Stupid question #348

[mort]

6.3v lamp on every vintage Fender circuit: is it normal for it to glow a little brighter/dimmer with the output of the amp while playing?

I think I've noticed this before but never thought of it as any sort of symptom. Someone is asking me so I thought I'd put the question out here and see if I stand to learn anything on the subject. The amp in question is a tweed era tremolux circuit that I built.

Note: the main reason he's contacting me is because last night while playing at half volume, the amp started humming, sound cut out, and then sound came back and he shut it down. Sounds like a tube trying to short out to me. Advised him to try his spare recto/power set and get back to me.

[Tom Phillips]

6.3v lamp on every vintage Fender circuit: is it normal for it to glow a little brighter/dimmer with the output of the amp while playing? ...

That is not normal.

[ThermionicScott]

...The amp in question is a tweed era tremolux circuit that I built...

I've had poor luck with new-production light holders. They frequently lose contact with the bulb and go dark, or dim erratically as they make partial contact due to amp vibrations. Bending the contacts sometimes helps, but doesn't always.

Note: the main reason he's contacting me is because last night while playing at half volume, the amp started humming, sound cut out, and then sound came back and he shut it down. Sounds like a tube trying to short out to me. Advised him to try his spare recto/power set and get back to me.

You might check the rest of your heater wiring while you're at it. If one of the output tubes has intermittent heater power, it will cause the amp to go hummy and weak at times. Another possibility is poor contact at the socket pins -- cleaning and tightening could help.

[elipsey]

6.3v lamp on every vintage Fender circuit: is it normal for it to glow a little brighter/dimmer with the output of the amp while playing?

I think I've noticed this before but never thought of it as any sort of symptom. Someone is asking me so I thought I'd put the question out here and see if I stand to learn anything on the subject. The amp in question is a tweed era tremolux circuit that I built.

Note: the main reason he's contacting me is because last night while playing at half volume, the amp started humming, sound cut out, and then sound came back and he shut it down. Sounds like a tube trying to short out to me. Advised him to try his spare recto/power set and get back to me.

These have always done alright by me:
https://tubedepot.com/products/numbe...and-amplifiers

Edit: Backing off of my origninal post a little. I think it might be smart to check out the fillament supply just to be on the safe side, but I defer to the experise of others here.

[mort]

I don't suspect a problem with the bulb base. The dimming is not sporadic or random.


Thanks for the confirmation that the dimming with output is not normal. The amp is in WV while I'm in FL, but if we can't come to a solution via messages and such then I'll have him ship me the tubes and chassis. I suppose if a power tube is shorting to the filament, then that could cause the bulb to dance to the music. I wouldn't expect it to come back to life after making a loud hum and cutting out sound. If it were a tube short to the filament I would expect it to stay shorted. Any thoughts on that?

[Leo_Gnardo]

while playing at half volume, the amp started humming, sound cut out, and then sound came back and he shut it down. Sounds like a tube trying to short out to me. Advised him to try his spare recto/power set and get back to me.

This amp has a bigger problem than just bulb going dim. May be an short somewhere, or something else going on. The lamp going dim is a symptom of a large current draw, or its connections are corroded - probably the lamp base itself - bulb base loses good contact when shaken around with those loud notes.

Yes lets see what happens with fresh rectifier & power tubes. If that doesn't fix it, gotta go inside. Have your friend keep a hand near the standby/off switch, slap it off fast if it shows any further funkiness.

[Pedro Vecino]

Bad contacts in bulb holders are very common for a long time. They accented with vibrations.
I use this system. Sometimes in both contacts.