New power tranny: rectifier and power lamp blow (Silvertone 1482)

[melvin]

... to ground, yes. I think that should work fine.

When I suggested using the two heater windings each for a different part of the circuit, I was trying to think like someone winding a transformer. Most amps with a rectifier tube have two heater windings. This is because most of them use a rectifier with a 5 volt heater; 5u4, etc. I would think that one winding's purpose was to supply the rectifier. Out of habit, it may have been given it's own winding. Which one? I dunno. But it seems possible that one may have a higher current handling capacity than the other...choose wisely.

By the way, I made the suggestion right after you had installed a ss rec, so I didn't expect you to go for it anyway.

[Robert M. Martinelli]

I need one more clarification here...
I suppose that each separate heater winding, being without a central tap, will need to be referenced to ground, right?
While one winding is already ground-referenced via the two 100 ohm resistors at the pilot lamp, where should I put the other 100 ohm couple for the other winding?
EDIT: if I supply the 6AU6 and the power tubes (which are ground-referenced at the pilot lamp legs) with one heater winding, and the two preamp tubes with the other winding, may I simply attach the two new 100 ohm resistors to pins 4-5 and 9 respectively of one of the preamp tubes?

Carlo,
the wires are very short and their resistance is very low if compared to the two 100 Ohm resistors, so it shouldn't make much of a difference where you put them. Twisting the heaters' supply wires, at least on the preamp tubes, is much more important IMHO ( as I already told you, P-P stages are hum-canceling, so they're less sensitive to hum, anyway, twisting those heaters' wires too won't do any harm ).

Cheers

Bob

[slidincharlie (Carlo P)]

Thank you guys.

Bob, I will twist and rearrange all heater wires using some new green-coated heater wire that I have (and put the second 100ohm couple too, for good). Most wires in this amp are old whitish-yellowish stuff that isn't easy to track when you need to.

Melvin, this tranny was rewound copying the original (burned) one, and it has got its own separate 6V rectifier heater winding. I don't know why there is another double winding for the tubes heater supply with a common center tap (if I interpret thing correctly). So the two windings that I will use to supply different parts of the circuit are the same current-wise; only difference is that one supplies about 6.4 Vac and the other about 6.6 Vac.

[MWJB]

What is the dc current draw of the 6V6s?

Your heater winding isn't coping. If you can reduce current draw throught 6V6s to a point that still gives you a decent tone, that will reduce the load on the PT a little.

Personally, I'd get a small (2A) auxilliary 6.3VAC transformer and run the 12AX7s and the 6AU6 off that. Don't forget to give the auxilliary filament xformer it's own virtual centre tap.

...or buy another PT.

...or rewire the 12AX7s as per oldr Silvertones, as a series load for the 6V6 cathodes, in conjuction with a cathode resistor.

[melvin]

Thank you guys.
and it has got its own separate 6V rectifier heater winding. I don't know why there is another double winding for the tubes heater supply with a common center tap

I thought the original had one 6V3 winding for all the heaters including the rectifier. Yours has a 12V center tapped one? Does it also have a separate 6V rectifier winding as you stated above? I don't understand.

[slidincharlie (Carlo P)]

I thought the original had one 6V3 winding for all the heaters including the rectifier. Yours has a 12V center tapped one? Does it also have a separate 6V rectifier winding as you stated above? I don't understand.

Melvin, I'm sorry, I got confused...
The tranny has a center tapped "double winding" (sorry about the terminology, I don't know the correct term) wound for 12V across the ends. It has a double-wire center tap. I gave the rewinder the wrong instructions, so he did the wrong job .

[slidincharlie (Carlo P)]

Final (?) report

Now I have two separate heater voltage supplies: one to the 6AU6 and power tubes (2x6V6), the other to the preamp tubes (2x12AX7). Each one is referenced to earth via two 100 ohm resistors. I have maintained the solid state rectifier.
The power tranny stays warm (not too much) after about two hours operation.
The heater voltage is still 5.9 Vac all over the place: I expected a little bit more (especially after all the work involved with the double heater supply setup)...
The B+ is still low (around 318 V on the plate of the 6V6's) even with a 270 ohm resistor at the rectifier.
The power tubes are biased around 10.5W, which sounds fine for a cathode biased amp (don't know if it is class A), no? With the same tubes (but higher B+) this amp used to see 12W plate dissipation with the previous PT and tube rectifier.

To be true the amp sounds damn good

I believe I'll leave it as it is, if you guys don't see major potential problems derivating from the low heater voltage.

In the meantime I thank all of you who gave me very precious advice.

[Mars Amp Repair]

Say
I know I'm just jumping in here after everyone elses hard work, but if you power at least the 6X4 with one winding & use the other for all the other tubes, it would at least reduce the current powering the highest number of tubes by at least one 6X4 filament draw and probably not be that difficult to rewire. glen

[slidincharlie (Carlo P)]

if you power at least the 6X4 with one winding & use the other for all the other tubes, (...)

Glen,
there is no longer a 6X4 in there. I have installed a solid state rig (two diodes plus one resistor), as suggested above by others.

[J M Fahey]

Ciao Carlo.
Obviously only one of the windings is not enough for *all* heaters.
Use one for the 6V6's and the other one for the rest.
By the way, i guess vendetta hasn't fully dissapeared there yet (here in Buenos Aires it still exists), please check that the transformer winder's great-grandfathe didn't somewhat offend your great-grandfather's family. There must be some reason for what he did to you
Juan Manuel Fahey

[slidincharlie (Carlo P)]

Juan,
as I said in my "Final (?) report" above I used one winding to feed the 6Au6 and 6V6's heaters, the other for the 12ax7's.
Vendetta... lol... yes maybe I should investigate...