A problem with a tube receiver

[gaetan8888]

the first half of the tube 6AQ8 is the RF amplifier. It is a wide band amplifier and it is not input tuned. The output is tuned. Attach if you can a long insulated wire to pin6. This is now your input to the tuned circuit. Any different? while you are trouble shooting check if you can the diodes D2 and D3, these are crucial to detecting the audio signal from the FM, also C60 the 5uf 25 volt cap.. Audio output comes from the junction of C52 C53 and ground

Hello

I'm back.

I've put a long insulated wire to pin6 of 6AQ8, there was no differences.

I've check the diodes D2 and D3 and C60 (the 5uf 25 volt cap). They are all ok.

Thank

Bye

Gaetan

 

[Wavebourn]

Something is definitely broken around V301.

 

[gaetan8888]

Hello

Wen I've tested this 6AQ8 (V301), it was a bit low result, under normal, but not dead, do V301 need to be in good shape or a lowing tube would work anyway in that tuner circuit ?

Thank you

Bye

Gaetan

 

[DF96]

Have you tried the local oscillator test I suggested (with the second receiver)? A low 6AQ8 might refuse to oscillate, depending on how much spare gain there is in the circuit. Any dampness in the components could make things worse.

6AQ8 tend to be worked quite hard in this type of circuit so don't last very long.

 

[gaetan8888]

Have you tried the local oscillator test I suggested (with the second receiver)? A low 6AQ8 might refuse to oscillate, depending on how much spare gain there is in the circuit. Any dampness in the components could make things worse.

6AQ8 tend to be worked quite hard in this type of circuit so don't last very long.

Hello

I don't have another receiver.

Maby my 6AQ8 are too low.

Thank

Bye

Gaetan

 

[gaetan8888]

Hello

I've found a NOS 6AQ8 to replace the old 6AQ8 and there still no radio music coming out from the fm tuner section.

So it is not a low 6AQ8 who are the problem.

Thank

Bye

Gaetan

 

[DF96]

You need to borrow another receiver, so you can check whether the local oscillator is oscillating. Any cheap portable would do. Each receiver should be able to hear the oscillator from the other receiver, probably at 10.7MHz above or below the tuned frequency.

Otherwise you need an RF sig gen. You can't diagnose RF stuff without some test gear. Another receiver for the same band is an absolute minimum.

 

[multisync]

see if you can pick up a "gid dip meter" on ebay or an inexpensive high freq freq counter. The grid dip meter is probably more sensitive than a freq counter. Long before afordable high freq osciloscopes anybody working on rf equipment, hams, cb-ers, techies etc one of the first pieces of test equipment purchased was a grid dip meter. The other bigie was a rf probe. The rf probe is essentially a germanium diode with a small capacitor to ground. It would detect, rectify the rf signal and produce a small dc level. Used with an rf sweep generator an envelope of the rf circuit was displayed on low bandwith osciloscopes of the day.

ask around on diyaudio if there are any "hams", shortwave guys/gals near where you live. They may have the stuff you are looking for and may wish to help you out.

A receiver can be any fm radio.