68 Deluxe Reverb seems to drop in volume

[nwguy]

After playing my sfdr, the volume seems to drop in volume. I say seems because I am questioning my ears at this point. Is there any way to test this

[Alex R]

If you feed a steady tone in you can measure the AC voltage the amp develops across the speaker terminals. Do it before and after playing, then you'll get an objective measure of what the amp's doing. What your ears are doing is a whole nother matter!

[Alex R]

And actually, if you don't have a tone generator if you just make a whole lot of guitar noise through it with the AC voltmeter connected you will see a maximum figure.

[ThermionicScott]

My ears tend to drop in volume after loud playing.

Have the electrolytic caps ever been replaced? That amp is nearly 40 years old at this point.

- Scott

[dchang0]

That's the way human hearing works. Our ears become acclimated to louder volumes as we are exposed to them. That's one big reason the soundmen start the opening band quietly and keep raising the volume as the show goes on.

It also explains how we can have a conversation while at a loud venue. Our minds dial down the music's volume.

Still, you should make the measurements. One signal generator that most guitarists have on hand is the A440 on their tuners. It's annoying to leave it on at high volume, but it's a steady input.

[Amp Kat]

Fletcher Munson curves messing with you maybe. You can get a dB SPL meter for pretty cheap at Radio Shack. Set it up and watch the level as you play and it won't lie.

[km6xz]

Does the tone change or noise increase. Does the sound get more distorted?
What change ratio are you noticing? Is it half a loud, 2/3rds etc?

Our hearing is based on perceived difference, not absolute levels...all our senses work like that. Our ears/brain change in sensitivity for our awareness of loudness when in a loud environment. A major full tilt system in a concert is usually run at a very high average level so very quickly our brains become less sensitive to level and only differences in level, the dynamics. If you are playing loudly, there is a good chance that what you are noticing is our internal AGC(Automatic Gain Control) that shifts our perceived average sound level. Does the sound level return if you leave the room for 10 minutes and return?

[nwguy]

Yes the amp has been re-capped
All power supply and cathode bypass