Will new filter caps lower plate voltage?

[bluesguitar]

I recently acquired a '66 Twin Reverb. All filter caps, bypass caps, and bias cap were stock original. The plate voltage measured 455 volts. After changing all caps the plate voltage is now 440 volts. I've done a number of cap jobs on my other vintage amps, but never experienced such a before/after plate voltage difference. Anyone had a similar experience? Any of you "Grizzled Veterans" know why this is?

[Phil_S]

If Va went down, the Ia must have gone up. Did youset/check bias on your power tubes after the cap job?

Did you check all the resistors in the B+ ladder? Maybe you had one with a dry joint and when you hit it with the iron, you fixed it?

[martin manning]

I would think if anything the amount of ripple on the DC supply would go down, and you would measure a higher DC voltage after the re-cap. Are you sure your line voltage didn't change?

[bluesguitar]

If Va went down, the Ia must have gone up. Did youset/check bias on your power tubes after the cap job?

Did you check all the resistors in the B+ ladder? Maybe you had one with a dry joint and when you hit it with the iron, you fixed it?

I did nothing to the bias. Same tubes and everything. Funny thing is the bias has not changed. In fact it seemed to have gone down a mA or two, but I didn't have it on very long and it may have needed to warm up a bit more.

[bluesguitar]

I would think if anything the amount of ripple on the DC supply would go down, and you would measure a higher DC voltage after the re-cap. Are you sure your line voltage didn't change?

I don't know how to check the line voltage. But, now I have no previous reference. All seems well with the amp. Just noticed the plate voltage difference by accident when I went to adjust the bias. Unfortunately there was no more travel on the pot to increase the bias voltage, so I had to leave it as it was.

[martin manning]

By line voltage I just mean the VAC at the wall socket. It could easily vary enough from day to day or day to night in one day to cause the ~3% change in DC voltage you observed.

[bluesguitar]

By line voltage I just mean the VAC at the wall socket. It could easily vary enough from day to day or day to night in one day to cause the ~3% change in DC voltage you observed.

Good point. I did measure the amp from a completely different area of my house than originally. I'll have to try it from the same outlet as before.

[Structo]

If you have an old house there can be differences in the wall voltage but usually any change in wall voltage will be due to increased demand on the electrical utility during peak times.

Like at dinner time when everyone is using their ranges to cook will draw down the voltage a few volts.

Some areas are worse than others.

At my house however, the voltage is pretty constant between 120v-121vac.