Newbie's First Questions RCA TS 721 Restoration

[Chris K]

Originally Posted by Yamamaya42

you will have to work out why you are losing the +225V at the point of the bleeders to the point of the 1k resistor r185, where you saw the negative voltage. SOMETHING in the red wiring from the two points is messed up.

You are correct and I got it! All the voltages are now correct on the pins of all 3 tubes and the speaker makes a whisper of a crackle when I touch the pins of the audio output tube with the meter probe! Can't believe it nor can I tell you exactly what it was. I just went through the schematic and ran down the voltage of every wire and made some changes as to how I had wired the electrolytic caps. Amazing and at the 11th hour. Thank you so much for your help and advice. Now I can go on vacation with a smile on my face

[Notimetolooz]

You did replace R153A & B, one connected to the 225V and the other connected to -85V. One of the wires from those points could have gotten to the wrong one.
When you get back you might have to replace C160 since it could of had a reverse voltage on it.
The reverse leakage that it caused probably loaded down the -85V to -67.5V.

[Chris K]

Originally Posted by Notimetolooz

You did replace R153A & B, one connected to the 225V and the other connected to -85V. One of the wires from those points could have gotten to the wrong one.
When you get back you might have to replace C160 since it could of had a reverse voltage on it.
The reverse leakage that it caused probably loaded down the -85V to -67.5V.

Up in Cape Cod...7 hour drive from Philly! Yeah I'm also questioning my choice of 700ohms for the 225V side of things on R153. There was a discrepancy between Riders and Sams. I'm thinking I should go with 20W on both sides and 1100 and 610 ohms like it is in Riders (Sams showed 10W for both and 700 and 510 ohms respectively). I blew 2 10W 700s on that same side and I attributed it to heat. The one in there now, flush mounted to the resistor housing with thermal paste, is 15W 700 ohm and it seems to be holding up ok but I think I'll order resistors by the specs in the Riders to install when I get home.

[Chris K]

If an original resistor is wirewound does it matter if it's replacement is not wire wound? I found some film, flush mount resistors rated at 20 watts and the same resistance but they are not wirewound.

[bandersen]

No, it doesn't matter. I'm surprised there are 20 watt film resistors.
They also make adjustable wirewound power resistors that will fit on the original mounting.

[Yamamaya42]

they make the, 20w and larger, like
TAH20P150RJE

[Kevin Kuehn]

For this particular application I'd suggest staying with the larger surface area of conventional wirwound resistors.

The black metal housing they mount in is a convection chimney which is intended to pull in cooler air from below and flow upward across the large surface of the original ceramic wirewounds and out the top. Smaller package resistors will run significantly hotter unless they are mounted on a large heat sink. Heat dissipation is all about surface area and air flow.

[Chris K]

Originally Posted by bandersen

No, it doesn't matter. I'm surprised there are 20 watt film resistors.
They also make adjustable wirewound power resistors that will fit on the original mounting.

Got them through Mouser...they look like transistors

[Chris K]

Originally Posted by bandersen

No, it doesn't matter. I'm surprised there are 20 watt film resistors.
They also make adjustable wirewound power resistors that will fit on the original mounting.

Where did you get those Bob? I googled for wirewound ceramic resistors and came up empty.

[bandersen]

Mouser. They're made by Ohmite - same old company that's been making them for decades. Not cheap, but the quality is good.

https://www.mouser.com/c/passive-com...ite&series=210

Another options to retain the look and original mounting while keeping the price down is put a couple in parallel.

For example to get 610 ohms, use a 25W Ohmite 750. Note the sample image is deceiving. They are nowhere near that long.
https://www.mouser.com/ProductDetail...Qtnr75uQ%3D%3D
with a smaller 5W 3.3K in parallel. You could hide it behind for appearance.

[Chris K]

Originally Posted by bandersen

Mouser. They're made by Ohmite - same old company that's been making them for decades. Not cheap, but the quality is good.

https://www.mouser.com/c/passive-com...ite&series=210

Another options to retain the look and original mounting while keeping the price down is put a couple in parallel.

For example to get 610 ohms, use a 25W Ohmite 750. Note the sample image is deceiving. They are nowhere near that long.
https://www.mouser.com/ProductDetail...Qtnr75uQ%3D%3D
with a smaller 5W 3.3K in parallel. You could hide it behind for appearance.

Thank you so much. I have several packages for several options on the way. I ordered 2 of the 25 watt Ohmite resistors, a 750 and 1K ohm. They are not adjustable but probably close enough to the original values. I also have a Vishay 20 watt 1100 ohm wire wound coming to replace the 700 ohm I currently have on the 225v side. I'll have a choice between aesthetic appearance or the ease of just changing one resistor. One of the factors will be the size of the Ohmite resistors.

[Notimetolooz]

Keep in mind that the reason that a resistor burns up could very well because there is a problem elsewhere. You should check the voltage across those resistors as soon as possible. As was said from the resistance value and the voltage across the resistor can be used to calculate the actual power dissipated.

By the way, wirewound resistor do not fail (or drift) very often unless they are dissipate too much power.

Those resistors are more properly called "dropping resistors" because the current through them drops the voltage. The term "bleeder resistors" is used more often across a capacitor to gradually discharge it.

[Yamamaya42]

I have seen more power resistors (wire wound) fail due to age and degeneration than anything else, mostly due to corroded leads / terminals that works its way into the part and disrupts the connection internally.
I.E, Creeping green death! :O

[Chris K]

Originally Posted by Notimetolooz

Keep in mind that the reason that a resistor burns up could very well because there is a problem elsewhere. You should check the voltage across those resistors as soon as possible. As was said from the resistance value and the voltage across the resistor can be used to calculate the actual power dissipated.

By the way, wirewound resistor do not fail (or drift) very often unless they are dissipate too much power.

Those resistors are more properly called "dropping resistors" because the current through them drops the voltage. The term "bleeder resistors" is used more often across a capacitor to gradually discharge it.

Yes that did occur to me since that was the only one of the 2 original dropping resistors open and the only side where I kept blowing new wire wound resistors. I will check the input before I put in the new ones.

[Chris K]

Originally Posted by Yamamaya42

I have seen more power resistors (wire wound) fail due to age and degeneration than anything else, mostly due to corroded leads / terminals that works its way into the part and disrupts the connection internally.
I.E, Creeping green death! :O

Doing lots, maybe too much, studying on vacation!