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ANOTHER - Impulse buy -- Magnavox 8802

gadget73 said:
100 ohm screen resistors you're talking about? Only particular reason to not go really low watt parts is the voltage rating. These won't be dropping much of anything so it doesn't so much apply, but generally the physically smaller the resistor, the less voltage you can drop across them. The bigger 1/2 watt types are usually 350v, but the small ones are 200 or 250. It goes up or down from there depending on the resistor in question.

for bleeders in a power supply you might want 1 or 2W parts even if they don't dissipate anywhere near that, simply for the voltage rating.
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Sorry for another Wattage question -- For the Heaters -- I see a 220 ohm requirement -- Looking at the wire size - I am thinking a Larger WATT value may be required - higher than the 1/4 or 1/2 standard --- is that correct ?
 
gadget73 said:
Old transformers can be a great value, not all old iron is good but plenty is. I know nothing specifically about Eico 40 transformers but I have a hard time believing they aren't at least decent. You'll be making roughly half the power that these were originally paired with, so that also tends to improve performance.
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Absent real data ----- I guess ---MY default is -- A question -what is the consensus ?- (opinions Welcome )- Preferably the --experience ---of others --- Who Know,-- and have a good reputation.
Glowing reports - say something - but i would rather have REAL numbers ---
 
How are the 220 ohm resistors used in the heater circuit? To make a derived center tap? If using two of them with the mid point grounded it's even less stressful as each resistor only sees 3.15V. If it is for a different use then not sure.
 
What numbers would make you feel better?

So, I'm having trouble keeping up with the various flipping and flopping you tend to do @S Swanson - exactly WHAT iron are you intending to use on this 8800? Eico ST-40 or ST-70 or other?

The Eico ST-40 iron would be a better fit here- the ST-40 was cathode biased, so those transformers are ~8K plate to plate impedance, which is a good match for the 6V6GT. You would be running these (As @gadget73 indicated) at half their rated power, so by "taking it easy" the transformers would be in a much sweeter spot performance wise. These are good classic iron. I would expect =spectacular= results.

The ST-70 used fixed bias, so the plate to plate impedance on those are more like 6.6K, probably a better fit for a 6L6 type tube.
 
wparks said:
What numbers would make you feel better?

So, I'm having trouble keeping up with the various flipping and flopping you tend to do @S Swanson - exactly WHAT iron are you intending to use on this 8800? Eico ST-40 or ST-70 or other?

The Eico ST-40 iron would be a better fit here- the ST-40 was cathode biased, so those transformers are ~8K plate to plate impedance, which is a good match for the 6V6GT. You would be running these (As @gadget73 indicated) at half their rated power, so by "taking it easy" the transformers would be in a much sweeter spot performance wise. These are good classic iron. I would expect =spectacular= results.

The ST-70 used fixed bias, so the plate to plate impedance on those are more like 6.6K, probably a better fit for a 6L6 type tube.
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OK--- Was I was unclear ? The question about the ST 70 transformers was ABOUT A FUTURE Project (see post 170 ) and has nothing to do with the 8802 -
I made A choice (see post 178 and 179 ) So yes The Plan is to use the Eico st40 Iron - -- BTW - pretty sure the ST70 iron would not fit the chassis - BUT again That was Not ON THE TABLE--- as a option - and never was -- I probably should have started another Thread about those transformers (A compatibility question )-- as recommended - per Gadget's recommendation -- --( see-- I think post 175 )
In any case - If i seemed to Flip flop on the transformers - that was PERHAPS of NOT KNOWING what was the wise choice . FULL Circle -- as i said - If i am testing everyone's patients I apologize - and A quick note; Sometimes my writing can seem way More Strident --than Intended.
Perhaps a happy face emoji would help?
 
No worries, no patience tested, just sometimes have trouble following the design as it evolves as several options were discussed. Just want to be helpful so I have to keep track of what you're building. I think you will be tickled pink with the ST-40 iron.

As to the virtual center- it's not even really that important. Please do not connect the 6V6 cathodes together. That virtual center point between the two 220 ohm resistors just connects to =any one= 6V6 cathode, just to hold the filament supply up above ground. As @gadget73 mentioned, since any one 6V6 socket has all of the required connect points, it's easiest to install these resistors on just one 6V6 socket, from one side of the filament to cathode, and other side of filament to cathode. like this:

1789338155946.png
 
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