PP 2E22 amp rebirth

[huggygood]

 

[huggygood]

I found a PT 360 Vac in my archives, it doesn't have 5v but it's not a big deal.
So, do we resurrect it as is or do we apply modifications to it?
already, the counter-reaction to give it a little more stability.
Does anyone have another idea or should we continue like this?

 

[jcalvarez]

I'd restore it to the previous working condition, and use it as starting point. Before that I'd recommend confirming resistor values on the schematic against the real thing.

 

[huggygood]

I can already confirm that the feedback resistor is indeed 1k.
there is only a 6 ohm winding on the secondary, no 4 or 8 ohm.

 

[OldHector]

Could the power transformer had windings coupled back to front? I did that once on a PCB mounted 110V + 110V to 12V transformer and it also had an 'unscheduled disintegration' after short period.

 

[huggygood]

There is little chance since it worked for two years for me, plus at least 4 years before that.

 

[jcalvarez]

I can already confirm that the feedback resistor is indeed 1k.
there is only a 6 ohm winding on the secondary, no 4 or 8 ohm.

Are your speakers 8 ohms?
In general, I find the 4K opt not a good match for the 2E22 as a pentode, I guess that's the reason for the amount of NFB.
I did some simulations with 7.6K and 6.6K and the figures improve a lot.
Output power is quite low for the tube because of the low plate current at 0V g1. Interesting that the 2E22 datasheet shows curves for positive suppressor grid, could be a venue to investigate when you get things running. Also AB2, the tube can handle quite a bit of g1 current.

 

[huggygood]

That's what bothers me, most of my speakers are 4ohm/6ohm apart from my JBL L100 century and I only have one winding on my opt.
Hence my questioning about identical reconstruction or not.

 

[jcalvarez]

Do you have details about the ouptut transformer, like dcr, max dc current etc? Maybe a KT88 based rebuild, but you probably need a bigger PT.
What kind of output power would you be happy with? You mentioned that you liked the sound when it was working, so maybe that's the answer. Unless you want to experiment a bit, then the sky is the limit 😉

 

[astouffer]

Same thing happened to my Heathkit IP-32 power supply. Turned it on one day and the transformer let out a foul smelling smoke. Luckily a parts unit showed up at the next hamfest and I was back in business.

 

[jcalvarez]

Just by replacing the output tubes to EL34 (no even bias changes) you at least double the output power. There is space for a bigger power transformer. Providing the OPTs can handle it, of course.

 

[as_audio]

The supply of the burnt amp is differnt to the one in first post.