tone control
 

My last project ( that went well) was a RCA 45x table top radio. The tone is a little high for my taste, but there is not a tone control. Is there any place I can add a small cap to adjust the tone?

Not sure which 45X you have, NostalgiaAir lists a number of them with suffixes. The first one is a small table model with 4" speaker.

The simplest kind of tone control is a "losser" type which just cuts high frequencies, thus making lower frequencies sound louder. It doesn't actually boost the bass. A 4" speaker can't handle bass anyway. However, you can try this: tack a small cap (like .001mfd.) from the grid of the first audio tube to chassis ground and try it. Experiment with larger and larger caps until you find the one you like. Bear in mind that if too large it will cut too much treble and you could get into a situation where you have to turn up the volume to hear the set and the speaker could be overtaxed.

Reece

You could also put a pot in series with the cap to ground thus giving you an adjustable tone control. Value for the pot around .25 to 1 meg not critical. When you find the sound you like measure the pot and put in a fixed resistor.
Terry

I can't find mine exactly. Mine is almost the same as the 45x1. The only diiference is a 68mmf cap going to the osc. coil mine does not have. My tube placement is different also. Other than that electrically they are the same.

If you change the value of C7 that will change the hi frequency response. The more capacity the more it will cut your hi frequencies.
Terry

Forgot another point: since most table radios were made pinching pennies, they didn't put in large audio coupling capacitors since the speakers couldn't produce much low frequency response anyway. But you can try replacing C14 and C16 with larger caps. The larger the caps, the more lower frequencies the audio section can produce, with highs remaining the same. I'd try .047 mfd. and see how it works. If that's too much bass for the speaker to handle without distorting, try smaller. This plus the tone cap previously discussed should help.

Reece

As Reece pointed out in the inexpensive sets the speaker is usually small thus limiting the bass response. There is another reason for this is as it will require better power supply filtering so that the 60cy hum is not heard. The small speaker allows manufacturers to use less filtering because the speaker isn't very effective at 60cy hence not much hum is heard.Bigger coupling caps aren't going to make much of a difference with a small speaker. With a bigger speaker and bigger coupling caps it will improve the bass response but may need to increase filtering to reduce hum. The older AC DC sets with electrodynamic speakers use their field coil as a choke in the power supply. This helps filter out the hum.
Terry