Radiola 18 Speaker Matching transformer

4/30/2007 2:58:55 AMDave Froehlich

Hello All,
Which speaker transformer will work with an RCA Radiola 18 so that an 8 ohm speaker can be used with it?
Most of the time the Model 100 speaker is used with a Radiola 18 but I have seen and heard speakers from that time that had electro-magnets and a speaker transformer. The Model 106 speaker, for example. There's a speaker like that with the Radiola 62. I have worked on one of those and it sounds amazing with a 71A output tube. But there's no information about the speaker transformer.
I think it would be one with a 2000 ohm primary.

Thanks,

Dave

4/30/2007 10:07:07 AMRadiodoc

Dave,

An output transformer with a primary AC impedance of around 3000 Ohms should work ok.

Radiodoc

:Hello All,
: Which speaker transformer will work with an RCA Radiola 18 so that an 8 ohm speaker can be used with it?
: Most of the time the Model 100 speaker is used with a Radiola 18 but I have seen and heard speakers from that time that had electro-magnets and a speaker transformer. The Model 106 speaker, for example. There's a speaker like that with the Radiola 62. I have worked on one of those and it sounds amazing with a 71A output tube. But there's no information about the speaker transformer.
: I think it would be one with a 2000 ohm primary.
:
:Thanks,
:
:Dave

4/30/2007 11:51:12 AMDoug Criner

Dave, are you intending to use an electrodynamic speaker (which has a separate field coil)? That would be a horse of a different color.

But, if you intending to use an 8-ohm permanent-magnet speaker, then the speaker matching xfmr will do the job.
Doug

:Dave,
:
:An output transformer with a primary AC impedance of around 3000 Ohms should work ok.
:
:Radiodoc
:
::Hello All,
:: Which speaker transformer will work with an RCA Radiola 18 so that an 8 ohm speaker can be used with it?
:: Most of the time the Model 100 speaker is used with a Radiola 18 but I have seen and heard speakers from that time that had electro-magnets and a speaker transformer. The Model 106 speaker, for example. There's a speaker like that with the Radiola 62. I have worked on one of those and it sounds amazing with a 71A output tube. But there's no information about the speaker transformer.
:: I think it would be one with a 2000 ohm primary.
::
::Thanks,
::
::Dave

4/30/2007 12:51:59 PMThomas Dermody

With a speaker matching transformer that has both primary and secondary taps, you can pick the primary tap that gives ideal voltages as well as ideal sound quality. I think that it is the best option. Lower primary impedances increase power output, but can decrease bass. As long as you keep the plate voltage appropriate with no signal, you can choose all sorts of options.

Thomas

5/1/2007 3:50:58 PMDave Froehlich

Thomas,
The universal transformer is kind of expensive. I was trying to avoid that one if I could. But if I can't, that's the one I'll use.

Thanks,

Dave
:With a speaker matching transformer that has both primary and secondary taps, you can pick the primary tap that gives ideal voltages as well as ideal sound quality. I think that it is the best option. Lower primary impedances increase power output, but can decrease bass. As long as you keep the plate voltage appropriate with no signal, you can choose all sorts of options.
:
:Thomas

5/1/2007 3:49:35 PMDave Froehlich

Doug,
No, I was just trying to remember which Hammond speaker transformer to use. The 71A doesn't produce a lot of power but it can sound very good just the same. A small inexpensive transformer like one in an AA5 radio would be fine but, unfortunately it has the wrong primary impedance. Other speaker transformers that will work, are very expenisve. But maybe I can find a suitable inexpensive speaker transformer.

Thanks,

Dave
:Dave, are you intending to use an electrodynamic speaker (which has a separate field coil)? That would be a horse of a different color.
:
:But, if you intending to use an 8-ohm permanent-magnet speaker, then the speaker matching xfmr will do the job.
:Doug
:
::Dave,
::
::An output transformer with a primary AC impedance of around 3000 Ohms should work ok.
::
::Radiodoc
::
:::Hello All,
::: Which speaker transformer will work with an RCA Radiola 18 so that an 8 ohm speaker can be used with it?
::: Most of the time the Model 100 speaker is used with a Radiola 18 but I have seen and heard speakers from that time that had electro-magnets and a speaker transformer. The Model 106 speaker, for example. There's a speaker like that with the Radiola 62. I have worked on one of those and it sounds amazing with a 71A output tube. But there's no information about the speaker transformer.
::: I think it would be one with a 2000 ohm primary.
:::
:::Thanks,
:::
:::Dave

5/1/2007 3:52:01 PMDave Froehlich

Radiodoc,
I thought it was 2000 ohms. OK 3000 then.

Thanks,

Dave
:Dave,
:
:An output transformer with a primary AC impedance of around 3000 Ohms should work ok.
:
:Radiodoc
:
::Hello All,
:: Which speaker transformer will work with an RCA Radiola 18 so that an 8 ohm speaker can be used with it?
:: Most of the time the Model 100 speaker is used with a Radiola 18 but I have seen and heard speakers from that time that had electro-magnets and a speaker transformer. The Model 106 speaker, for example. There's a speaker like that with the Radiola 62. I have worked on one of those and it sounds amazing with a 71A output tube. But there's no information about the speaker transformer.
:: I think it would be one with a 2000 ohm primary.
::
::Thanks,
::
::Dave

5/1/2007 4:05:58 PMDoug Criner

Dave, here are a couple of points for you to chew on.

