Regal Model 30 Tube Amp Filter Caps and More?

[Enzo]

Did you check the coupling caps for leakage? That wax covered...thing... on the left would almost certainly be leaky by now. It is a rare waxed cap that survives this long. But realaly I'd suspect the bright yellow caps as well. Look for DC on th wrong ends of all those.

[misterc57]

...... Taking your word that it's not coming from the speaker.

Touching the speaker I feel no vibration or movement. Also the vibration occurs as soon as the power is turned ON, before tubes are warmed up.

[Chuck H]

Transformer vibration is caused by magnetic forces between the laminations.
As these forces are always attractive (in each half-cycle) the result is frequency doubling.
So the fundamental frequency of vibration is 120Hz.

Thanks. Makes sense. So I'm back to what I said about it first then. Many transformers resonate.

Maybe a gasket between the transformer and the chassis.?.

EDIT: That said, I once had a heck of a time trying to find the noise in a similar amp. It turned out the chassis, which was the same type of rolled steel with no ends like this one, would resonate at certain audio frequencies and vibrate against the cabinet.

[misterc57]

Did you check the coupling caps for leakage? That wax covered...thing... on the left would almost certainly be leaky by now. It is a rare waxed cap that survives this long. But realaly I'd suspect the bright yellow caps as well. Look for DC on th wrong ends of all those.

Wax cap 10 uF 25V replaced (amazing how tiny the new cap 10 uF 50V) is compared to the old one. One of the 4 .1 uF yellow oil cap is leaking, 110 V on one side, 6 V on the other side. Other 3 have a small mV reading.

[Chuck H]

Wax cap 10 uF 25V replaced (amazing how tiny the new cap 10 uF 50V) is compared to the old one. One of the 4 .1 uF yellow oil cap is leaking, 110 V on one side, 6 V on the other side. Other 3 have a small mV reading.

A leaking coupling cap nearly always puts positive voltage on a tube grid. This can heat the bias for that tube and cause damage. If the leaky cap happened to be coupling the power tube grid the excess current may even cause the power transformer to resonate (though it seems unlikely). Anyway, those paper and oil caps are prone to leakage with age and they're not getting younger.

So, the added electrolytic caps on the two inner sockets are cathode bypass caps? That's how it looks. They don't seem to be part of the stock circuit as shown in the opening post but shouldn't hurt anything.

I did notice that you left the original cathode bias resistor on the power tube. Did you check that for drift? Well, without a schematic I guess we wouldn't know. They usually drift high, which is better than low but it's always best to at least know what that resistance is so you can measure the DC voltage at the plate and cathode (and grid in case there's a leaky cap) of that tube to calculate an approximate bias.

I had thought the 10uf cap was the power supply filter for the preamp. At a 50V rating I don't suppose it is.

[misterc57]

So, the added electrolytic caps on the two inner sockets are cathode bypass caps? That's how it looks. They don't seem to be part of the stock circuit as shown in the opening post but shouldn't hurt anything.

Yes cathode bypass caps. They were part of the original multi-cap. Blue 10 uF 25 V and yellow 10 uF 25 V.

I am looking to see what I have for .1 coupling caps. They do not need to be polarized, right?

I had thought the 10uf cap was the power supply filter for the preamp. At a 50V rating I don't suppose it is.

Original value 10 uF 25V. Connected to cathode of 6SC7, maybe another cathode bypass cap.

[Chuck H]

Non polar film caps in .1uf/100n value do not need to be polarized caps at all. As to the 10uf/25V cap,.. I think it must have been another cathode bypass cap. 10uf was probably a compromise by the manufacturer relative to parts availability and expense. The goal (I'm sure) was full bypass. You could use a plain ol 22uf electrolytic cap there if you already have one. If you want to stay schematically accurate to the design then use a 10uf. This would surely be a polarized cap because of it's high uf value. Anything rated 10V or better is fine.

[misterc57]

All caps replaced. Vibration mostly mitigated by adding weather strip to bottom of chassis to reduce vibrations against the wood cabinet. Thank you to all for the help! Always greatly appreciated.

[Chuck H]

Ah! But you STILL have the old cathode bias resistor in place. And I mentioned these are prone to drift. And still no bias information from your measurements.

Just trying to help as best we can.

[misterc57]

Ah! But you STILL have the old cathode bias resistor in place. And I mentioned these are prone to drift. And still no bias information from your measurements.

Just trying to help as best we can.

Appreciate it! Amp sounds great but I will get back with measurements. Currently have another project on my bench. Thank you!!!