

Thomas

:Hi Jeremy
:
: Your matching transformer seems low in primary resistance. Maybe it was made for transistor circuits? I would expect the primary to have a DC resistance around 300-500 ohms. Try to find an output transformer from an old tube radio.
:
:Norm
:
::Thanks for the info Thomas. This is very useful.

One more thing about what I said about that 1:1 transformer for isolating the headphones from B+: It is not just any 1:1 transformer. It has a primary and secondary impedance similar to that of a standard pair of high impedance headphones (2000 ohms). You can use any 1:1 audio interstage transformer with fair results, but there were transformers designed specifically for the purpose.

Also, I forgot to mention that the reason why your speaker is quiet, even with a properly matched output transformer (about 600 ohms primary, and about .25 ohms secondary), is because a one tube radio is not strong enough to drive a speaker loudly without a stage of audio amplification.

T.D.

Thanks everyone! Your help is very useful.

The speaker that i'm using came from an old transistor radio. I could not get it to work, so I used the speaker and the variable cap.
Thanks again for the help!

The transformers help a little. Maybe I will try adding the audio output stage.

:.....yeah...I was thinking that it sounded more like a filament transformer. The secondary of a filament transformer is often close to that of an output transformer, but the primary is down around 30 ohms or so. Filament transformers can often look like output transformers. I bet that if you put that transformer primary across 120 volts AC, you'd get a standard filament voltage out the secondary (say 6.3 volts or 5 volts).
:
:Thomas
:
::Hi Jeremy
::
:: Your matching transformer seems low in primary resistance. Maybe it was made for transistor circuits? I would expect the primary to have a DC resistance around 300-500 ohms. Try to find an output transformer from an old tube radio.
::
::Norm
::
:::Thanks for the info Thomas. This is very useful.