The impedance seen by the ouput tube isn't all that critical. I doubt that most people would be able to tell much difference within a tolerance of -50% and +100% of rated values.

The xfmr itself doesn't present a specific impedance to the output tube. The xfmr just reflects the impedance of the load connected to the secondary (say an 8-ohm speaker) to the primary side, by the factor of the turns-ratio squared.

If you have a surplus output xfmr, AA5-type or whatever, go ahead and try it.

:Radiodoc,
: I thought it was 2000 ohms. OK 3000 then.
:
:Thanks,
:
:Dave
::Dave,
::
::An output transformer with a primary AC impedance of around 3000 Ohms should work ok.
::
::Radiodoc
::
:::Hello All,
::: Which speaker transformer will work with an RCA Radiola 18 so that an 8 ohm speaker can be used with it?
::: Most of the time the Model 100 speaker is used with a Radiola 18 but I have seen and heard speakers from that time that had electro-magnets and a speaker transformer. The Model 106 speaker, for example. There's a speaker like that with the Radiola 62. I have worked on one of those and it sounds amazing with a 71A output tube. But there's no information about the speaker transformer.
::: I think it would be one with a 2000 ohm primary.
:::
:::Thanks,
:::
:::Dave

5/1/2007 4:24:23 PMDave Froehlich

Radiodoc,
Thanks, I'll try one.

Dave
:Dave, here are a couple of points for you to chew on.
:
:The impedance seen by the ouput tube isn't all that critical. I doubt that most people would be able to tell much difference within a tolerance of -50% and +100% of rated values.
:
:The xfmr itself doesn't present a specific impedance to the output tube. The xfmr just reflects the impedance of the load connected to the secondary (say an 8-ohm speaker) to the primary side, by the factor of the turns-ratio squared.
:
:If you have a surplus output xfmr, AA5-type or whatever, go ahead and try it.
:
::Radiodoc,
:: I thought it was 2000 ohms. OK 3000 then.
::
::Thanks,
::
::Dave
:::Dave,
:::
:::An output transformer with a primary AC impedance of around 3000 Ohms should work ok.
:::
:::Radiodoc
:::
::::Hello All,
:::: Which speaker transformer will work with an RCA Radiola 18 so that an 8 ohm speaker can be used with it?
:::: Most of the time the Model 100 speaker is used with a Radiola 18 but I have seen and heard speakers from that time that had electro-magnets and a speaker transformer. The Model 106 speaker, for example. There's a speaker like that with the Radiola 62. I have worked on one of those and it sounds amazing with a 71A output tube. But there's no information about the speaker transformer.
:::: I think it would be one with a 2000 ohm primary.
::::
::::Thanks,
::::
::::Dave

5/1/2007 5:04:36 PMDoug Criner

Dave, by the way, I noticed that RadioDaze sells an all-purpose, 5-W AA5 audio xfmr for $10.95:
http://www.radiodaze.com/RD-transformer01.htm

It has a center-tapped secondary, so you can hook up an 8-ohm speaker two different ways, giving either 2K or 4K ohms on the primary.
Doug

:Radiodoc,
: Thanks, I'll try one.
:
:Dave
::Dave, here are a couple of points for you to chew on.
::
::The impedance seen by the ouput tube isn't all that critical. I doubt that most people would be able to tell much difference within a tolerance of -50% and +100% of rated values.
::
::The xfmr itself doesn't present a specific impedance to the output tube. The xfmr just reflects the impedance of the load connected to the secondary (say an 8-ohm speaker) to the primary side, by the factor of the turns-ratio squared.
::
::If you have a surplus output xfmr, AA5-type or whatever, go ahead and try it.
::
:::Radiodoc,
::: I thought it was 2000 ohms. OK 3000 then.
:::
:::Thanks,
:::
:::Dave
::::Dave,
::::
::::An output transformer with a primary AC impedance of around 3000 Ohms should work ok.
::::
::::Radiodoc
::::
:::::Hello All,
::::: Which speaker transformer will work with an RCA Radiola 18 so that an 8 ohm speaker can be used with it?
::::: Most of the time the Model 100 speaker is used with a Radiola 18 but I have seen and heard speakers from that time that had electro-magnets and a speaker transformer. The Model 106 speaker, for example. There's a speaker like that with the Radiola 62. I have worked on one of those and it sounds amazing with a 71A output tube. But there's no information about the speaker transformer.
::::: I think it would be one with a 2000 ohm primary.
:::::
:::::Thanks,
:::::
:::::Dave

5/1/2007 4:59:54 PMRadiodoc

Dave,

You may want to check out:

http://radioremembered.org/outimp.htm

One can apply a variable AC voltage to the primary of an audio output transformer of unknown primary impedance and ultimately figure the primary impedance.

Radiodoc