Hammond Ao35 iron??

[davebolden44]

Would anybody know it the hammond ao35 power transformer can handle the current demands for one more 12ax7? I am leaning towards yes it easily could but I just wanted to be sure and see if anyone has done this and had positive results. Thanks!

[Stevem]

my crystal ball is in the shop getting a polish and wax job, so forgive for having to ask what the other tubes are you have hooked up to this Transformer, and also how many?

[davebolden44]

Typically they are made to use 2- 12ax7s
2-EL84s and a 5y3 rectifier. I dont want to change the power amp I just essentially want to add an ef86 to that lineup. I should have said that instead of a 12ax7. I have been building these with 1 ef86 and a 12ax7 PI but I wanted to add an extra gain stage or 2 to experiment.

[wpaulvogel]

I think the heater supply is adequate for what you’re asking. The HT winding is kinda saggy and using it for more than 2 EL84 or 2 6v6 would probably not be advisable or I should say maintaining the 8k output transformer impedance would be best.

[Stevem]

I would have no concern about the Pt powering another preamp tube DC wise, the question is does the transformer filament winding have the extra.300 amp to light up the tube without the 6.3 volts dropping down to below 5.9 volts.
If the transformer can’t sustain 5.9 volts with the added 12AX7 wired in then it’s just a matter of time before that Pt burns up.

[davebolden44]

That would be my concern also. The transformer seems to be built quite stout but looks can be deceiving. I have a few auxiliary filament transformers but real estate is scarce and I dont want to induce any hum....

[sluckey]

I would not hesitate to add one more 12AX7.

[Phil_S]

So, if you don't know, breadboard the required sockets and hook up the heaters. See what you get. Let the heaters cook for a while.

Remember, those old Hammond organs are probably from the era of 115V mains. If you have 120VAC at the wall socket, that alone will give you a 4.3% boost. Just because you get your heaters to 6.3V, it still isn't certain the amp-rating of the winding will hold up. However, the added burden is small, so, probably it will be OK anyway.

[davebolden44]

I am hoping. I am optimistic about it. I will give it a shot and monitor it as was mentioned.

[wpaulvogel]

I built an amp with 3 12ax7 and 2 EL84 using that transformer. It didn’t sweat it. Like I said before it’s the HT winding that’s saggy.

[davebolden44]

Technically what I am adding to the amp is an ef86 which I believe draws less filament current than a 12ax7 anyway. Its just nice to hear of others who have done this for some reassurance.