New Project, Finger's Crossed

[J Luth]

Thanks eschertron.

10 watt seams kind of large but I'm still a rookie.

I should have looked closer at the schematic to see the 10W 200W. DOH! The old brain saw it a 10 ohm.

[eschertron]

Thanks eschertron.

10 watt seams kind of large but I'm still a rookie.

I should have looked closer at the schematic to see the 10W 200W. DOH! The old brain saw it a 10 ohm.

Golden age engineering. Circuit analysis would probably reveal that 5W is plenty for a normally-operating stage. We'd need the expected (or actual) voltages to know.

edit: why do those two wire-wound resistors need to be replaced? Of all the components, they'd be least likely to suffer from age.

[J Luth]

The voltage at the 5k resistor is 500v with only the rectifier installed, it drops to 300 with all tubes installed and warmed up.

I will recheck the resistors again now that I know what the correct value.

[J Luth]

What to do on a heavy snow day.
Got the MASCO somewhat working, new resistors and capacitors. Fired it up and it hums a bit so I start looking for things, found a few bad solder joints and fixed them. Hum is there but not too bad. Moved the output transformer to a different location which helped. This is not a question about the hum, which may come later, it’s about what I am experiencing.

Here’s what is weird, well at least weird to me.
All tubes removed and the output transformer disconnected from the tube sockets and the resistor but the 4ohm speaker tap or any or all of the speaker taps connected and common connected it still has hum through the speaker. The farther I move the output transformer away from the chassis and the power transformer the less it hums just about down to none. If the output transformer is completely disconnected no hum which stands to reason, it only does it with the taps connected. It also does the same with all the tubes installed.

[Enzo]

Try turning the OT 90 degrees. Look at atypical old Fender. The power transformer sits in a chassis hole so the laminations are flat - parallel to the chassis surface. The Output Transformer is mounted standing up, so the laminations are standing perpendicular to the chassis. The two transformer lamination stacks are perpendicular. If your OT makes hum out the speaker even when the power tubes are disconnected, that is a common reason.

[J Luth]

Enzo,

Yup, I tried that also. The transformers are the same as Fender amp. Power transformer laminations lay flat, output transformer vertical. The output transformer was right beside the power transformer with the laminations facing each other so I figured it would be better to move it and turn it. What I did was to move the output as far away from the power transformer as possible and turned it 90 so the the bell was facing the power transformer not the laminations. It was better like that. The thing is I get the hum through the speaker with any or all of the output taps connected but the primary leads are disconnected and no tubes. That seems strange to me, how can I get output if the primary leads are disconnected?

[The Dude]

......how can I get output if the primary is disconnected?

It's being radiated into the OT from another source. Most likely the PT. It's the same principal as how the transformer itself works. Primary and secondary do not connect directly to each other, yet signal still gets from one to the other.

[Enzo]

Oh one tiny remote possibility. I am really stretching to make this. If your PI tube is installed, there is some current flowing through the tail, and is COULD somehow send a tiny current through the feedback line to the OT secondary. I sure wouldn;t bet my dessert money on it though.

[J Luth]

Well that appears to be the case since everything is disconnected. Anyway to stop it or cut it down? Although it's not that bad.The amp actually sound pretty good connected to 2 10" speakers and playing a guitar through it.

[J Luth]

No tubes installed.
With the tubes installed it is no louder but it does vary a little with the volume and tone pots and gets noticeably louder with the volume turned way up, but I would expect that.

[Enzo]

The hum you hear with no tubes is probably not same hum as the hum that turns up with the controls. Hum is not generic, it has multiple sources, and each source needs its own solution.

[J Luth]

Pretty much all better now. Moved the output transformer and turned it 90 degrees to the power transformer. Moved a few wires around, re-soldered a few connections and it's fairly quite.

[J Luth]

The Masco is almost done.
All re-capped, replaced all the resistors, new input jacks, moved and rotated the output transformer, nice and quite and sounds good with a guitar. The turntable now works, new mounting grommets, new power wires, a bit of oil on the motor bearings and a piece of shrink tubing on the spindle that drives the wheel. The plater turned real slow and would barely turn with a record on it and the tone arm on the record. The shrink tubing cured that. The crystal cartridge was all dried out, I cut up a piezo element and stuck it in there and it works even sounds like it is turning at the correct speed. A bit low volume but it works, the owner can send the cartridge out and have it rebuilt if he wants. New tubes might be a good thing he can also re-tube if he wants. A couple of brackets and it should be done. I have to raise the turntable part about 3/4" higher do to the new output transformer location, the turntable motor hits it.

[olddawg]

That heat shrink trick on the spindle won't work very long. There used to be a product kind of like nail polish with fine sand in it that was used to paint spindles. Also "Rubber Restore" for the idler surface. If the rubber is hard as a rock I think there are still places that will rebuild the idler.

[Enzo]

SOunds like you need a new idler wheel or a new idler tire.