Bad Cat Black Cat 30R Low B+

[bobloblaws]

1. How much is the AC Main voltage.

121VAC

2. On how much voltage is set up voltage selector on main transformer.

I don't know that it has a selector

3. Is the main (first) elco 33 + 33u/ 450V new or "like new"

Definitely not new, but I tried a new one in it's place as an experiment and it did not change the B+

[vintagekiki]

I don't know that it has a selector

How many connections does the MT have on the primary. Two or more.

1)

[Helmholtz]

Mains input should be ok, as heater voltage is fine.

What AC voltages do measure at rectifier tube pins 4 and 6 wrt ground?

[bobloblaws]

What AC voltages do measure at rectifier tube pins 4 and 6 wrt ground?

285VAC on each side wrt ground, 570VAC across the pins, pre-diode of course. Most of the troubleshooting I had done with the protection diodes removed, I've since re-installed brand new ones as one of the existing ones was bad. In any case, B+ has been the same in both cases.

[vintagekiki]

285VAC on each side wrt ground, 570VAC across the pins, pre-diode of course. Most of the troubleshooting I had done with the protection diodes removed, I've since re-installed brand new ones as one of the existing ones was bad. In any case, B+ has been the same in both cases.

How much does 285VAC on each side change with and without 4 x EL84 output tubes?

[bobloblaws]

How much does 285VAC on each side change with and without 4 x EL84 output tubes?

296VAC each side.

[vintagekiki]

296VAC each side.

Is 296VAC each side with or without 4 x EL84 output tubes?
If the voltage of 296VAC decreases with the load (with 4 x EL84 output tubes) it can be a sign that the secondary is wound with a thinner wire, so during the load the AC voltage drops, and thus the DC voltage drops.

Question
Does the MT heat up noticeably during operation?

[bobloblaws]

Question
Does the MT heat up noticeably during operation?

The whole amp heats up real hot, this model is known for that.

[vintagekiki]

B+ is still around 330V whereas I'm expecting 350-360V as previously discussed.

Almost every Fender tube schematics describes the technical protocol on the basis of which the measurements were performed.
The voltage you measured is within the predicted limits (+/- 20%).

Example
https://elektrotanya.com/fender_concert_super_type_pr244_sm.pdf/download.html

[vintagekiki]

Rectifier tubes of same type can vary in voltage drop.

https://music-electronics-forum.com/forum/amplification/guitar-amps/theory-design/47034-rectifier-tube-voltage-drop

https://ampgarage.com/forum/viewtopic.php?f=6&t=9275

https://www.diyaudio.com/forums/power-supplies/89970-rectifier-voltage-drop.html

https://300guitars.com/articles/rectifier-tube-voltage-drop-chart/

https://el34world.com/Forum/index.php?action=dlattach;topic=20320.0;attach=58492

https://www.diyaudio.com/forums/tubelab/283863-handy-table-common-rectifier-specifications.html

https://www.audioasylum.com/cgi/vt.mpl?f=tubediy&m=253355