Five valve T.R.F too much treble .

[vinrads]

I have just finished constructing a power supply for this set , 120v HT 2 volt and 2x grid bias volts ,the set works fine but there is excessive treble , I am using a suitable output tx with the pm2a output valve, tried different transformers , adding a c across the primary helps ,but I think this is just masking the problem ,Any help appreciated.Mick.

[toshiba tony]

Too much treble on MW. I would kill for that. Perhaps it is suffering from lack of bass.

[Herald1360]

Does it have transformer coupling in the audio stages? They're unlikely to let much LF audio through. Unless you want to start modifying the set to tailor the sound to suit your taste I would think you're stuck with it.

Find a "woolly" old loudspeaker perhaps?

[Hartley118]

Originally Posted by Herald1360

Does it have transformer coupling in the audio stages? They're unlikely to let much LF audio through. Unless you want to start modifying the set to tailor the sound to suit your taste I would think you're stuck with it.

Find a "woolly" old loudspeaker perhaps?

No reason for transformer coupling to be poor at LF unless it’s a cheap low inductance job. It’s after all only one more transformer in an audio chain featuring many transformers. However, many of today’s MW transmissions do have an audio lift around their top end, I think to try to compensate for the narrow IF bandwidth of most receivers. A wide band receiver such as your TRF may well therefore sound a bit ‘toppy’, as does my AR88 when switched to its widest bandwidth.

Adjust your HF roll off to your taste.

Martin

[vinrads]

Hi you really need to hear this on a hi fi speaker the treble it's piecing ,a quick update I found that a 100k resistor across the sec of the inter stage tx improves the sound to an acceptable level on a 8x5 bog standard spk, The PM2A I am using is a 5 pin for a bit more gain . I must say the set is very well behaved for a trf .Mick.

[Hartley118]

I guess that you're hearing the self- resonance of the coupling transformer - those vintage jobs did use a lot of wire to achieve enough primary inductance, leading to a high leakage inductance which would resonate with stray winding capacitance. Your load resistor is the appropriate fix to damp the resonance.

You may be a pioneer, being the first to feed the output of the circuit into a hi-fi speaker! Any speaker of the period probably benefited from the HF resonance correcting its natural treble rolloff.

Martin

[Edward Huggins]

That looks like a half-decent elliptical speaker. And it has a doped centre cone to emphasise HF response!

[AC/HL]

... and no baffle, which won't help the bass either.

[Heatercathodeshort]

And 50 years between the radio and the speaker. J.

[vinrads]

Originally Posted by AC/HL

... and no baffle, which won't help the bass either.

The bass is not a problem , the cabinet is a pretty good resonator ,I have a few 30's speakers that will go nicely with the radio, Mick.

[stevehertz]

Originally Posted by vinrads

Hi you really need to hear this on a hi fi speaker the treble it's piecing

A 1920s radio would never have been connected to a hifi speaker, such a test serves no real purpose. And it would have been connected to a speaker with a much reduced treble response than your modern eliptical speaker, and probably had a better bass response too. That's your problem, it'd probably sound fine and authentic through a 1920s speaker, and that's what you should be trying it with. I appreciate that you probably don't have one, but I'm sure that's the problem nonetheless.

[vinrads]

O.K I do have several vintage speakers, but they were in the loft ,that's why I was using the 5x8 spk Update! it's now running on a 1930's spk and it still needs the damping resistor .cheers Mick.