SVT with 3.6 ohm plate resistors

[Randall]

Got a vintage SVT in today. Guy says it is the first year they made them, and has been converted to 6550's. I don't know what that means exactly in this case.

It has a whitened 6550, with it's 3.6 ohm 5W plate resistor burnt to a crisp. One of the other resistors has been replaced with a 5 ohm 5W, and the other four are original 3.6 ohm. AFAIK 3.6 ohm 5W is no longer available, and Fliptops sells a 5.1 ohm 6-pack for vintage SVTs. Would this be the way to go? And shouldn't it have been done when the 6550s were put in? That's what I see on one of the 6550 equipped schematics.

[Leo_Gnardo]

It has a whitened 6550, with it's 3.6 ohm 5W plate resistor burnt to a crisp. One of the other resistors has been replaced with a 5 ohm 5W, and the other four are original 3.6 ohm. AFAIK 3.6 ohm 5W is no longer available, and Fliptops sells a 5.1 ohm 6-pack for vintage SVTs. Would this be the way to go? And shouldn't it have been done when the 6550s were put in? That's what I see on one of the 6550 equipped schematics.

The white 6550 has either decided to be a milk bottle or much more likely is now an air tube as opposed to a vacuum tube, so can it and get a working one. I've seen 3.6, 4, 5, and 10 ohm resistors in the plate function. Value isn't really all that important and I expect would be hard to tell the diff even if you had a Heinz 57 variety of R's there. They are supposed to act as fuses if an output tube shorts. Not much of a sonic signature, except an open-circuit one will play you the sound of silence.

FWIW I get mine from Mouser. If you need to get a bunch of other items, tools, shop supplies, that may be a place to go shopping.

[gingertube]

.. They are supposed to act as fuses if an output tube shorts...

I thought they were supposed act as anode stoppers to supress parasitic oscillation ???

Cheers,
Ian

[Leo_Gnardo]

.. They are supposed to act as fuses if an output tube shorts...

I thought they were supposed act as anode stoppers to supress parasitic oscillation ???

Cheers,
Ian

Waylll, I s'pose you could wrop a swatch of wire 'round each of em, hey if they're Wire Wound doesn't that also act as a micro choke..... And have seen a tiny inductor in McIntosh tube amps. Trick question Ginger! My best "educated" guess is - they're dual purpose.

Have seen some old SVT with carbon comp in that position. To enhance the smoke factor when the output tube shorts.

I stop parisitics best with Ivermectin.

For those who may care, Randall has his question and more answers at Music Electronics Forum too.